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Filters or Stubs ?
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by MM0BQI on April 21, 2002
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I have just set up my SO2R station using an MP and IC-746. The IC suffers QRM from the MP making receiving very difficult. As this is a simple setup I think I would klike to instal tuned stubs to cut down the interference but would welcome your comments and experiences
Thanks
Jim MM0BQI
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RE: Filters or Stubs ?
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by oe5oho on April 22, 2002
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Try stubs first and see if it works for you. You can tune your stubs with most antenna analyzers (download MFJ or AEA manuals for the tuning procedure) with satisfactory results. Use a simple T-connector just behind the PA and the same cable as you use it for feeding your antenna. If it doesn�t help YOUR situation try to borrow a TRX-filter and see if it helps together with your stubs (you might want to check if it works without the stubs too). Either build it yourself or buy one if it does the job for you. One solution is also to just have a RX-filter like the Bavarian Contest Club preselector (see http://www.bavarian-contest-club.de/projects/presel/list.htm). Remember that for a RX only filter you need to have a TRX which is providing the RX-path at the rearpanel - or you need to do a small modification to your TRX. As in all cases BEFORE you go into the trouble of building stubs or testing filters - TX on rigA at full output (turn the beams at worst case scenario towards onto each other), instead of the rigB on the 2nd antenna connect a SWR-powermeter and a 50ohm dummyload to measure the powerlevel which is present on the 2nd antenna while TXing on the 1st antenna with rigA. Then you know if it is worth going for some RX-protection or not. VY 55 de Oliver OE5OHO.
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