[TowerTalk] Laws of Physics Repealed!

[Kim Elmore]

My dad (W5JHJ, SK) used an AV640 for a number of years on 40 m when we 
had a schedule between OK and CO on 40 m every Sunday afternoon. It was 
up about 10 ft above the ground attached to the eave of the roof. As I 
recall, it tuned by the book after assembly. It looked wobbly but held 
up fine for many years. I used double hose clamps on everything and also 
Ox-Gard on every mechanical connection. The only problem I recall with 
it (other than it was rather complex to assemble) was that there was a 
strap from the matching assembly to the vertical element that flexed 
slightly as the antenna moved in the wind. That strap finally broke due 
to fatigue, so I fashioned another one and it worked FB after that.

I vaguely recall that the instructions said there was a sweet spot in 
the mounting height; 10 - 30 ft or something like that. I never quite 
understood why and it was never an issue, anyway.

73,

Kim N5OP

On 10/24/2015 6:23 PM, Roger (K8RI) on TT wrote:
> From my experience with the AV640, I am impressed with it on 40 meters 
> (Its lowest band) mounted at 25 and 32 feet with it matching the 
> center fed,sloping half wave on average for DX.  Due to its 
> sensitivity to nearby objects I wouldn't recommend it as a limited 
> space antenna. OTOH if that's the only space available, I'd use one.  
> Get it as high as possible, or convenient.   Tripod roof top mount, 
> short pole or tower.
>
> I do have one caveat for both antennas.  There are a lot of mechanical 
> connections for jumpers, coils, traps and stubs subject to corrosion. 
> I'm not down wind from any nearby industry, but I still get a lot of 
> degradation of solder and Al to Al connections.  The solder turns grey 
> and just crumbles away. Al to Al held by screws often gets a buildup 
> between the Al pieces.  I have needed to redo a number of the coil and 
> jumper connections on the AV640.  I've had good luck with liquid 
> Electrical tape. Around here the clear Krylon doesn't last long.  YMMV
>
> As a comparison, All of my C3i antennas (one 7L 6-meter, two 12L 147, 
> and two 11L 440s) have had all solder joints for the matching networks 
> fail. What solder was left would crumble to powder when rubbed between 
> my thumb and fore finger.  Those all had several coats of clear 
> Krylon.  They are getting liquid electrical tape.
>
> 73
>
> Roger (K8RI)
>
>
> On 10/24/2015 6:48 PM, Jim Brown wrote:
>> On Sat,10/24/2015 6:49 AM, Daniel Danny Horvat wrote:
>>> There is no R6 antenna, there is a R-6000 antenna which I designed for
>>> Cushcraft followed by R8 antenna which was covered in K7LXC & N0AX 
>>> report
>>> with high score.
>>
>> Congrats on your work, Danny.  It's not easy getting good performance 
>> with small size!
>>
>>> I was against implementing a 80m on R8 vertical back then (1998) due 
>>> low
>>> efficiency and narrow bandwidth. MFJ has no problem to claim 
>>> anything just
>>> to sell.
>>
>> N0AX acknowledged this in his write-up of their tests. Only a fool 
>> would expect otherwise. :) His advice for all of these antennas as a 
>> class was to buy one rated for at least one band lower than you 
>> intend to operate with it.  That is, if you want to work 40, buy one 
>> that will work 80, and don't expect good performance on 80M from a 30 
>> ft vertical.
>>
>>> Verticals,  R5/R7 R6000 R8 and also clones AV620, AV640 are IMO better
>>
>> My friend K9OR, a very good op on a very small lot in Evanston (near 
>> Chicago), has done very well with an AV640 on the roof of his small 
>> ranch-style home.
>>
>>> than 43 foot verticals or even worse CHA250 and clone verticals.
>>
>> I suggest that anyone considering an HF vertical or other antennas 
>> for limited space take a look at these pieces on my website.
>>
>> http://k9yc.com/VerticalHeight.pdf
>>
>> http://k9yc.com/43FtVertical.pdf
>>
>> http://k9yc.com/VertOrHorizontal-Slides.pdf
>>
>> 73, Jim K9YC
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk at contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>
>

-- 

Kim Elmore, Ph.D. (Adj. Assoc. Prof., OU School of Meteorology, CCM, PP 
SEL/MEL/Glider, N5OP, 2nd Class Radiotelegraph, GROL)

/"In theory there is no difference between theory and practice. But, in 
practice, there is." //– Attributed to many people; it’s so true that it 
doesn’t matter who said it./