Are the parasitic elements insulated from the boom?
73
Roger (K8RI)
On 1/3/2016 Sunday 1:46 PM, Robert Harmon wrote:
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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