Quote:
Originally Posted by n4xyz
Hi, I don't know if this is the right bucket but I need advice from experienced RV hams. I installed a fiberglass push-up pole 31 feet, on the ladder of my 5th wheel. It is feed with an Icom AH4 tuner grounded to frame feed from an IC-706mk2g. On 40m I have terrible feedback RF getting in the mic. I put clip on needs on the coax and tuner control at both ends. The operating position is in the rear of the 5er, only about 5 feet away. What are my options to reduce the rfi. Seems to work ok on other higher bands.
Thoughts would be appreciated.
Dave N4XYZ
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By "clip on needs" I think you mean clip-on ferrite beads. If you meant something else, you'll have to explain.
If the RF is getting into the microphone, it may be that it's being picked up by the microphone cable. Try wrapping that cable five or ten turns through a ferrite toroid at the radio end, or at the mike end, or at each end. Depending upon the size of the connector, this may require a rather large toroid. To see whether RF
is being picked up by the mike cable, you could wrap it temporarily in aluminum foil, grounded to the radio at the radio end and connected to nothing at all at the microphone end. If that cures it, it's RF picked up by that cable, for sure. The foil is not suggested as a permanent fix -- just as a diagnostic tool.
Clip-on ferrites aren't totally worthless, but on 40 meters (a fairly low frequency) they likely don't add enough inductance to have much effect. Several turns through a toroid will be
many times more effective than any clipon, for several reasons. For example, three turns would add nine times as much inductance as a perfect clipon. But you could try the clipons first since you have them and it's easy.
This assumes there's no RF on the outside of the radio itself. If there is, work on that first. Ultimately you may have to replace those clipons with toroids.
Of course you have grounded the radio itself directly to the frame of the trailer, and not with just any old skinny wire but with a nice fat, thick braid. That ought to go without saying, but I guess it doesn't hurt to ask.