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[RFI] VHF-AM radios

To: <rfi@contesting.com>
Subject: [RFI] VHF-AM radios
From: EDWARDS, EDDIE J" <eedwards@oppd.com (EDWARDS, EDDIE J)
Date: Tue, 23 Jan 2001 15:33:30 -0600
Excellent Dale!  I do remember hearing about slope detection, don't remember
where though.  It works like a champ.  I'm sure that's all we did on the old
multi-band rcvrs since the frequency display was analog and not accurate.
I'm listening to the NOAA stn right now in AM mode by tuning 9 to 10 kc
higher or lower.  It's not perfect but it does work.

Thanks for jogging my old memory Dale. :^)

73,
de ed -K0iL


> -----Original Message-----
> From: dgsvetan@collins.rockwell.com [SMTP:dgsvetan@collins.rockwell.com]
> Sent: Tuesday, 23 January, 2001 1:21 PM
> To:   EDWARDS, EDDIE J; rfi@contesting.com
> Subject:      RE: [RFI] VHF-AM radios
> 
> 
> I believe that the ham rigs which offer coverage of AM Aircraft Band
> receive, actually have a separate AM IF and detector system for that part
> of VHF.  I suspect that the radio micro-P simply switches in the correct
> detector chain for whichever frequency range the user wants.  Most modern
> rigs use "one-chip wonder" FM receiver strips after the front end (usually
> from Motorola or Philips), and there are a few equivalent chips for AM
> reception (Harris or Philips).  However, I have seen the AM stuff done
> with
> discretes in some sets, apparently because that was cheaper than a special
> IC.
> 
> Those of us who used to operate 2m AM (eons ago) know that it is possible
> to use a technique called "slope detection" to copy FM sigs with an AM
> receiver.  This does require being able to CAREFULLY and SLOWLY tune the
> receiver so that you can locate the center of the IF on either side of the
> FM carrier (the "slope") where the changes in deviation "swing" (which are
> a phase change) produce a limited amount of amplitude change.  I have no
> clue if the sets under discussion employ that technique, but they might.
> If so, then these could make good VHF line noise detectors, but you might
> want to work on some means to add a signal strength indicator.  You might
> also keep in mind using a VHF multi-mode rig.  Some of the newer ones
> ('706, '817, '847) offer AM operation on 6 and 2 meters;  others, like my
> FT-290, offer SSB, but no AM.  However, if the noise blanker is disabled,
> impulse noise comes through just fine.  A real noise tracking advantage
> for
> the FT-290 and the new FT-817:  battery operation and a carry strap.  If
> you have the FBA8 C cell case for the '290, it will go anywhere you can
> go.
> The '817 appears to have batteries self-contained, as did the old
> (remember
> this?) IC-202.
> 
> 73, Dale
> WA9ENA
> 
> 
> 
> 
> 
> "EDWARDS, EDDIE J" <eedwards@oppd.com>@contesting.com on 01/23/2001
> 10:08:34 AM
> 
> Please respond to "EDWARDS, EDDIE J" <eedwards@oppd.com>
> 
> Sent by:  owner-rfi@contesting.com
> 
> 
> To:   "'RFI'" <rfi@contesting.com>
> cc:
> 
> Subject:  RE: [RFI] VHF-AM radios
> 
> 
> 
> I have often wondered how those radios perform dual-mode rcv.  I have one
> at
> home that rcvs 110-180Mhz in one band --one mode.  Seems like something I
> should know, but have never ran across this info.
> 
> I tried it with my R7000 on my desk and the audio quality of the AM air
> xmissions in FM-narrow mode is very poor, and the NOAA xmission is
> unintelligible on AM.  FM wide is also very bad.
> 
> Anyone know this secret?
> 
> de ed
> 
> > -----Original Message-----
> > From:   Kelly Boswell [SMTP:kboswell@conwaycorp.net]
> > ----- Original Message -----
> > From: "Pete Smith" <n4zr@contesting.com>
> > To: <rfi@contesting.com>
> >
> > There FM.
> >
> > > Are the NOAA weather broadcasts AM or FM?
> >
> >
> > --
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> 
> 

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