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G8MNY > TECH 15.05.07 17:11l 94 Lines 4164 Bytes #999 (0) @ WW
BID : 14717_GB7CIP
Read: GUEST OE7FMI
Subj: HF Rx Suckout Trap
Path: DB0FHN<DB0NOE<DB0GAP<DB0FSG<DB0MRW<OK0PKL<DB0GRL<SR6BBA<SR1BSZ<F4BWT<
ON4HU<DB0RES<ON0AR<GB7CIP
Sent: 070515/1402Z @:GB7CIP.#32.GBR.EU #:14717 [Caterham] $:14717_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (New May 07)
(8 Bit ASCII Graphics use code page 473 or 850)
When doing demo stations with more than 1 Tx on different bands, QRM between
stations is quite normal, even with the high Q tuned circuit of an ATU.
This arrangement also stops the Rx safety lamp circuits from blowing up if
fitted.
Here is one method to remove most of the problem from the aerial lead. (from a
system built up for 2 FT101s by G0SYR years ago & revisited for more modern
rigs.)
STATION A STATION B
\|/ \|/
³ ÚÄÄÄ¿ ÚÄÄÄÄÄÄÄ¿RF ÚÄÄÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄÄÄ¿ RFÚÄÄÄÄÄÄÄ¿ ÚÄÄÄ¿ ³
ÀÄ´ATUÃÄ´Rx TRAPÃÄÄÄ´TRANCEIVER³ ³TRANCEIVERÃÄÄÄ´Rx TRAPÃÄ´ATUÃÄÙ
ÀÄÄÄÙ ³ B FreqÃÄÄÄ´ ³ ³ ÃÄÄÄ´ A Freq³ ÀÄÄÄÙ
ÀÄÄÄÄÄÄÄÙPTTÀÄÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÄÄÙPTTÀÄÄÄÄÄÄÄÙ
It uses switchable tuned traps that are only in circuit on Rx. If the
tranceivers have a transverting loop through port, then the circuit is quite
simple, otherwise a relay operated by the PTT is needed as well.
THE TRAP
It is only in Rx, so there is no high voltages, but good quality components &
layout in a sold metal box are needed to give the good Q & deep reject notch on
a 50ê line.
coax coax coax
TXR>ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄ>ANT Rx<ÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄ>Relay
_³ Socket Port o In/Out Port
Relay\_ \_ SW
( (
L1 (___ O R L1 (___
+12V>ÄÄÄÄÂÄÄÄÄÄ¿ ( ³ Band ( ³ Band
_³_ ÚÄÄÁÄÄ¿ L2 ( / Switch J U S T L2 ( / Switch
D2/_\ ³relay³ (___³ (___³
³ ÀÄÄÂÄÄÙ ³_ ³_
PTT>Ä´<ÃÁÄÂÄÄÄÙ ³/| ³/|
D1 o Out/In === C1 === C1
/ SW /³ /³
ÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄ ÄÄÄÄÄÄÄÄÁÄÄÄÄÄ
C1 2x 350pF Air spaced (MW radio cap)
L1 1uH, 12 Turns 1mm Enamelled Copper Wire on 1cm former (oval egotube).
L2 10uH, 44 Turns of 0.7mm ECW on 1cm former (oval egotube).
Both coils are on the same Úı±±±±²²²²²²²²²²²Ä¿
former in line, wound in the ³ ±L1±±²²²²L2²²²²² ³
same direction. So more L in Àı±±±±²²²²²²²²²²²ÄÙ
series & less L when L2 shorted. / | \
FRONT PANEL
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³ 160/80m ___ ³
³ (o) 80Üúú_._úúÜ40 ³ The band switch is
³ 40m-10m 20Ü/ / n \ \ ³ colour coded, & the
³ 15Üúú / \ úúÜ160³ same colours mark
³ 10ܳ ³ ( ) ³ ³ ³ the ham bands on
³Filter Out |_| ³ the dial. Connect to
³ (o) ³ Rx & mark the band
³ In ³ ends etc. by nulling.
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
IN USE
Typical notch depth is 30-40dB, but tuning is critical for the peak. However
notching the QRM down by 20dB or so generally removes all overload QRM.
0dB´--------------. .-------------------
-10dB´ \ /
-20dB´ | |
-30dB´ |
-40dB´ '
ÅÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄÄÂÄ
0 2 4 8 10 12 14 16 18 20 22 24 26 28 MHz
You should note that 2 stations operating locally have QRM paths other than
the aerial! eg. via mains leads, poor coax, poor metal case screening etc.
Tx MIXING
High levels of coupling between aerials can cause QRM to other HF services as
the Tx PA can mix the 2 signals!
So there is still a need to have the aerials seperated enough, so that there is
next to no power seen by the PA. eg. the SWR bridge ATU on station A (between
ATU & Tx) should not be indicating power from station B.
Why don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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