[ICOM] Icom rigs and atmospheric noise

[John Geiger]

Hi Jim,

I don't doubt the receiver is very quiet internally. 
Have already tried that.  I am wondering if I am
seeing true atmospheric noise (unfixable), or some
sort of man made noise that needs to be fixed.

John NE0P

--- Jim Isbell <millenniumfalcon at cableone.net> wrote:

> On 40 meters I find noise levels as high at S8
> regularly in the evening 
> on a Collins 75S-1  I don't think you can judge a
> receiver by the noise 
> level which is always above the no signal level of
> the receiver.  Try 
> removing the antenna and see if the noise level
> drops to your 
> expectation.  If it does then what you are seeing in
> normal of that 
> band.  If it remains high then its the receiver.
> 
> John Geiger wrote:
> 
> >Here is a question for the list about there
> >experiences with Icoms.  I recently picked up an
> Icom
> >740 based on its reputation for having a quiet
> >receiver and a great NB.  I am thinking that I have
> a
> >problem with power line noise, or something like
> that,
> >and so far the power company has done nothing
> really
> >to try and fix it.  I am now wondering if maybe my
> >expectations are too high.
> >
> >According to the ARRL review of the 740, its MDS
> >(noise floor) is -133dbm with the preamp off, and
> >-141dbm with the preamp on.  They don't mention
> what
> >bad that is on.  On the higher bands, with the
> preamp
> >off, I am seeing a noise level around S1 or so. 
> Very
> >nice and quiet, and the notch filter will remove
> that
> >even more.  When I turn the preamp on, the noise
> level
> >will rise to S4 or S5 sometimes.  I noticed this
> >yesterday during the NAQP.  It pretty much sounds
> like
> >regular static, though.  No buzzing or anything
> like
> >that.  Given the MDS numbers from the ARRL review,
> >would S4 be an expected atmospheric noise level
> with
> >the preamp on?  I generally run it with the preamp
> off
> >on the lower bands, and it does seem fairly quiet
> >there, although I was seeing some S8 bursts on 75
> >meters last night.  
> >
> >I guess I am starting to think that maybe I really
> >don't have much power line noise.  Maybe I just
> have a
> >sensitive rig with some good old mother nature
> static,
> >and a little bit of the crud you get from living in
> >the city with neighbors on every side.  I have been
> >driving myself half crazy trying to find a rig with
> a
> >S1 or lower noise level, and maybe I just have too
> >high of expectations.  I have a short memory and
> >cannot really remember what things were like in
> other
> >locations I lived in. Of course I probably had less
> >sensitive rigs also.
> >
> >Any opinions?
> >
> >73s John NE0P
> >
> >
> >		
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> >----
> >Your Moderator: Dick Flanagan K7VC,
> icom-owner at mailman.qth.net
> >Icom Users Net: Sundays, 1700Z, 14.316 MHz
> >Icom FAQ: http://www.qsl.net/icom/
> >
> >  
> >
> 
> 
> ----
> Your Moderator: Dick Flanagan K7VC,
> icom-owner at mailman.qth.net
> Icom Users Net: Sundays, 1700Z, 14.316 MHz
> Icom FAQ: http://www.qsl.net/icom/
> 



		
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