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G8MNY > TECH 05.11.10 11:31l 101 Lines 3995 Bytes #999 (0) @ WW
BID : 65523_GB7CIP
Read: GUEST
Subj: Simple /P HF dipoles.
Path: IZ3LSV<IW0QNL<ON4HU<ON0BEL<ZS0MEE<UA6ADV<GB7CIP
Sent: 101105/0136Z @:GB7CIP.#32.GBR.EU #:65523 [Caterham] $:65523_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (May 04)
(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.
AERIAL
The design uses simple bell wire (LS wire) that is approximately 70ê as the
balanced feeder & the same wire split to make up the dipole.
Tree Dipole Length Adjustment 2nd
Supports ><--->< Support
Ú- - - - - -oÄÄÄÄÄÄÄÄÄÄÄÄÄÄÒÄÄÄÄÄÄÄÄÄÄÄÄÄÄo- - - - Ä Ä ¿
| String Clamp>³º³< String |
| ³º³Straw |
| ³º³ |
| Bell º |
| Wire º |
Tie º Tie
Off ºto shack Off
Or use as inverted V Pole
on a F/Glass pole. Support
Which is easier to /ÄÒÄ\
change direction. /'>³º³<`\
/' ³º³ `\
/' ³º³Straw`\
/' Bell º `\
/' Wire º `\
/' º `\
Steak\.'String º String`./Steak
to shack
The 30cms lightweight plastic drinking straw 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 tension.
THE BALUN
This is placed at the rig end....
Balanced Joiner Plastic
ÍÍÍÍÍÍÍÍÍÍÍÍ:ÍÍÍÍÍ» Tape ÉÍÍÍÍÍÍ(Ä SWR/Rig
feeder c)))))))))))o PL259
Ferrite Rod
Cut the feeder to a suitable length as it 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 onto 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.
TESTING
With a Tx Or With a Rx only
ÚÄÄÄÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄ¿
Balun Ä´ SWR METER ÃÄÄ´ RIG ÃÄMic Balun Ä´ NOISE BRIDGE ÃÄÄ´ Rx ³
ÀÂÄÄÄÄÄÄÄÄÄÄÙ ÀÂÄÄÂÄÙ ÀÂÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÙ
_³_ DC ÀÄÄÄKey _³_
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.
IN USE
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 50ê system.
To keep the feeder balanced @ 70ê 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.
Why Don't U send an interesting bul?
73 de G8MNY @ GB7CIP
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