[AMRadio] Re: Carrier with one sideband


Bob Macklin macklinbob at msn.com
Thu Feb 7 18:38:41 EST 2008


The method of generating AM with a SSB transmitter by reinserting carrier
was a common mode of operation in the late 50's and early 60's. The TV video
signal works this way.

It is my understanding the modern RICEBOXES that generate AM do it in the
exact way.

I know it is not real AM but may people just don't have access to a good
Johnson transmitter or DX-100.

Bob Macklin
K5MYJ
Seattle, Wa,
"Real Radios Glow in the Dark"
----- Original Message -----
From: "D. Chester" <k4kyv at charter.net>
To: <amradio at mailman.qth.net>
Sent: Thursday, February 07, 2008 3:22 PM
Subject: [AMRadio] Re: Carrier with one sideband


>
> > 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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