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Author Topic: S.E.M. Mk2 QRM Eliminator  (Read 3093 times)
G3HEE
Member

Posts: 2




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« on: August 16, 2012, 09:47:31 AM »

Would anyone have a copy of the circuit diagram and component specifications for one of these ?


Regards

Peter
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G3RZP
Member

Posts: 4954




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« Reply #1 on: August 16, 2012, 02:45:09 PM »

All I can say is that nearly thirty years ago when I was on the RSGB Technical and Publications Committee, we had more complaints from members about that company and its products  than of any other.
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G8JNJ
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Posts: 496


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« Reply #2 on: August 17, 2012, 12:45:43 AM »

Hi Peter,

I have  page on my website with details and circuits of various noise cancellation circuits including the SEM.

http://g8jnj.webs.com/rfnoisecancellation.htm

Don't expect too much from the design. It can work under some circumstances. But most of the time you may find that it does very little.

Most of the perceived noise cancellation is actually just a psycho-acoustic effect, associated with reducing the signal level. This is very apparent when using it in conjunction with an SDR radio with real time spectrum display. In many cases, both the signal and noise level are reduced to the same extent. The actual signal to noise ratio remains more or less the same.

But using the SEM I can obtain a 30dB notch on a spurious signal from my home alarm system control panel. But this takes a lot of fiddling with the controls, and does not remain stable over a long period of time.

Regards,

Martin - G8JNJ

www.g8jnj.webs.com
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G3HEE
Member

Posts: 2




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« Reply #3 on: August 17, 2012, 12:35:29 PM »

Many thanks for your help, but since posting my enquiry another amateur who was listening to me talking about my problem (I "fried" the transistors inadvertently due to an inadvertent polarity error when changing to a new PSU)  has very kindly e-mailed me the necessary schematic and component list.

73   Peter
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K0OD
Member

Posts: 2590




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« Reply #4 on: August 17, 2012, 04:22:41 PM »

G8JNJ: 
Quote
Most of the perceived noise cancellation is actually just a psycho-acoustic effect, associated with reducing the signal level.

I suspect that's all the noise reduction that happens with those outboard audio DSP boxes, all the rage about 15 years ago. With that perception increasing with the cost of the accoutrement and the number of its knobs.   
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