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[aprssig] Voice Alert

Steve Noskowicz noskosteve at yahoo.com
Mon Sep 17 02:23:43 UTC 2007


Hi Ken and welcome to APRS --- sometimes a love-hate
part of the hobby.(;-)

I'm not the APRS Guru others are here.  I'm a long
time RF Engineer familiar with radio, but let me
summarize a few things I'm pretty sure I understand.
 
 Your test was a very good one, indeed – good catch!


>  [snip] Remember I've been having a problem 
> getting digi'd and into a Igate?
> ... I took the tone off ... I ... 
>  [now] get digi'd a LOT more often...

>  get a "my pos" on the display and 2...4 beeps...
> I have the "beep" ... "mine".  
>  My understanding is each time it beeps ... 
>  received a packet from a different digi?

FINE POINT:  My understanding is that the D700 does
the "MY POS" & MINE-Coo-Coo-beep when it (correctly)
receives the beacon/packet that it just transmitted
'regardless of the source'.  Of course, any one digi
*shouldn't*  'peat you more than once, therefore, it
_should_ indicate how many digis 'peated you – and
your D700 heard.    I call those  "Echos".  
    When the new WIDEn-N came, my echoes dropped from
up to 5, to rarely more than 2.  The D700 also
"CooCoos" for message Echos, but the display shows MY
MESSAGE.


> [should CTCSS]  make a difference as to how often I
was digi'd.  

   No. It *shouldn't*,  but it can...  IF something is
right on the edge and sometimes works – such as:

1- Your radio has some kind of a Transmit Deviation or
frequency problem.  
     IF you have a local expert who can do some
measurements it is easy to see if your D700 is set
correctly.  There is a Maintenance mode that can be
used to set the deviation, but I don't remember if the
CTCSS or TNC can be set, or (more likely) just the
audio deviation.  If this is a new radio, this is very
unlikely.  If it is used, the former owner could have
changed the settings in the Maintenance mode.  I also
haven't looked into setting the D700 master oscillator
on freq, though I do have a service manual.

2- The digipeater is not set up very well.  
     Audio levels and deviation are something not all
hams are familiar with.  When setting up a digi, this
is an aspect that should be looked at *very* carefully
– with a scope and all.  Things that matter include:
levels into the TNC, where the audio is taken from the
receiver (before / after the de-emphasis  - I don't
know which is "correct" – OR before or after the
squelch gate), distortion in the receiver (If the ham
hasn't Listened and/or measured this, it could be off,
or go off in time, and he wouldn't know it), and, and
the digi receiver frequency.  
   With Voice Alert being a standard, I suspect
(unless someone has a reason not)  that a high pass
filter should be inserted ahead of the TNC to
eliminate the Tone.  The TNCs shouldn't have to deal
with it since it can reduce overall sensitivity to the
packets.  They may have this, I don't know.  
If forced, I'd probably put my money on the Horse
named Bad Digi.  

    Something which can add confusion (read inhibit
progress if not known) to doing APRS tests like this. 
Set up properly, a digi will not repeat EVERY beacon
you send if you sit in one place and repeatedly squawk
(you can turn BCON off and back on to force an
immediate beacon – after it hears a clear channel). 
Digis are supposed to limit this to prevent
Katrina-like conditions on .39.  If you don't move,
you are only supposed to beacon every 30 minutes to
conserve bandwidth and digis enforce this by cutting
you off until 30 minutes has passed – mileage may vary
depending how the digi-OP set it up.  
I do not know what precision in the lat/lon is used
for this, so I do not know how the random variations
in a GPS position affect this feature – is it handled
as the same posit, or is each variation a new posit
.?.?


> After all, there is a 100 hz tone sent along with
the packet isn't there?  

     Yes.  The 100 Hz tone is there along with the
APRS (AX.25) packet tones.  That way, other mobiles
near you will open their squelch and allow the ham to
hear your "Squawk" (and visa-versa) and know someone
is in voice range.  
  Then, there's this time this local Radio Guru
couldn't figure out how Kenwood would let such a bad
software error through which was allowing random
beacon "squawks" to be heard in the speaker.    Until,
that is, he remembered that he had set up voice alert
and was prompted to think about what it really meant
by a comment from a local  (Thanks, Robbie) APRS Guru
– d'oh!   time.  Yep, that was me – and I have even
designed CTCSS and squelch circuits.  Oh well, I'm
entitled.


> Be gentle when calling me DUMB!!! After all, I am a
newbie here {grinning}
 I'm not aware of that ever happening here.  These
guys are adults...On the other hand, the Gurus have,
on occasion, gotten rather testy with each other – as
will happen anywhere.  ( ; - )

Well, I think that covers it.  That's all I can think
of ... until *after* I hit the SEND button.

73, Steve, K9DCI
P.S.  Even the Gurus have errors on their APRS web
pages.

It goes without saying, though I'll say it...IF I have
any errors here, someone will correct me.


Click

===================
 Posts by the following were also read:
Eric J. Goforth, N6GOF
Ev, W2EV
Randy Allen, KAØAZS
=================
> This would not surprise me if the digi is not 
> properly adjusted ...many people ignore ...
> Now the thing to do is to work with the 
> digi operator and see if he can make some
> adjustments at the digi audio path to clean 
> this up maybe
Bob. Wb4APR

73 de Ken H> K9FV



       
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