G8MNY > TECH 21.06.18 08:30l 104 Lines 4215 Bytes #8 (0) @ WW
BID : 26018_GB7CIP
Subj: Simple /P HF dipoles.
Sent: 180621/0618Z @:GB7CIP.#32.GBR.EURO #:26018 [Caterham Surrey GBR]
To : TECH@WW
By G8MNY (Aug 13)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
At a local club meeting, I was trying to explain how to make a simple /P aerial
for /P 40m+15m (or any band) dipole without the need for an ATU.
The design uses simple bell wire (LS wire) that is approximately 70ŕ as the
balanced feeder & the same wire split to make up the dipole.
Tree Dipole Length Adjustment 2nd
Supports ><--->< Support
┌- - - - - -o──────────────Ď──────────────o- - - - ─ ─ ┐
| String Clamp>│║│< String |
| │║│Straw |
| │║│ |
| Bell ║ |
| Wire ║ |
Tie ║ Tie
Off ║to shack Off
Or use as inverted V Pole
on a F/Glass pole. Support The inverted "V" will be
Which is easier to /─Ď─\ lower resonace than the
change direction. /'>│║│<`\ same length at height, so
/' │║│ `\ shorter wire length needed.
/' Bell ║ `\
/' Wire ║ `\
/' ║ `\
Stake\.'String ║ String`./Stake
The 30cms lightweight plastic drinking straw or other tube, over the feeder
keeps the split feeder together & allows you 60cm of overall length adjustment
without any wire cutting. The clamp is any strong screw cable clamp (from a
mains plug) & is used to stop the feeder splinting anymore with the dipole
This is placed at the rig end....
Balanced Joiner Plastic
════════════:═════╗ Tape ╔══════(─ SWR/Rig
feeder c)))))))))))o PL259
Cut the feeder to a suitable length, as a whole roll is fairly lossy.
Wind the Rig end lead of the bell wire 20 turns around a ferrite rod from a MW
radio (or 10 turns on a medium sized ferrite ring). Tape it on firmly to
provide some protection against damaging the ferrite. Collect to a PL259 plug.
Pass one of the stripped wires through one of the outer case holes, while at
the same time push the other one through the centre pin. Be careful that the
heat does not damage the wire insulation when soldering up.
Put a joiner (2 way block) on the balanced end, so there is no excuse to
throwing the ferrite balun around when /P.
With a Tx Or With a Rx only
┌───────────┐ ┌─────┐ ┌──────────────┐ ┌────┐
Balun ─┤ SWR METER ├──┤ RIG ├─Mic Balun ─┤ NOISE BRIDGE ├──┤ Rx │
└┬──────────┘ └┬──┬─┘ └┬─────────────┘ └────┘
_│_ DC └───Key _│_
Put aerial up.
1/ With a Tx check SWR at the bands edges, or a Noise bridge & a Rx check the
match over the frequencies wanted. Determine if the aerial needs to be
shortened or lengthened.
2/ Lower middle of aerial & adjust the feeder clamp to give more or less
dipole length & re-clamp out back up & re-tension dipole if needed.
3/ Redo 1 until the aerial is optimised. This should then be about right for
most /P sites at that frequency.
The fine tuning length will easily allow the dipole to be resonated for either
CW of SSB ends of the bands, & permit the increase in length if the aerial is
very high or reduced if too much ground capacitance with a low aerial/objects.
The SWR matched is usually better that 1.5:1 on a 50ŕ system.
To keep the feeder balanced @ 70ŕ try to keep it of the ground (long grass OK)
or large metal objects.
This design is not too strong that it will pull roofs off etc in a storm!
It is not to heavy to put up put your own!
It is an ideal throw together/away aerial.
See my TECH bul on "Coiled Choke Balun for HF".
Why Don't U send an interesting bul?
73 de G8MNY @ GB7CIP
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