What's going on at 3.915 & 3.905 mhz?

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  • Updated 3 years ago
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When tuning on 80m when I pass through 3.915 and 3.905mhz I hear a relay clicking in the radio. It doesn't matter if I am going up or down the band. Sometimes it will move the noise floor line up or down by -5 to -8. Sometimes also the background of the Panadapter will slightly change intensity. As best I can tell, the signals I receive either above or below 3.915 are unaffected. 
The question is: What is the relay all about?  Why does the noise floor line move?
Thanks for any input.
73
Ken
W0KRD
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Ken Davis

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Posted 3 years ago

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EA4GLI - 8P9EH - Salvador

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It doesn't happen to me. Is your ATU enabled?
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k3Tim

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Can you turn off the ATU and retest?  
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EA4GLI - 8P9EH - Salvador

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No worries. :) I am lurking on the forum waiting for the 1.6 announcement to pop up and just going through every single post! 
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EA4GLI - 8P9EH - Salvador

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At least you replied right away. The other day I took the time to post a complete tutorial with pictures on how to setup something on N1MM and the person that asked hasn't even acknowledge the answer. That was almost a month ago. 
(Edited)
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k3Tim

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Somewhere in the SDR software manual it talks about how the ATU works.  Something like every 100Kc it sets up a new tuning data set  for the particular band.  I've noticed with my end-fed ATU code can sometimes do it more frequently and when you roll past one of the "node points" the ATU relays click for the next setting.  It also seems a wide band, 80 to 75 meters, one can tune the lower CW portion and if you meander up-dial to the top end of 75, the ATU won't have the tuning settings (at first run) and drop out / off.  Once the entire band is tuned it's saved.

Once setup the ATU is pretty much transparent except for an occasional click.

Before ATU memories, just changing modes (CW to RTTY) would require a retune.  It's nice to bee past that minor inconvenience.


Tim
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Ken Davis

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Oh that is great information. Thanks for the education.
Ken
W0KRD
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DrTeeth

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I get a similar clicking when tuning around, not that often though and I do not have the ATU installed. IIRC, it happens whilst tuning through top band
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G8ZPX

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check ATU, preamp, antenna selection settings etc. as these are all "per-band" and may (will) change as you slide out of a designated ham band in to general/broadcast bands. Also, watch for any button/slider changes on-screen as the relay clicks in/out that should tell you what is changing.