Ten-Tec 229B review

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Ten-Tec

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Chris Lorek G4HCL finds that L has all the best

tunings.

For many amateurs operating on the HF bands, particularly 80m and 160m, an aerial tuning unit or ATU is an absolute necessity. This matches the impedance of the aerial system to the output impedance of your transmitter, giving maximum power transfer into the aerial system, and possibly more importantly safeguarding your expensive power amplifier devices from blowing up!

impedance at full power of 3000 ohms. A modified 'L Match' arrangement is used

(more of this later), with a large tuning capacitor of 3.5kV voltage rating and a silver plated multi-turn roller coaster coil of 28^H to provide a continuously variable inductance. A sliding cursor along the front panel window together with a calibrated adjustment knob gives an indication of the inductance in circuit, the capacitor knob graduated with a 0-10

The KW ATU Veteran HF operators will know the

KW 'Eee-Zee' match ATU well, on sale

many years ago and regarded by many

amateurs as the ultimate of the day. The

latest KW ATI) is featured in the Ten-Tec range as their Model 229B, and is claimed

to match virtually any unbalanced load, at

all the power the law will allow, from

1.8MHz to 30MHz. We thought it would be a good idea to try it out, even to the extent of loading up the house drainpipes and having worldwide QSOs.

scale to show the amount of variable capacitance in circuit.

Four SO-239 aerial input sockets are

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(g\M/

-O OUT IN <

provided, a front panel switch being used to select these in use. One of these sockets is internally linked to a screw terminal to allow a long wire aerial to be connected in place of aerial connection No.4 if required. An optional balun may also be internally fitted, to allow a balance input to be matched to a 50ohms unbalanced line to feed your transmitter. A large screw connection is also provided on the rear of the case to allow connection of an RF ground, very important and of course essential when using long wire aerials.

A front panel meter gives a readout

of switched forward or reverse power,

with full-scale ranges of 200W and 2000W. A further rotary 'SWR SET' potentiometer is provided, to allow direct SWR readings to be given following adjustment to match the forward power level. Applying a DC supply provides internal backlighting of the meter scale and inductance position cursor.

Circuitry

The matching circuit is basically an 'L' network using an inductor-capacitor arrangement in an L-formation. This arrangement does have the advantage

that only two adjustable components are

used rather than three. Because there are no internal nodes in the network, the maximum circuit voltages and currents

that occur in the ATI) are never greater than those present at the input or output

connections. Also, because there are only

two components to adjust, there is only

comp

—oc

Offerings

The aerial tuning unit comes in a large metal case, 139mm x 330mm x 279mm, its physical size together with the large tuning controls giving you an idea of its quoted power handling capabilities of 2kW. The output matching range is specified as at least 10:1 SWR, at any phase angle, with a maximum input

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IN O-

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Fig.l. The circuit of the KW ATU's switching arrangement.

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HAM RADIO TODAY JULY 1989

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Fig.2. The L-match connections.

SW1

BYPASS

tor, supplied with the tuner, may be soldered into circuit as required to provide extra capacitance if needed.

LOZ

LOWEST

BOTH SWITCHES VIEWED

FROM REAR IN BYPASS MODE

0.3uH

INPUT

SWT a

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:S7/77

OPTIONAL I •

BALUN

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-+J305]5>n I

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JUMPER FOR

BALANCED LINE (BALUN KIT REQUIRED)

one setting of each that will provide a perfect match, providing a quicker method of tuning up in practice. The fundamental low-Q network provided gives lower circulating currents hence lower loss for a given power level, and also provides a reasonably broad bandwidth when compared with other networks using essentially higher Q. The inductor in the L configuration is always in series with the transmission line, providing a natural low-pass filter effect hence reducing the levels of any harmonics from the transmitter power amplifier.

HI E

HIGHEST

C2-5

ALL 470p HI-

^-0

SWIb

18uH

0-2-

06 .I..

25p-T-

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4 3 2 1

ANTENNA SWITCH

OUTPUTS

parallel with the variable wide-spaced tuning capacitor, to provide a greater degree of impedance matching range, four 470pF ceramic capacitors being used. On 160m though, some low impedance may require more than the 2400pF total provided in the ATU with the variable capacitor at full mesh. Under these conditions, a further lOOOpF IkV capaci-

SW2

vci

40-500p 5

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Stray Reactances At high frequencies, in the case of

only a slight mismatch as the load

impedance approaches 50 ohms, the

values of inductance and capacitance

required for matching become small, and

the stray inductance and capacitance

present in an ATU circuit may exceed this. Rather than simply switching to Bypass mode on the KW ATU to directly connect input to output, the designers seem to have thought of everything by adding a small compensating capacitor of 25pF and inductor of 0.3/jH into the circuit to counteract this problem, shown as C7 and LI on the accompanying circuit of the tuner section of the ATU. Hence finetuning adjustments may be made to low values of mismatch, if needed.

In Use

I have used several types of ATU in the past, my usual one being simply a Japanese type matching my HF transmitter lineup, which tends to get used more as an aerial selector than anything else. With perfectly matched resonant aerials, there is of course little need for an ATU, but many amateurs, myself included,

I used the KW ATU in two forms, firstly to fine tune the impedance of my resonant aerials when I shifted in frequency from one end of the band to the other, and secondly as a true complex impedance transformer to tune a non-resonant aerial system.

All aerials have a resonant point, when using high-Q aerials such as trapped verticals the VSWR raises as you approach the band edges. In my case inserting the ATU allowed this to be corrected right down to a VSWR of 1:1 to feed my transceiver, this ideal match giving the benefit of better PA perform-

not have this ideal on all bands.

Limitations

• Life is not all roses, unfortunately, and as with most things the L configuration does have its disadvantages. First of

all, it can only match impedances either higher, or lower, than the 50ohm output

depending upon whether the capacitor

comes before or after the series inductor, as shown in the accompanying diagram. To provide this switching function a large internal cermic switch (SW1) is used in the ATU, with a corresponding front panel indication of LO or HI. This switch is also used to place additional capacitance in

HAM RADIO TODAY JUi.Y 1989

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Page 3

room, of course.'

ance such as linearity and power transfer. It is important to note that the VSWR still

remains at the aerial itself and along the coax feed line to the ATI), hence using such a tuner at the transmitter end

only improves the match to the trans-

mitter itself.

After some garden work laying new

turf, I took advantage of the situation by

burying over 50 copper earth radials of various lengths stretching towards the extremities of my garden. Living in a residential area with the need to reduce the visible aspect of my aerials as much as possible, I thought I at loading this being a wire disguised behind the plastic drain guttering of my two-storey house. This idea is actually described in the ARRL Antenna Book, using bonded

up a

would try the ATU

top-loaded vertical aerial,

metal guttering. In my case, one downpipe at the base of the radial system was the vertical section, while the horizontal guttering at the roof provided the top loading. The ATU was placed indoors about a metre from the vertical and ground feeds.

In use, the ATU provided a very good performance, matching the wire system right down to a VSWR of 1:1 on

I was very impressed. A coax feed led from the feedpoint to the shack, where my Ten-Tec Hercules HF solid-state linear amplifier was used to power the system up. The aerial performance when fed with

this system is of course not relevant to the

ATU's matching capabilities, but I was certainly impressed with the results

obtained on 20m when compared to my two other resonant 20m aerials in use at the time, this being another story!

Even when using the legal maximum power of 400W pep, I never experienced any 'flashover' in the ATU which I have found under some high-impedance matching conditions with other ATUs even when using lower powers. This improvement is due to the L match arrangement used. The ATU was used for several weeks on the well-used 14MHz port of my packet radio node, to ensure a good test, and gave unfailing performance. What more can I say?

My thanks go to HRS Electronics for

the loan of the Ten-Tec Review equipment.

all bands.

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HAM RADIO TODAY JULY 1989