Dummy wrote:
"One wide-band antenna was hooked up on a spectrum analyzer."

Years ago, from time to time, I`d hear the sheriff`s dispatcher in the
background, and sometimes TV Channel 8 audio, when monitoring a certain
2-meter amateur repeater. It stopped when the Sheriff changed
frequencies.

Turns out the difference between the sheriff and Channel 8 frequencies
matched the IF of my Icom radio. When the repeater opened my squelch,
there the other signals were.

In 1949 I used to turn on the Mighty 790 here before 5:00 a.m. when we
signed on back then.

From my monitor loudspeaker I could hear KTRH, the 50 KW station about
15 miles away which was already broadcasting. The tiny 740 KHz signal
was mixing with the carrier in my final and being rebroadcast. Now both
stations are owned by Clear Channel so it would make no difference. It
made no difference then either because the 740 KHz signal on the 790 KHz
signal was more than 50 dB down. That`s under the FCC requirement at the
time.

I think the spectrum analyzer antenna is clean and the "spur" is a
simple mixing product.

Best regards, Richard Harrison, KB5WZi

Are you using a switch mode power supply to run your radio's?

You can get modulation products produced by switching noise on the supply rail.

Regards

Robin Cassidy

"Robin Cassidy VK3AYZ" wrote in
message om...
Are you using a switch mode power supply to run your radio's?

You can get modulation products produced by switching noise on the supply
rail.

Why do switchers have such a reputation in ham radio?

I realize it's possible to hose up a switcher design pretty thoroughly, (you
can also make a 7805 into about a 2W transmitter on 160M if you're not
careful), but I've never seen the sorts of problems that I keep hearing
associated with them..

BTW, I design switchers, and use them for power supplies in low noise
systems, without shielding or other expensive "voodoo" of any kind.

When designed properly, they are very efficient, and very nearly "silent".

Dave VanHorn wrote:

"Robin Cassidy VK3AYZ" wrote in
message om...

Are you using a switch mode power supply to run your radio's?

You can get modulation products produced by switching noise on the supply

rail.

Why do switchers have such a reputation in ham radio?

I realize it's possible to hose up a switcher design pretty thoroughly, (you
can also make a 7805 into about a 2W transmitter on 160M if you're not
careful), but I've never seen the sorts of problems that I keep hearing
associated with them..

BTW, I design switchers, and use them for power supplies in low noise
systems, without shielding or other expensive "voodoo" of any kind.

When designed properly, they are very efficient, and very nearly "silent".

1) Leakage Inductance from the core allows a small magnetic field to be
radiated.

2) By their nature they require a 'small' ripple voltage to exist on the
output as a consequence of the switching principle.

3) The input power, the raw power, is being modulated by the switching
cycle. This generates a transient pulse power on the input lines that
easily couples noise via various susceptibilities into the receivers.

4) The variable switching cycle, or the varying switching duty cycle,
creates broadband noise.

5) All of which are potential sources of trouble in a communications
receiver that wants to find a 0.16 uV/meter signal in the presence of noise.

As a designer of switchers, have you ever had to Qualify a switcher to
MIL-STD-461 and 462?. There is a conducted interference test on the
input power lines to the switcher that is brutal. The ripple on the
output fails the requirement of MIL-STD-462. The radiated emissions have
to be controlled, etc. The switching transients from ALL sources cause
EM Susceptibility in related equipment.

It's not impossible to design switchers for a quiet environment, but
I've spent $millions on getting them quiet enough to meet
MIL-STD-461/462 requirements.

3) The input power, the raw power, is being modulated by the switching
cycle. This generates a transient pulse power on the input lines that
easily couples noise via various susceptibilities into the receivers.

Only if you fail to decouple the input properly.

4) The variable switching cycle, or the varying switching duty cycle,
creates broadband noise.

5) All of which are potential sources of trouble in a communications
receiver that wants to find a 0.16 uV/meter signal in the presence of
noise.

Potential, yes I suppose.
As I said, I know you can make them perform badly, but it's just not that
hard to make them perform well enough that they won't be noticed on your
receiver, assuming you don't make it a practice to connect the power supply
directly to the antenna inputs.

The receiver itself may create more noise than a properly designed switcher.

As a designer of switchers, have you ever had to Qualify a switcher to
MIL-STD-461 and 462?.

That one I haven't. My hamshack dosen't require MIL-STD-461 either. That's
a large complicated battery of tests, that by it's very nature is expensive
to test to, even if you were testing a D-Cell battery.

I have several switchers in use, all commercial designs, and they are barely
detectable on my R-8500 or FT-847. I haven't had to go to any extremes (or
even any measures at all) to quiet them.

My PCs are another matter, they have needed ferrites on the cables, and EMI
absorption material inside the case, but that has proved to be managable.

(Robin Cassidy VK3AYZ) wrote in message . com...
Are you using a switch mode power supply to run your radio's?

You can get modulation products produced by switching noise on the supply rail.

Regards

Robin Cassidy

I think there are no tests that can be conducted to determine the
source of the spurs. RF radiated from antenna could cause interference
and non-linearity at spectrum itself. Unless I could 100% shield the
spectrum from RF, all tests would be invalid. Even if I stood faraway
from spectrum, the spurs could also be observed. However, by
transmitting into spectrum using 50 Ohm coaxial cable, no spurs were
seen. Possibly because RF was transmitted into spectrum without any
leakage which could have large effect in causing interference.

And can get EVEN WORSE! Tho realize that these type supplies seldom
used,nowdays, back in dark ages, had SQUARE WAVES-- generate infinate order
of (if memory serves me) odd harmonics!! when filters went bad, baseband
looked like a picket fence on spectrum anaylizer! ant, at 600 channels,
that loaded to about 2.5 MHz!! But you could hear these heck of a lot
higher with low band rcvr!! Jim NN7K


"Dummy" wrote in message
om...
(Robin Cassidy VK3AYZ) wrote in
message . com...
Are you using a switch mode power supply to run your radio's?

You can get modulation products produced by switching noise on the
supply rail.

Regards

Robin Cassidy

I think there are no tests that can be conducted to determine the
source of the spurs. RF radiated from antenna could cause interference
and non-linearity at spectrum itself. Unless I could 100% shield the
spectrum from RF, all tests would be invalid. Even if I stood faraway
from spectrum, the spurs could also be observed. However, by
transmitting into spectrum using 50 Ohm coaxial cable, no spurs were
seen. Possibly because RF was transmitted into spectrum without any
leakage which could have large effect in causing interference.