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ZL3AI > APRDIG 29.11.06 07:20l 184 Lines 6772 Bytes #999 (0) @ WW
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To : APRDIG@WW
Today's Topics:
1. Proper deviation levels (scott_at_opentrac.org)
2. Re: Proper deviation levels (Stephen H. Smith)
3. RE: Proper deviation levels (Robert Bruninga)
4. Re: Proper deviation levels (Ray Wells)
5. RE: Proper deviation levels (scott_at_opentrac.org)
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Message: 1
Date: Mon, 27 Nov 2006 19:04:34 -0800
From: <scott_at_opentrac.org>
Subject: [aprssig] Proper deviation levels
I know this just came up recently, but I can't find it. What's the accepted
standard deviation for APRS? Or more specifically, what should the
deviation be for the high and low tones, so I can check pre-emphasis as
well?
And thanks to everyone who made suggestions for comm test sets. I got my
HP/Agilent 8920A today and I'm having loads of fun with it. And when I'm
not using it for testing, it makes a pretty decent (if rather expensive) FM
radio for listening to music in the lab. =]
Scott
N1VG
------------------------------
Message: 2
Date: Mon, 27 Nov 2006 19:44:57 -0800
From: "Stephen H. Smith" <wa8lmf2_at_aol.com>
Subject: Re: [aprssig] Proper deviation levels
scott_at_opentrac.org wrote:
>I know this just came up recently, but I can't find it. What's the accepted
>standard deviation for APRS? Or more specifically, what should the
>deviation be for the high and low tones, so I can check pre-emphasis as
>well?
>
>And thanks to everyone who made suggestions for comm test sets. I got my
>HP/Agilent 8920A today and I'm having loads of fun with it. And when I'm
>not using it for testing, it makes a pretty decent (if rather expensive) FM
>radio for listening to music in the lab. =]
>
>Scott
>N1VG
The peak deviation which will result from the higher of the two tones
(2200Hz) should be about 3.5-3.75 KHz . This should result in the low
tone (1200) deviating about 2.5-2.9 KHz. [Deviation should be
proportional to the modulating freq so the high tone should be 2200/1200
of the deviation of the low tone.] Theoretically the high tone
could be deviated a full 5 KHz but there will then be no margin for
transmitter or receiver frequency error if the receiver has a narrow
passband. One is much better off slightly under-deviated in order to
tolerate frequency error at either end.
--
Stephen H. Smith wa8lmf (at) aol.com
EchoLink Node: 14400 [Think bottom of the 2M band]
Home Page: http://wa8lmf.com --OR-- http://wa8lmf.net
NEW! TNC Test CD
http://wa8lmf.net/TNCtest
JavAPRS Filter Port 14580 Guide
http://wa8lmf.net/aprs/JAVaprsFilters.htm
"APRS 101" Explanation of APRS Path Selection & Digipeating
http://wa8lmf.net/DigiPaths
Updated "Rev G" APRS http://wa8lmf.net/aprs
Symbols Set for UI-View,
UIpoint and APRSplus:
------------------------------
Message: 3
Date: Mon, 27 Nov 2006 23:30:04 -0500
From: "Robert Bruninga" <bruninga_at_usna.edu>
Subject: RE: [aprssig] Proper deviation levels
>... Theoretically the high tone could be deviated
>a full 5 KHz but there will then be no margin for
>transmitter or receiver frequency error if the
>receiver has a narrow passband. One is much better
>off slightly under-deviated in order to
>tolerate frequency error at either end.
And this is ESPECIALLY true when working the APRS Satellites since they add
+/- 3 KHz of frequency error due to Doppler. Some of these wide-splattering
signals we hear all the time on 144.39 would never make it into ARISS or
PCSAT's except at the center of the pass.
By the way, the ISS is back on the air with APRS digipeating finally after
being off for 90 days... Oops, I just checked it and the last packet is
now 24 hours old... I guess it may be off again?
Bob, WB4APR
------------------------------
Message: 4
Date: Tue, 28 Nov 2006 15:35:40 +1100
From: Ray Wells <vk2tv_at_exemail.com.au>
Subject: Re: [aprssig] Proper deviation levels
>The peak deviation which will result from the higher of the two tones
>(2200Hz) should be about 3.5-3.75 KHz . This should result in the
>low tone (1200) deviating about 2.5-2.9 KHz. [Deviation should be
>proportional to the modulating freq so the high tone should be
>2200/1200 of the deviation of the low tone.] Theoretically the
>high tone could be deviated a full 5 KHz but there will then be no
>margin for transmitter or receiver frequency error if the receiver
>has a narrow passband. One is much better off slightly
>under-deviated in order to tolerate frequency error at either end.
Scott,
I concur with Stephens remarks but add another two comments.
The ratio Stephen mentions only holds true if the radio conforms to
6dB/octave. Consider both tx and rx in this regard (my old FDK Multi-750
had almost no high tone after deemphsis).
The second consideration applies if audio is fed into the microphone of
the tx. If you have sufficient drive level to push the tx audio into
limiting/compression, you may very well end up with equal tone levels on
your service monitor. Such a signal will produce high tone at
approximately half the level of the low tone after deemphasis in a rx,
rather than both tones being approximately equal, as presented to the
TNC. XR2211/2206 based TNC's don't take kindly to the high tone being
lower in level than the low tone.
Ray vk2tv
------------------------------
Message: 5
Date: Mon, 27 Nov 2006 21:19:21 -0800
From: <scott_at_opentrac.org>
Subject: RE: [aprssig] Proper deviation levels
>The ratio Stephen mentions only holds true if the radio conforms to
>6dB/octave. Consider both tx and rx in this regard (my old
At the moment I'm just making sure everything's kosher on the TX side -
i.e., the relative levels of the tones are right as they exist on-air.
Proper deemphasis is a separate problem.
>rather than both tones being approximately equal, as presented to the
>TNC. XR2211/2206 based TNC's don't take kindly to the high tone being
>lower in level than the low tone.
Tell me about it.
At least I'm now able to directly verify that the preemphasis filter in my
T2 board for the DR-135T is working right. The internal connection isn't
preemphasized, and I didn't want to make the TM-D700's mistake of
transmitting flat when everyone else is expecting 6 dB/octave.
Oh, and on an unrelated note, I've got support for the La Crosse WS-2300
series weather stations in the Tracker2 now. Haven't been able to back-port
it to the OpenTracker yet, but I'm working on it. If anyone has a station
they want to test out (plus an OpenTracker or T2) let me know.
Scott
N1VG
------------------------------
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