Fellow Chasers of the lost RF,
There has been much discussion on the reflector about tuner losses
but most seems to be theory and conjecture. It would be good to see some
typical figures for tuners (into random antennas). How do Elecraft, Z-match,
balanced tuners, Johnson matchbox and tuners with output baluns compare when
working into complex loads? The following is an easy way to find out.
Simple Method for Measuring Antenna tuner loss with reactive loads
I haven't tried this method but it should work. It is easy to
measure the efficiency of a tuner with resistive loads. The problem is with
complex reactive loads, as it is not possible to measure the output with
simple instrumentation. The following is a very simple procedure but does
require the use of 2 other tuners capable of matching similar loads. Let us
assume that we want to know the loss of antenna tuner "A" when it is matched
to an unknown antenna load. In the following, all measurements are made with
pure resistive 50 ohm loads so a simple power meter can be used.
1. Tune tuner "A" for lowest SWR with antenna (note settings)
2. Connect output of tuner "A" to output of tuner "B"
3. Connect input of tuner "B" to 50 ohm dummy load
4. Tune tuner "B" for lowest SWR
5. Measure power loss through tuner "A" + tuner "B"......... (XdB)
6. Repeat steps 2, 3, 4 and 5 replacing "B" with tuner "C".. (YdB)
7. Repeat steps 2, 3, 4 and 5 using tuner "B" and "C"....... (ZdB)
A little simple algebra:
Tuner "A" + tuner "B" = XdB
Tuner "A" + tuner "C" = YdB
Tuner "B" + tuner "C" = ZdB
Add the first 2 lines
2A + B + C = X + Y
Substitute "Z" for "B" + "C"
2A = X + Y - Z
Loss of tuner "A" = (X + Y - Z)/2dB
Notes:
The exercise is much simpler when you have 2 identical tuners. All
you have to do is half the loss measured through the 2 tuners.
The same power meter should be used for power input and for power
output as meter calibrations are not accurate enough. A more accurate way is
to measure the RF voltage across the tuner input and across the dummy load,
to find the power loss.
This could be an interesting club meeting project to compare a wide
variety of tuners.
73 and enjoy
Tony Fegan VE3QF K2 # 490
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