[GreenKeys] Questions on troubleshooting an antenna

[George B. Hutchison]

Tony - - -

I have been away from ITTY for about the past five days because I have been 
dealing with a field day operation (my first since 1969) and experiencing 
the mediocrity of a favorite (Not Mine) antenna callled a G5RV.

IMHO the G5RV is a pile of crap. It is not resonant at any frequency that I 
can see, and requires something most people call an antenna tuner, which is 
little more than a jumble of coils, capacitors, and a lump of ethereal 
belief called "HOPE IT WORKS".

Last night I put together an 80/40 meter dipole which simply consists of a 
1:1 center balun, and four pieces of antenna wire each roughly 33.5 feet, 
one on each side of the balun, a separating insulator on each side, and then 
the second piece of wire going to an end insulator then to some 
non-conducting line to the support, a 70 foot tower on one end and a wire 
fence on the other, with the insulating pieces being roughly 25 feet in 
length.

There are 4 inch pigtails on either side of the inner insulators that, when 
twisted together make an 80 meter dipole resonant at around 3590 KHz. 
Untwist the wires and the thing is resonant at around 7120 KHz.

A Bird wattmeter shows max forward power and no reflected power at the 
mentioned frequencies, indicating that IT WORKS.

I used an MFJ Antenna Analyzer to set the antenna up, (first time use of one 
for me) and the antenna just plain WORKS.

I understand that you have limited space, thus the short radials and the 
hefty coil on the PVC Pipe.

First, the higher the number of radials is OK, up to about 36. After 36 or 
so radials you are throwing money away on copper that gives you little 
additional performance. Most broadcast engineers will tell you that about 95 
percent of the ground current action occurs within 15 feet of the base of a 
vertical antenna, so you are right at the edge when it comes to radial 
length. What you have done should work. An article in a recent issue of QST 
supports the effect of the number and the length of the radials.

A physically short antenna requires inductance at the base, so the coil is a 
good feature. The trick is to get the right number of turns in the coil for 
the 18 foot pigtail in order to attain resonance.

If you know anyone who has an MFJ Antenna Analyzer, offer them a very nice 
lunch if they will bring it over and help you seek the right number of turns 
you need to make your system work.

I have plans on getting an MFJ Analyzer as soon as I can save up the coins 
to do so, as I was astounded that the performance of the dipole was exactly 
as shown it would be on the MFJ!!!

There are two meters and a digital readout on the MFJ. one is SWR, and the 
other is radiation resistance/impedance.

The digital readout shows the applied frequency, calculated SWR, reactance, 
and something else I forget at this moment.

Many people interpret the MFJ label as meaning "Mighty Fine Junk", but when 
the performing results closely reflected what the MFJ said was happening, I 
quicky became a believer!

Don't sweat the insulated wire on the radials. The insulation does not 
apparently affect performance, and will keep your ground system intact over 
the long haul.

Hope this llittle dissertation helps.

W7TTY