[AMRadio] AM vs. broadband line noise


John Coleman jc at pctechref.com
Mon Sep 17 15:03:49 EDT 2007


Actually that is about it.  In reception, the advantage is the signal to
noise ratio.  By having a 1/2 bandwidth and all else being equal then you
will have a 3 DB drop in noise.in a lot of situations the bandwidth on older
AM receivers is several times what it is on a modern SSB RCVRs   The caveat
here is all else is generally not equal.  In a lot of situations the
bandwidth on older AM receivers is several times what it is on a modern SSB
RCVRs.   Product detection, especially balanced product detection, has a
pretty nice advantage and most modern SSB gear uses it whereas most of the
AM stuff doesn't.  "Full bandwidth AM balanced product detection" requires
synchronization with the incoming AM.  With out the SYNC it is pretty
useless for AM.  But if you ever get to use one you will want it.  When the
going gets rough, I have used regular product SSB detection for AM and there
is an advantage because of the reduced bandwidth. I have found it is best to
use a filter where the carrier insertion is 300 HZ from the skirt of the
filter so that low frequency audio is rolled off pretty quick and the
carrier beat is not detected.  This of coarse, make the received audio a lot
like the majority of SSB signals but as I said it is for when the going gets
rough.  "Full bandwidth AM balanced product detection" increases the
reception so that it is only slightly less advantageous in signal to noise
ratio and sound so much better that standard SSB detection.

Most of us like to run AM because of the "GOOD OLD SOUND", experimenting,
building and camaraderie involved.  Signal to noise ratio business is for CW
and PSK.  A LITTLE JOKE

John

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of Michael Mertes

 It occurred to me that I have too much line noise here.
I am not shy about transmitting with my low power AM
setup, but I'm not going to do that if I can't hear
anything. I've had this problem for just over a year,
so it is something I will have to chase down soon
enough, but I just don't have the time right now.

So I have a question for the group; since I have never
really pursued AM seriously before. It is this: How
does line noise affect AM as opposed to SSB. It seems
as though I have much better reception with SSB on the
same bands and can work SSB; where AM is just wiped
out. One point certainly is the wide bandwidth and
less signal/noise on AM, but that doesn't seem to be
the whole of it. Does anyone have an educated guess,
or is it just my observation only?

Thanks,

Mike/KZ5M






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