[AMRadio] Converting old 1.8-4.0 MHz AM Marine Radios


Jim candela jcandela at prodigy.net
Fri Sep 10 13:26:07 EDT 2004



Hi Group,

    Just a note here to mention my limited experiences with commercial uses
of AM. I once looked at a 2.182 Mhz ship to shore radio. It worked, but as I
recall the AM operation was poorly modulated in several ways: low modulation
percentage, high distortion, and poor RF linearity. Fixing the rig enough to
proudly call CQ on 160 or 80 meters was more than I wanted to take on, so I
passed it up. It wasn't broke, but just built for minimum cost, size,
weight, and so on.

   I once was on a project where we built a commercial aircraft transmitter
(110-136 Mhz) for communication and jamming purposes. This was back around
the time we bombed Libya. Anyway We had a 500 watt PEP rig that gave me
fits. The manufacturer of the linear amp had a carrier detect circuit (COR)
to enable the amplifier. Whenever the AM modulated drive went to zero power
(even for a millisecond) the relays kicked out. This was a problem because
whenever the drive momentarily over modulated negatively, the linear would
start cutting out, in, out, and so on. I had to build a negative cycle
loading circuit to limit the maximum negative going modulation to 70%. Since
this rig was primarily for jamming anyway, hey a little over modulation was
no big deal. I went around and around with the linear maker to change his
COR time constant which he finally did.

   Ever listen to AM aircraft? To me these rigs vary greatly, and often are
terrible examples of why we still use AM for commercial avionics.

Regards,
Jim

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net]On Behalf Of W7QHO at aol.com
Sent: Friday, September 10, 2004 11:04 AM
To: amradio at mailman.qth.net
Subject: Re: [AMRadio] Converting old 1.8-4.0 MHz AM Marine Radios



In a message dated 9/10/04 8:25:43 AM, kb4cvn at yahoo.com writes:


> One of my customers (...and an old ham friend) is the senior tech at
> large marine dealer/service shop in Southern California.  The other day
> while discussing a technical issue with a radio we got chatting about 2
> MHz marine radios, and the old AM Radiotelephone rigs.  He mentioned
> that he had a 20-foot shipping container's worth of the equipment
> sitting in his warehouse, the business owner would love to get rid of!
> He had pulled a couple of them out recently and they still worked OK! 
> ...Would I be interested in 1, 2 or more of them?
>

Mark,

Care to pass contact information along?   Myself and some of my friends out
here would be glad to find homes for these rigs.

Dennis D. W7QHO
Glendale, CA
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