Can any one point me to a good expalnation of why PSK31 should be operated
at low power ???

Have heard for a 100 Watt rig keep it throttled back to 35 Watts also heard
50 Watts.

I think it has to do distortion if higher power is used

But would like to see some detailed info on this

Post here as I must remain anon on the NG's

Thanks


--
Keyboard In The Noise

Opinions are the cheapest commodities in the world. Author unknown but
"right on"

"Keyboard In The Noise" wrote in message
news:n%2yc.34114$tI2.12543@fed1read07...
Can any one point me to a good expalnation of why PSK31 should be operated
at low power ???

PSK-31, more so than most modes, requires that amateurs respect each other's
need to communicate. It is a very narrow band mode, and requires
astonishingly low power to be effective. PSK is even more narrow banded
than CW. The narrower the bandwidth, the less power you need to make it
above the noise. Furthermore, on PSK, the DSP algorithms are good enough
that you only need to be barely above the noise for 100% copy. Once you
have achieved 100% copy there is nothing to gain by having a stronger
signal.

Most amateurs use SSB rigs on PSK. Unlike CW, where a sharp filter can keep
a strong station out of the passband (and out of the AGC), on PSK the entire
PSK band is one SSB signal wide. If there is one strong station, that
station is going to prevent everyone else on the band from hearing their own
QSOs. Running 100 watts on PSK is the very definition of a LID.

Have heard for a 100 Watt rig keep it throttled back to 35 Watts also
heard
50 Watts.

35 watts is probably tops for most conditions. A good operator will keep
his power well below that, and only crank it up to 35 or so when conditions
are truly horrid.

I think it has to do distortion if higher power is used

Most SSB rigs can't deliver full power continuously. They are rated for peak
power at a very low duty cycle. Many will toast their finals at 100 watts
continuous. Depending on the rig and how you make the measurements, many
cannot make more than half power without distortion, and distortion on PSK
is a very bad thing. But this should be a moot point anyway. Most of the
time you should be able to make the contact at a watt or so. Sometimes you
may need to crank it up to 5 or 10, but if you need a lot more than that,
something is very wrong. Most likely, some other LID on the band is running
100 watts.

Sadly, PSK seems to be experiencing the sort of power warfare that makes 20
phone such an awful place. A few years ago, it was rare to hear a station
running more than 2 or 3 watts. Now it seems like 20 is a lot more common.
Unfortunately, a lot of 20 watt stations means that other stations need to
run higher power, too.

I am speaking here of 14 MHz and up. On the lower frequencies, especially
3.5 MHz, there is a need for a little more power. But at 14 MHz and up, the
only reason to need more than about a watt is because QRM from stations
running too much power are interfering with the receiving station.

...

"Keyboard In The Noise" wrote in message
news:n%2yc.34114$tI2.12543@fed1read07...
Can any one point me to a good expalnation of why PSK31 should be operated
at low power ???

PSK-31, more so than most modes, requires that amateurs respect each other's
need to communicate. It is a very narrow band mode, and requires
astonishingly low power to be effective. PSK is even more narrow banded
than CW. The narrower the bandwidth, the less power you need to make it
above the noise. Furthermore, on PSK, the DSP algorithms are good enough
that you only need to be barely above the noise for 100% copy. Once you
have achieved 100% copy there is nothing to gain by having a stronger
signal.

Most amateurs use SSB rigs on PSK. Unlike CW, where a sharp filter can keep
a strong station out of the passband (and out of the AGC), on PSK the entire
PSK band is one SSB signal wide. If there is one strong station, that
station is going to prevent everyone else on the band from hearing their own
QSOs. Running 100 watts on PSK is the very definition of a LID.

Have heard for a 100 Watt rig keep it throttled back to 35 Watts also
heard
50 Watts.

35 watts is probably tops for most conditions. A good operator will keep
his power well below that, and only crank it up to 35 or so when conditions
are truly horrid.

I think it has to do distortion if higher power is used

Most SSB rigs can't deliver full power continuously. They are rated for peak
power at a very low duty cycle. Many will toast their finals at 100 watts
continuous. Depending on the rig and how you make the measurements, many
cannot make more than half power without distortion, and distortion on PSK
is a very bad thing. But this should be a moot point anyway. Most of the
time you should be able to make the contact at a watt or so. Sometimes you
may need to crank it up to 5 or 10, but if you need a lot more than that,
something is very wrong. Most likely, some other LID on the band is running
100 watts.

Sadly, PSK seems to be experiencing the sort of power warfare that makes 20
phone such an awful place. A few years ago, it was rare to hear a station
running more than 2 or 3 watts. Now it seems like 20 is a lot more common.
Unfortunately, a lot of 20 watt stations means that other stations need to
run higher power, too.

I am speaking here of 14 MHz and up. On the lower frequencies, especially
3.5 MHz, there is a need for a little more power. But at 14 MHz and up, the
only reason to need more than about a watt is because QRM from stations
running too much power are interfering with the receiving station.

...

My opinion only

- PSK has a pretty constant output that can exceed the duty cycle of a
SSB transmitter. Hence reducing the drive to a lower output is kind of
like the same average output on SSB

- PSK is also sensitive to non linearity and ALC/VOGAD/processors make a
mess of it. The trick to setting it up is to supply a test tone and
adjust the mic gain for zero indication on the ALC meter.

It is also worthwhile doing some linearity checks. ie using the PC sound
card (PSK test signal) alter the output by -3 and -6dB. Check that there
is a corresponding linear change in RF output power.

Cheers Bob VK2YQA

Keyboard In The Noise wrote:
Can any one point me to a good expalnation of why PSK31 should be operated
at low power ???

Have heard for a 100 Watt rig keep it throttled back to 35 Watts also heard
50 Watts.

I think it has to do distortion if higher power is used

But would like to see some detailed info on this

Post here as I must remain anon on the NG's

Thanks


--
Keyboard In The Noise

Opinions are the cheapest commodities in the world. Author unknown but
"right on"

My opinion only

- PSK has a pretty constant output that can exceed the duty cycle of a
SSB transmitter. Hence reducing the drive to a lower output is kind of
like the same average output on SSB

- PSK is also sensitive to non linearity and ALC/VOGAD/processors make a
mess of it. The trick to setting it up is to supply a test tone and
adjust the mic gain for zero indication on the ALC meter.

It is also worthwhile doing some linearity checks. ie using the PC sound
card (PSK test signal) alter the output by -3 and -6dB. Check that there
is a corresponding linear change in RF output power.

Cheers Bob VK2YQA

Keyboard In The Noise wrote:
Can any one point me to a good expalnation of why PSK31 should be operated
at low power ???

Have heard for a 100 Watt rig keep it throttled back to 35 Watts also heard
50 Watts.

I think it has to do distortion if higher power is used

But would like to see some detailed info on this

Post here as I must remain anon on the NG's

Thanks


--
Keyboard In The Noise

Opinions are the cheapest commodities in the world. Author unknown but
"right on"

Here is an answer I received else where

Tis what I was looking for

Thanks to all who responded
------------------------------
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.


--
Keyboard In The Noise

Opinions are the cheapest commodities in the world. Author unknown but
"right on

Here is an answer I received else where

Tis what I was looking for

Thanks to all who responded
------------------------------
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.


--
Keyboard In The Noise

Opinions are the cheapest commodities in the world. Author unknown but
"right on