[TowerTalk] 40 meter beam question

[Jim Thomson]

Date: Fri, 6 Nov 2015 13:08:36 -0600
From: Richard Thorne <rthorne at rthorne.net>
To: towertalk at contesting.com
Subject: Re: [TowerTalk] 40 meter beam question

I installed an M2 40MLLDD four element yagi at 130' over the summer.  
Absolute fantastic antenna, full band below 2.0:1 swr.

Rich - N5ZC

On 11/6/2015 12:55 PM, john nistico wrote:
> I have picked the pair of 107ft crank up towers to be installed at the new qth now for the antennas. I am currently using a force 12 620/340 and a force 12 515/510 I love the antennas except the 40. It is very narrow banded and seeing as I do phone RTTY and CW I wonder if anyone can suggest something better?
>
> John J. Nistico
> 911 Electric Inc.
> 516.325-8993



##  The M2 40MLLDD  doesnt work on 20m, so lets discount that for the time being..and the 40MLLDD may well  resonate on 15M. 
The easiest fix for the F12  620 / 340  is to add a DPST relay + 2 small coils in a nema box....  at the 40M DE feedpoint.   We are only talking about
a  3-4 turn coil in each leg..on a 1.5 inch ID.  The 40M  DE is then re-tweaked, tips shortened, so it resonates up in the phone band, say  7200 or 7250, etc.  With
relay activated, coils are shorted out..and it resonates in the phone band.  De-energize the relay, and coils are now in the circuit, and DE resonance  drops down 
lower in freq, to  cw + rtty.     You could also use a DPDT relay.  Then you can select the default to be  phone portion..with relay de-energized. 

##  I added a nema box to my f12  340N, DE only.   Consists of 4 x SPDT  gigavac G2 relays..and  two coils.  Each coil is made from  1 inch wide silver plated strap,
and wound flat, like a 10M  linear amp tank coil.  Like 4-5 turns per coil  Coils are  1.5 inch ID.  Strap coils have zip for C between turns.   Again,  DE is tuned for the upper portion of 40M.
With the 4 x SPDT vac relays, I can then get a total of 4 segments across the 40M band.   IE:  flat swr across the entire band.  1st set of relays is tapped 
at 1/3  along each coil.  2nd set of relays is used to short out the remaining 2/3 of each coil.   Then you end up with a combo of  0/3, 1/3, 2/3, 3/3   4 segments in all.

##  2 x vac relays and 2 x coils can be used... to achieve just two segments..which is probably plenty good enough  for a lot of applications.   The DE is easy to get to on the
340N, right next to the bottom of the mast.  Ditto with balun + hairpin.  Again, the DE tips have to be tweaked to resonate up high in the top of the 40m band.    

##    Id get that all sorted out before you install the 620 /340 on the new crank up.   I used vac relays since I wanted 100% reliability.   IF you can find a good DPST  or DPDT vac relay,
then you only require one relay to get 2 segments.   IF SPDT  relays are used, then 2 of em are required to get the same 2 segments.   Flat strap coils  are easy to wind, and everything done
with machine screws, etc.   Zero loss in the strap coils, and the vac relays will handle a ton of current on 40m band. 

##  F12 made 40m relay + coil switched nema boxes.... and I have then for both 80 + 40m.   But the mech DPST 30A relays used, like P+B and deltrol,  always ended up with int
contacts..pita.   The gigavac ham G2 relays can be bought with machine screw terminations...perfect for strap.  And also 12 vdc or 26.5 vdc coils.   I also silver plated the strap coils
with the cool-amp glop..made by the cool-amp company in Ore.  Hairpin is made from  .25  or  .375 inch OD  silver plated copper tubing.   then the heavy duty balun and 393 teflon /silver coax. 
Ok, now you can stuff 10 kw into it, right across the 40m band.    swr is flat..and nothing can blow up.   100% reliable contacts in the vac relays. 

Jim   VE7RF