Vectronics SWR-584B User Manual

TABLE OF CONTENTS

1.0 INTRODUCTION................................................................................................................................................ 1

1.1 A Quick Word about Accuracy............................................................................................................... 1

1.2 Typical Uses............................................................................................................................................ 2

1.3 Frequency Range..................................................................................................................................... 4

2.0 POWER SOURCES ............................................................................................................................................. 4

2.1 External Power Supply............................................................................................................................4

2.2 Using Internal Batteries........................................................................................................................... 4

2.3 Using Rechargeable “AA” Type Batteries.............................................................................................. 5

2.4 Using Conventional “AA” Drycell Batteries...........................................................................................5

2.5 “Power Saving” Mode (sleep mode)....................................................................................................... 6

3.0 MAIN MENU AND DISPLAY............................................................................................................................ 6

3.1 General Connection Guidelines............................................................................................................... 6

3.2 Power-up Display.................................................................................................................................... 7

3.3 Main MODE descriptions........................................................................................................................ 7

3.4 Blinking “VOLTAGE LOW” display warning....................................................................................... 8

4.0 MAIN (OR OPENING) MODE........................................................................................................................... 8

4.1 General Connection Guidelines............................................................................................................... 9

4.2 Antenna SWR.......................................................................................................................................... 9

4.3 Coax Loss ................................................................................................................................................ 11

4.4 Capacitance.............................................................................................................................................. 11

4.4 Inductance................................................................................................................................................ 12

5.0 ADVANCED OPERATION ................................................................................................................................14

5.1 Forward.................................................................................................................................................... 14

5.2 General Connection Guidelines............................................................................................................... 15

5.3 (Magnitude of) Impedance mode............................................................................................................ 15

5.4 Return Loss and Reflection Coefficient mode ........................................................................................ 16

5.5 Distance to Fault mode............................................................................................................................ 16

5.6 Resonance Mode...................................................................................................................................... 18

5.7 Percentage Transmitted Power................................................................................................................ 18

6.0 ADJUSTING SIMPLE ANTENNAS................................................................................................................... 19

6.1 Dipoles.....................................................................................................................................................19

6.2 Verticals................................................................................................................................................... 19

6.3 Tuning a simple antenna.......................................................................................................................... 19

7.0 TESTING AND TUNING STUBS AND TRANSMISSION LINES.................................................................. 20

7.1 Testing Stubs ........................................................................................................................................... 20

7.2 Velocity Factor of Transmission Lines ................................................................................................... 21

7.3 Impedance of Transmission Lines or Beverage antennas........................................................................ 22

7.4 Adjusting Tuners ..................................................................................................................................... 23

7.5 Adjusting Amplifier Matching Networks................................................................................................ 23

7.6 Testing RF Transformers......................................................................................................................... 24

7.7 Testing Baluns......................................................................................................................................... 24

7.8 Testing RF Chokes .................................................................................................................................. 25

8.0 TECHNICAL ASSISTANCE............................................................................................................................... 25

SWR-584B Instruction Manual HF/VHF SWR Analyzer

1.0 INTRODUCTION

Attention

excessive external voltages applied to the ANTENNA connector will damage this unit .

Description

The SWR-584B RF analyzer is a compact battery powered RF impedance analyzer. This unit combines four basic circuits; a 1.8-170 MHz variable frequency oscillator, a frequency counter, a 50 ohm RF bridge, and an eight-bit micro-controller. This unit makes a wide variety of useful antenna or impedance measurements, including coaxial cable loss and distance to an open or short.

Primarily designed for analyzing 50 ohm antenna and transmission line systems, the SWR-584B also measures RF impedances between a few ohms and several hundred ohms. It also functions as a signal source and frequency counter. The frequency range of impedance measurement is 1.8 to 170 MHz, in six overlapping bands.

1.1 A Quick Word about Accuracy

Inexpensive impedance meters have limitations. The following text details several common problems and reasons they occur.

Measurement errors. Unreliable readings are rooted in three primary areas:

1.) Signal ingress from external RF sources, usually strong AM broadcast stations.

2.) Diode detector and A/D converter errors.

3.) The impedance of connectors, connections, and lead lengths.

Virtually all low cost impedance m eters use broad-band vol tage detect ors. The reason virtually all analyzers use broadband detectors is cost. Narrow band detectors are very expensive, since the detector system would have to use at least one selective gain-stable receiver. Narrow band detectors would price antenna and impedance analyzers far outside the price range of most casual users.

Broadband detectors are sensitive to out-of-band external voltages, and solutions to most out-of-band interference are not simple. Common low-pass or band-pass filters behave like small transmission lines of varying impedances on different frequencies. Low-pass or high-pass filters change impedance and SWR readings, just as an additional section of transmission line would. This modification of impedance caused by filters severely limits their usefulness.

One solution to this problem (often mentioned by users) is to increase internal generator power. Unfortunately the power required to operate a clean, harmonic-free broadband VFO system greatly reduces battery life. In this unit, more than 70% of the total battery drain (-150 mA) is used to produce the low harmonic distortion test signal.

Most RF interference problems occur on lower frequencies, since high power AM broadcast signals couple well into large antennas (especially 160 meter verticals). MFJ offers an adjustable filter that attenuates all offfrequency signals while having virtually no small effect on measurements between 1.8 and 30 MHz. Properly used, this adjustable filter reduces external interference while having nearly no measurable effect on desired measurements.

Read section 2.0 bef ore attempting to use this product. Incor rect power supply voltages or

SWR-584B Instruction Manual HF/VHF SWR Analyzer

Component limitations are another source of inaccuracy.

linear. The accuracy of the SWR-584B is enhanced by the use of special microwave zero-bias Schottky detectors with matching compensating diodes. Each unit is individually compensated to provide the best possible linearity with both high and low impedance loads, making the A/D converter's 1/2 percent resolution the primary limitation.

Connection lengths are another p roblem.

bridge and output connector upset readings, especially when the impedance is very high or very low. The SWR584B minimizes this problem by using surface mount low capacitance microwave components with nearly zero lead length.

Unlike instruments that present readings outside the reliable range as exact numbers, the SWR-584B gives a display warning. If (Z>650) appears on the display, the impedance is greater than 650 ohms and outside the reliable instrument range.

Connection lengths between components in the bridge and the

Diodes detecting very small voltages are non-

1.2 Typical Uses

The

SWR-584B

Antennas:...................................SWR, impedance, reactance, resistance, resonant frequency, and bandwidth

Antenna tuners:..........................SWR, bandwidth, frequency

Amplifiers:.................................Input and output matching networks, chokes, suppressors, traps, and components

Coaxial transmission lines:........ SWR, length, velocity factor, approximate Q and loss, resonant frequency, and

Filters:........................................SWR, attenuation, and frequency range

Matching or tuning stubs:..........SWR, approximate Q, resonant frequency, bandwidth, impedance

Traps:.........................................Resonant frequency and approximate Q

Tuned Circuits:..........................Resonant frequency and approximate Q

Small capacitors:........................Value and self-resonant frequency

RF chokes and inductors: ..........Self resonant frequency, series resonance, and value

Transmitters and oscillators:......Frequency

can be used to adjust, test, or measure the following

impedance

The

SWR-584B

Cable length (feet) Cable Loss (dB) Capacitance (pF) Impedance or Z magnitude (ohms)

The

SWR-584B

than -25 dBf) signal of approximately 3 Vpp (approximately 20 milliwatts) into 50 ohm loads. The SWR-584B internal source impedance is 50 ohms.

Note

A more complete description of the SWR-584B's features and proper measurement methods

can be found by reading the sections on the particular measurement you wish to make. Consult the table of contents for the various applications.

measures and displays the following:

Impedance phase (degrees) Inductance (uH) Reactance or X (ohms) Resistance or R (ohms)

is useful as a non-precision signal source.

It provides a relatively pure (harmonics better

Resonance (MHz) Return loss (dB) Signal Frequency (MHz) SWR (referenced to 50 ohms)

SWR-584B Instruction Manual HF/VHF SWR Analyzer

1.3 Frequency Range

The FREQUENCY switch selects the following internal oscillator frequency ranges. (A small overlap outside each range is provided):

1.8 - 4 MHz 27 - 70 MHz 4 - 10 MHz 70 - 114 MHz 10 - 27 MHz 114- 170 MHz

2.0 POWER SOURCES

Read this section before connecting this device to any power source. Improper connections or incorrect

voltages may cause damage to this product!

2.1 External Power Supply

MFJ has an optional power supply, the MFJ-1315, that satisfies all external supply requirements. We recommend only using this supply.

Voltage must be more than 11 volts, and preferably less than 16 volts, when the unit is on and operating. Maximum “sleep mode” and “OFF” voltage (when the power supply is lightly loaded by this unit) is 18 volts. The supply must be reasonably well filtered. The supply must not have a grounded positive lead!

The SWR-584B can be used with an external low voltage dc supply’s (MFJ-1315 AC adapter recommended). The ideal supply voltage is 14.5 volts dc, but the unit will function with voltages between 11 and 18 volts. The current demand is 150 mA maximum. (Be sure you read the battery instructions if you use also install batteries!)

The SWR-584B has a recessed 2.1 mm power-type receptacle near the RF connectors. This receptacle is labeled “POWER 12VDC”.

The outside conductor of the POWER receptacle is negative, the center conductor positive.

Inserting a power plug in the “POWER 12VDC” receptacle disables internal batteries as a power source. Internal batteries, although disabled for operating power by inserting a power supply plug, can still be trickle charged.

WARNING: REVERSE POLARITY OR EXCESSIVE VOLTAGE CAN DAMAGE OR DESTROY

THE SWR-584B. NEVER APPLY MORE THAN 18 VOLTS, NEVER USE AC OR POSITIVE GROUND SUPPLIES!

2.2 Using Internal Batteries

When batteries are initially installed, a small black-plastic internal jumper must be re-positioned or checked for proper position. The battery setting jumper is located inside the unit at the top of the printed circuit board near the area of the OFF-ON switch and power connector. This jumper is accessed by removing eight screws along the both sides of the SWR-584B. After the cover mounting screws are removed, remove the entire back cover. The black plastic jumper fits over two of three adjacent pins. It must be properly positioned for the type of battery used (either rechargeable or non-rechargeable).

SWR-584B Instruction Manual HF/VHF SWR Analyzer

For battery replacement, batteries are accessed by removing the SWR-584B’s small rear panel. The battery cover is secured by 2 Phillips head screws.

2.3 Using Rechargeable “AA” Type Batteries

CAUTION: Avoid using external power sources having less than 13 volts

if rechargeable batteries are installed. If external supply voltage is too low, the charger will not work properly and batteries will eventually discharge. We recommend charging batteries with the SWR-584B power switch off, with enough charging time to establish full battery charge (at least ten hours).

When using rechargeable batteries, an external supply that remains between 14 and 18 volts should be used. Typical battery charging current is 10-20 mA through an internal charging system. The internal charger trickle charges internal batteries any time a proper external voltage is applied, even when the SWR-584B is turned off. The MFJ-1315 supply fulfills all power supply requirements.

When using rechargeable batteries, the internal black plastic jumper located inside the cover (near the external power jack on the circuit board) must be set to the proper position. If it is not set to the proper position, the batteries will not charge. With rechargeable batteries, the internal charger jumper located on the printed circuit board near the power jack should be set like this:

2.4 Using Conventional “AA” Drycell Batteries

Try to use good quality alkaline batteries. Conventional batteries will work fine, but good quality alkaline batteries offer less risk of battery leakage and equipment damage and usually provide longer service and shelf life.

If you use any type of non-rechargeable dry cell battery, remove weak batteries immediately. Batteries must be removed before storing this unit for extended periods of time (longer than one month).

WARNING: WHEN USING CONVENTIONAL NON-RECHARGEABLE BATTERIES, THE

CHARGING SYSTEM MUST BE DEFEATED!

When using conventional non-rechargeable batteries, the internal jumper located on the printed circuit board near the power jack must be set like this:

SWR-584B Instruction Manual HF/VHF SWR Analyzer

2.5 “Power Saving” Mode (sleep mode)

The operating current drain of the SWR-584B is approximately 150 mA.

Battery life is extended by using an internal "Power Saving” mode. “Sleeping” battery drain is less than 15 mA. If you do not make MODE switch changes, or change frequency more than 50 kHz during any two minute time period, a power saving (Sleep) mode begins. “Sleeping” is indicated by a blinking “SLP” message in the display’s lower right corner, as shown here:

To wake the unit up, momentarily press the

Disable the “Power Saving” mode by pressing and holding the “MODE” button before power is applied (or before the “POWER” button on the unit is turned on). You must hold the “MODE” button and only release it after the copyright message appears.

If the “Power Saving” mode is successfully disabled on power up, when the “MODE” button is released the display will momentarily indicate:

‘‘MODE’’

‘‘GATE’’

button.

3.0 MAIN MENU AND DISPLAY

WARNING: NEVER APPLY RF OR ANY OTHER EXTERNAL VOLTAGES TO THE ANTENNA

PORT OF THIS UNIT. THIS UNIT USES ZERO BIAS DETECTOR DIODES THAT MAY BE DAMAGED BY EXTERNAL VOLTAGES. READ SECTION 2.0 BEFORE APPLYING POWER TO THIS UNIT! INCORRECT SUPPLY VOLTAGES CAN ALSO DAMAGE THIS UNIT.

3.1 General Connection Guidelines

The “ANTENNA” connector (SO-239 type) on the top of the SWR-584B provides the RF measurement output connection. This port is used for SWR or other RF measurements, with the exception of the Frequency Counter mode.

The “POWER” connector (2.1 mm type) is described in section 2.0. Be sure to read section 2.0 before operating this unit, since incorrect power supplies can damage this unit.

SWR-584B Instruction Manual HF/VHF SWR Analyzer

The “FREQUENCY COUNTER INPUT” connector (BNC type) is for use as a frequency counter only. It is described in section 4.x.

Note

The following is a descr iption of the opening or default m enu used by the SW R-584B. T his unit

also has an advanced user section in section 4.0.

3.2 Power-up Display

After turning on the "POWER" switch, or after applying external power with the “POWER” switch on, a sequence of messages appears on the display.

The first message is a program version, this "VER" number indicates the software version.

The second message is the software copyright date.

Note

Holding the switch on, and continuing to hold the appears, causes a "POW ER SAVING OFF" message to appear just as the released. This message appears just before the voltage check. This message confirms the battery saving “sleep mode” has been disabled.

The third message is a voltage check. It displays the operating voltage, indicating battery charge or external power supply voltage.

The final power-up display is the “working” display described in 3.2 (Impedance R&X) below.

Two panel meters indicate SWR and Impedance of loads connected to the “ANTENNA” port.

If you press the “MODE” button, the mode changes. After releasing the “MODE” button, the display will show the proper data for the new mode. The five main (or opening) menu modes are described below.

“mode”

button in continuously before applying power or turning the

“POWER”

“MODE”

button down until the copyright message

“MODE”

button is

3.3 Main MODE descriptions

If th e “MODE” button is momentarily pressed during normal main (or opening) mode operation, the SWR-584B changes display modes. When the mode first switches, the measurement mode comes up on the screen for a few seconds. The five display modes are described below:

Impedance R&X is the initial power-up mode. In this mode, the SWR-584B LCD (liquid crystal display, with numbers and letters) shows frequency in MHz, SWR, the resistive part of load impedance (R=), and the reactive part of load i mpedance (X=). The IMPEDANCE meter displays the complex impedance (Z in ohms), and the SWR meter displays SWR.

SWR-584B Instruction Manual HF/VHF SWR Analyzer

Coax Loss, the second mode, is reached by pressing the “MODE” button once. The liquid crystal display (LCD) indicates the test frequency and approximate loss of any 50 ohm coaxial cable, 50 ohm attenuator pad, or 50 ohm transformer or balun (for differential mode current only). In this mode, the 50 ohm device or cable under test must not be connected or terminated by a load resistance at the far end. If the device under test is terminated, measured loss will be higher than actual loss.

Capacitance in pF is the third mode. The LCD shows measurement frequency, capacitive reactance (Xc=) in ohms, capacitance (C=) in picofarads or pF. The Impedance meter indicates reactance in ohms, and the SWR meter displays SWR.

Inductance in uH is the fourth mode. The digital display indicates measurement frequency, capacitive reactance (Xl=) in ohms, inductance (L=) in microhenries or µH. The Impedance meter indicates reactance in ohms, the SWR meter displays SWR.

Freq. Counter is the fifth and final function of the main mode. The BNC connector labeled FREQUENCY COUNTER INPUT should connect to the RF sample you want to measure. The sensitivity of this port ranges from 10 millivolts at 1.7 MHz to 100 millivolts at 180 MHz. The “GATE” button controls the gate time of the frequency counter. Longer gate times are accompanied by additional digits in the display, increasing counter resolution.

WARNING: NEVER APPLY MORE THAN TWO VOLTS OF PEAK VOLTAGE, OR ANY DC

VOLTAGE, TO THE FREQUENCY COUNTER BNC PORT.

3.4 Blinking “VOLTAGE LOW” display warning

If supply or battery operating voltage is less than eleven volts, a blinking “VOLTAGE LOW” warning is displayed. Pressing the “MODE” button during a low voltage warning will disable the warning, and allow operation with low supply voltage. Readings might not be reliable when operating with supply voltages of under 11 volts.

4.0 MAIN (OR OPENING) MODE

WARNING: NEVER APPLY RF OR ANY OTHER EXTERNAL VOLTAGES TO THE ANTENNA

PORT OF THIS UNIT. THIS UNIT USES ZERO BIAS DETECTOR DIODES

SWR-584B Instruction Manual HF/VHF SWR Analyzer

THAT ARE EASILY DAMAGED BY EXTERNAL VOLTAGES OVER A FEW VOLTS. BE SURE THE POWER SUPPLY IS CORRECT, AS DESCRIBED IN SECTION 2.0, BEFORE OPERATING THIS UNIT.

A basic understanding of transmission line and antenna behavior and terminology is very important in understanding information provided by the SWR-584B. Most explanations are available in the ARRL Handbooks, and they should suffice for amateur applications. Avoid relying on popular rumor, or unedited, poorly edited, or self-edited handbooks or articles.

4.1 General Connection Guidelines

The “ANTENNA” connector (SO-239 type) on top of the SWR-584B provides the RF measurement output connection. This port is used to measure SWR or perform other RF impedance measurements, with the exception of the Frequency Counter mode.

WARNING: NEVER APPLY EXTERNAL VOLTAGES OR RF SIGNALS TO THE ANTENNA

CONNECTOR.

Remember to use proper RF connections. Keep leads as short as possible when measuring components or any system or device that is not a 50 ohm coaxial system. When measuring 50 ohm coaxial systems or antennas, interconnecting transmission lines may modify impedance and SWR. Use properly constructed 50 ohm coaxial cables of known quality to avoid errors.

4.2 Antenna SWR

To measure SWR of an antenna or antenna tuner input:

a.) If the antenna does not use a dc grounded feed system, momentarily short the antenna lead from shield to

center. This prevents static charges from damaging the SWR-584B’s zero bias detector diodes.

b.) Immediately connect (in the case of a non-dc grounded feed system) the antenna lead to the SWR-584B

“ANTENNA” connector.

c.) Set the “FREQUENCY” knob to the proper frequency range.

d.) Turn the SWR-584B “POWER” switch on, while watching the display. Battery voltage should be “OK”, and

indicate more than 11 volts and less than 16 volts.

e.) The main or opening mode opening menu displays frequency, SWR, resistance, and reactance on the LCD,

along with SWR and impedance on the analog meters. In this mode, the resistance (real part) and reactance (imaginary part) of the system impedance is displayed in ohms.

f.) Adjust the “TUNE” knob until the counter displays the desired frequency, or until you find the lowest SWR.

SWR-584B Instruction Manual HF/VHF SWR Analyzer

Advanced antenna measurement modes are available and described in section 5.0, but unless you fully understand them we suggest you avoid them. Most advanced features are different ways of displaying the same basic information given in the main or opening mode menu.

Antenna hints:

Display readings are the SWR, impedance and resonant frequency of the antenna system at the point in the system the SWR-584B is connected. The impedance and resonant frequency (frequency where reactance crosses zero) at the point where this unit is connected might not be the resonant frequency of the antenna itself.

This unit (or any other impedance measuring device) displays the antenna’s impedance, 50 ohm SWR, and resonant frequency as modified by transmission line “transformer” actions of the feedline and other components between the antenna and the SWR-584B. If the line is 50 ohms, this unit will always display the antenna’s true SWR, with the exception of a slight reduction in SWR with longer or more lossy feedlines.

1.) RESONANT F REQUENCY is where reactance is zero ohms, or in some cases as close to zero ohms as the

SWR-584B indicates. Since resistance has nothing to do with resonance, the resonant frequency is NOT always at the point of lowest indicated SWR (although they certainly can be the same). The most desirable load is almost always the load with lowest SWR, even though it may not necessarily be the point of no reactance (resonance).

2.) An IMPEDANCE of 50 ohms can be composed both resistive and reactive components. If the impedance is

50 ohms, but the SWR is not 1.0 to 1, the likely cause is reactance makes up part or all of the impedance. Contrary to popular (but very incorrect) misconceptions, it is impossible to obtain a perfect 1 : 1 SWR when the load is reactive, even if the complex impedance is 50 ohms.

A good example is a 50 ohm nearly pure reactance load. The SWR-584B LCD will indicate R=0 X=50, while the impedance meter reads 50 ohms. The SWR would overflow (SWR>25), since the reactive 50 ohm impedance load absorbs almost no power from the source and has a nearly infinite SWR.

3.) Even if a perfect transmission line is cut to an exact electrical half-wave (or a multiple thereof ) it is a true half-wave multiple only on one frequency in that band. On a slightly different frequency the line will not represent the true feedpoint impedance of the antenna. The line is only “impedance transparent” when lossless and when an exact multiple of 1/2 wl. The longer the transmission line in wavelengths, the “more length critical” it becomes and the less accurate measurements become.

4.) If the feedline is not an exact multiple of 1/4 wl, the resonant frequency of the antenna might be shifted higher or lower by the transmission line. A mismatched non-quarter wave multiple feedline adds reactance that can cancel antenna reactance at frequencies where the antenna is not resonant.

Multiple antenna and feedline combination resonances commonly occur with dipoles, where reactance crosses zero (indicating resonance) at some frequency other than the antenna’s actual resonant frequency. This is a normal effect.

5.) If the line is a 50 ohm line, has no radiation or parallel currents, and if the line has minimal loss, moving the analyzer to another point on the line will NOT change SWR reading. Impedance and resonant frequency might change from line transformation effects, but the SWR will not change.

SWR-584B Instruction Manual HF/VHF SWR Analyzer

6.) If SWR changes with coaxial line length, line placement, or line grounding (any distance away from the antenna) changes, the feedline has one or more of the following shortfalls:

a.) The feedline is carrying common mode current and radiating. b.) The feedline is not a 50 ohm line. c.) The feedline has high loss.

4.3 Coax Loss

The second main (or opening) mode is “Coax Loss”. Access this mode by turning the SWR-584B on and stepping to the Coax Loss display. In this mode, the SWR-584B LCD indicates frequency and coax loss in dB. The meters are disabled. This mode was designed to measure 50 ohm cables, but measures differential mode loss in many types of 50 ohm transmission line transformers and choke baluns, as well as loss in 50 ohm attenuator pads.

CAUTION: Do not measure conventional transformers, or attenuators and

coaxial cables, with impedances other than 50 ohms. When making measurements, the opposite end of the device under test must have an open circuit, a short circuit, or a pure reactance for termination. Any loss resistance will make attenuation appear worse than it actually is.

To measure loss:

1.) Connect the SWR-584B to the 50 ohm cable, attenuator or transmission line type balun or transformer you wish to measure. Be sure the distant end of the component you are testing is not terminated in any resistance.

2.) Turn the SWR-584B on. After the display reaches the opening measurement function, press the mode switch once.

3.) The display should momentarily flash “Coax Loss”.

4.) Read the loss in dB at any frequency this unit covers.

4.4 Capacitance

Note

The SWR- 584B measures reactance, and converts react ance to capacitance. The SW R-584B

can not determine if the react ance is actually inductive or capacitive. You can usually determ ine the type of react ance by adjust ing frequency. If freq uency is increased and reactance (X on the display or Impedance on the meter) decreases, the load is capacitive at the measurement frequency. If frequency is reduced and reactance decreases, the load is inductive at the measurement frequency.

SWR-584B Instruction Manual HF/VHF SWR Analyzer

“Capacitance in pF” is the third mode. It measures capacitance values (in pF) at an adjustable frequency. Normal measurement range is from a few pF to a few thousand pF. Capacitance is calculated using measured reactance (X) and operating frequency.

The SWR-584B becomes inaccurate measuring reactances below 7 ohms or above 650 ohms. If the reactance of the component is in the inaccurate range, “C(X<7) [X]” or “C(Z>650)” will be displayed. Capacitance values will not be displayed if measurement accuracy is questionable.

To measure capacitance:

1.) Turn the SWR-584B on and step through with the mode switch until the “Capacitance in pf” display appears.

2.) Connect the capacitor across ANTENNA connector with the shortest leads possible, or wi th the lead length normally used in the working circuit.

3.) Adjust the frequency to the closest frequency possible to the working frequency that does not produce a range warning. C(Z>650) is one warning, and C(X<7) is another. C(X=0) indicates the capacitor appears as a near perfect short to the SWR-584B.

When measuring a capacitor, the display value will likely change with test frequency. This happens because stray inductance in the capacitor, and in wires to the “ANTENNA” connector, are in series with the capacitor. Effective capacitance does change with frequency, and is often quite different from dc or low frequency ac values. At higher frequencies the effective capacitance increases, reaching infinite capacitance when the capacitor and stray inductance becomes series-resonant.

The frequency where the capacitor’s impedance, and the leads connecting to the capacitor, becomes (X=0) is the series resonant frequency. Bypass capacitors are sometimes intentionally operated at or near the series or self resonant frequency, but most applications are at frequencies far below the series resonant frequency.

The IMPEDANCE meter will indicate reactance (X in ohms) of the capacitor.

4.4 Inductance

Note:

The SWR- 584B measures reactance, and converts reactance to inductance. The SWR-584B

can not determine if the reactance is actually inductive or capacitive. You can usually determine the type of reactance by adjusting frequency. If frequency is increased and reactance (X on the display or Impedance on the met er) decr eases, the load is capacitive at the measurement frequency. If frequency is reduced and reactance decreases, the load is inductive at the measurement freq uency.

SWR-584B Instruction Manual HF/VHF SWR Analyzer

“Inductance in uH” is the third mode, and measures inductor values in microhenries (uH) at an adjustable frequency. Normal measurement range is from less than .1 uH to a maximum of 60 uH. Inductance is calculated using measured reactance (X) and operating frequency.

The SWR-584B becomes inaccurate measuring reactance below 7 ohms or above 650 ohms. If component reactance is in the inaccurate range, “L(X<7) [X]” or “L(Z>650)” will be displayed. An inductance value will not be displayed if measurement range is questionable.

To measure inductance:

1.) Turn the SWR-584B on and step the mode switch through until the “Inductance in uH” display appears.

2.) Connect the inductor acr oss ANTENNA connector with the shortest leads possible, or with the lead length normally used in the working circuit.

3.) Adjust to a frequency as close as possible to the working frequency, but one that does not produce a range warning. L(Z>650) is one warning, and L(X<7) is another. L(X=0) indicates the inductor appears as a near perfect short to the SWR-584B, and indicates frequency is too low or the inductor too small to measure.

When measuring an inductor, the displayed inductance value will sometimes change with test frequency. This happens because of stray capacitance in the inductor, and in wires to the “ANTENNA” connector. At radio frequencies inductance often changes with frequency, and is often different from dc or low frequency ac values.

The IMPEDANCE meter will indicate reactance (X in ohms) of the inductor.

Note:

Lead length and placement, as well as inductor desig n, will affect inductance readings and incircuit performance. With increasing frequency, measured inductance usually increases. At some frequency an inductor oft en becomes an “open” circuit, with infinite reactance. At others it becomes a short.

SWR-584B Instruction Manual HF/VHF SWR Analyzer

5.0 ADVANCED OPERATION

WARNING: NEVER APPLY RF OR ANY OTHER EXTERNAL VOLTAGES TO THE ANTENNA

PORT OF THIS UNIT. THIS UNIT USES ZERO BIAS DETECTOR DIODES THAT ARE EASILY DAMAGED BY EXTERNAL VOLTAGES OVER A FEW VOLTS.

The advanced mode is reached by pressing and holding the GATE and MODE buttons together for several seconds. Upon release of the buttons, and “ADVANCED” message will appear. The following modes are available from the ADVANCED menus:

Impedance......................................................................... SWR, impedance magnitude, phase angle of impedance

Return Loss and Reflection Coefficient...........................SWR, return loss, impedance, reflection coefficient

Distance to fault................................................................ SWR, impedance, and distance to fault

Resonance.........................................................................SWR, resistance and reactance

Transmit efficiency...........................................................SWR, impedance and forward power as a percentage of

apparent power

5.1 Forward

In the ADVANCED mode, the SWR-584B measures distance to fault, impedance, reactance, resistance, and standing wave ratio (SWR).

It also measures and displays other terms used to describe SWR. These esoteric SWR descriptions include return loss, reflection coefficient, and transmitted power as a percentage of apparent power in the system. Some of these terms are misleading because their name does not necessarily describe what really happen in a system. We strongly recommend persons unfamiliar with information supplied in special modes avoid using them.

SWR-584B Instruction Manual HF/VHF SWR Analyzer

The SWR-584B contains a 50 ohm bridge, with voltage detectors across each leg. An eight-bit microcontroller processes these voltages, and applies formulas to derive useful information. from the voltages. The basic calculations are resistance, reactance, SWR, and complex impedance. In accuracy challenged modes, the system cross checks itself and outputs a weighted average of the most reliable information. T he system is limited by the eight bit A-D conversion and data processing, some data jumping occurs at the edges of a least-significant-bit changes in the detected voltages.

While we have attempted to make this unit as accurate as possible, some of the formulas contain square and other high order functions. The resolution of the detectors is about 1/2 percent, and we use the most direct calculation possible. Still, some errors are unavoidable for certain impedance values.

A basic understanding of transmission line and antenna behavior and terminology is very important in understanding complex information provided by the SWR-584B. Most explanations are available in the ARRL Handbooks, and they probably suffice for most amateur applications. Avoid unedited or self-edited amateur handbooks or articles, or check them against professional sources. For complex questions or for critical information, we recommend using books written, reviewed, and edited by professional engineers.

5.2 General Connection Guidelines

The “ANTENNA” connector (SO-239 type) on the top of the SWR-584B provides the RF measurement output connection. This port is used to measure SWR or perform other RF impedance measurements, with the exception of the Frequency Counter mode.

The “ANTENNA” connector has about +7 dBm output into 50 ohms (~ .5 volts RMS), and appears like a 50 ohm source resistance (open circuit voltage ~1 volt RMS). Harmonics are at least 25 dB down over the operating range of the SWR-584B. While the VFO is not stabilized, it is useful as a crude signal source.

The “ANTENNA” connector is not dc isolated from the load, external voltages will couple directly into internal detectors.

WARNING: NEVER APPLY EXTERNAL VOLTAGES OR RF SIGNALS TO THE ANTENNA

CONNECTOR. PROTECT THIS PORT FROM ESD.

Use proper RF connections. Keep leads as short as possible when measuring components or non-50 ohm systems. When measuring 50 ohm systems, interconnecting transmission lines will modify impedance and SWR. Use properly constructed 50 ohm coaxial cables of known quality to avoid errors.

5.3 (Magnitude of) Impedance mode

Impedance is the first mode in the advanced menu. The opening display indicates:

In this mode, the SWR-584B LCD displays frequency, impedance or Z magnitude (in ohms), and phase angle ( θ ) of impedance. The meters indicate SWR and Impedance. The maximum impedance limit is set at 650 ohms, indicated by the standard display of (Z<650).

SWR-584B Instruction Manual HF/VHF SWR Analyzer

Note

Stray connector capacitance (4.4 pF) will be lower than 650 ohms at f req uencies higher than 60

MHz. This small stray capacitance will not affect high freq uency measurements, and produces only minor errors in reading Impedances under a few hundred ohms at VHF.

5.4 Return Loss and Reflection Coefficient mode

The Return Loss and Reflection Coefficient mode is the second measurement mode in the Advanced mode menu. This mode is reached by pressing and releasing the MODE button one time, after entering the Advanced mode menu. You can also reach it, an all other modes, by stepping through Advanced modes with the MODE button until the display indicates Return Loss and Reflection Coefficient.

The Return Loss and Reflection Coefficient mode measures and displays return loss in dB and voltage reflection coefficient in percent on the LCD. The meters indicate SWR and impedance.

To use this mode, connect the load to be measured to the ANTENNA connector, adjust the frequency to the desired frequency range, and read the results on the MFJ-259 LCD and panel meter displays.

5.5 Distance to Fault mode

The Distance to Fault mode is the third measurement mode in the Advanced mode menu. This mode is useful for determining cable length, or distance to an open or shorted connection. This mode is reached by pressing and releasing the MODE button two times, after entering the Advanced mode menu. It can also be reached (and all other advanced modes) by stepping through Advanced modes with the MODE button until the display indicates “Distance to Fault” (or other desired function).

If a balanced line is used, operate the SWR-584B only from internal batteries. Keep the SWR-584B a few feet away from other conductors or earth, and do not attach any wires (other than the stub) to the unit. Use the ANTENNA connector’s shield for one lead and its center pin for the other. Two wire balanced lines suspended in a straight line a few feet away from metallic objects or ground.

Coaxial lines can lay in a pile or coil on the floor. Internal or external power can be used, and the SWR-584B can be placed on or near large metallic objects with no ill effects. Coaxial lines connect normally, with the shield grounded.

The Distance to Fault mode measures the electrical distance in feet to a transmission line fault or mistermi nation. To obtain physical distance, multiply electrical distance by feedline velocity factor. If the distance is displayed

must

SWR-584B Instruction Manual HF/VHF SWR Analyzer

as 75 feet, and the transmission line is a typical RG-8 solid dielectric cable with a velocity factor of 0.66, the distance is 75 x .66 = 49.5 feet.

There is one limit to this mode, the mistermination or fault must not be periodically frequency sensitive. For example, this mode will find the distance to a remote selective circuit (like a standard link coupled antenna tuner) that appears as a short or open at all frequencies but one. It will not reliably find the distance to a low pass filter unless the test frequency is above the filter stop-band. This mode will work properly if the mistermination is a nearly pure resistance, but will not work reliably if the load is a mostly pure reactance.

To confirm reliability, make two or more groups of measurements on different starting frequencies at least one octave apart. If measured distances agree, they are almost certainly very reliable. The more base frequencies used to confirm distance, the more assurance we have that distances are correct.

To measure fault distance:

1.) Select a frequency where the Impedance meter is at the lowest deflection possible and where minimum reactance displayed on the SWR-584B LCD, or where the reactance crosses zero. The reactance zerocrossing frequency is the frequency where reactance rises when the SWR-584B is adjusted either higher or lower in frequency.

2.) Press the “GATE” button. The blinking “1st” will change to a blinking “2nd”.

3.) Tune the analyzer higher or lower in frequency until the Impedance meter reads the very next lowest impedance point on the meter, and reactance displayed on the LCD crosses zero or is at the lowest possible again. A non-zero minimum of a few ohms is acceptable.

4.) Press the “GATE” button again, and the display will indicate distance in feet.

Multiply the distance in feet by the velocity factor of the cable. The result is the physical distance in feet.

Example: The SWR-584B indicates 13 feet, and the cable is a standard foam cable with a velocity factor of

0.80. 13 multiplied by .80 is 10.5 feet. The fault is about 16 feet away.

5.6 Resonance Mode

SWR-584B Instruction Manual HF/VHF SWR Analyzer

The Resonance Mode primarily draws attention to reactance, displaying reactance on the IMPEDANCE met er. In this mode, the SWR-584B measures frequency, SWR, resistance (R= ), and reactance (X= ). When reactance is zero, the system is said to be resonant.

Note

Zero reactance or resonance can occur on frequencies where the antenna is not actually

resonant. Conversely, the antenna may appear to contain reactance even at its true r esonant frequency when measured through a f eedline.

A less than perfectly matched antenna and feedline, when used with a feedline that is not an exact multiple of 1/4 wavelength (0, 1/4, 1/2, 3/4, etc.), will have reactance added by the feedline. The added reactance may coincidentally cancel the antenna’s reactance, making the system resonant. The SWR of the system, if the feedline is a 50 ohm feedline with minimal loss and free from common mode currents, will not change as the feedline length is changed. This is true even if the resonant frequency or reactance changes.

This mode functions like other SWR and impedance modes, with the exception the IMPEDANCE meter measures reactance. This allows the operator to easily observe frequencies where system reactance crosses zero.

5.7 Percentage Transmitted Power

Percentage Transmitted Power mode is the final measurement mode available in the Advanced mode menu. This mode is reached (after entering the Advanced mode menu) by pressing and releasing the MODE button four times. It can also be reached (as all other advanced modes are) by stepping through advanced modes with the MODE button until the display indicates “% Transmitted Power”.

Percentage of transmitted power is yet another way of describing SWR. It is similar to mismatch loss, but SWR data is expressed as a “percentage of transmitted power”.

CAUTION: The name ‘‘% Transmitted Power’’ may mislead those unfamiliar

with SWR and energy transfer in a system. Power ‘‘transmitted’’ or transferred to a load can be nearly 100% even if the ‘‘% Transmitted Power’’ display indicates a system has nearly zero percent transmitted power. Conversely, ‘‘% Transmitted Power’’ can be measured as nearly 100%, and the actual transmitted power might be very low.

6.0 ADJUSTING SIMPLE ANTENNAS

SWR-584B Instruction Manual HF/VHF SWR Analyzer

Most antennas are adjusted by varying the length of the elements. Most home made antennas are simple verticals or dipoles that are easily adjusted.

6.1 Dipoles

Since a dipole is a balanced antenna, it is a good idea to put a balun at the feedpoint. The balun can be as simple as several turns of coax several inches in diameter, or a complicated affair with many windings on a ferromagnetic core.

The height of the dipole, as well as it's surroundings, influence the feedpoint impedance and feedline SWR. Typical heights result in SWR readings below 1.5 to 1 in most installations when using 50 ohm coaxial cable.

In general, the only adjustment available is the length of the dipole. If the antenna is too long it will resonate too low in frequency, and if it is too short it will resonate too high.

Remember feedline length, when the antenna is not exactly the same impedance as the feedline, modifies the impedance along the feedpoint. The SWR will remain constant (except for a small reduction in SWR as the feedline is made longer) if the feedline is a good quality 50 ohm cable. If feedline length changes SWR at any one fixed frequency, the feedline either has common mode currents that are detuning the antenna or the feedline is not a true 50 ohm cable. Common mode currents are caused by lack of a balun or other installation errors.

6.2 Verticals

Verticals are usually unbalanced antennas. Many antenna manufacturers incorrectly downplay the need for a good radial system with a grounded vertical. With a good ground system, the SWR of a directly fed quarter-wave vertical can be nearly 2 to 1. SWR often improves if the ground system (and performance) is poor.

Verticals are tuned like dipoles, lengthening the element moves the frequency lower, and shortening the element moves the frequency higher.

6.3 Tuning a simple antenna

Select any mode that indicates SWR. Tuning basic antennas fed with 50 ohm coaxial cable can be accomplished with the following steps:

1.) Momentarily short the feedline center conductor and shield, then connect the feedline to the

2.) Adjust the

3.) Read SWR, and adjust the

4.) Divide the measured frequency by the desired frequency.

5.) Multiply the present antenna length by the result of step 4. This will be close to the antenna length actually needed.

Note

This method of tuning will only work on full size vertical or dipole ant ennas that do not employ

loading coils, traps, stubs, resist ors, capacit ors or capacit ance hats. These antennas should be

SWR-584B

frequency to the desired frequency.

SWR-584B

frequency until the lowest SWR is found.

SWR-584B

SWR-584B Instruction Manual HF/VHF SWR Analyzer

tuned according to the manufacturer’s instructions while tested with the SWR-584B, until the desired SWR is obt ained.

7.0 TESTING AND TUNING STUBS AND TRANSMISSION LINES

7.1 Testing Stubs

Resonant frequency of any impedance stub or transmission line can be measured. Select the first (or opening) measurement mode in the MAIN menu.

Connect the stub under test to the "ANTENNA" connector of the SWR-584B.

Note

The line must be open circuited at the far end for odd multiples of 1/4 wave stubs (i.e. 1/4, 3/4,

1-1/4, etc.) and short circuit ed for all half-wave stub multiples (lik e 1/2, 1, 1-1/2, etc.).:

If a balanced line is used, operate the SWR-584B only from internal batteries. Keep the SWR-584B a few feet away from other conductors or earth, and do not attach any wires (other than the feedline) to the unit. Use the ANTENNA connector’s shield for one lead and its center pin for the other. Two wire balanced lines suspended in a fairly straight line a few feet away from metallic objects or ground.

When tuning critical stubs, gradually trim the stub to frequency. Adjust the feedline or stub using the following method:.

1.) Determine the desired frequency and theoretical length of the feedline or stub.

2.) Cut the stub 20 percent longer than calculated, and short the far end of a half-wave (or multiple of a halfwave) stub or feedline. Leave the far end open for feedlines or stubs that are 1/4 wavelength or odd multiples of 1/4 wl long.

3.) Measure frequency of lowest resistance and reactance, or lowest impedance. For fine tuning look only at the “X=?” display. Adjust for X=0, or as close as X=0 as possible. The frequency should be about 20% below the desired frequency if everything worked as planned during the length calculation.

4.) Divide the measured lowest “X” frequency by the desired frequency.

5.) Multiply the result by the length of the feedline or stub to find the required length.

6.) Cut the stub to the length calculated in step 5, and confirm lowest “X” is on he desired frequency.

must

7.2 Velocity Factor of Transmission Lines

SWR-584B Instruction Manual HF/VHF SWR Analyzer

The SWR-584B accurately determines velocity factor of any transmission line. Select the Distance to Fault mode, the third measurement mode in the Advanced mode menu. This mode is reached by pressing and releasing the MODE button two times after entering the Advanced mode menu. It can also be reached (and all other advanced modes) by stepping through Advanced modes with the MODE button until the display indicates “Distance to Fault in feet”.

The Distance to Fault mode measures the electrical length of a transmission line. To obtain velocity factor, you must know the physical length of the line. If the distance displayed is 75 feet, and the transmission line is actually 49.5 feet long, the velocity factor is 49.5 divided by 75, for as result of 0.66 vF.

Note

The far end of the line can be either open circuited or short circuited. The line can not be

terminated in any impedance other than an open or short.

To confirm reliability, make two or more groups of measurements on different starting frequencies at least one octave apart. If measured distances agree, they are almost certainly very reliable. The more base frequencies used to confirm results, the more assurance you will have results are correct.

must

To measure velocity factor:

1.) Select a frequency where the Impedance meter is at the lowest deflection possible and where minimum reactance displayed on the SWR-584B LCD, or where reactance crosses zero. The reactance zero-crossing (or minimum reactance reading) is the point where reactance rises when the SWR-584B is adjusted either higher or lower in frequency.

2.) Press the “GATE” button. The blinking “1st” will change to a blinking “2nd”.

3.) Tune the analyzer higher or lower in frequency until the Impedance meter reads the very next impedance minimum, and where reactance displayed on the LCD again crosses zero. A non-zero minimum of a few ohms is acceptable.

SWR-584B Instruction Manual HF/VHF SWR Analyzer

4.) Press the “GATE” button again, and the display will indicate distance in feet.

Use the following procedure:

1.) Measure the physical length of the line in feet.

2.) Divide the display reading by the actual feedline length.

Example: 27 feet (physical length) divided by 33.7 feet (measured length) equals .80 . The velocity factor

is .80 or 80%.

7.3 Impedance of Transmission Lines or Beverage antennas

The impedance of transmission lines between a few ohms and 650 ohms can be directly measured with the SWR584B. Lines of higher impedance can be measured if a broadband transformer or resistance is used to extend the SWR-584B’s range. Select any measurement mode that indicates resistance (R=) and reactance (X=).

If a balanced line is used, operate the SWR-584B only from internal batteries. Keep the SWR-584B a few feet away from other conductors or earth, and do not attach any wires (other than the feedline) to the unit. Use the ANTENNA connector’s shield for one lead and its center pin for the other. Two wire balanced lines suspended in a fairly straight line a few feet away from metallic objects or ground.

Beverage antennas must be directly connected to the SWR-584B.

Using fixed resistances:

1.) Terminate the line or antenna in a non-inductive resistance somewhere around the expected value.

2.) Connect the transmission line or antenna directly to the frequency (near the expected operating frequency) until the lowest resistance and lowest reactance is measured.

3.) Record the impedance value.

4.) Adjust the frequency until the highest resistance and lowest reactance is measured.

5.) Multiply the highest resistance by the lowest resistance, and find the square root of the result.

SWR-584B

"ANTENNA" connector. Adjust the

must

SWR-584B Instruction Manual HF/VHF SWR Analyzer

Example: The highest resistance is 600 ohms, the lowest is 400 ohms. 400 x 600 = 240,000. The square

root of 240,000 is 490. The impedance is 490 ohms.

Using a potentiometer or resistor decade box:

1.) Connect the transformer).

2.) Adjust the frequency and note only the SWR change.

3.) Adjust the termination resistance until the SWR remains as constant as possible with very large frequency changes around the operating frequency range.

4.) The resistance of the termination resistor is the surge impedance of the system.

SWR-584B

to one end of the system (in this case you can use a broadband matching

7.4 Adjusting Tuners

The SWR-584B can be used to adjust tuners. Connect the SWR-584B "ANTENNA" connector to the tuner's 50 ohm input and the desired antenna to the normal tuner output. This connection can be made with a manual RF switch to facilitate rapid changeover, provided that switch has better than 50 dB port isolation.

WARNING: ALWAYS CONNECT THE COMMON (ROTARY CONTACT) OF THE SWITCH TO

THE TUNER. THE SWITCH MUST CONNECT EITHER THE SWR-584B OR THE STATION EQUIPMENT TO THE TUNER. TRANSMITTING EQUIPMENT MUST NEVER BE CONNECTED TO THE SWR-584B.

1.) Connect the

2.) Turn on the

3.) Adjust the tuner until the SWR becomes unity (1:1).

4.) Turn off the

SWR-584B

to the tuner input.

and adjust it to the desired frequency.

and re-connect the transmitter.

7.5 Adjusting Amplifier Matching Networks

The SWR-584B can be used to test and adjust RF amplifiers or other matching networks without applying operating voltages.

The tubes and other components should be left in position and connected so that stray capacitance is unchanged.

To measure input circuits, a non-inductive resistor equaling the approximate driving impedance of each individual tube is installed between the cathode of each tube and chassis.

To measure tank circuits, a resistor equaling the calculated tube operating impedance is connected from the anode to the chassis with short leads.

SWR-584B Instruction Manual HF/VHF SWR Analyzer

The antenna relay (if internal) can be engaged with a small power supply. The amplifier’s external RF input and output connectors are now connected to the amplifier’s RF matching networks.

The appropriate network can now be adjusted. When the analyzer shows 50 ohms and a 1:1 SWR at the operating frequency with the proper amounts of capacitance to set the system Q, the networks are working.

CAUTION: The driving impedance of most amplifiers changes as the

drive level is varied. Do not attempt to adjust the input network with the tube in an operating condition with the low level of RF from the SWR-584B.

7.6 Testing RF Transformers

RF transformers designed to operate with 25-100 ohm termination on one of the windings can be tested with the SWR-584B.

The 25 to 100 ohm winding is connected through a very short (less than one electrical degree long) 50 ohm cable to the "ANTENNA" connector on the SWR-584B. The other winding(s) of the transformer is terminated with a low inductance resistor equal to the desired load impedance. The SWR-584B can then be swept through the desired transformer frequency range. The impedance and bandwidth of the RF transformer can be measured.

Transformer efficiency can be measured by comparing the source voltage from the SWR-584B to the load voltage, and using standard power level conversions.

7.7 Testing Baluns

Baluns can be tested by connecting the 50 ohm unbalanced side to the SWR-584B "ANTENNA" connector. The balun must be terminated with two equal value load resistors in series. The resistor combination must have total resistance equal to balun impedance. For example, a pair of 100 ohm carbon resistors are required to properly test the 200 ohm secondary of a 4:1 balun (50 ohm input).

Measure SWR while moving a jumper wire from point "A" through point "C".

To the VEC-584B's

"ANTENNA"

connector

BALUN

Clip Lead

A properly designed current balun is the type most effective for maintaining current balance. It has the highest power capability and lowest loss for given materials. It should show a low SWR over the entire operating range of the balun with the clip lead in any of the three positions.

A well designed voltage balun should show a low SWR over the entire operating range when the clip lead is in position "B". It will show a poor SWR when the clip lead is in position "A" and "C". SWR should be about the same in either position “A” or “C”.

SWR-584B Instruction Manual HF/VHF SWR Analyzer

A voltage balun should also be tested by disconnecting the outer connections of the two resistors and connecting each resistor in parallel. If the voltage balun is operating properly the SWR will be very low with the resistors connected from either output terminal to ground.

To the VEC-584B's

"ANTENNA"

connector

BALUN

7.8 Testing RF Chokes

Large RF chokes usually have frequencies where the distributed capacitance and inductance form a low impedance “series-resonance”. This series resonance occurs because the choke acts like a series of back to back L networks. This causes three problems:

First, impedance from end to end in the choke becomes very low.

Second, the voltage at the center of the resonant point becomes very high, often causing severe arcing.

Third, the current in the winding becomes very high, often resulting in severe heating.

Troublesome series resonances can be detected by installing the choke in the operating location, and connecting only the SWR-584B from end to end through a short 50 ohms jumper cable. By slowly sweeping the operating frequency range of choke, dips in impedance identify low impedance series-resonant frequencies. By moving a small insulated screwdriver’s blade along the choke, you will find a point where the series resonate impedance suddenly changes. This is the area that has the highest voltage, and the area that adding or subtracting a tiny amount of capacitance will have the largest effect. By removing turns to reduce capacitance, or adding capacitive stub at this point, the resonance can be shifted out of the desired frequency range.

A small change in capacitance has a much larger effect than a small change in inductance, because the ratio of L to C is so high.

8.0 TECHNICAL ASSISTANCE

If you have any problem with this unit first check the appropriate section of this manual. If the manual does not reference your problem or your problem is not solved by reading the manual, you may call VECTRONICS at 601-323-5800. You will be best helped if you have your unit, manual and all information on your station handy so you can answer any questions the technicians may ask.

You can also send questions by mail to VECTRONICS, 300 Industrial Park Road, Starkville, MS 39759 or by FAX to 601-323-6551. Send a complete description of your problem, an explanation of exactly how you are using your unit, and a complete description of your station.

Vectronics SWR-584B User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual