[TowerTalk] Changing interaction of M2 40M4LLDD on 15

[StellarCAT]

Jim,
Good question (why doesn’t M2 just redesign it).... note on the F12 the distance from the boom to the LL is considerably less than 1/4 wave on 15.... once the LL is reached I believe (and another antenna manufacturer whom I talked to agrees) it acts as a trap to isolate the antenna up to that point... and since it is short – the resonance on 15 isn’t there (but would be there on 12!). The 40M4LLDD has almost a 1/4 wave on 15 up to that point which would mean a rather large change to the antenna to (possibly) eliminate the resonance. Also most say “so what” .... not knowing how they’re being impacted and thus there is no pressure to make the change. I believe now with 3 manufacturers making antennas (40M) designed not to interact at least on 15 there might be some amount of pressure. 

Also note this is not at all to impugn M2... I believe they make an excellent line of antennas for a quite reasonable price. When done I’ll have with one exception an all M2 antenna farm from 40 through 2 meters – 9 yagis in all. The one exception is the F12 Magnum 80.75 rotary dipole which I love and which worked extremely well in Arizona. It will be at the top at 144’. 

I tried using the Optibeam model shorted at the boom end ... that didn’t work. So Instead I tried using what VE4XT had suggested to me which was to short it at the far end... and that seems to work well. You can indeed adjust the length to move the resonance point – and if not careful it can end up instead at 17 meters... the final model I have puts it above 17M and has 30:1 SWR above 20 meters through 30 Mhz. 

NOTE: this whole discussion – this possibility of a test is thrown out for those in a position like myself to test it if they want to... I have the antenna, new in the box. I will assemble it and try it. We’ll see. I’ll report the results. 

Gary 
K9RX


Date: Mon, 15 Feb 2016 08:56:36 -0500From: "StellarCAT" <rxdesign at ssvecnet.com>To: "tower" <towertalk at contesting.com>Subject: [TowerTalk] Changing interaction of M2 40M4LLDD on 15Hello 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.Gary MyersK9RX

## so why doesn’t M2, just build the damned thing right the 1st time ??? Optibeam uses decoupling stubs on their version of their 4 el 40m yagi. One on each side of boom,so 8 x stubs in all. The stubes on the optibeam appear to be small gauge al, coming out from the 40m els..at at right angle for a couple of inches, then parallel to the ele for a couple of feet. Far end of stub is held in place with a small insulator back to the ele. You can see the concept on their install manual. Done right, the 40m yagi can be very close to a 15m yagi. These ants have to resonate some where, so the resonance will no doubt be shifted higher up in freq. 

## F12s N series of 40m eles, on their 1-2-3 ele 40m ants.... don’t resonate on 15m. However they will resonate on aprx 24 mhz...which will screw up a 12m yagi. f12 claims their N series of 40marrays can be within just 3 feet of another F12 monobander or tribander ( 20-15-10m). F12 didn’t use stubs. They used longer eles, ranging from aprx 59 feet for the ref to 51 feet for the dir. Longer eles + LL rods. 

## This 40m yagi and interaction to a 15m yagi has been an issue for decades now.....and is easily resolved. Dunno why the folks at M2 have not figured it out...yet. Jim VE7RF