[FADCA] 9.6KB Throughput vs 1.2KB

[Russell Oder]

Chuck, thank you for your call Friday. I am glad Bud asked these questions
as I am having to make some financial decisions and explore some technical
issues.

I am considering trying to set up my Spectra UHF and VHF radios to handle
voice and data to compliment the work we are starting on - running voice and
data through MSR2000s and MSF5000s.  As you know we have a number of Mitreks
that Bud has been working on to put on the links and LANs for 9600 bps.  We
need to know soon wheter they are worth the squeeze that Bud and Charlie are
putting out to get them ready. We also have a "fortune" in crystals already
purchased - we have more money in the crystals than radios.

With your comments to me on Friday regarding models and features,  we need
to determine if we can get the radios we discussed, what the cost and
service benefits are (throughput and technical support requirements) of one
vs the other.

Should we just start with what we have and change out as opportunity and
fortune afford us the opportunity? (I havn't won the Lotto yet this week and
time is drawing close on getting things up and running, in fact from the
sign near my house none of us has won this time.)

What is the possiblity of being able to have a Tait radio on the switch as
well as the client at the Hamfest?  Is this one of the subjects where the
call to Linda should go tomorrow?

Russ
----- Original Message ----- 
From: "Chuck Hast" <wchast at gmail.com>
To: "Florida Amateur Digital Communication Association"
<fadca at mailman.qth.net>
Sent: Sunday, November 21, 2004 9:25 PM
Subject: Re: [FADCA] 9.6KB Throughput vs 1.2KB


> On Sun, 21 Nov 2004 18:42:23 -0500, bud thompson <budt at cfl.rr.com> wrote:
> > The radio baud rate of 9.6kb is 8X as fast as 1.2kb...
>
> I am going to sound like a politician here, but it depends on how your
link is
> set up, and how clean the path (including radios ) is
>
> >
> > We all know the throughput rate is not 8X as fast.
>
> With large frame sizes, and a clean path indeed it will be 8X. The reason
you
> do no see the 8X is because of the voice radios which are far from nice
clean
> data boxes. If you try it on a wire you will see the difference and it
will be
> quite impressive. If you try it on a true data radio again you will
> see that data
> flows quite rapidly and you will find that it will be 8X+ because your
data box
> will have very short TXD times which most radios used in 1k2 service will
not
> have. Now if you do the 1k2 and 9k6 on the same data boxes you will indeed
> see that the speed difference is 8X. This was all the more brought home to
me
> when I started working with the Tait radios, in fact I link to the Tampa
switch
> from the Linux FPAC test switch, I will pull say a heard list or a
> traffic list off of
> the switch, if I am using the kenwood in the car I can hear both the 440
link
> and of course the bearer channel off of the fpac switch. And the TX time
delta
> is just about 1/8 of that of the 1k2 channel. It is QUITE noticable.
>
> > What I don't know is this:
> >
> > What is a reasonable comparative throughput rate of 9.6KB compared to
1.2kb?
>
> With reasonable radios and all of your timers set right you should get
> from 60 - 70%
> of the 8X, if you use data radios and use directional antennas to kill
> the multipath
> you will get your 8X.
>
>
> > Premise:  While we may not make a 'perfect' 12kb test, we are used to
1.2kb
> > and will accept almost anything that works.  So, if we observe a 1.2kb
10k
> > file transfer with few, if any, retries, we will consider that our
> > baseline...
> >
> > Now we move to 9.6kb... where we have much less experience...
> >
> > All I'm concerned about is encoding/decoding in the absence of noise.
Let's
> > assume the RF path/link has virtually no influence.. this is a bench
test.
> >
> > If the 10k file can be received in 3 minutes using 1.2kb...
> >
> > What can we expect to do using 9.6kb?
> >
> > Half the time (1.5 minutes?)
> >
> > Give me a range - I'm not interested in technical details regarding
AX.25
> > parameters, etc... just your experience on what we can expect.
> >
> > I see no reason to go to 9.6kb if it takes 80% of the time that 1.2KB
> > takes.. hardly worth it.
> >
> > Where is the break over?  - 50%...40%
>
> On the bench you will get 8X I have done that with TEKK radios, too bad
they
> quite making the KS-900, it could be whooped up to have a TXD of < 10ms
> and with the proper filters in it, it would pass a text book eye.
>
> The killer is the use of radios that are not designed for data and are
> nothing more
> than a compromise between the two in most cases. Even the D-7 which I have
does
> a good job decoding 9k6 but the TXD is a bit high needed about 100ms if I
recall
> correctly.
>
> I should have a tait radio at the hamfest on the switch so you can see
> the speed with
> which data will come in when the path is good and you have a clean TX and
RX.
>
>
> I know I got long on this, but a little TLC on these links and you
> will get the 8X you
> are looking for.
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