I believe that Bell Labs many years ago published that the ratio of average
to peak speech power was 15 or 16 db.
As to the .25 second meter time constant I remember reading somewhere that
it was according to the meter manufacturers published specs on the meter.
Not sure if that was in the FCC rules, a clarification letter that they put
out or in some other publication.
Lots of transmitters of that era did not even have alc in them or any other
speech processing.
Alc is good for only 2 or 3 db of average increase before heavy distortion
raises its head. So even with alc under the old rules one could run
considerably more effective power than is allowed today under the new rules.
For those that doubt just watch the plate current meter on your transmitter
when you are hitting a little alc which should mean you are making maximum
peak envelope power, if everything is properly tuned, and figure what that
power input calculates to. On a 100 watt output radio the average power will
be in the order of 15 to 30 watts.
73
Gary K4FMX
> -----Original Message-----
> From: Karl-Arne Markström [mailto:sm0aom@telia.com]
> Sent: Sunday, October 15, 2006 6:00 AM
> To: Tom W8JI; Gary Schafer; 'AMPS'
> Subject: Re: [Amps] "10 Meter Ban" to be lifted ...
>
> For unprocessed speech, the CCIR long ago established an 8 dB peak/average
> ratio.
>
> This may be on the low side, as I have seen 9 and even 10 dB ratios in
> literature about
> FDM carrier system loading.
>
> Using unprocessed speech and the 1 kW average input limit, it would have
> been possible to run > 3 kW PEP output,
> from a typical SSB transmitter, but since communications effectivity is
> dependent of averaged signal/noise ratios,
> this would have been quite pointless.
>
> Regarding the 0.25 s plate meter time constant, it was found in the
> amateur radio regulations
> of many countries, including Sweden. I have also wondered about the
> "enforceability" of such a rule.
>
> 73/
>
> Karl-Arne
> SM0AOM
>
> ----- Original Message -----
> From: "Tom W8JI" <w8ji@w8ji.com>
> To: "Gary Schafer" <garyschafer@comcast.net>; "'AMPS'"
> <amps@contesting.com>
> Sent: Sunday, October 15, 2006 11:17 AM
> Subject: Re: [Amps] "10 Meter Ban" to be lifted ...
>
>
> > > There was no limit on the peak envelope power we were
> > > allowed to run; only a
> > > limit on the average power as read on the plate meters.
> > >
> > > Peak envelope power can range from 5 to 10 times or
> > > greater than the average
> > > power we see on the plate meter with voice.
> >
> > OK, I see your point. Good point Gary and one that almost
> > everyone misses.
> >
> > Conventional thought is the peak to average power ratio is
> > only about 2:1. While that may be true for processed speech
> > (even through ALC), it isn't true for unprocessed speech.
> >
> > So technically, using the meter response dictated by early
> > FCC rules, we could run 10kW PEP input or more on occasional
> > voice waveform peaks without making the meter exceed the
> > legal 1000 watts indicated input on suppressed carrier phone
> > transmissions.
> >
> > While the FCC increased carrier mode power like RTTY, FM,
> > and CW it decreased peak power and average power of AM and
> > peak power of unprocessed or lightly processed SSB.
> >
> > My only addition to that is the very short duration peak
> > doesn't mean much for communications, so we didn't lose much
> > in that way (except on AM). Anyone using processing already
> > restricted the peak-to-average ratio (which also increases
> > communications effectiveness) and would not have seen such a
> > dramatic reduction in peak power. In other words the peak
> > didn't mean that much anyway when the speech was processed
> > to improve communications effectiveness.
> >
> > Good point Gary.
> >
> > 73 Tom
> >
> >
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> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
> >
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