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#1
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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. |
#2
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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 |
#3
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"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. |
#4
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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 |
#5
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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. |
#6
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![]() 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. |
#7
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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 |
#8
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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! |
#9
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"~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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