On 2/22/2014 12:25 PM, Conrad Farlow wrote:
Can anyone suggest what the duty cycle for sensibly processed SSB would
be during contest conditions? When an LD-MOS PA is backed off to achieve
good linearity then the efficiency reduces from 80% at P3dB for CW or
100% duty cycle data modes down to around 65% for IMD3 of better than
-30dBc. The thermal impact of this is quite severe and I am trying to
calculate what is acceptable for SSB during a typical contest.
Personally I am looking at 6m and above but it holds true for HF
amplifiers as well.
As others have said, it's best to measure the temp. The RF exposure
calculations and hand book say 20% for unprocessed SSB, but voice
characteristics can vary that quite a bit, so I'd go with Carl's
estimate of 25%. Because the duty cycle is so low for unprocessed SSB,
"I'd think" it'd be easy to double that without tremendous processing.
OTOH many rigs and particularly those with bipolar finals have pretty
miserable IM figures to begin with and bad gets worse pretty quick.
I'd try to find the practical settings that give the cleanest signal.
Only recently have SS rigs began to approach the IM figures of the old
Collins S-Line. Even some of the mighty expensive rigs have pretty
crappy IM figures. They have receivers that have passed the point of
practical numbers for intercept points, dynamic range, selectivity, and
have a sensitivity that is far, far below the band noise, yet they seem
to be ignoring the transmitted signal which is one of my pet peeves.
73
Roger (K8RI)
I know that it is difficult to say what the ratio of TX/RX time is but
lets be pessimistic.
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