David Robbins wrote:
> Ok, thanks for all the testing suggestions and comments. Below I will
> try to answer all the questions and suggestions so far. I also find it
> hard to believe it is produced by the amp, but am running out of other
> causes.
>
> I have tracked the spur from 21000 to 21450 (tx from 14000 to 14300) it
> is always exactly 1.5 times the tx frequency, the frequency of it is not
> affected by the amp tuning controls. The onset point does vary with
> load, near 14000 the swr is about 2:1 and the spur doesn't start till
> about 1kw output, at 14300 the swr is 1.2:1 and the spur is there at
> about 200w output from the amp but is much more sensitive to the amp
> tune control.
>
> I have generated it with and without the input bandpass filter and the
> output stubs in all possible combinations with 2 different radios.
>
> I unfortunately don't have an adequate dummy load right now, but even at
> almost 1:1 swr at the best frequency for the stack the spur is still
> there as loud and predictable as ever. (note the stack is 300' from the
> shack, with the shack off the side of the beams, and there is no other
> sign of rf feedback in any equipment, all grounds have been checked)
>
> I have swapped the ft-1000mp for a ts-870, there was no change in the
> spur at all.
>
> The amp does not have a qsk board.
>
> There is nothing in the rx antenna jack on the ft-1000mp or the ts-870.
>
> I can't believe it is a design flaw as the amp functioned normally for
> several years with no problems. And this is so repeatable now that I
> can't believe we didn't notice it or that someone else hasn't also seen
> it in multi station contest operations.
>
> David Robbins K1TTT
---------------------------------
Dave,
What are you listening to the spur on? Could it be generated in the
receiver? When you listen to it is it a clean carrier or is there any other
modulation on it?
Try turning off the computer? Any other electrical items that might have a
1.5 mhz oscillator in them? Local radio station at 1500kc?
73
Gary K4FMX
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