If the resistor does not have the same impedance as the line, the measured Z will vary cyclically as in Fig. 4 but the peaks and nulls will not be as pronounced. Let:

Zo = Line Impedance

R t = resistor terminating the line

If you measure the minimum Rs at the frequency F-1/4 discussed on Page 6, the line impedance is very dose to:

This equation ignores line losses and any small “imaginary" part of Zo. For best accuracy, Rt should be close to Zo.

CHECKING BALUNS & TRANSFORMERS

If you have a 1:1 balun, connect a 50 ohm resistor to its output (where the antenna would normally go) and measure Rs, Xs, and SWR at the balun input. This should be a fairly constant 50 ohms with little X. (First check any variation R, X, and SWR of the VA1 by connecting the resistor directly to the VA1.) If you have a 50 ohm to 200 ohms (4:1) balun connect a 200 ohm resistor to the balun output and check for 50 ohms at the input. Expect a higher SWR at the highest and lowest frequencies.

Testing of a balun at high power is necessary to see such things as core saturation, arcing, etc. To be safe, you should use an in-line SWR meter, such as our WM-1, which works at 5 watts, and watch for any drastic change in SWR as power is increased.

ADDING RADIALS TO A VERTICAL

You put up a vertical antenna (1/4 wave). You have a few radials. Now you want to boost your signal, so you add more radials. But how do you tell how much good they did?

A 1/4 wave vertical has a theoretical base impedance of about 38 ohms at resonance (Rs=38, Xs =0) with hundreds of radials. Lets say you measure the base impedance at 58 ohms. This means you have about 20 ohms (58-38) of ground loss.

So about 1/3 of the antennas Z is in ground loss, and so 1/3 of your power is lost. Now, you add a few radials and find a lower impedance at resonance. You can now see how much your ground loss has been reduced.

Many caveats: The 38 ohms depends on antenna thickness and assumes an antenna in the clear, and radials that don’t slope. So you can’t be too precise here. But the method is also useful for very short loaded verticals, where most of Z is ground loss.

TUNING A TUNER WITHOUT TRANSMITTING

Figure 7 shows how to do this. We don’t make this switch, but an ordinary 5 to 20 amp SPOT toggle switch in a small minibox will work fine. Just keep leads short..a few inches. Be sure there is no possibility that the transmitter can feed directly into the Analyst. This could burn out the analyst instantly!

MEASURING TRAP RESONANT FREQUENCY

Connect the Analyst across the trap as shown in Fig. 8. Keep the leads widely spaced so stray capacitance is not added.Tune the frequency until the highest impedance occurs. This is the resonant frequency of the trap. At resonance, Z will probably read “H” so you may have to average two frequencies on each side of resonance where Z reads the same, say 800 ohms. To avoid “H,” you could connect a resistor, say 500 to 1000 ohms, across the trap. The highest Z still indicates resonance.

USE AS A SINE WAVE GENERATOR

The VA1 output is a low distortion sine wave , about 2 V p-p with no load, and an output impedance of 140 ohms; a 140 ohm load cuts its output in half.

TRAP

Frequency

VA1 Page 7