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Problem with an IC-706 & SWR spikes
IC-706MkIIG was working perfectly. Typical setup is 30 watts output, PSK31 or RTTY, via short length of coax to an MFJ tuner, thence to ladderline running to 250' low horizontal loop. Working with no problems BEFORE I decided to rearrange my radio area. Rearranged my gear and ran into trouble as soon as I fired things back up. On two bands the SWR is never less than nearly 2:1, as indicated by the MFJ meter, but much much higher by the 706's internal meter. Try to tune the antenna system; if you dial in less inductor than it wants, or a capacitor setting it doesn't like, SWR suddenly spikes to infinity and the tx shuts off after a second. (Tuning is done at lowest power setting, not 30 watts.) The 706 works fine on 6, 10, 12, 20, 30, and 40. (I worked a guy in California on 12, just checking things, and after we cleared a ZL called ME on the frequency--ZL on 30 watts is clearly "working fine.") But on 15 and 17 meters, it will NOT achieve a low SWR, and sooner or later it WILL oscillate or denooberate or whatever it is doing and spike the SWR, and shut down. I tried a lot of things--different coax, etc.; nothing made a difference. (I was thinking at the time that it was the rearranging equipment that caused the problem.) Then I did the systematic testing and found the problem is only on 15 and 17 meters. (Fifteen's my favorite band, too.) Now the only two things I can think of are A.) some problem with the big loop, that presents some weird resonance on 15 and 17. Or more likely, B.) some problem with a component in the 706, one in the output section that is specific to 15 and 17 meters. Thoughts? TIA! _______________________________________________ Ken Kuzenski AC4RD ken . kuzenski at duke .edu _______________________________________________ All disclaimers apply, see? www.duke.edu/~kuzen001 |
#2
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Problem with an IC-706 & SWR spikes
Ken,
This is a well known problem and is discussed in the following thread: http://www.eham.net/forums/Elmers/108193 The Icom service bulletin 928 is @ http://home.comcast.net/~ad5x/images...ulletin928.pdf An easier fix than 928 by AD5X @ http://home.comcast.net/~ad5x/images...bilityRevA.pdf Good luck - Roger |
#4
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Problem with an IC-706 & SWR spikes
Ken,
Thanks for the update. Its always nice to know when something works out. Phil (AD5X) has a good site - you can find lots of good stuff there. Roger |
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