On Sun, 2009-04-19 at 21:37 -0400, Martin Ewing wrote:
> On Sun, Apr 19, 2009 at 9:24 PM, Dr. Gerald N. Johnson
> <email@example.com> wrote:
> On Sun, 2009-04-19 at 21:19 -0400, Martin Ewing wrote:
> > On Sun, Apr 19, 2009 at 3:00 PM, Bob McGraw - K4TAX
> > > ... And oh by the way, my AM transmitter doesn't use any
> > > sideband bandwidth than current technology SSB rigs and in
> many cases it
> > > uses less.
> > >
> > > 73
> > > Bob, K4TAX
> > >
> > I've been around since the AM era, myself, but I don't see
> how DSB AM
> > doesn't take at least twice the bandwidth of SSB for the
> same voice input.
> > 73 Martin AA6E
> Except that some with delusions of broadcast voice grandeur
> transmit 6
> KHz or more of audio bandwidth.
> 73, Jerry, K0CQ
That's 6 KHz of audio bandwidth on SSB. They accomplish little but
splatter and transmitting the noise of their dog barking and the fans on
their computer in most of that bandwidth. Hollingsworth wasn't pleased
> X kHz SSB -> 2*X kHz AM DSB (more actually, since there is some SSB
> bass cutoff > 0 Hz)
> Choose your X.
I'm perfectly aware of the math. Been aware of it for 51 years or more.
> I wonder if anyone still does DSB suppressed carrier? That was a lot
> easier to generate and still gave substantial power benefits over AM
> with carrier. Poor man's SSB.
I tried it once, back about 1957 or '58. On 40 meters. The SSB purists
at the time were shocked when they noticed my side band suppression
wasn't detectable and they found I wasn't running Collins or Central
Electronics gear and didn't have PTT or VOX. They stopped talking to me.
While DSB suppressed carrier is easy to generator, it doesn't save on
spectrum, and when received with a SSB receiver half its transmitter
power and spectrum is wasted. There were commercial proponents of DSB
suppressed carrier with a proper receiver phase locked to the suppressed
carrier that rejected in pass band QRM because it wasn't phase locked to
the two side bands and because the receiver was phase locked to the two
sidebands, tuning was automatic requiring no operator skill. There were
several articles about that in the December 1956 Proceedings of the IRE
An alternative I've used on VHF in the long past was very narrow FM so
that there were no second order modulation products. It has the same
spectrum as AM with carrier, but the relative phase of the carrier to
the sidebands is shifted 90 degrees. There is not amplitude variation,
but copied exalted carrier with a SSB receiver it had great audio
quality and super simplicity. I used a crystal microphone with one stage
of starved current transistor gain to drive a varactor on the 8 MHz
crystal of my 2m transmitter. The only mode simpler to transmit was CW.
> 73 Martin AA6E
73, Jerry, K0CQ, Am extra since 1958.
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