Vectronics SWR-66 User Manual

SWR-66 Dip Meter Adapter Owner's Manual

VECTRONICS

SWR-66 Dip Meter Adapter

INTRODUCTION

Thank you for purchasing the SWR-66 Dip Meter Adapter. The SWR-66 Dip Meter Adapter
works with your Vectronics SWR-584 HF/VHF SWR Analyzer.

The SWR-66 Dip Meter Adapter is a kit consisting of 2 coupling coils and a UHF to RCA female
adapter. The larger probe coil covers 1.8 through 50 MHz, and offers maximum sensitivity in the
10 to 20 MHz range. The smaller probe coil covers 20 through 175 MHz, and offers maximum
sensitivity in the 100 to 150 MHz range.

DIP METER THEORY OF OPERATION

The SWR-66 Dip Meter adapter is very versatile. When properly used, it can make accurate
measurements of many different RF circuits. The following description will help you get
maximum accuracy and versatility from the SWR-66.

The SWR-66 is designed to adapt a S WR Analyzer to work as a dip meter. Your SWR analyzer
contains an internal bandswitched oscillator circuit. The oscillator is buffered to increase the
signal level and prevent the load from affecting the oscillators frequency. The high level RF
output covers all Ham bands below 170 MHz and is available on the ANTENNA jack.

The SWR Analyzer also contains a meter used to measure the unbalance in an impedance bridge
circuit. As the load on the ANTENNA connector approaches 50 ohms resistive, the meter reads
a lower amount (toward 1:1).

By connecting a small coil through the adapter to the ANTENNA connector, an SWR Analyzer
can be used to test ex ternal circuits for resonance. The magnetic field surrounding the coupling
coil provides the required connection or coupling to the circuit under test. The meter on the
SWR Analyzer is then used to measure the amount of RF signal absorbed by the circuit under
test. The meter reads lower as resonance is approached.

Any resonant circuit will absorb RF from the coupling coil as long as the circuit is tuned to the
same frequency as the oscillator in the SWR Analyzer. As the "Q" of the circuit under test
increases, the dip will become sharper and deeper. High "Q" circuits absorb more RF energy in a
narrow range of frequencies. If the "Q" of the circuit under test is low or coupling between the
coupling coil and the inductor in the circuit under test is inadequate, the dip shown on the meter
will be small or perhaps not even visible.

Unlike the tuning coils of a conventional grid dip meter, the SWR-66 coupling coil is not a part
of a resonant tank circuit. This adapter depends on the "Q" of the external circuit to improve the
circuit coupling. If the external circuit has a very low "Q", the coupling will have to be increased
by placing the inductor of the external circuit very close and in line with the axis of coupling coil.

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SWR-66 Dip Meter Adapter Owner's Manual

This has the advantage that stray coupling is reduced and frequency pulling of the oscillator is
eliminated. Frequency readings can thus be made with more precision.

To insure accurate readings always keep the coupling as loose as possible while still getting a
readable dip.

Maximum coupling is obtained when the coupling coil is either placed inside a larger coil under
test, placed against a coil of equal size or placed over a coil of small size. When using the
smaller coil to couple with a very small coil, such as a molded inductor, the outer plastic sleeve
must be removed or cut to allow the molded inductor to be inserted into the small coupling coil.
Otherwise coupling may be insufficient to create a dip.

Once a dip is found the coupling coil and the inductor of the circuit under test should be
separated until the dip is barely evident. The frequency should be read at this point for maximum
accuracy.

The coupling coil can be removed and the coupli ng coil jack can be used t o direct ly feed a one or
two turn link coil on a toroidal inductor. The coupling can be easily varied when testing resonant
circuits containing toroids by adding or removing turns from the coupling link. Never try to
couple with the standard method of using a double link. The air wound external link acts like a
shorted turn on the toroid and lowers the inductance. This "shorted turn affect" will cause
inaccurate measurements for many types of toroids.

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