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G8MNY  > TECHNI   22.11.21 09:10l 160 Lines 7443 Bytes #999 (0) @ WW
BID : 53757_GB7CIP
Read: GUEST
Subj: HF Rx Suckout Trap
Path: PI8DRE<PI8CDR<DB0RES<DB0ERF<DK0WUE<F1OYP<VE3CGR<LU9DCE<LU4ECL<GB7CIP
Sent: 211122/0759Z @:GB7CIP.#32.GBR.EURO #:53757 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                                      (Updated Aug 19)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

When doing demo stations with more than 1 HF Tx on different bands (or with a
nearby ham), QRM between stations is quite normal, even with the high Q tuned
circuit of an ATU.

Here is one method to remove most of the problem from the aerial lead. (from a
system built up years ago for 2 FT101s by G0SYR & 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 "Teed in series tuned traps" (notch) that are only in
circuit on Rx. If the transceivers have a transverting loop through ports, then
the circuit is quite simple, otherwise a relay operated by the PTT is needed as
well.

This device also stops the Rx safety lamps (if fitted) or Rx front ends from
blowing up.

THE TRAP
It is only connected in Rx mode, so there is no high voltages to deal with, but
good quality components & layout in a sold metal box are needed to give the
good Q & deep reject notch on the 50ê line.

           50ê coax                                    coax      coax
TXR o)ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄ(o ANT                Rx<ÄÄÄÄÄÂÄÄÄÄÄÄÄÄ>Relay
    _³_                 ³     _³_ Socket            Port     o In/Out  Port

                   Relay\_                                   \_  SW
                          (                                    (
      LED              L1 (___                  O R         L1 (___
+12V>Ä´>ÃÄÄÂÄÄÄÄÄ¿        (   ³  Hi/Low                        (   ³  Hi/Low
      D1  _³_ ÚÄÄÁÄÄ¿  L2 (   ø/ Band        W I T H   A    L2 (   ø/ Band
          /_\ ³relay³     (___³  Switch                        (___³  Switch
     D3  D2³  ÀÄÄÂÄÄÙ      ³_                Rx  P O R T        ³_
 PTT>´<ÃÄÄÄÁÄÄÂÄÄÙ         ³/|                                  ³/|
              o Out/In    === C1                               === C1
              / SW        /³  Tune                             /³  Tune
     ÚÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄ                          ÄÄÄÄÄÄÄÄÁÄÄÄÄÄ
    _³_

D1   LED/1N4001
D2&3 1N4001
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.      /    |           \

If you are using a rig accessory socket for ptt relay power, be careful not to
short it, Andy G0FTD recommends a series LED as a fuse. If your relay is not
very RF isolating to the winding or you experience Tx mode lock up add a
capacitor (1nF) across the PTT line.

FRONT PANEL
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³                               ³     Scale calibrating:-
³    160/80m         ___        ³     connect to Rx & mark
³ Band (o)      80Üßú_._úßÜ40   ³     the band ends etc.
³    40m-10m  20Ü/ /  n  \ \    ³     by nulling signals.
³             15Üúú  / \  úúÛ160³
³            10ܳ ³ (   ) ³ ß   ³     The band switch is
³      Out           |_|        ³     colour coded, & the
³Filter(o)                      ³     same colours mark
³      In         Notch Tune    ³     the ham bands on
³                               ³     the dial.
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

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 Rx overload QRM.

Notch Rx attenuation width, does not extend to the next ham band, so adjacent
bands like 5MHz & 10MHz can just be used while notching out the 7MHz band etc.

Notch Depth
 0dB´ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ-.._     _..-ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ
10dB´                              \   /
20dB´                               | |
30dB´                                |
40dB´                                '
    ÀÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÂÄÄÂÄÄÄÄÄÂÄ
          1.8          3.5     5     7     10    14  18  21   28 MHz

Note that 2 stations operating locally, have QRM paths other than the aerial!
e.g. via mains/12V leads/Mic, poor coax, poor metal case screening etc.

The trap does NOT remove any of the other station's Tx harmonics, so you still
will have some spot frequencies to avoid. e.g. a 100W of CW on 3.510 MHz will
give a strong signal on 7.020 MHz & that can't be notched out! Also the trap
does NOT remove any of the other station's broad band Tx noise or spurious, so
you have to put up with that, but read on!

TX MIXING & ATU BAND FILTER ACTION
High levels of coupling between Tx aerials can cause QRM to other HF services
as the Tx PA can mix its own signal & with other strong ones!

 100W_³              TxA                     ³_   0dBc
  10W_³               ³    TxB               ³_ -10dBc
   1W_³               ³     ³                ³_ -20dBc 
100mW_³        A-B    ³     ³    A+B         ³_ -30dBc
 10mW_³         ³     ³     ³     ³          ³_ -40dBc
  1mW_³  A-2B   ³     ³     ³     ³    A+2B  ³_ -50dBc
100uW_³   ³     ³     ³     ³     ³     ³    ³_ -60dBc
      ÀÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÙ

So there is still a need to have the aerials separated enough, so that there is
next to no power seen by the PA. e.g. the SWR bridge ATU on station A (between
ATU & Tx) should not be indicating power from station B (SWR direction).

          STATION   A      close aerial  B
     A 100W>            \|/  <direct    \|/
ÚÄÄÄÄÄÄÄ¿  ÚÄÄÄ¿  ÚÄÄÄ¿  ³   <pick up    ³   e.g.
³ TX PA ÃÄÄ´SWRÃÄÄ´ATUÃÄÄÙ               ÀÄ< 100W
ÀÄÄÄÄÄÄÄÙ  ÀÄÄÄÙ  ÀÄÄÄÙ  <10W B?
      <100mW B?  <100mW B?

With a good enough Q between the aerial & the Tx stage in this example 100mW
(-20dB of aerial signal) gets to the PA & will produce unwanted products in the
PA (acting as a Mixer) say at 10mW each, these then have to go back through the
same tuned circuit to reach the aerial @ 100uW each. With valve PA equipment
the high Q of the PA tank circuit also helps a lot, but this is not present on
a modern solid state broadband HF PA.

This is where a manual "T" or "Pi" Hi Q ATUs come in to their own, by providing
more band isolation (20dB off resonance & 18dB/O cut off), compared to the
simpler 2 component "L" type ATU (Automatic types).

       oÄ´ÃÄÂÄ´ÃÄo     oÄÂÄÄLÄÄÂÄo       oÄ´ÃÄÄÂÄÄo      oÄÄLÄÄÂÄÄo
            L           ===   ===              L              ===
       oÄÄÄÄÁÄÄÄÄo     oÄÁÄÄÄÄÄÁÄo       oÄÄÄÄÄÁÄÄo      oÄÄÄÄÄÁÄÄo
  Loss
  0dB´     /\              /\                /\._         _./\
 10dB´    |  \._        _./  |            _./    ~       ~    \._
 20dB´  _/      ~      ~      \_        -~                       ~-
 30dB´-~                        ~-
     ÅÄÄÄÄÄÄÄÄÄÄÄ      ÄÄÄÄÄÄÄÄÄÄÄ      ÄÄÄÄÄÄÄÄÄÄÄ      ÄÄÄÄÄÄÄÄÄÄ
         T ATU           Pi ATU            L ATU           L ATU
       Good LF cut     Good HF cut       some LF cut     some HF cut



Why don't U send an interesting bul?

73 de John G8MNY @ GB7CIP



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