[CQ-Contest] What RF voltage OK at Rx in SO2R?

Marijan Miletic, S56A artinian at siol.net
Mon Sep 24 09:04:55 EDT 2001

I lost W2SC email address due to BadTrans virus infection received from one
of cq-contest reflector recepients so let me answer Tom's question here.

Yaesu puts low voltage bulb ahead of 4 diodes.  Cold bulb has a very low
resistance of few Ohms and doesn't affect RX sensitivity much.
High RF makes it glow with much increased resistance.  I had 12 V car bulb
as an emergency light in my shack when long wire antenna was connected and
local 300 kW AM BC TX was runing :-)
RX didn't work without it as switching diodes were A_mplitude M_odulated.
BCI rejection filter was later installed.

73 de Mario, S56A, N1YU
www.miletic.net or http://artinian.bit.si/radio.htm
  ----- Original Message -----
  From: Marijan Miletic, S56A
  To: 'Marijan Miletic, S56A'
  Sent: Monday, September 24, 2001 7:56 AM
  Subject: RE: [CQ-Contest] What RF voltage OK at Rx in SO2R?

  Mario -

  This is a much better idea than 1/16 amp fuses.

  I assume that your circuit is two diodes in series forward biased toward
  ground and two in reverse to clip both peaks of the wave.  I would presume
  that a relay between the signal and the diodes is necessary to disconnect
  them during Xmit.

  Do you think the diodes could take it if there really were 7V on the input
  or should I try 4 diodes each way?

  73, Tom W2SC 8P1A

  -----Original Message-----
  From: Marijan Miletic, S56A [mailto:artinian at siol.net]
  Sent: Sunday, September 23, 2001 8:59 AM
  To: cq-contest at contesting.com; Jerry Flanders
  Subject: Re: [CQ-Contest] What RF voltage OK at Rx in

  1W or 7 V RF at 50 Ohms is a safe bet for RX survival.  You
  might install
  two pairs of back-to-back protection Si diodes to keep RF at
  1,5 V which is
  also within IMD3 RX capabilities.

  Using bandpass filters is highly recommended.  Coax stubs
  are cheaper
  solution due to lower Q.

  WRTC-2000 measurements with 100 W TX and tribander showed
  about 3 V RF on
  nearby wideband 40 m long Windom antenna.

  73 de Mario, S56A, N1YU with few smoked RX repaired.
  www.miletic.net or http://artinian.bit.si/radio.htm

    ----- Original Message -----
    From: Jerry Flanders
    To: cq-contest at contesting.com
    Sent: Sunday, September 23, 2001 2:43 PM
    Subject: [CQ-Contest] What RF voltage OK at Rx in SO2R?

    I am trying to set up for RTTY SO2R and have two

    1. What voltage levels can solid state rigs safely
  tolerate from nearby

    2. I read about guys using stubs as well as filters in
  SO2R. How much of
    this is just to protect the rx hardware, and how much is
  there to improve
    normal rx on band A while tx on band B is underway?

    I would like to avoid smoke testing the rx front ends on
  my FT-1000D and
    IC-756PRO if possible. I intend to measure actual voltage
  present on my
    (well separated) rx antennas while transmitting and
  determine from that if
    I actually need protection, and to what degree. This is
  aside from the
    question of rx overload, which I can see for myself once I
  get it all in
    actual operation. My immediate goal is to see if I can
  safely tx w/o smoke
    before I start working with stubs or filters.

    Jerry Flanders  W4UK

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