[Amps] Duty cycle for processed SSB in contest conditions?

[Roger (K8RI)]

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.