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G8MNY  > TECH     21.06.18 08:30l 104 Lines 4215 Bytes #8 (0) @ WW
BID : 26018_GB7CIP
Read: GUEST
Subj: Simple /P HF dipoles.
Path: ED1ZAC<ED1ZAC<GB7CIP
Sent: 180621/0618Z @:GB7CIP.#32.GBR.EURO #:26018 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
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.

AERIAL
The design uses simple bell wire (LS wire) that is approximately 70 as the
balanced feeder & the same wire split to make up the dipole.

Tree            Dipole Length Adjustment              2nd
Supports                ><---><                       Support
- - - - - -oo- - - -   
| 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       /\            lower resonace than the
change direction.      /'><`\          same length at height, so
                     /'      `\        shorter wire length needed.
                   /'     Straw`\
                 /'   Bell         `\
               /'     Wire           `\
             /'                        `\
     Stake\.'String                String`./Stake
                       to shack
   
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
tension.

THE BALUN
This is placed at the rig end....

Balanced   Joiner   Plastic
:ͻ   Tape  ( SWR/Rig
feeder           c)))))))))))o  PL259
                  Ferrite Rod

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.

TESTING
With a Tx                                      Or With a Rx only
       Ŀ  Ŀ                   Ŀ  Ŀ
Balun Ĵ SWR METER Ĵ RIG Mic        Balun Ĵ NOISE BRIDGE Ĵ 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.

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 50 system.

To keep the feeder balanced @ 70 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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