While a bit more than 100% positive modulation is possible, it comes
with distortion of the modulating waveform, and when hams (in the long)
past have invented schemes for 200% or greater positive modulation that
claimed to not splatter, the FCC took their licenses when they used
those schemes on the air.
Without a standard for the dB per S unit, all a signal strength meter
shows is when the signal peaks or disappears, otherwise the readings are
in squirds, neither reproducable, nor comparable between receivers. But
then in the past 50 years when a receiver has approached as much as 6 dB
per S unit (like Collins S-line) it was considered "stingy."
So now in DX contacts, it seems like any signal detected is 59(9) so
what the meter shows doesn't matter.
73, Jerry, K0CQ
On 6/12/2010 11:30 AM, Ron Castro wrote:
That would almost be the case for standard pulse-width modulation or
plate modulation, except for positive peaks > 100% which is common in
commercial broadcasting (The FCC allows 125% peak positive modulation,
but it's possible to do much more). In this case, Doug Smith, the
original software engineer on the Orion designed a DSP circuit that
actually increased the carrier as the modulation pushed past a certain
point. There was a detailed explanation in his website, but
unfortunately the site is gone. There may be articles about this in QEX.
BTW, although the agreed-on standard for an S-Unit is 6 dB, many radios,
including the Orion II with the newest firmware in, use 3 dB. The late
Jerry Cebik had an excellent article on the genesis of the S-Unit and
the RST system, but that's gone from the web too.
Ron N6IE
www.N6IE.com
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