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[aprssig] APRS on UHF?

Bill Vodall WA7NWP wa7nwp at gmail.com
Thu Nov 27 18:13:28 UTC 2008


This is going to be a bit of a busy day here on the sig...

On Wed, Nov 26, 2008 at 6:43 PM, Bob Bruninga <bruninga at usna.edu> wrote:
>> Hardware for 9600 baud has never been
>> easier with the out of the box
>> D710 functionality and forthcoming
>> data rigs from OpenTracker and
>> TinyTrak families...
>
> Except that 9600 baud pays a 7 dB penality in decoding and a 6 to 9 dB penalty in RF path loss, so unless you have some really great mountain digis that can see line of sight to your intended area of couverage, the performance is very poor compared to 2 meters.
>
> Yes, with ideally-designed-and-tuned radios, you can get most of that 7 dB back, but you cannot get the 6 dB worse range at UHF back without having 9 dB gain verticals at the digis on UHF. Then you are only 3 dB worse than VHF...
>
> Again, it makes a nice alternate input if you can afford he many dB loss in performance.  But you have to consider all this in your plans.

Your global statement of "performance is very poor compared to 2
meters" is just plain inaccurate and takes away for the vast goodness
UHF and 9600 have to offer APRS and packet radio.

Any communications setup consists of a whole string of dB +'s and -'s.
  Add all the numbers, stir in little details like link budgets,
activity levels, modulation methods and CPU processing.   Take the
result, and throw it away.

All that matters is if it works.

For my daily 14 mile commute essentially through the Microsoft Campus
to the junction of I90 and I405 -- 9600 UHF on 440.800 MHz works
better then the legacy system on 144.390 MHz.   Not only do I get a
more useful track -- my Mother said so -- but I see lots of info
that's not available on 144.390 MHz.   I see the quakes, 6 meter DX
Spots and a half dozen AMSATS in addition to the ISS.

UHF doesn't go as far as VHF..   That's a good thing in a busy area -
not a negative...

So - False is "performance is very poor" because "you have to consider
all this..."

73
Bill - WA7NWP

PS.   Example of 9600 UHF packet history:
http://www.findu.com/cgi-bin/raw.cgi?call=WA7NWP-7



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