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 Post subject: Accidental Noise Suppression
PostPosted: Jan Thu 04, 2018 8:30 pm 
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Joined: Oct Thu 15, 2015 8:22 pm
Posts: 92
Location: Baltimore, MD
Happy New Year to all,

I came across something pretty interesting when I placed two Bendix tabletop radios close to each other. Some background, I have a noisy PC power supply and sump pump battery charger in the same room with my radios. Both are switch mode regulators and put out a lot of noise.

Basically, I placed a 526 on my pool table and turned it around to get the best reception. Then, I placed a 636 next to it back to back. The 636 was plugged in but powered off. I noticed that when I tuned the powered off 636 through the band I could get much improved reception on the 526 radio especially if the 636 is tuned to the high end. When I tuned the 636 to the same frequency as the 526 the reception dropped off markedly. Also, If I unplug the powered off 636 the noise suppression disappears.

I have done some reading on ARF about adjacent loop antennas improving reception of DX stations but I dont recall any usage to reduce noise.

Any thoughts on this appreciated. I'm guessing the noise is somehow filtered to ground through the 636 radio circuitry.

Best Regards,
BobH


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 Post subject: Re: Accidental Noise Suppression
PostPosted: Jan Thu 04, 2018 8:46 pm 
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Joined: Mar Mon 17, 2008 5:05 am
Posts: 5527
Location: Ashhurst, New Zealand
Your 636 is also picking up the signal and reinforcing the signal into the 526. No different from those "Select-a-tenna" things. More signal equates to more AGC voltage reducing the gain and hence reducing the noise.

It seems that with the radios back-to-back you are getting cancellation rather than addition - try turning the 636 around so that both radios are facing the same way.

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 Post subject: Re: Accidental Noise Suppression
PostPosted: Jan Fri 05, 2018 2:40 pm 
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Joined: Oct Thu 15, 2015 8:22 pm
Posts: 92
Location: Baltimore, MD
Martin,
Thanks for the reply!

I had forgotten about the AGC line. When I turned the 636 around the reception worsened but then the antennas were not as close together.

Regards,
BobH


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 Post subject: Re: Accidental Noise Suppression
PostPosted: Jan Fri 05, 2018 4:55 pm 
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Joined: Jun Wed 14, 2006 11:49 pm
Posts: 7362
Location: Leo, IN or Zellwood, FL
yes, Signal increase but not noise reduction.
John k9uwa

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