|[AMRadio] AM vs. broadband line noise|
ellenjoanne2003 at sbcglobal.net
Sat Sep 15 23:32:50 EDT 2007
I have a similar situation here. I live in a nice apartment, but the
location is in the RF Hole of Calcutta on certain bands (of which 75m is one
of them). I not only live in an apartment building, with mini flourescents
in the hallways (you've gotta love those things), my building is 100-150
yards west of about 2 dozen power lines. 12 of them are of the wonderful
125 or 250 kV transfer variety that are routed on 100 foot tall steel towers
(can you say buzz? - sure you can, I knew you could), as a result, the noise
blankers on my receivers, are always on. To make things even more
interesting, I have two AM, BC stations with nice big antenna arrays, that
are less than a mile from me, that give me AM breakthrough on all of my
rigs, to a greater or lesser degree (one's an all sports format, the other
one is a country station), on certain freqs.
How do I deal with all of this? I don't think I'll ever completely get rid
of it. But I do try to minimize it as much as possible. I spent $200 on a
Timewave ANC-4 noise cancelling antenna system (basically it uses an active
antenna as a noise sensing antenna; the signal from this antenna is used to
phase out the noise you're receiving; MFJ also makes a system too). It
works OK, but it's T/R switching is RF sensed, and after blowing the
resistor that acts as a safety fuse (so you don't nuke the noise canceller's
receiver front end, of it doesn't switch over to standby fast enough when
you transmit) for the second time in 2 months, I've about had it with it.
It's a pain to get out of its case to work on. The solder connections must
use Bismuth RoHS solder, because I just about had to scorch the circuit
board with a 100W solder gun, to get any solder to flow, the last time I
worked on it. I don't want to deal with that again, if other components are
bad. I could make up hard keying, but I don't have the tools (or a workshop
for that matter) to drill out the case for the keying line. Besides the
ANC-4, doesn't help my line noise situation all of the time. And, in some
cases, if I don't set it up right, the noise antenna will actually overload
my receiver with even more AM BCI.
So, I resorted to Plan B. I kludged together a separate receiving loop for
my SX-96. facing south (90 degrees from the powerlines). That helped a bit,
dropping what is often 10 or 20 over 9 line noise down to about S7 to S8.
Still not the greatest (occasionally I can get the ANC-4 down to S5 or S6),
but at least it's consistent. Recently, I tried out a quick and dirty
addition to Plan B. On AMfone, there was a thread dealing with some
shennanigans on 3892. In one of the posts, it was stated, that what seemed
to help with QRM, was to run the receiver in AM mode, but use LSB response.
An offhand comment was also made that doing this also seemed to help
reception during noisy band conditions. I gave it a try, and it has helped
my noise situation quite a bit. Since doing this (in the past week or so),
my noise has been lower by about 2 S units (S5 to S7), making it much easier
for me to receive AM. I can live with that. I'll just have to deal with
the fact that like operating QRP (which I've done since the 80s), there will
be times where it becomes "no can do", operating AM , due to receiver noise.
It's better than it was before. Hopefully optimizing the receiver loop,
will help things even more.
Ellen - AF9J
P.S. - I took a photo of my powerlines a couple of months back to show
another Amateur how bad my powerline situation is.
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