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G8MNY > TECH 28.08.06 21:04l 78 Lines 2820 Bytes #999 (0) @ WW
BID : 44108_GB7CIP
Read: GUEST DL1LCA DL1RX OE7FMI
Subj: Medium Wave Magnetic DF Loop
Path: DB0FHN<DB0MRW<DK0WUE<DB0RES<TU5EX<CX2SA<GB7CIP
Sent: 060828/1538Z @:GB7CIP.#32.GBR.EU #:44108 [Caterham] $:44108_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (New Aug 06)
The antenna commonly used for DXing MW station & reducing QRM etc.
The dimension are not strict & any large area loop will do.
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄ ÚÄ Ä¿
³ 6-10 turns ³ ³ /' 45ø ³ `\ /' 2x 1.4m
³ tuned plus ³ ³/' Brace ³ OR `\ /' SPREADERS
³ 1 O/P turn ³ ³ ³ `X'
³ ³ ³ WOOD SQUARE ³ ,/' `\ centre bolt
³ 1m x 1m ³ ³ FORMER ³ wire ,/ `\ & wing nut
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄ´_spacer À' `Ù
nails
ÚÄÄÄ¿ _
RxÄÄ¿ ( ³ /|
Ant ) ( === 2x >220pF
ÄÄÙ ( / ³
ÀÄÄÄÙ
The exact number of turns depends on the L you end up with per turn, the
frequency wanted & the tuning C used. An alternate to more turns for LF end
(LW) is a switchable 300-500pF cap teed across the tuning C.
The tuning C can be any of the old AM radio types mounted with a slow motion
drive on the frame if you can arrange that. Some people even use remote tuning
& loop rotation (eg. in loft) with servo from shack PC etc.
LOW Z RX
One turn provides a good drive for 50-75ê on MW. The lead can just be balance
Bell/LS wire etc.
HIGH Z RX
Generally there is so much signal, that 1 turn is also OK, but try 1-3 turns
for a car radio Rx high Z I/P for MAX Rx signal.
FERRITE ROD RX
With a ferrite rod Rx, no O/P turn is need, just place the Rx in/near the loop
for signal improvements of around 20dB. Note it greatly reduces image signals
on small Rx if tuned to the correct frequency.
ÚÄÄÄÄÄ¿ ///\
³ ³ [||Rx||]
³ ³ LS wire ³\\\/³
ÀÄÄÄÄÄÁ=======================/___/
If remote ferrite rod Rx needed (eg. in shack near QRM) use 1 turn & bell wire
feeder, to drive a few turns around the Rx (Rx ferrite in line).
LOOP AERIAL ORIENTATION
³Tx
___³___
\
\ ~-_
\ ~-_~ - _ _./³_ _ - ~ _
\ ~-_ ~- _ /_ ³ _ - - ~ _
~-_ ~ - _ ³ _ ³ _ - - ~
~ - _ ³ _/ _ magnet field
³/ component of RF
As MW Tx are all vertically polarized, loop orientation needs to be in the
vertical plane with one edge pointing at the Tx.
QRM SOURCES
Do not put loop aerial near mains wires running vertically in walls.
TV sets & computer screens have strong high frequency AC magnetic fields.
SMPSU in Computers economy lamps & even remote controls can all cause QRM.
Do not use it beside metal framed windows/doors as these can effectively be a
shorted loop & reduce Rx signal.
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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