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RE: [wsjtgroup] Protecting preamp when running 1.5 kw WSJT?

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  • Chet, N8RA
    Hi Bill, I do not know the specifics about your equipment. What I have done is to look at what max signal level the input of the preamp is rated to withstand
    Message 1 of 3 , Jul 30, 2009
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      Hi Bill,
       
      I do not know the specifics about your equipment.
       
      What I have done is to look at what max signal level the input of the preamp is rated to withstand without damage. 
      Then look at  the isolation spec (when that port is not selected) for a relay being considered, usually in dB.
      If that isolation is insufficient to reduce the transmit power bleeding over to the preamp to a safe level, than consider a 2nd relay in series with the first one's connection to the preamp. I've done that, with the second relay just switching the preamp input to a 50 ohm dummy load.
       
      73
      Chet, N8RA


      From: wsjtgroup@yahoogroups.com [mailto:wsjtgroup@yahoogroups.com] On Behalf Of Bill Dzurilla
      Sent: Thursday, July 30, 2009 5:36 PM
      To: moon-net@...
      Cc: wsjtgroup@yahoogroups.com
      Subject: [wsjtgroup] Protecting preamp when running 1.5 kw WSJT?

       

      Could someone give me ideas on how to protect a mast-mounted preamp when transmitting a full 1.5 kw in WSJT modes?

      I had first hoped that the SSB MHP-145 would be a good solution, but its 1.5 kw rating is only for CW/SSB. It only can handle 750w in continuous carrier modes.

      I have also looked at Al's set-up at wa4ewv.net and other similar 2 relay, 2 coax systems. It seems that the Tohtsu CX-800N and CZX-3500 are popular choices. But these are rated at 1,000 watts and I'm concerned if they can handle 1.5 kw. Some have told me that it's not an issue due to line losses that reduce power at the antenna to near 1,000 w, even if there is 1.5 kw coming out of the antenna. But I only have a short coax run and should be able to deliver well more than 1,000 w to the antenna with my Lunar Link amp.

      If you have any ideas for relays or diagrams of a complete system, please let me know. My transceiver is an IC-7000 and it is not easily modified for a receive-only antenna jack, which some folks have done with other, larger transceivers.

      Thanks for info and 73,
      Bill NZ5N

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