[TowerTalk] Changing interaction of M2 40M4LLDD on 15

[StellarCAT]

hello to all and forgive me for what appears to be, although unseen by me 
for whatever reason, duplicate posts. I sent my posts in on Sunday - nothing 
showed here (although other posts were coming in as usual - I always look at 
the archive files) ... resent it on Monday ... then sent the third one late 
Tuesday which I THOUGHT would only go to the moderator since my posts didn't 
seem to be making it... again - apologies.

To the replies:

-all element halves would need this
-I'll need to go back to my modeling and thought process going back and 
forth with Greg, W8WWV who very kindly used NEC4 to test it (as well I was 
testing using NEC2 here) ... bottom line is I was able to use a model of the 
40M4LLDD dipole ... so for now just a single element ... and it showed a 
resonance just below 15 .... that was good...

so then I added this dipole to my model for a M2 15M6DX .... 30' separation 
between them.... no interaction whatsoever... even at very close spacings. 
Obviously something wasn't working in the model.

Let me add to this the fact that I had asked if people would check their 40 
on 15 for resonance and I got 2 replies back saying it was low - one, N5ZC, 
saying actually very low SWR. That to me suggests it will most definitely 
interfere with the pattern of the 15. Note I've done a good bit of modeling 
over the last nearly a year and it is clear to me that gain is the least 
sensitive variable effected by interactions... you almost have to try to get 
a reduction in gain... SWR is next and it is indeed more sensitive... but FB 
is the most sensitive. The pattern can quite quickly get screwed up reducing 
FB by > 5db and changing lobes etc. Some, maybe most would say - so what - 
but if you have the opportunity to 'do it right' ... or at least account for 
these things and reduce their effects you can get to where the paper work 
(models/etc) say you should get...

So anyway long story short - when you model 4 dipoles of equal lengths 
(which is what the 15 sees from the 40 - up to the LL start point as it is a 
'trap' in essence and that length up to that point is very close to 
resonance on 15 all by itself) I now CAN see quite a bit of interaction... 
when I add the 'stub' all that goes away and you can stack the 40 over a 15 
within ... I can't remember for sure but it was like 7' or so with just some 
interaction.... greater than about 12' there is essentially none. Going by 
memory here - I'll need to go back through my notes.

I plan on trying it on my 40 - I have a 36' R45 'test' tower that I put up 
("little DUDE", it will eventually be a 109' tower with 10's and other 
things on it) ... an RT Innovations RTR45 'hazer' type rig ... and will be 
using a hex-copter (thanks to a local ham with a dipole and a XG3 as a 
exciter to check for ) ... oh - one more thing. The most 'telling' variable 
in modeling - is the FB center point. So if you measure it - you can adjust 
all elements to center on your desired center point - THEN adjust the match. 
The match/DE has very little effect overall to the rest of the element re FB 
other than being an exciter. ... so this test will find the center point of 
the FB and either confirm my rebuild antenna is what I hope it is. So I'm 
doing that for 15 and 20... and then I'll test the 40 checking SWR at 36' 
.... and then add the stubs and recheck it - the key being SWR on 15 
(actually 20 and above). I'll use a SARK 110 to do this.

So if you are interested in the details drop me a line off list and I'll 
pass it along.

Gary
K9RX

ps: I just checked the 15 ... this is a 15M6-125 structure changed to give 
me 15M6DX performance including better stacking... the SWR 3' off the ground 
was phenomenal. We'll see how it holds up at the test height of 37'.

-----Original Message----- 
From: jimlux
Sent: Tuesday, February 16, 2016 4:35 PM
To: StellarCAT
Subject: Re: [TowerTalk] Changing interaction of M2 40M4LLDD on 15

On 2/14/16 6:42 AM, StellarCAT wrote:
> Hello to those that have the 40M4LLDD.... I believe I have found a way to 
> eliminate the interaction of the 40 to a 15. I’ve done a good bit of 
> modeling and came up with a possible solution. I’m happy to pass this 
> along to anyone that wants to try it. I’d love to know if it works as 
> modeled. Write to me at my QRZ email address for details.
>
> I hope to build the antenna, test it at 36’ (test tower) and then add this 
> to see if indeed it does the trick. Note although I (believe) I know what 
> needs to be done I don’t yet know how it would be done mechanically – i.e. 
> the specifics. It isn’t really complicated at all, pretty basic change in 
> principle so shouldn’t be difficult.
>

It posted fine on the list.