[TowerTalk] Duo band 20/15 meter beam

[StellarCAT]

considering the alternative - relays and coils as you say which I'm not 
against at all and am a bit surprised they're not used more ... I have a F12 
Magnum 80 dipole with 3 relays and it use to cover the entire band with no 
more than a 1.6:1 SWR ...

or a 2 element yagi where the FB is far more narrow

I'd take the dual DE.

but your point is well taken.

g.

[I say 'use to' re the 80 because in my new installation, new as of just 
over 2 weeks ago, its become apparent the 20 elements that are 7' below the 
T bars are screwing with the Q of the system and the curve is not as 
broad... I modeled the effects of the 80 over the 20 .... and found there is 
about a 3 db loss in FB on 20 due to the proximity of the T bars - but 
didn't think I'd need to do the reverse - model the 20 against the 80 and 
consider the effects of the front director which is almost directly below 
the T bar at that end and only ~7' down and the reflector which is also 
close to that T bar.  ... alas - hindsight is wonderful. Had I to do over 
again I'd strip the T bars and make it 14' longer to get back the added BW 
they, in free space, provide making the antenna 90' long instead of the 
current 76']


-----Original Message----- 
From: Jim Thomson
Sent: Monday, November 7, 2016 11:46 AM
To: towertalk at contesting.com
Subject: [TowerTalk] Duo band 20/15 meter beam

Date: Mon, 7 Nov 2016 08:40:40 -0500
From: "StellarCAT" <rxdesign at ssvecnet.com>
To: <towertalk at contesting.com>
Subject: Re: [TowerTalk] Duo band 20/15 meter beam

hmm.... really? Don't hold a pattern? The testing I did on the 40M4LLDD
showed quite good FB across the band with a measured ~15 db at the bottom, a
peak around 30 at around 7.13 and still a good 15 db at the top at 7.3....
an Optibeam OB4-40 has similar numbers (after I increased the length of all
the elements by 3.5"). I measured a good 20 db at 7011 and around 30 at 7.13
... while still at least ~ 15 at the top of the band. The gain, although not
great for the size of the antenna, is even less sensitive to where you are.

Both dual DE's.

Gary
K9RX

## 15 db  FB  at both ends of the band..and 30 in the middle is exactly what
Im talking about.  You would still get that, whether it had single or dual 
DE.
The dual DE is just providing for a flatter swr.  They could have used 
relays
+ tapped coils in each leg of the feedpoint, and used a single DE, and got 
the
same results. But in terms of simplicity, just adding a 2nd DE is 
reliable..+ cheaper.

##  I used 4 x  spdt  ceramic vac relays +  1 inch wide silver plated cu 
strap coils,
with 1 coil in each leg. All inside the oem F12 ssb /cw nema relay box. 
Then  I end up
with 4 x segments on 40M, = flat swr across the entire band.   But the relay 
box is on the
DE only of my  F12  340N.   I could have added boxes on the REF + DIR as 
well, for
improved FB, since it peaks at the lower end of the band, but chose not to. 
I can easily get to the
DE, since its next to the mast.  Any problems with a box at each end of the 
boom, and the entire
yagi  would have to come down.

##  In retrospect,  I could have used 2 x SPDT relays, and ended up with 
just 2 x segments,
which would have been plenty.   But I had loads of new gigavac  g2 relays, 
so used em.

Jim   VE7RF