[aprssig] FYI: APRS freq spec questions

Kenneth Finnegan kennethfinnegan2007 at gmail.com
Sun Mar 29 20:03:13 CDT 2015

What is this "Kai's Sheet"? I've never heard of it.
Kenneth Finnegan

On Sun, Mar 29, 2015 at 1:41 PM, Steve Noskowicz <noskosteve at yahoo.com> wrote:
> My version of Kai's sheet is vers 11 - Apr 2009, so if you find something
> newer it may have more.  I don't see anything better right now.
> --
> Regards, Steve Noskowicz
> Science & Technical Adviser
>   http://www.challengerillinois.org/
> ________________________________
> From: Kenneth Finnegan <kennethfinnegan2007 at gmail.com>
> To: TAPR APRS Mailing List <aprssig at tapr.org>
> Sent: Saturday, March 28, 2015 10:16 PM
> Subject: Re: [aprssig] APRS freq spec questions
> To answer one of my own questions on this, testing the T vs C access
> commands with K4JH on his THD72a, it appears that I guessed correctly.
> T100 will configure your radio to only encode a PL of 100Hz, where
> C100 configures your radio to both encode and decode 100Hz. I would be
> interested in seeing how radios respond to both at once ("T100 C127").
> --
> Kenneth Finnegan
> http://blog.thelifeofkenneth.com/
> On Mon, Mar 16, 2015 at 2:17 PM, Kenneth Finnegan
> <kennethfinnegan2007 at gmail.com> wrote:
>> Greetings fellow APRSers,
>> First, a quick note: my master thesis on APRS has been defended and
>> accepted, so you can now retrieve the final draft of my thesis online
>> here: http://digitalcommons.calpoly.edu/theses/1341/ There are still
>> some issues/typos in that document, but it has been set in stone and
>> I'm moving on with life.
>> Having taken a hiatus from APRS and writing for a few months in the
>> search for a job (which still hasn't born fruit yet...), I'm starting
>> to again poke at my notes from my thesis where topics didn't make the
>> cut for the limited scope of my thesis. I completely ignored the
>> contents of APRS packets, so now that I'm FREE of the reigns of an
>> academic institution dangling a piece of wallpaper over my head, I can
>> start look at APRS with much smaller brush strokes.
>> Let us talk about the frequency spec:
>> http://www.aprs.org/info/freqspec.txt What follows is a few point by
>> point interpretations, questions, and suggestions based on a casual
>> reading of the 9 May 12 freq spec.
>> The way I read it, the freq spec consists of a 10 octet frequency,
>> followed by a number of optional five or ten octet modifiers. The spec
>> seems to imply that these modifiers are limited to two, but that seems
>> arbitrary and limiting to me. I would suggest that an arbitrary number
>> of modifier fields be explicitly allowed. Clients MUST parse at least
>> two fields, but may continue to parse modifier fields until they reach
>> the end of the comment text or a modifier that they do not understand/
>> appears to have a syntax error.
>> The freq is expressed via "###.###MHz", or "###.## MHz" if the ones of
>> kHz doesn't need to be specified. This seems odd to me to complicate
>> this spec by allowing a space. When would a user only want to specify
>> a frequency to 10kHz instead of 1kHz resolution?
>> What is the expected behavior below 100MHz? Should the number be zero
>> padded ("052.525MHz"), space padded (" 52.525MHz"), or left justified
>> ("52.525MHz")? This last one violates the 10 octet rule for the
>> primary frequency term.
>> What is the expected behavior for frequencies >1GHz? Should they
>> continue to be expressed to one hundredths of MHz? ("1286.200MHz" -
>> This violates the ten octet rule) Should they be allowed to float the
>> decimal place? ("1286.20MHz" - This is a bloodly mess for static
>> parsers) Should they be allowed to specify their frequency in GHz to
>> the least significant digit that isn't zero? ("1.2862GHz" - Often
>> violates the ten octet rule and a freaking disaster for stupid
>> parsers)  I would suggest we allow higher frequencies to break the ten
>> octet rule and keep everything in MHz.
>> Edit: I now finally see the MICROWAVES section at the bottom... I
>> don't know how I feel about this solution vs those considered above...
>> This plus the delimiter issue (" ", "/", or "" after 7 octet data
>> extensions) means to me that pretty much the only way to find the
>> start of a freq spec is to scan the entire comment field for [0-9A-O
>> ]?[0-9][0-9]\.[0-9][0-9][0-9 ][MG]Hz and start there...
>> Moving on to the modifier terms... Every modifier term consists of a
>> space, one identifier, and three octets of payload (with the exception
>> of the rx freq term).
>> I would suggest that FFF.FFFrx follow the same convention as the
>> primary frequency in that it is always expressed in MHz, allowed to
>> violate the ten octet rule for >1GHz frequencies, and follow the same
>> conventions for <100MHz padding.
>> There are three squelch access modifiers: T, C, and D. The case of
>> this identifier specifies the channel bandwidth, so uppercase TCD
>> indicates 25kHz channels, and lowercase tcd indicates 12.5kHz
>> channels. I'm ok with limiting this to those two bandwidths.
>> What is the difference between the T tone and C CTCSS terms? I'd guess
>>  that it means that a T repeater has tone access but carrier squelch,
>> where CTCSS allows the users to both encode and decode PL. Is this
>> correct?
>> What about repeaters with split PLs? (Which I deal with regularly due
>> to passive intermod issues) I would suggest that we allow two access
>> modifiers, where the first is the user encode frequency, and the
>> second is the user decode frequency.
>> For example, the W6BHZ VHF repeater (which has a 91.5Hz input and
>> 127.3Hz output) would then be expressed as "146.760MHz T091 C127
>> -060". The UHF side uses 127.3Hz on both input and output, and should
>> be expressed as "442.300MHz C127 +500"
>> A repeater using digital input and PL output would be "FFF.FFFMHz D023
>> C127", PL input and digital output as "FFF.FFFMHz T127 D023", a
>> repeater using identical digital codes be "FFF.FFFMHz D023" and split
>> codes as "FFF.FFFMHz D023 D754" (not that I think anyone would want to
>> do that... but that's a mechanism vs policy issue)
>> Are all tone bursts >1kHz? 1750Hz is the only one I've heard of. I
>> dislike the replacing a 1 with an l trick...
>> I'm ok with limiting the +### and -### to 10kHz-9.99MHz splits.
>> Anything beyond that includes a FFF.FFFrx modifier instead. Sucks to
>> be a 23cm repeater on APRS, I guess... (i.e. W6PIY/1.2GHz becomes
>> "1286.200MHz 1274.200rx C100") I'd be more comfortable with saying
>> "implicit offsets are implicit" if the freq spec included that list of
>> standard repeater offsets, but that's another whole can of worms...
>> I look forward to any comments. I'm sorry I keep showing up just to
>> stir the pot around here.
>> --
>> Kenneth Finnegan, W6KWF
>> http://blog.thelifeofkenneth.com/
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