Thanks Eric,
I understand you think AGC in high dynamic range radio like K3 is not a
necessity for the op with high dynamic range ears.
Actually the range should be close to 90-95 db on nowadays bands where 59+40
signals co-exist with 1S unit signals very often. I also figured from your
post that other ops from VP6DX team choose not to use AGC not because of
some sort of problem existed in that version of the firmware but purely
because they prefer adjusting RF gain manually to squeeze out the most from
the pile up.
What about the DSP then. I experienced that myself operating from 8Q7 in the
past and many others confirmed my impressions that modern DSP based radios
are no good when pulling call signs from the pile up of many stations when
the average level of that pileup is close to the MDS of the radio. For
example we could not use Orion in the expedition on a weak pile up on 10 and
15 meters while the same operators could easily pick out calls using IC775.
Therefore I would be happy to have a radio where DSP could be switched on or
off depending on the situation. Did you notice the above mentioned effect
while using K3?
73, Igor UA9CDC
Privet Igor --
As best I can remember, we used MCU v1.66 and DSP 1.52.
I didn't use the AGC because I did not need it. The point of automatic
gain control is to adjust the gain of the various stages of the receiver
in order to
a) avoid distortion/overdriving a stage, and
b) bring signals up/down to a comfortable listening level.
(b) is not relevant to an operator who is working a pileup. (b) is
relevant to an operator who is monitoring a frequency with one station
transmitting.
For operating a pileup, there are a variety of tools the brain uses to
distinguish the many signals:
-- pitch (CW)
-- style of speaking (speech) or keying (CW)
-- artifacts; e.g., auroral flutter, chirp, etc.
-- strength (all).
AGC tends to reduce the difference in signal strength, and so removed
valuable information.
In situations where static crashes interfere with reception, AGC hang
time on a loud static crash also increases the length of time that a
specific static crash interferes with reception.
I used headphones with good audio isolation between my ears and the rest
of the world around me. That allows me to set receiver gain levels with
the underlying antenna/band noise just above my threshold of hearing...
and to use at least 80 dB of my hearing range for listening. In this
quiet listening environment, I don't need AGC.
Even in a less-than-quiet listening environment, if a band is just open
weakly (e.g., 12m to Europe), the range of signal strengths in the pileup
can be smaller: maybe less than 30 dB between band noise and the strongest
signal. So AGC isn't needed here either.
My ideal AGC in these situations is one that only makes changes in
receiver gain when a stage in the receiver is about to be over-driven
(e.g., the A/D converter)... and removes those changes relatively quickly.
Even then, it might be fine to allow the receiver to be over-driven (a
static crash contains no information). If a signal I want to copy is
over-driving the receiver, the best solution often is to reduce the RF
gain manually during the duration of the time when I want to copy that
station. If that station is just "interference" (e.g., a loud USA station
on 80m CW calling VP6DX, when I want to work northern Scandinavia and
northwest Russia/western Asia during the brief opening), I have other
controls (filter bandwidth, notch) than might be better to use that gain
reduction (automatic or manual) that could suppress the desired weak
signals.
So, almost any AGC system is inappropriate for a DXpedition or content
environment... as long as the receiver and one's own ears have enough
dynamic range to handle all the signals presented to it. The K3 has more
dynamic range than other receivers.
73,
-- Eric K3NA
on 08 Mar 13 Thu 02:26 Igor Sokolov said the following:
Almost all of the operators ran the K3 with AGC off (all modes).
-- Eric
Eric, can you explain what did you not like about AGC in K3?
Did you notice any problems with DSP being permanently on in K3 when
listening to heavy pile ups?
73, Igor UA9CDC
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