Re: Spurious transmission on 6m
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It is known that the 857 tents to have spurious oscillations once in a while. I think it is a feedback from the filters into the first stages of the RF generation. What I suggest is: ?- remove top and bottom enclosure ?- clean all mating surfaces, I use sandpaper
?- I add thin 1 mm gaskets (foam over fabric) to improve contacts ?- check all screws that hold the board down.
?- close the unit, add the four screws from mounting into a car. Be careful not to use too long screws ?- I also add ferrite loaded elastomer on the inside of the enclosure on the RF power amp side. I do not know if this helps and is needed.
Overall, I think very good contact of the PCB to the frame and the lids to the frame are needed. Last time when I had oscillations I found that I had forgotten to add a screw to the lid
David?? OE6NZM / AD0PY / DL7ZM
Hello All,
Since a couple of days I have an annoying problem when operating 6m,
I have the power output limited to 30W, but sometimes I see the A-meter of my PSU going all the way up while transmitting. Power output and ALC go to max, no matter what, even without modulation. This happens on all modes.
I checked with a spectrum analyzer, and found out that when this happens, it outputs a high signal on around 47MHz, and nothing on the expected frequency. This happens irregularly, sometimes it is ok for hours, and suddenly it's not, for a couple of transmissions. Often it resets after a few transmissions.
I believe I have seen it on other HF bands as well, but recently I have only been able to replicate it on 6m. In any case, it seems to happen more frequently on 6m.
It looks like some oscillation is going on in the unit, causing maximum output on a wrong frequency?
I removed all the input and output connections (except the antenna and mike), but this does not change the behaviour. My antenna is reasonably well adjusted, VSWR <1,5. I haven't checked it with a dummy load yet, will do that later.
Does anybody recognizes this?
73
Peter/PA3FQH
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