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.
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