Hank, thanks for the input.
I didn't like my relay idea but when I wrote that post I hadn't yet
seen a workable alternative aside from full size parallel tubing
dipoles for each band. I could do that, but the amount and size of
aluminum would be getting to a point of concern for the rotator and
mast.
I have looked at the OB1-4030 several times. If budget would allow,
I would just buy one and be done with it. I'm not too confident
about building one since I really don't understand the operating
principle with that stub tapped on a coil.
I am unable to find the referenced M2 antenna on their web site.
73,
Paul N1BUG
On 03/17/2016 02:47 PM, HankP wrote:
Paul-- I think it can be done a LOT easier than relays -
I saw a suggestion for a trap - that can definitely be done - look at
OPTIBEAM 30-40 M dipole -
I have a M squared 40M1L linear loaded 40 M dipole - I played with nothing but
a parelled 30 M dipole hanging under the 40M1L and connected right at the
balun . It appeared it would work - but I was also trying to get a 12 meter
resonance at the same time . That 40M1L linear loading is really screwy
it has a resonance very close to 12 meters and "sucked" the resonance of any
paralleled 12 meter dipole so it was virtually impossible to make oine I trusted
for a $350 crane run . (BTW I emailed with K6MYC a couple or three times about
this and he confirmed he had seen that sort of thing ._ I was up against
a scheduled crane run and just dropped the whole idea - the 40M1L has a
"stinger"
at the linear loading that gives a 17 meter resonance and that works great.
Your concern about the voltages across a trap is well founded - if you read
carefully , most of the commercial 30/40 or triband dipoles will NOT handle
1500 watts . M2 has a 30-40 meter dipole they are advertising - might be
worth looking at how they do that . It appears to use the coil approach
that they offer as a non linear loaded 40 M1 dipole. I would have to look
back at my notes or do a quick 30/40 meter paralleled dipole EZNEC and see
how that works . I have to run now but - if I had it to do over again.
I would have bought the OPTIBEAM 30/40 m dipole or make a copy .
I have an old KLM 40 M linear loaded 3 40 m dipole that git hit by lightning
and blew up the center insulator - I have a project to see if that could be
modified to make a 30/40 m dipole by basically just playing between the
linear loading and tip lengths and a capacitor across the linear loading
but seems like that has not made it to top of project piles.
Mi dos Centavos - as many say down here
73 Hank K7HP
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