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  • Charles Scott
    Bob: Perhaps this is what you think, but perhaps it s not. The FT-100 did in fact have this kind of a problem. Significant HF energy entering the VHF/UHF
    Message 1 of 4 , May 1, 2006
      Perhaps this is what you think, but perhaps it's not.
      The FT-100 did in fact have this kind of a problem. Significant HF
      energy entering the VHF/UHF antenna could cause transmit frequency
      stability problems. This was related to the problem where stray RF in the
      radio did the same thing and was why some of the internal grounding
      modifications where done. So, yes, you could be right that your problem
      was HF energy coming in the VHF/UHF port. How much of this RF you get from
      your 2 Meter antenna would depend on the antenna and feed design. Some
      antennas would be significantly worse than others.
      It could also have been RF coupled onto the shield on the outside of the
      2 Meter feed line. This could result in considerable RF at the radio that
      could be causing problems by getting in on the power, microphone, or other
      connections to the radio. Perhaps the reason it did this on 80 Meters and
      not the other bands has to do with some resonance related to the length of
      the transmission lines.
      To determine which is the real cause, you could insert a coax switch in
      the line on the 2 Meter connection to the radio and switch the antenna in
      and out while transmitting on 80 Meters to see if that has any effect. If
      you still have the problem with the 2 Meter antenna switched out, it's
      getting to the radio on the outside of the transmission line. That problem
      can be fixed by "decoupling" that line at some point to prevent the RF from
      getting there (coil the coax cable, ferrite chokes, whatever).

      Chuck - N8DNX

      On Sun, 30 Apr 2006, Bob wrote:

      > Hi Group,
      > Something happened to my 897 when I was setting up a couple of new
      > antennas and I thought I would share it with you.
      > I set up a 40 foot long inverted "L" antenna running from my FC40
      > tuner going up about 25 feet or so and then the end of the "L" being
      > tied off to the masting that holds my 2m horizontal loop antenna.
      > The wire of the antenna was approximately 5 feet away copper tubing
      > that makes up the loop.
      > It worked fine all day and I thought I had done it right the first
      > time as I had operated on 2-40m with no problems.
      > When I tried to operated on 80m late in the evening the rig was just
      > not cooperating and was beeping and the fast/slow modes were changing
      > every time I transmitted or talked on 80m ssb.
      > If I cut back the power on 80ssb the problem went away so just for
      > the heck of it I removed the coax for the 2m antenna from the 897 and
      > the problem went away.
      > It seems the hf signal was feeding back into the radio through the 2m
      > side of things.
      > Antenna has been moved and the problem solved but it had me wondering
      > for a few minutes. The funny thing is that on my car I have an 80m
      > antenna on the trunk and the vhf/uhn antenna on the roof and have
      > never had this problem with my 857.
      > Just thought I would mention it to you
      > 73bob
      > VA3QV/VA3RCS
      > Yahoo! Groups Links
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