I live in a neighborhood where there is horrendous noise to the point
where I can't receive weak signals. My setup has an RME DB-20 R.F.
preamp feeding the Hammarlund. The antenna is just a wire I ran through
the trees away from any power lines. Some of the noise was coming from
early generation CFL's, some from my SCR touch lamp which makes noise
even while off. Even cell phone battery chargers and AA NiMH chargers
seem to have switching supplies in them and they probably all came from
China. I turned off my plug strip feeding this mess and the noise went
down but was still there. I turned off everything in the house and still
had noise.
When I put my scope on it the noise was synced to a major peak at both
the 90 degree and 270 degree points and did look like scr noise.

Now the hard part.
Can I put a noise blanker between the preamp and the radio?
I know that Hammarlund had a noise blanked circuit but these are very
hard to find and usually a lot of $$$$.
I am/was an electronics engineer for over 30 years but I find myself at
a loss as to what I should build or buy.
A noise blanker on the antenna input to the preamp seems like a good
place to put a blanker but the signal off the 25 foot 'long' wire might
not be enough to work with. My thinking is that it would be good to
intercept the noise before it even gets into thee tuned circuits and
causes ringing or some other side effect.

Ideas please.
Thanks,
Bill Baka

In Bill Baka
wrote:

Can I put a noise blanker between the preamp and the radio?
I know that Hammarlund had a noise blanked circuit but these are very
hard to find and usually a lot of $$$$.
I am/was an electronics engineer for over 30 years but I find myself
at a loss as to what I should build or buy.
A noise blanker on the antenna input to the preamp seems like a good
place to put a blanker but the signal off the 25 foot 'long' wire
might not be enough to work with. My thinking is that it would be good
to intercept the noise before it even gets into thee tuned circuits
and causes ringing or some other side effect.

Noise blankers are usually inserted in the IF chain and work at a single
frequency, and on signals of relatively high amplitude. Trying to get
something to work across the complete range of frequencies you're
listening to might be a real engineering trick.

Have you considered a noise cancelling receiver like the MFJ 1025/1026?

They use a separate noise antenna (the 1026 comes with one) and combine
the signal from it and your regular receiving antenna and then apply
phase shifts to either enhance or cancel signals that are received by
both antennas. The method is effective in theory, but I have no idea how
well the theory is implemented with these products.

http://www.mfjenterprises.com/Produc...uctid=MFJ-1025

--
Bert Hyman W0RSB St. Paul, MN

On 05/22/2010 08:46 AM, Bert Hyman wrote:
In Bill Baka
wrote:

Can I put a noise blanker between the preamp and the radio?
I know that Hammarlund had a noise blanked circuit but these are very
hard to find and usually a lot of $$$$.
I am/was an electronics engineer for over 30 years but I find myself
at a loss as to what I should build or buy.
A noise blanker on the antenna input to the preamp seems like a good
place to put a blanker but the signal off the 25 foot 'long' wire
might not be enough to work with. My thinking is that it would be good
to intercept the noise before it even gets into thee tuned circuits
and causes ringing or some other side effect.

Noise blankers are usually inserted in the IF chain and work at a single
frequency, and on signals of relatively high amplitude. Trying to get
something to work across the complete range of frequencies you're
listening to might be a real engineering trick.

Have you considered a noise cancelling receiver like the MFJ 1025/1026?

They use a separate noise antenna (the 1026 comes with one) and combine
the signal from it and your regular receiving antenna and then apply
phase shifts to either enhance or cancel signals that are received by
both antennas. The method is effective in theory, but I have no idea how
well the theory is implemented with these products.

http://www.mfjenterprises.com/Produc...uctid=MFJ-1025

Sounds like it might be worth a try, but I don't have any $$$ to buy
anything right now. I'm on disability so my income does not go too far.
Thanks for the fast response.
Bill Baka

Bill Baka wrote:
I live in a neighborhood where there is horrendous noise to the point
where I can't receive weak signals. My setup has an RME DB-20 R.F.
preamp feeding the Hammarlund. The antenna is just a wire I ran through
the trees away from any power lines. Some of the noise was coming from
early generation CFL's, some from my SCR touch lamp which makes noise
even while off. Even cell phone battery chargers and AA NiMH chargers
seem to have switching supplies in them and they probably all came from
China. I turned off my plug strip feeding this mess and the noise went
down but was still there. I turned off everything in the house and still
had noise.

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.

Now the hard part.
Can I put a noise blanker between the preamp and the radio?

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).

I know that Hammarlund had a noise blanked circuit but these are very
hard to find and usually a lot of $$$$.

These actually go into the IF strip, and to be honest they aren't really
very effective against the kind of noise problem you are encountering.
They are great for the occasional impulse from things like arcing power
lines or ignition noise, but the whines and drones from switching supplies
aren't so easy to deal with.

I am/was an electronics engineer for over 30 years but I find myself at
a loss as to what I should build or buy.
A noise blanker on the antenna input to the preamp seems like a good
place to put a blanker but the signal off the 25 foot 'long' wire might
not be enough to work with. My thinking is that it would be good to
intercept the noise before it even gets into thee tuned circuits and
causes ringing or some other side effect.

What's happening is that those side effects are happening inside your
preamp. Why do you need the preamp at all? The receiver sensitivity
should be okay by itself, and the dynamic range of the receiver front end
is better than any solid state preamp.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

On 05/22/2010 09:43 AM, Scott Dorsey wrote:
Bill wrote:
I live in a neighborhood where there is horrendous noise to the point
where I can't receive weak signals. My setup has an RME DB-20 R.F.
preamp feeding the Hammarlund. The antenna is just a wire I ran through
the trees away from any power lines. Some of the noise was coming from
early generation CFL's, some from my SCR touch lamp which makes noise
even while off. Even cell phone battery chargers and AA NiMH chargers
seem to have switching supplies in them and they probably all came from
China. I turned off my plug strip feeding this mess and the noise went
down but was still there. I turned off everything in the house and still
had noise.

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.

Now the hard part.
Can I put a noise blanker between the preamp and the radio?

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

I know that Hammarlund had a noise blanked circuit but these are very
hard to find and usually a lot of $$$$.

These actually go into the IF strip, and to be honest they aren't really
very effective against the kind of noise problem you are encountering.
They are great for the occasional impulse from things like arcing power
lines or ignition noise, but the whines and drones from switching supplies
aren't so easy to deal with.

I am/was an electronics engineer for over 30 years but I find myself at
a loss as to what I should build or buy.
A noise blanker on the antenna input to the preamp seems like a good
place to put a blanker but the signal off the 25 foot 'long' wire might
not be enough to work with. My thinking is that it would be good to
intercept the noise before it even gets into thee tuned circuits and
causes ringing or some other side effect.

What's happening is that those side effects are happening inside your
preamp. Why do you need the preamp at all? The receiver sensitivity
should be okay by itself, and the dynamic range of the receiver front end
is better than any solid state preamp.

The preamp really is only useful above 20 MHz, so it isn't even used
most of the time. The Hammarlund has great sensitivity below 20 MHz but
can use the boost above that. The only thing I have been able to receive
up there is CB chatter, so that is probably not worth it.
With my scope synced to 60 Hz I can see two big spikes and lots of
little ones that take a while to settle down.
Thanks for the reply,
Bill Baka
--scott

Bill Baka wrote:

With my scope synced to 60 Hz I can see two big spikes and lots of
little ones that take a while to settle down.
Thanks for the reply,
Bill Baka

What sort of antenna are you using? You might be able to configure
something, although I'm not exactly sure what, that can provide more
directivity and maybe escape from some of the junk noise.

Don't just write it off because of the all the Chinese crap thats out
there. A problem crept up here once, right about Christmastime, where I
got a steady rhythmic buzz a couple of times per second. Figured it was
a neighbors Christmas lights or something. Switched off all my breakers
and it persisted. Could hear it several hundred feet away from my house
on a portable radio. It was everywhere, impossible to null or peak.

But it persisted for months AFTER Christmas. Then a main breaker to my
house (in the panel out front with the meter) crapped out and had to be
replaced. Guess what? No more noise!

So there I was putting up with the noise and blaming neighbors and Red
China and the problem was something so simple - just difficult to localize.

Just food for thought.

Good luck,

Bill M

I can vouch for the MFJ noise cancelling antenna. However, you have to
keep re-adjusting
it as you change frequency. Not by much, but it requires re-tweaking.
It makes the noise
practically dissapear, without the artifacts of a noise limiter.
Perhaps you can find one on ebay,
Or appeal to a ham club or two for a loaner or a donation.

On 05/22/2010 01:40 PM, Bill M wrote:
Bill Baka wrote:

With my scope synced to 60 Hz I can see two big spikes and lots of
little ones that take a while to settle down.
Thanks for the reply,
Bill Baka

What sort of antenna are you using? You might be able to configure
something, although I'm not exactly sure what, that can provide more
directivity and maybe escape from some of the junk noise.

I have a sort of long wire, 25 feet, and the other side is grounded to a
chain link fence. There is not enough room to put up much else unless I
run a wire to the house behind me. Yup, two rental houses on one lot.
My stepdaughter lives in the back and I don't even know if she could
figure out the concept of radio DX noise. She is a cable TV addict and
not at all inclined to radio. I do have a radio direction finder that I
can run with a solar cell I picked up, so I can walk it around in the
sun and try to find the major noise source that way. When I scoped it,
it looked like a lot of SCR's triggering at various points so I kind of
figure it may be SCR light dimmers.

Don't just write it off because of the all the Chinese crap thats out
there. A problem crept up here once, right about Christmastime, where I
got a steady rhythmic buzz a couple of times per second. Figured it was
a neighbors Christmas lights or something. Switched off all my breakers
and it persisted. Could hear it several hundred feet away from my house
on a portable radio. It was everywhere, impossible to null or peak.

But it persisted for months AFTER Christmas. Then a main breaker to my
house (in the panel out front with the meter) crapped out and had to be
replaced. Guess what? No more noise!

Nah, my breakers are good. I have a touch lamp with an SCR in it
(Chinese, of course) and it makes noise even when turned off. Louder
when it is on. It does seem to be from other houses.

So there I was putting up with the noise and blaming neighbors and Red
China and the problem was something so simple - just difficult to localize.

Just food for thought.

Good luck,

Bill M

I think I will get my RDF and go hunting tomorrow.
Thanks,
Bill Baka

On 05/22/2010 04:44 PM, petev wrote:
I can vouch for the MFJ noise cancelling antenna. However, you have to
keep re-adjusting
it as you change frequency. Not by much, but it requires re-tweaking.
It makes the noise
practically dissapear, without the artifacts of a noise limiter.
Perhaps you can find one on ebay,
Or appeal to a ham club or two for a loaner or a donation.

One of my friends refers to MFJ as Mighty Fine Junk. How good is it?
Bill Baka

Bill Baka wrote:
On 05/22/2010 01:40 PM, Bill M wrote:
Bill Baka wrote:

With my scope synced to 60 Hz I can see two big spikes and lots of
little ones that take a while to settle down.
Thanks for the reply,
Bill Baka

What sort of antenna are you using? You might be able to configure
something, although I'm not exactly sure what, that can provide more
directivity and maybe escape from some of the junk noise.

I have a sort of long wire, 25 feet, and the other side is grounded to a
chain link fence. There is not enough room to put up much else unless I
run a wire to the house behind me. Yup, two rental houses on one lot.
My stepdaughter lives in the back and I don't even know if she could
figure out the concept of radio DX noise. She is a cable TV addict and
not at all inclined to radio. I do have a radio direction finder that I
can run with a solar cell I picked up, so I can walk it around in the
sun and try to find the major noise source that way. When I scoped it,
it looked like a lot of SCR's triggering at various points so I kind of
figure it may be SCR light dimmers.

yes, with puny antennas and rental houses and chain link fences and
stepdaughters who are "cable tv addicts" to blame you really must attack
some cogent RFI initiatives from your part. That's what I was alluding
to before.