[TowerTalk] Laws of Physics Repealed!

[Roger (K8RI) on TT]

A counterpoise does not violate the laws of physics although the claims 
for a loaded pole on 75 that's a little short for 40  is more a flight 
of fantasy.  But 31.5 feet is pretty much a quarter wave on 40.

I've used the Hy-gain AV640 and the R6.  Both advertize no radials, but 
they do use a counterpoise.  The antennas appear similar including the 
matching circuitry.  OTOH  the Cushcraft has several traps.  Both are 
only a bit short on 40, their lowest band.  Both now have a version that 
covers 75/80.

I use them as an example because hey are basically the same as the 75/80 
meter version, except for the short radiator on 75/80.

BUT

Once assembled, (there are a LOT of parts) the real world proved the 
AV640 and the R6 to be quite different.
Two or three sawhorses along with a couple of extra hands makes assembly 
easier, faster, and a lot less frustrating.
Be careful as the stubs can make it difficult to lay the antennas down.

The AV640 resonated in each band. The frequency for each band was easily 
set with no band to band interaction.
SWR at resonance in each band was less than 1.5:1.  Just assemble 
according to the directions, put it up, record the resonant frequency 
for each band, make adjustments according to the manual and it should be 
ready to go.

The matching system for the AV640 is a toroidal transformer isolated 
from the feed line by a toroidal choke. Resonance is set with capacity 
hats and tuned stubs.  Very small adjustments go a long way.  IOW these 
antennas are the equivalent of top hat loaded quarter waves.  I did not 
find full band coverage on 40, but most of the band was usable.

At first look the matching unit for the R6 appears to be identical to 
the AV640.

The R6 was, to put it mildly, a royal PITA. Our club president set up an 
R6 for a new ham.  It was not usable on any ham band.  He finally ended 
up rewinding the matching transformer to a different ratio to get a 
reasonable SWR.  I don't know the performance results of the modified R6.

I had the AV640 and a center fed, half waver sloper fed through an Alpha 
Delta AB2 (A/B) switch.
The AV640 was mounted on  a cheap 32' AL tower  (The kind I wouldn't 
climb on a bet even when I was young). 
http://www.rogerhalstead.com/ham_files/AV-640/AV640.htm  The sloper 
was/is at roughly 90 feet to the top end with close to a 45 deg angle.

This was during the past sunspot cycle low where 40 was open world wide 
for several days at a time.
I ran 1200W SSB and CW on HF and 800W PEP SSB & CW on 6-meters Yes, I 
know that's more than the ratings, but the Hy-gain engineer said it 
should take it and it did.  What it didn't take was wasps building a 
nest in the matching unit.
I did find that the sloper had to be kept well away from the vertical.  
The AV640 is VERY sensitive to nearby objects and particularly if they 
are resonant on 40.

Whether Oceania, or Europe, it was a  toss-up. IIRC At times the sloper 
won by as much  as an S-unit and at times the AV640 would win into the 
same area.  Replies were usually on the first call and from giving my 
call one time (Timing is important). Apparently the counterpoise works 
fine.  As the directions say to mount it at least 6 feet above 
conducting surfaces, I doubt the AV640 would do well with a good radial 
system.

Based on results and the AB comparisons, I believe the AV640 is an 
efficient radiator.
The R6?  It's been laying on sawhorses in the back yard for the past 3 
or 4 years.

The AV680?  I'd like to try one and run a few tests. I expect (hope) it 
to be at least a "useable" antenna on 75, but certainly no match for the 
slopers, let alone a quarter wave vertical. Without testing one, it 
appears as a way to get on 75/80, but certainly not my first choice, 
remembering that these antennas need to be well away from conductive 
objects.  I have a 75/80 fan dipole that works quite well. 
http://www.rogerhalstead.com/ham_files/AntennaSpreader1.htm

AV680? Maybe. R9? Based on the R6, not a chance.

73

Roger  (K8RI)

On 10/23/2015 4:13 PM, Donald Chester wrote:
> First there was the Gotham Vertical.  Then the infamous Max-Com automatic antenna matcher.  Now, Cushrcaft is in on the action.
>
> "R9"
>   vertical.  Low angle radiation gives incredible, easy, world-wide low
> band DX on 75/80m and 40m, plus it covers 30 through 6m with low
> VSWR on all bands, with broadband matching transformer; no antenna tuner
> needed. Low profile blends inconspicuously to keep your HOA happy.  31.5
>   ft tall.  Best of all, NO RADIALS NEEDED!!!
>
>   Only $639. Just plug in your plastic radio and talk, talk, talk!
>
> See November, 2015 QST, page 2.
>
> Amazing
>   that hams (or maybe I should say HAMs) swallow that crapola.  31.5 ft
> is only an eighth wavelength on 75/80m. The base impedance of a 1/8
> wavelength vertical is about 12 ohms. No matter how much gimmickry such
> as stubs, loading coils, toroidal transformers and porcupine spikes are
> added, that thing will basically be a dummy load unless it is used with a
>   SUBSTANTAL radial ground system.  A couple of 8' ground rods won't cut
> it.
>
> I had always considered Cushcraft, which has been in the business for decades, a reputable outfit, but this makes me wonder.
>
>
> Don k4kyv
>   		 	   		
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-- 

73

Roger (K8RI)


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