[TowerTalk] how does one accomplish a 'stub' for destroying resonance on yagi elements?

[Robert Harmon]

Gary,

How about if you  "open" the driven element and the directors with 
relays and then the 40M el's will be invisible
on 15.  ?

Bob
K6UJ




On 1/3/16 9:55 AM, jimlux wrote:
> On 1/3/16 6:18 AM, StellarCAT wrote:
>> How’s this for a solution... specifically for the antenna I have ... 
>> the M2 40M4LLDD which has linear loading wires that loop back towards 
>> and come close to the vertical uprights that support them... what if 
>> I installed a vacuum relay with one side connected to the center of 
>> the LL end ... and the other side to the upright thus when activated 
>> it would short the LL! This would most definitely destroy any 
>> resonances on 15. I could have the relays all connected together such 
>> that when 15 is the active band it automatically closes the relays... 
>> by using ferrites on the power lead to the relay it would isolate any 
>> other effects of the arrangement. Granted it is 8 relays ... but I 
>> believe it would be quite effective... thoughts anyone?
>>
>> I found a picture on how Optibeam does it and indeed I was right – 
>> they just use a parallel line to the element with a cap in series 
>> with this line to create a parallel tuned trap. But they have coils – 
>> and thus can do this readily ... the LLDD doesn’t and I don’t know 
>> that I could implement this outside the LL wires... but I’ll see... I 
>> understood, possibly incorrectly, that NEC2 can’t handle close wires 
>> – if it is spaced say
>> 3” would that model ok?
> is there a gap in the middle of the elements (all elements?) You could 
> put a LC network there that is low impedance at 40m (i.e. resonant) 
> and some non-zero Z at 15m. It should be possible to make something 
> that is pretty low loss with lumped elements.
>
> NEC is not all that good at modeling close conductors.
>
> Or, if you have existing loading components (the LL wires?) can you 
> add a tuned network/trap to them.  Have you called M2?  They might 
> have some ideas on where that trap could be.
>>
>> If I were to try this on the LL it would of course have to be on the 
>> far side of the LL... I’d suspect placement isn’t an issue since 
>> wherever it is placed it will destroy resonance on 15 ... with the 
>> flip side being not to introduce resonance, at least for me, on 20 
>> since I have 20’s nearby the 40...
>>
>> or... I could maybe just do a trap from the center close point of the 
>> LL wires back to the upright ... just not sure if that would be high 
>> enough impedance (when using it on 40) not to destroy performance on 40.
>>
>> or... a series trap shorting the LL lines ... again just not sure if 
>> it would be high enough impedance to not effect 40...
>>
>> I suspect both of these latter two wouldn’t be high enough impedance 
>> and it would noticeably effect 40.
>>
>> xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>> ok – sorry – stub.
>>
>> Specifically adding something to a 4 element 40 to eliminate 15 meter 
>> interaction? I believe Optibeam does this – not sure how they do it. 
>> Is this just using the element with a parallel line tuned through a 
>> cap for max current on 15? If so any suggestions on how long to make 
>> it and where specifically to put it on each element 1/2?
>>
>> Or is there a way to use a relay, open normally, closed when on 15 
>> that would add some impedance to the antenna causing it to be detuned 
>> at 15? Alternatively I can rotate the antenna 90 degrees but boy it 
>> would be so much better not to have to do that to avoid interaction 
>> on 15.
>>
>> thanks in advance,Gary K9RX
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