[Spooks] Re: On a related note

[Martin H. Potter]

Chris Smolinski wrote:
> 
> On a related note, E10 was booming in the East Coast last night on 6912 AM
> as well as a few other frequencies. I've noticed carriers up on 6930 and
> 6912 most evenings, this results in E10 being received in AM mode,
> although no het is heard, so the transmission must actually be in SSB.
> Anyone else hearing these carriers?
> 
> This was one of Havana Moon's theories - some numbers stations heard in AM
> actually transmit in SSB, with another transmitter site providing the
> carrier.
> 
> Of course it's possible that the carriers on 6912 and 6930 (as well as
> other E10 frequencies) is purely a coincidence ;-)
> 
> 73
> Chris
> 

There are in fact three different "modes" of single-sideband (SSB) :

- fully suppressed carrier (SSB as we normally think of it)
- reduced carrier (not fully suppressed)
- full carrier (like half an AM signal)

Early SSB transmitters were capable, after suitable adjustments, of all
three modes, but most commercial rigs now produce only SSSC
(single-sideband suppressed carrier, as SSB used to be called) unless
modifications are requested before they are built.  

As a variation, Station CHU uses full carrier but with reduced power in
the lower sideband, so the signal sounds OK in both AM  and USB. 
(Reception in LSB is poor.)  

Each of these three modes uses power more efficiently than AM and they
are more economical of bandwidth.  Obviously, for most purposes, the
fully suppressed carrier is best, but they each have their advantages.  

73, 
... Martin    VE3OAT