On 05/22/2010 06:30 PM, Scott Dorsey wrote:
Bill wrote:
On 05/22/2010 09:43 AM, Scott Dorsey wrote:

Welcome to the New Era. Everything has a switching supply in it. None
of them meet FCC Part 15 specs. Nobody at the FCC gives a damn. Write
your congressman and complain about the enormous arrays of CFLs, touch
lamps, and TV sets for sale at Wal-Mart which are patently illegal.

Tell me about it. Damn near everything that comes out of Walmart is
Chinese and if I buy anything it seems to fail just after any hope of
warranty. The noise seems to come from anything Chinese so I try not to
buy that stuff, but in many cases China is the only source.

Don't blame the Chinese. The Chinese make cheap crap because Americans
demand cheap crap. If Americans wanted good products, the Chinese would
make good products. But the American importers are constantly after the
Chinese factories to cut costs, not to improve quality, and so this is
what you get.

Really? I try to search for American products and pay a little more for
better quality, but so many companies have been killed off it is
sometimes impossible to buy American. People seem to have the attitude
"It won't cost me MY job" until it does. I bought a Kodak digital camera
hoping it would be at least 'non-Chinese' but when I got it out of the
box, sure enough, Made in China. Too bad not enough people can put cause
and effect together. I used to gripe about 'Made in Japan' 30 years ago,
but now even Japanese companies are farming things out to China.

No, and I think the preamp is probably a lot of your issue, that broadband
noise is saturating it. You might want to consider a more tightly tuned
preamp, possibly one with a front end that has outrageous dynamic range and
low noise (like, say a nuvistor or even a 6X8).

It does have switch so I can bypass the preamp and just go through the
radio. The preamp only gets overloaded by an AM station here on 1,600
KHz at 5,000 or 50,000 watts, even though the station is a good 5 miles
from me. If I hit that with the preamp on, yes it will overload, but
going straight to the Hammarlund still gives excellent tuning so in
order to get

We're not talking about catastrophic overload, we're only talking about
a little nonlinearity. It doesn't take much.

What happens is the channel is so strong the preamp gets mucked up. The
Hammarlund can still tune 1590 and it seems to be immune to a strong
station at 1600.

You have two problems:

1. Noise that is off-channel, maybe even out of band, which either winds up
being detected due to poor selectivity, poor shielding, or because
something in the front end or early IF (or in your case the preamp) is
mixing multiple noise sources together to form a beat product on your
channel.

2. Noise that is actually on-channel, on the exact frequency you are on.

The first one can be remedied by eliminating the preamp, making sure the
receiver front end is clean (ie. the first RF stage is perfectly linear)
and possibly adding a preselector.

The second one cannot be remedied. The noise blanker is one thing people
have used; it drops the whole signal out when the signal reaches a
limiting level and it good only for impulse noise that is stronger than
the signal.

One of the DSP boxes like JPS sells can help hide on-channel noise,
sort of.
--scott

Sorry, none of the above. I have my scope on the speaker leads and the
waveform indicates power line noise being fed back by SCR controlled
devices, and/or switching power supplies. Since my scope is vintage 1989
I can't freeze just one cycle to analyze. I paid over $2,200 for the
scope, brand new, for a project I was working on at the time. The
waveform looks like an SCR spike and then a gradual decay. That is the
best I can describe it for now. Nobody here has the doorbell problem
since the houses are old for about two blocks around me. I don't know if
it is one house, or many.
Detective work is needed.
Bill Baka