Jimmy Burrell wrote:
> Just built a wire vertical dipole (Lazy H style) yesterday for 80m
> (very similar to the one shown on EI7BA's web site here ). Since I
> am feeding the antenna asymeterically I knew an RF Choke would be in
> order. EI7BA recommends an FT240-61 with 12 turns of RG-58. Not
> having the recommend ferrite at hand, I proceeded to homebrew a choke
> out of a large diameter (~7") plastic coffee can and 20 turns of
> closely spaced RG-58 well secured.
>
> This apparently isn't good enough?? When testing at the antenna with
> my MFJ it is "spot-on" correct just like the model and resonant at
> the design freq. of 3.830. However when using the homebrew RF choke,
> resonance is just above 4 MHz. I did test without a choke at all and
> resonance was much much higher.
>
> Is this not enough choke at this frequency?
>
> Thank you,
>
> Jim...
> N5SPE
>
Hi Jimmy..
On my 80m H, I use an FT240-61 with 12 turns of RG-58 right at
the feedpoint. I also use another choke similar to yours, about 8ft
below the feedpoint, where it's weight can be supported on a timber
post. I have the same arrangement on 160m, except that I also have a
lot of beads on the coax between the two chokes.
If you don't have any ferrite cores, you can get some from an
old TV if you have one for junking. Take the winding off the line output
traffo, and you're left with a very useful square core. Also, you can
salvage chunks of ferrite from the deflection coils.. " Any port in a
storm" as they say.. {:o)
I'd be extremely interested to hear how that antenna works out for
you.. I've had great success with mine. I must give credit to Rudy
Severns N6LF, and his QEX article,
http://rudys.typepad.com/ant/files/antenna_vertical_loaded.pdf which
is where I got it from.
Vy 73
John EI7BA
http://www.iol.ie/~bravo/low_band_antennae.htm
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