[NLRS] [BC'ers] My new foot print on 432 MHz

[Dr. Gerald N. Johnson]

On 8/12/2015 9:53 AM, David Palm wrote:
> Thanks Jerry, that's a fascinating analysis ("How Close Can They be
> Stacked?")  I'm going to have to stack my antennas closer than I would
> like, but your data suggests that I should not take too big a hit.

Classical stacking analysis says they need to be separated so the 
effective apertures just touch. Rovers stack close and get by. My 
computer analysis to determine the effects and my one corroborating 
experiment show 1 wavelength on the high band has little effect on the 
high band antenna gain and none on the low band gain. And there is 
little grouping of the effect of spacing vs boom length but tight 
grouping on the chart of gain loss vs wavelength.
>
> Looking into it a bit more confirms that what I have here is a K1FO
> 22-element yagi.  I knew that this antenna would be "sharp", but it never
> occurred to me that one might get similar gain but with less critical
> pointing by stacking.  I am curious to see how this goes when I get this
> yagi on a rotor.  Maybe it'll turn out that I don't really like it either.

The stacking makes the elevation pattern tighter, but for most modes of 
propagation that's not an issue. The wildest example of stacking is 
K1WHQ Large Vertical Array with up to 16 5 element yagis stacked giving 
a 90 degree beam (at 10 dB down) in azimuth. Hardly needs a rotor when 
in Maine. If you can find Directive Systems web site it should still 
have that information. I concluded the FO-9 takes half the stacked yagis 
for the same gain and gives a 60 degree pattern at 10 dB down which 
makes for a lot easier aiming than the really long yagi like the FO-22 
and the 5 WL M2 I had up on 2m for a while. And the FO-9 gets the same 
gain as the M2 SSB 9, but on a shorter boom.
>
> Question for you and the group.  I was thinking about putting this 432 MHz
> antenna at the very top of the stack and using a section of either wood or
> PVC on top, so that the antenna isn't looking through a metal mast.  Is
> this a good idea?

Keep the metal mast down to under an inch and a quarter and I think 
thers' no problem. In NBS report 588 by Phisbecke, he found that so long 
as the pipes were perpendicular to the elements that even a Rohn tower 
didn't upset the yagi when the yagi was mounted on the side of the 
tower. That is the first report that lead to reproducible yagis and 
scalable yagis. Works by DL6WU published in UKW Berichte and VHF 
Communications did some theoretical designs that reproduce well and he 
worked out very good ways of determining boom effects on elements. K1FO 
spent years starting with DL6WU and NBS designs optimizing them for G/T 
and gain and improved them maybe a dB per boom length for gain and 10 or 
more dB front to side and front to back. Software for boom effects is 
available from GM3SEK yet, I think.

73, Jerry, K0CQ
>
> Thanks and 73,
>
> David  W9HQ
>
>
> On Tue, Aug 11, 2015 at 10:28 AM, Dr. Gerald N. Johnson<geraldj at netins.net>
> wrote:
>
>> I put up a K1FO 22 element 432 yagi in time for the UHF contest. It works
>> when you get it ON the station. The 3 dB beamwidth is about 23 degrees,
>> hardly more than the notches of the brake on a HAM-M style rotor. Aiming it
>> is super critical because its refined to have a very clean pattern. Moving
>> it less than 10 degrees moved N4PZ from asking "who is that?" to having a
>> QSO. For the narrow beamwidth I don't like it. I plan to build and stack 3
>> 9 element K1FO when I get a tower up. The gain will be similar, but the
>> beamwidth much wider in azimuth. I wrote about that combination in my
>> article about close stacking:
>> www.geraldj.networkiowa.com/papers/CSVHF2011/HowClose.pdf
>>
>> 73, Jerry, K0CQ
>>
>>
>