Dummy wrote:
The antenna was pointing to any angle and direction randomly while
transmitting. One strange behaviour observed. The spurs could only be
seen at certain angles of transmission only.

Spurs at 32khz and 62khz away from carrier would cause an interference
at adjacent frequencies. A simple test was being carried out. Two
radios. First radio had 502.025MHz as Tx and Rx frequency. While
second radio had 502.057MHz as Tx and Rx frequency. Transmitting at
502.025MHz would cause a interference on second radio, in which we
could hypothesize that spurs at 32kHz away was too high in amplitude
and thus causing interference to other frequency. So, the spurs were
real! It wasn't some kind of 'illusions' produced by spectrum
analyzer. I guess this is highly undesirable.

Besides, I'm sure those spurs weren't produced by radio internal
circuit as I couldn't see any spurs if radios were being transmitted
into spectrum analyzer directly using 50 Ohm coaxial RF cable. Even
with 4:1 and 8:1 VSWR load, there's no existence of spurs. Could the
antenna's match worse than VSWR 8:1? Perhaps the spurs were part of
the intrinsic characteristic of any antennas?

Maybe the culprit was TV transmitter nearby. I have yet to look into
that. Another test that can be done is to do transmission in a sealed,
interference-free room. If spurs still could be seen, I would say it's
the antenna's imperfection that produced the spurs. If spurs gone,
it's a good news that the spurs were coming from outer space, Mars
maybe.

I would be grateful if somebody could check this out on few radios to
see if this problem exists.

Could it be you're just expecting a little more from your IF filters
than they can realistically eliminate?

73, AC6XG