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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