[FADCA] Radio Spectifcaitons for 9.6kb

[Chuck Hast]

On 6/13/05, bud thompson <budt at cfl.rr.com> wrote:
> I've been eye-balling the May QST Product Review of the Yaesu FT-8800R Dual
> Band unit.  Something like that would be swell for the ARES EMCOMMs kit bag!
> 
> BER specs for 9.6kb are:
> 2M
> -12db SINAD 8.8 x 10E4
> - 16db  SINAD 3.0 x 10E5
> -50db SINAD <1.0 x 10E-5
> 
> 70cm
> -12db SINAD 8.7 x 10E4
> - 16db  SINAD 5.6 x 10E5
> -50db SINAD <1.0 x 10E-5
> 
> Not great numbers, but workable so long as the LAN has good coverage.
> 
> However- ARRL measures the Transmit-Receive turn around time (but not
> specifically related to packet testing.)
> "PTT release to 50% audio output)  S9 signal 2M 190ms; 70cm 220ms.
> 
> Does this mean we'd have to have a TXD in excess of 220ms for 9.6kb
> operation on UHF?  Kind of diminishes the throughput - but we have the same
> problems with our backbone Mitreks - can't run them reliably (stock) at less
> than about TXD150ms.  I'm hoping someone will find that magic mod to reduce
> that to below 70!
> 

Start looking for electrolytics, first in the audio circuits in fact
get RID of the audio
circuits if you can. Remove anything that is beyond your audio point
of entry and
exit. I have taken some motorolas to switching speeds of > 5m, back
when I worked
for Del Monte Fresh Fruit, we had some simplex autopatches that were used by
the company to make calls from the plantation areas, we took some motorola
radios and worked them over and took them from 150ms switching to a total of
10ms switching time (5 for each side) that was so fast that the RX window only
sounded like a short click and after you got used to it you realized
that you did
not loose a thing. Same thing should hold for your Mitreks, you will have to go
in and get rid of stuff that slows the switching down.
NOTE --- BE WARE ---
Also keep a spectrum analyzer at hand when you start working on the RF part
as you do not want to make changes that will create out of band or even out of
signal band trash when the radio switches. This is why I always started with the
audio stages as those caps were the ones that seemed to slow things down the
most.

> 
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-- 
Chuck Hast 
To paraphrase my flight instructor;
"the only dumb question is the one you DID NOT ask resulting in my going
out and having to identify your bits and pieces in the midst of torn
and twisted metal."