[AMRadio] RE:Carrier with one sideband


Clarke, Tom AIR4.0P NATOPS frederic.clarke at navy.mil
Fri Feb 8 12:50:06 EST 2008


I seem to remember that the aircraft radios we used during the 60-80s in
P-3s/C-130s etc (ARC-94/102 aka 618T) had a
selection called AME (AM equivalent).  It was explained to us (pilots)
by the techs that it wasn't a 
high level AM, but USB with carrier.  It sounded OK, but then again, it
was designed for communications
and not "easy listening"!  All the airways communication now days is
SSB, so the AME position rarely
gets selected.

Perhaps someone is familiar with that mode and can expand on it.

73 Tom/W4OKW

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Message: 2
Date: Thu, 7 Feb 2008 17:22:14 -0600
From: "D. Chester" <k4kyv at charter.net>
Subject: [AMRadio] Re: Carrier with one sideband
To: <amradio at mailman.qth.net>
Message-ID: <00b001c869e0$46357b40$47339f18 at D65Y8B21>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
	reply-type=original


> From: Peter Markavage <manualman at juno.com>

> A number of the early phasing type transmitters/exciters and SSB
adapters
> allowed you to operate on "AM" with just one sideband. So, only
operating
> DSB AM would really be an issue.


>> From: "Bob Macklin" <macklinbob at msn.com>

> Any of the Heath SSB rigs (SB-100/101, SB-400/401, HW-100/101) could
be
> modified to Vestigial SB. SSB with carrier reinserted.
>
> Bob Macklin
> K5MYJ


SSB with the carrier re-inserted is not the same thing as what we know
as 
AM.  It is nothing more than SSB with poor carrier suppression.
Reception 
with an envelope detector inherently generates severe distortion at 
modulation levels beyond about 20%.  This mode is useful only with a 
receiver with BFO that locks onto the "pilot carrier" to eliminate
frequency 
error in SSB reception, a technique that has in fact long been used in 
commercial services, with the carrier level reduced to about 20 dB below

p.e.p.  At modulation levels low enough to avert this distortion, known
as 
"quadrature distortion" it is very wasteful of power since the sideband 
power becomes a very small percentage of total radiated power.  Those 
amateur SSB rigs that transmit "AM" with carrier and one sideband sound
like 
CRAP.  Unless the receiving station is equipped with a proper receiver
with 
PLL carrier reinsertion, which includes very few amateur receivers, it
is a 
totally useless mode beyond simply getting someone's attention when they
are 
receiving in AM mode, in order that they may switch the receiver over to
SSB 
to receive the signal in normal SSB fashion.

This problem is inherent to the principles of modulation, and has
nothing to 
do with the quality of the equipment used.  Transmitting AM with one 
sideband is NOT a solution to the problem nor is it even a satisfactory 
option.

73,

Don k4kyv 




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