[TowerTalk] Vertjcals, Radials, etc.

[Jim Reid]

Hi again,

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:

"Hi Jim,

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 
test!!!

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
w8ji.tom@MCIONE.com"






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