[GreenKeys] Questions on troubleshooting an antenna

[Lee Mushel]

George,

Given the popularity of this "thing" I find it difficult to believe that you 
are only now finding the G5RV!   When I first saw a description of it I 
could immediately see why a lot of poor folks were thinking "the band is 
dead!"   And then I researched the origins of it and read G5RV's  (SK) 
description of what he had created and his own conclusion was that it wasn't 
much of an antenna beyond maybe a little performance on 20 meters which is 
the only frequency it had been designed for.   No one today seems to realize 
that the feedline is actually a radiating part of the antenna or that you 
must us a balun and you should avoid ordinary 300 ohm TV twinlead like the 
plague.   But you are right.   It is simply a very poor antenna, a fact 
that no one seems to want to admit so it just keeps on going......

73

Lee   K9WRU
----- Original Message ----- 
From: "George B. Hutchison" <w7tty at olypen.com>
To: "GreenKeys" <GreenKeys at mailman.qth.net>; <hunybuny at eskimo.com>
Sent: Sunday, June 27, 2010 8:18 AM
Subject: Re: [GreenKeys] Questions on troubleshooting an antenna


> 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
>
>
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