Tonno - ES5TV said
"But I find it extremely difficult to handle CW pile up as it is so much
more
difficult to read out single calls from pile up. They all sound the same and
form a mass of signals. It was very difficult this weekend on 160 to hear DX
station from the endless EU callers in his pile-up."
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Tonno, I would suggest looking at this article on the web
www.geocities.com/va3ttn/UsingOrionRX.pdf .
The name of the article is "Using Orion's Receiver" and it is written by one
of the guys on this list
Sinisa Hristov - YT1NT, VA3TTN. Although the "AGC function" has been
modified over time,
most of Sinisa's article remains valid and good help (S-meter in V2 now
follows the behavior of
older S-meters in many rigs, as described by Sinisa).
The performance of the Orion/Orion II AGC has varied over the many releases
of the V1 (Orion firmware)
and V2 ( Orion and Orion II firmware). Rob Sherwood mentioned, either on
this list or the Orion Yahoo group,
that Gary (Author of the V2 code) had imported some code from one of the
Ten-Tec military/commercial
receivers into the V2 firmware to try to reduce the "instantaneous gain
change" found with many DSP based IF
radio chains (There is no "diode/resistor/capacitor network" creating the
agc voltage over time - rather one
signal level measurement can reset the "gain/multiplier" of the DSP for some
period of time). So, what you
hear from the Orion or Orion II AGC can depend a lot of the firmware release
and the AGC settings you
are using with that release. However, there has not been updated information
from Ten-Tec on this since
the early days of the Orion. Rob Sherwood commented that the "new AGC code"
didn't seem to help the
"instantaneous AGC" issue.
We do know that you can not really "Turn off" the V1 or V2 AGC. If you turn
the AGC setting to "Off" you wind
up with the "fastest of fast" AGC settings possible. Doug Smith, one of the
authors of the V1 Orion Firmware, wrote
an article "Digital Automatic Gain Control for Radio Transceivers" which you
may find on the web. It does a good
job of explaining the general AGC design in the Orion/Orion II. In that
article he says "The OFF setting makes decay time
very short. FAST and OFF are such that the AGC may actually destroy the
envelopes of signals in the passband.
The net result is clipping, which produces distortion-- but you wanted it
fast, right?" I understand that the "decay rate"
at AGC-OFF setting is something like 2000db/S. I'm not sure what the
recently added "sloped AGC" is really
supposed to do for readabuility of signals in the Orion/Orion V2 code. It
would be interesting to hear Ten-Tec's
description of when they think it changes the readability of signals with
the Orion/Orion II.
Sinisa's article also talks about reducing the gain in the Orion. Of course
the gain across the Orion/Orion II
has changed in various releases of the V2 code. It also seems that the "gain
distribution" has changed. Sinisa's
article talks about the optimum ways to reduce the gain in the Orion - if
there is more gain then optimum (Optimum
being such that the receiver noise is about 2 S-units below the band noise).
This includes first turning off the preamp,
second inserting the Orion attenuation and finally reducing the RF gain.
This sequence reduces large signals before
they hit the early stages of the Orion - mixers and IF amps - and therefore
helps to minimize IMD and increase receiver
dynamic range - important for contest conditions.
The bottom line is that there are a lot of variables (Firmware release, gain
settings, AGC settings - etc)
that can go into how one hears the signals from the Orion or Orion II. Some
of these settings bring along
"unintended side effects" - like increasing the hang on the AGC can cause
strong CW signals in the passband
to "hide" weaker CW signals in the passband. Consequently, the "right
settings" are likely to change depending
on the environment in which you are trying to use the Orion/Orion II. Taking
ideas from others and testing
settings in your operating environments will likely find good performance
settings for you.
73, Merle - W0EWM
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