Ignore the peak power meter. It is a fiction and should be removed from
the console. In order to answer these continuous complaints, we have
placed arbitrary limits (clipping) on the values the meter would
otherwise display. It is a fiction and I no longer support its
existence. The peak power meter is a complete failure. It cannot be
made to work at all because there is no feedback mechanism from the
amplifier to this meter. It is not a sensor on the state of the
amplifier, it is a sensor on what is the peak value in the dsp buffer.
We would be better off with a "dBFS" meter.
Nothing more clearly demonstrates what was wrong with the early
incarnation of the AGC/ALC than this peak power meter issue. A single
sample, would crush the entire buffer down. You are seeing the same
phenomenon in this meter. Here a single large sample will say 200 watts
when the average power in the buffer is 40w and in fact the amplifier
has gone into compression. It was a mistake for me to ever add it and
I apologize for the constant consternation it has caused.
The forward power meter is only meaningful in the case of the amplifier
where there is an A/D and a bridge. Again, its accuracy is only as good
as the calibration and the impedances it sees. With the amplifier it is
a computation of the average power in the buffer and is not a sensor
measurement on the external 1 watt amplifier state.
Bob
N4HY
Eric Wachsmann - FlexRadio wrote:
Gary,
After I got this message, I went back and took my measurements again
using a scope. I am seeing peak power up to ~140W with the AVG power
around 45W depending on voice characteristics. This is what we were
targeting with the new ALC.
Why should you be happy with this? Because it is an extremely linear
ALC that allows you to over drive the heck out of the input without
having to worry about damaging your transmitter, and without splattering
all over the band.
Eric Wachsmann
FlexRadio Systems
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
Sent: Thursday, February 09, 2006 5:17 PM
To: [EMAIL PROTECTED]
Cc: FlexRadio@flex-radio.biz
Subject: Re: [Flexradio] PowerSDR Beta Preview 13 has been Released.
I read the release notes and, yes, I experience exactly what was
described:
// Note that because the ALC was non-functional
// in the last series of releases (since 1.4.5 started),
// the output power for inputs which are being overdriven
// will be attenuated. As a reminder, on SSB, you will
// not get 100W on a bird wattmeter. Something closer to
// 30 or 40W is a more reasonable expectation for average
// power for most voices/microphones.
Now, would someone please explain to me why I still see 100+ watts on
the
peak power meter of the SDR while the external wattmeter peak power
reads
about half that? Also, please tell me why I should be happy with half
the
power I used to put out. I assume the answer will be something like
"you
were overdriving and distorted before, now you are not". The signal
reports I got were nothing like that, I might add.
Sorry to pose questions which may be obvious to most, but I really
would
like to know.
Gary
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--
AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats,
NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman
Laziness is the number one inspiration for ingenuity. Guilty as charged!
