Paul Baldock wrote:
>
> I'd like to put up an 80M dipole trapped for 30M. Anybody have any design
> info?
>
> Paul
----------------
Hi Paul,
An 80 meter dipole will work quite well on 30 meters, all you need is a
tuner. No traps needed. However, if you do not have a tuner...
Cut your 30 meter dipole to length per the usual formula. The cap and
inductor used in the traps should each have a reactance of around 500
ohms. Thats around 31.5 pF and 7.8 uH for a 30 meter trap. The trap
will have a high impedance at 10.1 MHz and thus divorce the 80 meter
extension from the 30 meter dipole.
On 80 meters the trap will have an inductive reactance of around 190
ohms which means the overall length for 80 meter operation will be
shorter than for a normal 80 meter dipole. Add enough wire to each end
of the 30 meter dipole/trap to make a normal 80 meter dipole and then
start removing equal lengths of wire from each end until you get the
desired 80 meter resonance point. This can be calculated mathmatically
but I dont have the formula at hand.
You may have to readjust the 30 meter length and 80 meter length to get
best VSWR on both bands. Be sure both traps are resonant on the same
frequency.
Personally, I would use a tuner.
73 and Good Luck
Bob, W5AH
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