[PD] ssb / sdr
_ at whats-your.name
Tue Sep 2 06:50:44 CEST 2008
On Mon Sep 01, 2008 at 10:41:29PM +0100, Andy Farnell wrote:
> Single sideband modulation.
> It comes from radio culture really. In the modulation schemes for analogue
> broadcast you havethe same spectral model with radio waves as we
> use for sound synthesis. But using up more bandwidth by having two sidebands
> is less desirable if you want to squeeze more channels into the same spectrum,
> so SSB was devised to minimise interference between stations.
the carrier is a really loud sine, relative to the other material . reduced carrier was projected to occur (in the 70s/80s or so), with enough power for a phase reference under typical conditions.. i think -15db or so
so broadcasting the carrier and the duplicate sidebands saves a lot of energy ( in addition to spectrum )
its how Lou from Barcelona running 1.7kW sounds as good as Radio Exterior Espana running 250 kW or something insane
> The tradeoff is that fewer sidebands mean less information is carried by
> the signal.
nope the sidebands are typically identical but frequency mirrored
the main tradeoff is finding the beat frequency, without a carrier. to get the right pitch base for the spectral information. not only do you lose the phase reference, you lose the frequency reference!
> Anyone know any novel or unusual patches for SSB. Presumably, for a single frequency
> you need only a fixed delay.
im thinking about getting a QS1R and using PD for demodulation
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