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Old September 17th 07, 03:24 PM posted to rec.radio.amateur.moderated
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Default VLF 9 KHz

I've been following a conversation over on news:rec.audio.pro
originated by a guy who is getting what appears to be CW
RFI on his microphone(s) at 9 KHz. He also reported hearing
similar "whistling" on the AM BCB.

At first I thought of those submarine communication transmiters
in the Great Lakes area (the problem is in Michigan). But, although
they run megawatts, they appear to use either higher (14-60 KHz)
or lower (40-80Hz) frequencies. And the ones in upper Michigan
and Wisconsin appear to be shut down, anyway.

http://www.fas.org/man/dod-101/navy/...cmp/part07.htm

So is there anything at 9 KHz that could be an intermittent
source of CW? Some Googling around the inter-web didn't
turn up as much as I expected.


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Old September 17th 07, 07:56 PM posted to rec.radio.amateur.moderated
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Default VLF 9 KHz

Richard Crowley wrote:
So is there anything at 9 KHz that could be an intermittent
source of CW?


9 KHz is in the audio spectrum so it is probably
the product of mixing. What frequency is the
receiver tuned to? What are the IF frequencies?
What are the intermod possibilities?
--
73, Cecil http://www.w5dxp.com

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Old September 17th 07, 08:19 PM posted to rec.radio.amateur.moderated
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Default VLF 9 KHz

"Cecil Moore" wrote ...
Richard Crowley wrote:
So is there anything at 9 KHz that could be an intermittent
source of CW?


9 KHz is in the audio spectrum so it is probably
the product of mixing. What frequency is the
receiver tuned to? What are the IF frequencies?
What are the intermod possibilities?


It is being picked up directly by two Royer ribbon
microphones which contain an active impedance-
matching circuit implemented with a tube ("valve").
No IF involved there.

On his AM BCB receiver, he was complaining about
790KHz. We likely have no way of discovering his IF
frequency.


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Old September 17th 07, 08:51 PM posted to rec.radio.amateur.moderated
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Default VLF 9 KHz

Richard Crowley wrote:
It is being picked up directly by two Royer ribbon
microphones which contain an active impedance-
matching circuit implemented with a tube ("valve").
No IF involved there.


But it could certainly be intermod.
--
73, Cecil http://www.w5dxp.com

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Old September 17th 07, 09:06 PM posted to rec.radio.amateur.moderated
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Default VLF 9 KHz

Well,

Having thumbed through the articles on the other news group (Some 300
of them), I'm almost certain that this problem is with his equipment,
the grounding and shielding of that ribbon microphone and associated
preamp and is likely to originate with some kind of local
unintentional radiator located within his house (A switching power
supply, plasma TV, Cable tuner etc.) Listening to the audio provided
really makes me think there is some very noisy switching power supply
in this mix somewhere.

I would start by verifying that the shield on that "special" 7 pin
cable between the preamp and the mic is not damaged and I would invest
in some of the clip on RFI cores that you can loop the microphone
cable though a few times as close to the preamp as possible. He needs
to be 100% sure that he has eliminated all the possible grounding
problems (which it seems that he has a number based upon his posts) by
lifting power and signal grounds where necessary to make sure there is
only ONE path to ground from ANY piece of equipment.

In the end, I'll bet that it's the microphone/preamp that is to blame
and getting that fixed can be something way beyond the scope of what
can be discussed on Usenet effectively.

-= Bob =-

On Sep 17, 9:24 am, "Richard Crowley" wrote:
I've been following a conversation over on news:rec.audio.pro
originated by a guy who is getting what appears to be CW
RFI on his microphone(s) at 9 KHz. He also reported hearing
similar "whistling" on the AM BCB.




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Old September 17th 07, 09:07 PM posted to rec.radio.amateur.moderated
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Default VLF 9 KHz


This tube is likely the thing that's rectifying stray RF that happens
to come along for the ride so I suspect that the problem this guy is
having is more likely to be shielding or grounding issues. The source
of the RF is an open question, but I think it's a moot point because
he seems to be getting a lot of RF from a number of sources which
tells me there are some serious issues with his wiring. I would
entertain the theory that this tube is needing some neutralization and
may be doing some serious oscillation under certain external
conditions, but I wouldn't undertake a technical discussion of how to
fix that on Usenet given there is likely some 900 volts involved here
and somebody could get killed.

-= bob =-

On Sep 17, 2:19 pm, "Richard Crowley" wrote:
It is being picked up directly by two Royer ribbon
microphones which contain an active impedance-
matching circuit implemented with a tube ("valve").
No IF involved there.




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Old September 18th 07, 02:55 AM posted to rec.radio.amateur.moderated
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Default VLF 9 KHz

On Mon, 17 Sep 2007 15:19:26 EDT, "Richard Crowley"
wrote:

It is being picked up directly by two Royer ribbon
microphones which contain an active impedance-
matching circuit implemented with a tube ("valve").
No IF involved there.


Can you spell "audio rectification" ?? ggg
--

73 de K2ASP - Phil Kane

From a Clearing in the Silicon Forest

Beaverton (Washington County) Oregon

e-mail: k2asp [at] arrl [dot] net

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Old October 9th 07, 07:32 AM posted to rec.radio.amateur.moderated
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Default VLF 9 KHz

On Mon, 17 Sep 2007 10:24:47 EDT, "Richard Crowley"
wrote:

I've been following a conversation over on news:rec.audio.pro
originated by a guy who is getting what appears to be CW
RFI on his microphone(s) at 9 KHz. He also reported hearing
similar "whistling" on the AM BCB.

At first I thought of those submarine communication transmiters
in the Great Lakes area (the problem is in Michigan). But, although
they run megawatts, they appear to use either higher (14-60 KHz)
or lower (40-80Hz) frequencies. And the ones in upper Michigan
and Wisconsin appear to be shut down, anyway.

http://www.fas.org/man/dod-101/navy/...cmp/part07.htm

So is there anything at 9 KHz that could be an intermittent
source of CW? Some Googling around the inter-web didn't
turn up as much as I expected.


If you are away from 60Hz lines or have few issues with strong AC
buzz, the whistling is very likely a natural phenomenon between 8 and
10 Khz. I believe it to be something related to the earth's magnetic
field and have read something about this in the past. In fact, it was
a selling point of one popular VLF receiver years ago. It was
described as almost ghostly. I bet it was a Palomar VLF receiver ad!
The device has a large loop antenna.

The whistling may be even more clear, the further you are from power
lines. I'm also curious to know if the whistling is louder and more
noticeable when the solar cycle gets cranked up again in a few years.

73's!

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Old October 9th 07, 04:36 PM posted to rec.radio.amateur.moderated
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Default VLF 9 KHz

"~justusloonz~" wrote ...
"Richard Crowley" wrote:
I've been following a conversation over on news:rec.audio.pro
originated by a guy who is getting what appears to be CW
RFI on his microphone(s) at 9 KHz. He also reported hearing
similar "whistling" on the AM BCB.

At first I thought of those submarine communication transmiters
in the Great Lakes area (the problem is in Michigan). But, although
they run megawatts, they appear to use either higher (14-60 KHz)
or lower (40-80Hz) frequencies. And the ones in upper Michigan
and Wisconsin appear to be shut down, anyway.

http://www.fas.org/man/dod-101/navy/...cmp/part07.htm

So is there anything at 9 KHz that could be an intermittent
source of CW? Some Googling around the inter-web didn't
turn up as much as I expected.


If you are away from 60Hz lines or have few issues with strong AC
buzz, the whistling is very likely a natural phenomenon between 8 and
10 Khz. I believe it to be something related to the earth's magnetic
field and have read something about this in the past. In fact, it was
a selling point of one popular VLF receiver years ago. It was
described as almost ghostly. I bet it was a Palomar VLF receiver ad!
The device has a large loop antenna.

The whistling may be even more clear, the further you are from power
lines. I'm also curious to know if the whistling is louder and more
noticeable when the solar cycle gets cranked up again in a few years.


The OP finally discovered that the manufacturer had a
bad batch of tubes which intermittently broke into self-
oscillation in their circuit.



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