George has some very solid comments here. I totally agree.
73
Bob K4TAX
George W5YR wrote:
>
> Replies thus far have pretty well established that a major power increase
> is required to make much more signal at the "other end."
>
> We need to keep in mind also that even modest increases in power output,
> beyond the rated, designed power level, can quickly result in significantly
> increased disortion products on SSB and the digital modes.
>
> Bottom line: turning a pot to get 10-20 watts more out of any 100 watt rig
> will produce little if any effect on the S-meter at the other end, but the
> increased distortion will be quickly noticed!
>
> There are good reasons why transmitters are designed to operate at specific
> maximum power levels. Distortion level limits rank high on the list.
>
> On the matter of SSB, also bear in mind that for the typical male voice,
> the peak-to-average ratio in the voice signal going into the mic is about
> 13 db!
>
> That means that your 100-watt transmitter is going to be producing an
> average output power while you are speaking of about 13 db LESS than 100
> watts if you drive the output to 100 watts on voice peaks. For you
> purists, that is only an approximation because there is another 3 db figure
> in the math that we can leave out for now.
>
> That 13 db figure equates to a power ratio of 20! So, if your output
> wattmeter reads average power fairly accurately, it will show, on average,
> about 5 watts while you are talking! Most are not accurate at low levels
> and have different averaging characteristics, so I have observed that most
> meters tend to show around 10 to 15 watts output during SSB speech.
>
> Another bottom line: rather than trying to squeeze the last watt out of the
> rig by either turning up the wick or fighting a losing battle of SWR
> reduction, look carefully at speech processing used in sensible modest
> amounts to decrease that 13 db peak-to-average ratio and gain both an
> average power increase and a marked increase in intelligibility.
>
> Unfortunately, many rigs today tout "Compression" as a marketing feature
> while they actually do little more than pre-distort the signal to increase
> its average power. But, there are processors out there, some of them in
> rigs such as the Icom IC-756PRO, that can make a major difference in
> average power output as well as intelligibility. One of the very best was
> the early Ten Tec outboard unit that generated a SSB signal at a low r-f
> frequency, clipped and filtered it, and then heterodyned it back down to
> audio which was then fed into the mic input. Other units were the Vomax and
> the Comdel, neither of which is being made any more but which are available
> used.
>
> Worth looking into if you operate much SSB. Used conservatively, they can
> produce a 6-db gain in average power with little or no detectable
> distortion at the other end. Used agressively, they can achieve a 10 db
> increase although the speech quality suffers somewhat.
>
> One last point: anything that is done to alter the peak-to-average power
> ratio of the signal in the transmitter will increase the cooling
> requirement, so care must be taken to avoid overheating finals, etc.
>
> 72/73, George W5YR - the Yellow Rose of Texas QRP-L 1373 NETXQRP 6
> Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
> Amateur Radio W5YR, in the 55th year and it just keeps getting better!
> Icom IC-756PRO #02121 Kachina #91900556 IC-765 #02437
>
> K2ZF@aol.com wrote:
> >
> > In a message dated 5/15/01 3:37:57 AM !!!First Boot!!!, RMcGraw@InfoAve.Net
> > writes:
> >
> > <<
> > Richard:
> >
> > Think about "turned up a bit" in terms of what's required to make the
> > meter move on the other end. 1 S unit = 6dB Therefore from 100 watts
> > out to get 1 S unit increase on the other end will require a increase to
> > 400 watts. Nah, Omni won't do 400 watts.
> >
> > I connected a Tentec Centurion between my OMNI VI+ and the antenna. Now
> > I move the S meter almost 2 units.
> >
> > 73
> > Bob K4TAX
> > >>
> >
> > Bob, your right on the nose concerning the Omni 6 needing to run 400 watts
> > to
> > get that 1 (one) S unit increase. Tweaking the output of the Omni lets say,
> > 40 watts, for an output of 140 watts would be immeasureable on the other
> > side
> > of the QSO.
> >
> > Antenna couplers
> > Guys (and girls) that try to get that exact 1 to 1 swr thinking that they
> > will be heard better are fooling themselves. I used to think at one time, oh
> > gosh, my swr is 1.5 to 1, oh my goodness. The person on the other end will
> > not hear any difference between a 2 to 1 swr vs a 1 to 1.
> >
> > 73 to all de Jim K2ZF
>
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