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ZL3AI > APRDIG 08.03.04 18:32l 251 Lines 9283 Bytes #999 (0) @ WW
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Subj: TAPR Digest, Mar 06, 2/4
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From: ZL3AI@ZL3VML.#80.NZL.OC
To : APRDIG@WW
Subject: Re: TNC-2 and MFJ-1270 performance
From: "Robert Bruninga" <bruninga@usna.edu>
Date: Sat, 06 Mar 2004 09:59:19 -0500
X-Message-Number: 8
Fantastic work. I am so glad to finally see some performacne data. Yes
negative twist is disasterous and poor attention of digi owners to these
details is rampant in APRSdom and all packet for that matter. If you have
a formal paper or write up, I'd like the link. In the mean time, I am
going to copy your email below and provide a link toit on my FIX14439 web
page... Thanks!
B
b
>>>Mark Cheavens <mcheavens@usa.net> 3/5/04 11:41:45 PM >>>
I have done extensive testing of decode performance on MFJ-1270B and C's as
well as a wide range of PacComm TNC-2's (micropowers, Tiny-2's, TNC-200's,
etc.) as well as KPC-3's.
Testing has been done using a wide range of receivers and from being set up
properly to NOT-Properly to test decode performance. In ALL cases the TNC
was PERFECTLY aligned prior to testing.
Test results here will use an example radio that has a .25uV receiver.
(slight bacon frying when receiving voice).
I have NOT done as much testing for twist with the KPC-3 and no testing
with a KPC-3+ (which likely will not decode quite as well as the modem is
NOT designed for 1200/2200 tones)
KPC-3 will decode 100% of the packets at about .35uV
TNC-2's at about .5uV
MFJ's 2-3uV
Basically I have relegated all MFJ's to bench service only. I would NOT
even consider it for a digi doing weak signal work!
Twist:
If you use discriminator audio into the TNC you will end up with (assuming
the transmitter is working properly) 6db per octave of twist. Since 1200
and 2200 are (almost) an octave apart I will for the sake of this email say
that they should needs to be 6db of de-emphasis in the receiver before the
TNC to get the audio FLAT again.
What I have found is that all the TNC's I have tested had significant
improvement when getting the audio to within +3db of flat with a SLIGHT,
but steady improvement to about +1db of twist.
From +1db to Flat there was not much difference or NONE that I could
measure.
ALL OF THE ABOVE IS ASSUMING THAT THE HIGH TONE IS GREATER THAN THE LOW
TONE, HENCE THE +db.
Continuing past flat and adding negative twist (low tone greater than the
high tone) has almost immediate DISASTROUS results! at about -1db of twist
most TNC would almost stop decoding altogether.
I therefore try to engineer in about a 5db de-emphasis network. This allows
a +/- window that I think is ideal for people that DON'T set up there tnc's
and radio's using a service monitor correctly!
So, I am torn between the FAR superior code of using a TNC-2 with UI-Digi
code and using a KPC-3 with better decode performance.
The next phase I plan on doing (once moved into my new house) is to test
the TNC-X project and a KPC-3+. IF the TNC-X performs as well as the KPC-3
then I will move in that direction. A group of us have also looked at
adding some of the filtering design from a KPC-3 and retrofitting TNC-2's.
The audio reaching the modem is MUCH different!
In an ideal world I would use a disk less computer running dos or Linux
with Digi-Ned with KPC-3 quality decoders that was FIXED in KISS mode.
Digi-Ned is in my opinion the CLOSEST thing we have right now to fixing the
ENTIRE path problem. With a FEW additions to the code and putting it in a
rock solid computer we could ACTIVELY fix ALL the digi's!
(A disk less computer that has one serial port and NO moving parts for
under $100 is what is needed).
PS for testing of decode performance I have two files on my web site.
Both are wave files that are sequentially numbered packets that I open and
put into loop mode on a computer. The audio is then used as the input into
a service monitor so that the attenuator can be used to measure the decode
performance. One file is a FLAT audio file, the other has 6db of
Pre-Emphasis. Since most older service monitors only transmit what comes in
the pre-emphasis file is what is normally used.
http://www.cheavens.com/mark/radio/packetradio/
Mark Cheavens
KC5EVE
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Subject: RE: TNC-2 and MFJ-1270 performance
From: Mark Cheavens <mcheavens@usa.net>
Date: Sat, 06 Mar 2004 09:02:00 -0600
X-Message-Number: 9
A Pico is a different animal completely!
(I use one in my car for mobile operations since it is not good for much else)
A PacComm with UI-Digi CANNOT loose it's settings as they are hard coded
into the rom.
Mark
At 10:17 PM 3/5/2004 -0800, Dale Blanchard wrote:
>> (I've never actually seen a PacCom)
>>
>>[Mark] What do you attribute the superior performance of the PacCom to?
>>
>>My Pico- is very consistent in losing its settings. Makes it unusable.
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Subject: RE: TNC-2 and MFJ-1270 performance
From: Mark Cheavens <mcheavens@usa.net>
Date: Sat, 06 Mar 2004 09:04:48 -0600
X-Message-Number: 10
I didn't dig any deaper other than the different modem chips. Very similar
circuit design other than that.
The KPC-3 however does some filtering before the modem chip. Eventually I
would like to fix all the TNC's to decode close to the KPC-3.
Mark
KC5EVE
>[Mark] What do you attribute the superior performance of the PacCom to?
----------------------------------------------------------------------
Subject: RE: TNC-2 and MFJ-1270 performance
From: "Steve Slay - KC5MVY" <snslay@swbell.net>
Date: Sat, 6 Mar 2004 09:17:22 -0600
X-Message-Number: 11
>>My Pico- is very consistent in losing its settings. Makes it unusable.
Have you ever changed the internal battery? This could help.
Steve Slay
KC5MVY
Where am I now? http://tinyurl.com/i4ia
See the weather RADAR http://tinyurl.com/i4i7
Try this one http://tinyurl.com/i3ni
"Only two things are infinite, the universe and human stupidity, and I'm not
sure about the
former." Albert Einstein
----------------------------------------------------------------------
Subject: RE: TNC-2 and MFJ-1270 performance
From: "Steve Slay - KC5MVY" <snslay@swbell.net>
Date: Sat, 6 Mar 2004 09:23:20 -0600
X-Message-Number: 12
From: "Dale Blanchard" <wa7ixk@earthlink.net>
To: "TAPR APRS Special Interest Group" <aprssig@lists.tapr.org>
Cc: "TAPR APRS Special Interest Group" <aprssig@lists.tapr.org>
Sent: Saturday, March 06, 2004 12:17 AM
Subject: [aprssig] RE: TNC-2 and MFJ-1270 performance
>>My Pico- is very consistent in losing its settings. Makes it unusable.
Have you ever changed the internal battery? This helped mine.
Steve Slay
KC5MVY
Where am I now? http://tinyurl.com/i4ia
See the weather RADAR http://tinyurl.com/i4i7
Try this one http://tinyurl.com/i3ni
"Only two things are infinite, the universe and human stupidity, and I'm not
sure about the
former." Albert Einstein
----------------------------------------------------------------------
Subject: Re: TNC-2 and MFJ-1270 performance
From: "Russ Chadwick" <russ@wxqa.com>
Date: Sat, 6 Mar 2004 15:37:23 -0000
X-Message-Number: 13
----- Original Message -----
From: "Mark Cheavens" <mcheavens@usa.net>
>The next phase I plan on doing (once moved into my new house) is to test
>the TNC-X project and a KPC-3+. IF the TNC-X performs as well as the KPC-3
>then I will move in that direction. A group of us have also looked at
>adding some of the filtering design from a KPC-3 and retrofitting TNC-2's.
>The audio reaching the modem is MUCH different!
In an article describing the TNC-X, which was given in the DCC last Sept and
appears in the collection of articles, John Hansen describes the input
filtering to TNC-X on page 40. He uses a 1200 Hz 4th order Butterworth
highpass filter before the modem chip and reports that much improved
performance was seen with this set-up as compared to no input filtering when
receiving off-the-air packets. He also describes the results of some bench
testing with a spectrum analyzer.
My TNC-X performs very well receiving APRS packets along the front range of
Colorado.
Russ Chadwick KB0TVJ
www.wxqa.com
----------------------------------------------------------------------
Subject: Re: TNC-2 and MFJ-1270 performance
From: "Spider" <spider@rivcom.net>
Date: Sat, 6 Mar 2004 09:01:04 -0700
X-Message-Number: 14
>>>>Mark Cheavens <mcheavens@usa.net> 3/5/04 11:41:45 PM >>>
>>
>ALL OF THE ABOVE IS ASSUMING THAT THE HIGH TONE IS GREATER THAN THE LOW
And, I assume you've taken into consideration that clipping or limiting and
harmonic distortion have not been introduced in the transmitter of the
modulating station which can really hose up proper pre-emphasis.
Jim, WA6OFT
----------------------------------------------------------------------
Subject: Re: [aprsspec] Destination Addresses for Wx Stations andDigipeaters
From: "Robert Bruninga" <bruninga@usna.edu>
Date: Sat, 06 Mar 2004 11:00:37 -0500
X-Message-Number: 15
>>>"Christensen, Eric" asked
>
>I was looking at http://web.usna.navy.mil/~bruninga/aprs/tocalls.txt
>which lists the destination addresses for all things APRS. I see that
>APN3xx for KPC-3 digipeaters. What should the xx be?
The ROM version number. Use 83 for version 8.3
de WB4APR
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