How determine SSB PEP?
Greg Knapp
before, and I have some questions.
As I do not have a "peak" reading wattmeter, but instead have an "average"
reading wattmeter (the Heathkit HM-102) or the meter in the TS-940 (which I
think is also just an "averaging" reading wattmeter), how can you tell your
true SSB PEP output?
Do you read the meter and multiply the highest "peak" reading by some factor
(2x?, 1.3X?)? But, wouldn't those factors be inaccurate and have to change
if you turned on good RF speech processor, which "increases" your average
(and the "average" reading on your "average" reading wattmeter), but not
necessarily your peak?
Also, I am building an Oak Hills WM-2 QRP wattmeter. Do you know of any mods
to it that would allow it to read peak rather than average?
Thanks in advance for any light you might shed on this.
Greg, N6GK
Reg Edwards
load. Hold down the morse key when in CW mode and measure
the power output. That is the peak envelope power output
level. You sustained the max or peak RF envelope power long
enough to measure it accurately.
Instead of CW mode you can go over to FM and measure carrier
power. It will be the same as you obtained on CW with the
key held down long enough to measure it.
It is the same level as the power level on the peaks when
you bawl CQ into the mike when on SSB but which doesn't stay
at the peaks long enough for you to measure it.
If you are not completely satisfied with the forgoing
procedures, turn up the mike gain control and try to whistle
into the microphone long enough to measure Tx power output.
Or plug an audio oscillator into the mike socket.
It may be desribed as the maximum peak RF power which the
transmitter is capable of outputting. It is the rated output
power.
--
***********************************
Regards from Reg, G4FGQ
For free radio modelling software go to:
http://www.btinternet.com/~g4fgq.regp
***********************************
Greg Knapp <gkn...@freshrain.org> wrote in message
news:t4mna3t...@corp.supernews.com...
Greg Knapp
Thanks for the explanation. I am not sure I can apply your answer to my
specific problem. Let me explain.
I am using a TS-940 with the power level and mike gain turned down to enable
QRP operation in CW and SSB modes.
With CW, it's easy, just turn down the power level until the average reading
wattmeter says 5 W out. No problem.
But when I switch to SSB, where 10 W PEP is allowed for QRP, how do I know
when I am running the 10 W PEP? When my average reading wattmeter reads 10
W when I whistle into the mike? I have no idea if the TS-940 in SSB mode has
the same carrier/power level as when it is in the CW position, so I can't
depend on that, and so all I am left with is some reading on the averaging
meter, which varies depending on how close and loud I talk and whether I
have the speech processor on. How can I be sure that the highest I can
drive the needle on the averaging wattmeter is in fact the maximum "peak"?
Greg
down
"Reg Edwards" <g4fgq...@btinternet.com> wrote in message
news:92gl4q$8dt$1...@neptunium.btinternet.com...
> Load up the transmitter to maximum power output into a dummy
> load. Hold down the morse key when in CW mode and measure
> the power output. That is the peak envelope power output
> level. You sustained the max or peak RF envelope power long
> enough to measure it accurately.
SNIP>
budgie
<g4fgq...@btinternet.com> wrote:
(snip several methods to assess peak power)
Or load up the transmitter to maximum power output into a dummy
load. Use an oscilloscope to measure peak voltage, and calculate peak
power directly.
Paul Keinanen
<g4fgq...@btinternet.com> wrote:
>Load up the transmitter to maximum power output into a dummy
>load. Hold down the morse key when in CW mode and measure
>the power output. That is the peak envelope power output
>level. You sustained the max or peak RF envelope power long
>enough to measure it accurately.
This applies only for broadband transistorised amplifiers driven from
a regulated power supply, in which the PEP is the same as the
continuous output.
However, if the power supply is not regulated, the power supply output
voltage will drop much more during CW/FM than during SSB, thus
limiting the output power. In SSB, especially with the compressor
switched off, the unregulated DC voltage will remain high (close to
the peak value of the secondary of the mains transformer) and deliver
a higher PEP power than constant power.
For tube amplifiers, the PEP power can be 2 .. 4 times larger than the
rated continuous power due to the large thermal inertia of the anode,
thus the tube can be overdriven during each audio cycle.
The only way to reliably measure the PEP is to feed the transmitter
into a dummy load and monitor the voltage across the dummy load with
an oscilloscope. Use a dual tone audio signal and if not available,
say constantly 'AAAAAAAA' into the microphone. Increase the microphone
gain until the peak amplitude no longer increase and measure the peak
or peak-to-peak voltage. Square that voltage reading and divide it by
2 if this was a peak reading (or divide by 8 if this was a
peak-to-peak reading) and divide with the resistance of the dummy load
(usually 50 ohms). This is the effective RF power at the peak of the
modulating waveform, which is also the definition of PEP in ITU-R
radio regulations.
Paul OH3LWR
Reg Edwards
similar measure) to peak power. That's because the
statistics of speech vary widely from one person to another,
from one sex to another, from one day to another, from one
mood to another.
A power meter is needed with a long time constant which
'hangs up' on peaks long enough to display the power level
on peaks. One or two seconds is long enough. The meter
needle should rise very fast and fall slowly. Can be done
with a simple low-resistance diode to charge up a big
capacitor and a high resistance to discharge it. May need a
DC amplifier between the diode detector and the moving coil
meter to do the job properly.
But even that is unsatisfactory to control QRP PEP to some
accurately defined level. The PEP still varies according to
how loud the operator bawls into the mike.
The proper way to do it is to turn up the transmitter drive
and mike gain until the Automatic Level Control is FULLY
operative. This will fix PEP at some repeatable and
constant level regardless of who is holding the mike. It
will also give a moderate and desirable amount of speech
compression to improve intelligibility in a noisy
background.
THEN CONNECT AN ATTENUATOR BETWEEN THE TRANSMITTER AND
ANTENNA to set the required PEP level into the antenna.
It is impossible to control PEP by watching any sort of
meter when talking into the mike. It is also very easy to
cheat when supposedly you are on QRP.
--
***********************************
Regards from Reg, G4FGQ
For free radio modelling software go to:
http://www.btinternet.com/~g4fgq.regp
***********************************
Greg Knapp <gkn...@freshrain.org> wrote in message
news:t4o87m...@corp.supernews.com...
Clifton T. Sharp Jr.
> Load up the transmitter to maximum power output into a dummy
> load. Hold down the morse key when in CW mode and measure
> the power output. That is the peak envelope power output
> level. You sustained the max or peak RF envelope power long
> enough to measure it accurately.
I'm confused. Years ago the way to tune a linear to 2000W PEP was to set
the CW output to 1000W.
--
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cliff Sharp | Hate spam? Take the Boulder Pledge! |
| WA9PDM | http://www.zdnet.com/yil/content/mag/9612/ebert9612.html |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Rick
>> Load up the transmitter to maximum power output into a dummy
>> load.
>
>the CW output to 1000W.
Years ago the US law limited you to 1KW INPUT, so you could not load
the tx to 2 kw key down. So (i.e in the case of the Drake L4) you
loaded the amp to 1kw at lower plate voltage and then switched to
higher plate voltage and supposedly this was correct to get you 2 kw
PEP. (You would only see approximately 1 kw on the plate current
meter.)
BUT if you tuned to a cw output of 1kw and then you drove the amp to a
higher pep output on ssb, without changing the plate voltage you were
likely to be flattopping, or splattering.
Rick K2XT
Greg Knapp
E-mail or here on the newsgroup. Apparently it is quite difficult to measure
SSB PEP in real life QRP QSOs (as opposed to 2-tone tests) without an actual
PEP reading meter.
Especially thanks to Steve, KZ1X/4, who sent me the W1HUE PEP circuit mod to
the WM-1 / WM-2 which will allow direct reading of PEP on my
soon-to-be-built QRP wattmeter. It should do the trick.
Again, thanks to all who replied, I really appreciate it, and 73...
Greg, N6GK
Paul Keinanen
<gkn...@freshrain.org> wrote:
>I want to thank everyone for sharing their wisdom directly with me via
>E-mail or here on the newsgroup. Apparently it is quite difficult to measure
>SSB PEP in real life QRP QSOs (as opposed to 2-tone tests) without an actual
>PEP reading meter.
In addition, some rigs (e.g. the IC-706) are notorious for first
generating nearly the full power before the ALC limits the power when
the transmitter is operated at lowest power settings (e.g. for driving
a transmitter). With such transmitters using a peak reading meter with
hold, will show that first large initial peak.
Paul OH3LWR