wrote in message
ups.com...
Here are a couple messages I posted on eHam net. Any comments would be
appreciated.

Thanks,

Doug VE3XDB

--
MESSAGE #1:

Hi everyone,

I am thinking of building a center loaded fan dipole. One wire dipole
to cover 20 and 40 metres, and a second wire diple, connected at the
same feedpoint, to cover 30 and 17 metres. Coils would be placed at the
resonant point of the higher frequency, acting as both an RF choke and
a loading coil. My question is this. I would like to have the wire
beyond the coil as long as possible, but would still like the coil to
have enough inductance to act as an effective RF choke for the higher
band.

Other than through experimentation, how would one calculate or
determine this mix of inductance/length?

Best regards,

Doug VE3XDB

Regardless of what you do, this is going to be guaranteed to have lousy
bandwidth on 40 meters (and 30, but you don't care). The whole thing might
be easier if you have 4 dipoles at a common feedpoint. I haven't tried 4,
but did have 3: 40, 17, and 12 meters. You will want to have angular
separation between the dipoles, either horizontal or vertical, or a
combination. I did not measure it, but probably had about 15 degrees of
separation. Tune by trimming the lowest frequency antenna first.

If you still want the trap dipoles, you can always buy the traps from places
like AES. They will probably come with instructions. With 2 trap dipoles at
a common feedpoint, I suspect this will be very difficult to tune.

Tam/WB2TT