This discussion reminds me that most on this list are HFers and never
go above 30mcs (MHz). Or buy all their ham stuff and believe the
mfrs specs or meters without question. Probably do not build
homebrew equipment so never had to measure if such-an-such actually
is working (and at what level).
By now I should have made a few of you angry at my post. Good!
For most arm-chair operators a Bird and Bird load will be more than
adequate to determine power and SWR to +/- 5% full scale reading. It
was my main antenna meter when working as a professional
technician. Rugged, fairly accurate, dependable (don't drop it off the tower).
A good non-inductive 50-ohm resistive load and a scope able to
measure over 50-MHz will do better.
Next some better directional couplers will give more accurate return
loss (SWR).
My "standard" is using better than good directional couplers (>20 dB)
with my HP-432A mw power meter using up to 10 mw signal
sources. This is usable to 18 GHz. With use of high power coax
attenuators, I can measure power as high as the rating of the
attenuator. I use 50-dB directional couplers on 1296 to measure my
600w amp (58 dBm).
XG3 is a good 1mw source (0 dBm) up to 200-MHz, though not real
accurate in frequency (which is not that important for
power/reflected power). But harmonic energy exists unless you use a
filter since the output is a square wave.
I recently bought a used Bird HP 8202 500w load (good to 2500-MHz)
which I can use with amps up to 1500w (as long as transmission is
kept short - less than a minute; most tests take only a few
seconds). I have a Bird 25w load which I have used up to 150w for
short measurements. If it feels hot stop until cool again.
But as a new young ham (1960's) I bought a cantenna (paint can filled
with mineral oil and resistor load immersed) for HF stuff and a
Knight-Kit SWR meter. But as I got older and had more cash I got better stuff.
A dummy load that you can trust to be SWR 1:1 is good thing to check
those SWR meters or antenna analyzers with. Handy when measurements
seem to be "all over the map". Use it to test coax cables, for instance.
73, Ed - KL7UW
http://www.kl7uw.com
Dubus-NA Business mail:
[email protected]
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