The following email came in this morning from Tom,
W8JI. He has "de-subscribed" from the reflectors for
a time, so has asked that I post there for him.
Follows his input on the topic:
Sorry I'm slow on this. If this doesn't make it to the appropriate
reflectors, please post it for me. I've unsubscribed so I can get my
low band towers all up. (Today I finished a 260-280 ft HAAT tower on
a rise in my west pasture.)
> Use of accurate attenuator:
> nor the willingess to hand select all the needed accurately measured
> resistors to assemble such a unit; so I will buy something!
MFJ makes a surface mount resistor attenuator that is like the ARRL
unit but has the CORRECT resistor sizes.
It is within ~ 1/2 dB worse case for attenuations below 40 dB. ALWAYS
use a pad between the RX and any attenuator you use, so the early
steps remain accurate. Otherwise if the receiver is off, initial
attenuation settings will be off. The manual explains this (I hope).
I use just such a pad, but mine is a prototype calibrated to .05 dB.
You might want to add an in/out switch like I did, so you can pop it
in and out quickly.
By the way, I use an enhanced gain 4 square on 160 meters. It
models and measures on groundwave to have almost 7 dB gain over a
single element, which I can also run. Other than conditions of space
diversity fading lasting only 30 seconds or so, the pad measurement
shows gain as just over six dB on sky-wave.. so this is a good
The thing to remember is tests like for ground systems give results
good ONLY at one location, until a lot of people verify the results
for other soil conditions of a similar type.
When I recently tested another elevated vertical system, I "A-B"ed
the test antenna against a dipole at 120 feet and another similar
height vertical with a large ground system. In that case, the results
were fairly easy to see using the pad, and improvements tracked
closely with groundwave field strength readings.
73, Tom W8JI
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