[TenTec] Power Query

[George, W5YR]

Bob, when PSK31 is in idle mode, it is a two-tone signal having a peak to
average power ratio of 2:1 or 3 db. So, if your average-reading meter shows
17 watts and YOU ARE NOT FLAT-TOPPING OR OTHERWISE DISTORTING THE SIGNAL,
then your peak power or pep is 34 watts. 

This should be well within the linear range of the Jupiter. 

About the only way you can really be sure about what you are doing with
PSK31 is to examine the r-f output envelope of the transmitter signal while
in PSK31 idle mode. You should see the classic two-tone wave pattern that
was in the ARRL Handbook for many years. The peaks should be clean and
continuous, looking like sine waves without any flattened portions, etc.

The most power that you can run with any transmitter under these conditions
is that power level which produces a clean two-tone output signal without
distortion of the signal peaks. The numerical measure of this is the
3rd-order IMD distortion component. It should be at least 25 db below peak
power and preferably more than 30 db below. Most modern rigs if not
overdriven, etc. can produce -25 to -30 db IMD performance.

Most PSK31 operators find that average power levels in the 15 to 30 watt
range - corresponding to pep levels of 30 to 60 watts - are more than
adequate for PSK31 operation. Most transmitters tend to increase their
intermodulation distortion product generation as power output goes up.

As in most of ham radio, there is nothing to be gained by running more
power than it takes for the guy at the other end to copy you. With PSK31,
you run the risk of a broad signal and interfering with others if you try
to run more power than your equipment is capable of handling while still
maintaining 3rd-order IMD performance of -25 db or better.

>From your description, I would say that you have the Jupiter in a "sweet
spot" and I would just operate and enjoy the comments about your clean
signal! Increasing the power to "all she will do" would buy you less than
one S-unit at the other end, but would probably broaden your signal
considerably.

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


Robert Steele wrote:
> 
> When operating digital modes such as PSK311 they say you should set the
> power output to about half max in order to avoid distortion so as to be sure
> that you are not radiating too broad a signal.
> 
> I notice that when I set the power knob on the Jupiter to about 40%, then
> adjust the microphone gain so thaat ALC light just not come on when the TX
> light is on and PSK31 is idling, the forward power meter indicates about 17
> watts, with the SWR meter at 1.1.
> 
> Question:   would I still be in the linear output range of the transceiver
> if I increased the power knob to 80 % and readjusted the mic gain so that
> the ALC light still is just below limiting? If I used fan cooling on the
> heat sinks would this be satisfactory for the transmitter?

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