"Tam/WB2TT" wrote in message ...
"Dummy" wrote in message
om...
Roy Lewallen wrote in message
...
More thoughts along the lines of John's comments, 32 kHz is about twice
the frequency of the horizontal line component of TV video. Do you have
any TV transmitters reasonably close by?

I've had problems with detected video on a couple of occasions, getting
into audio circuits. After I redesigned the audio circuits to look more
like VHF/UHF circuits -- laid out, bypassed, and filtered for VHF/UHF --
the problems disappeared. A working hypothesis is that there's a strong
TV transmitter getting into your transmitter via the antenna and/or its
transmission line, then getting detected and modulating your
transmitter. In the case of my audio problems, the vertical scan
component was worse, resulting in a "hum" that varied with the picture
of the offending TV station. You might take a close look at the spurs
and see if they vary with a local station's picture.

Roy Lewallen, W7EL

John Smith wrote:
Your spurs sound very strange, too close in 32 kHz, 62KHz, normally
they are
further out several MHz if generated by the RF chain. That is like an
audio
part/circuit getting into the transmit RF. Try rearranging or
twisting up
the power cables to the radio.
If spurs are low, not much power is there, so little damage to radio
rts. -65dBc sounds good for a CB. The farther you look down the more
spurs
there. The antenna could be reradiating RF power back onto circuit
components, which could be a cause too.

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.

I think somebody else mentioned this in passing, but it is worth considering
whether RF is getting into the radio via the microphone cable, or whatever
the driving source is. You say the spurs change when you rotate the antenna.
Do they go away when the radio is at an antenna nul? Can you key the radio
with the microphone unplugged? If not, have somebody look at the spectrum
analyzer while somebody else is moving the mic cable around.

This might be grasping at straws, but worth copnsidering.

Tam/WB2TT

Even with microphone unplugged, the spurs still could be seen. At
certain angle of transmission, the spurs would seem to be disappeared.
I have no idea where the spurs came from.