[AMRadio] Re: Carrier with one sideband


Peter Markavage manualman at juno.com
Thu Feb 7 20:06:23 EST 2008


Although not a true AM mode as the seasoned amateurs might define it, one
sideband with carrier inserted, can work reasonably well, and does
especially well in crowded band conditions. Actually Don, the last time
we worked on 75 M, one early morning last Fall (or maybe late Summer), I
was running the 100V with only one sideband and carrier inserted and
driving a Johnson Courier amp. You must have had one of these "special
receivers" because you never once mentioned anything unusual about the
signal. Over the last several years of running the 100V, I never announce
when I running one sideband, or double sideband, with carrier inserted
when operating the AM mode. No one has ever commented on any unusual
characteristics of the signal either way.

If your in-country radio regulations limit you to a 3 KHz maximum
bandwidth, going this route at least gets on the AM mode.

Pete, wa2cwa

On Thu, 7 Feb 2008 17:22:14 -0600 "D. Chester" <k4kyv at charter.net>
writes:
> 
> 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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