[TenTec] OMNI VI Power Output

[George, W5YR]

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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