Jose
Que gusto de nuevo...
I have been doing a bit of 9k6 stuff both on the amateur said and on
the ham side. So far experience has shown that depending on the radio
(more RX than TX) deviation can be anywhere from 2.5 to 3khz, with
2.7 being about the best compromise.
Here in Tampa we have some links between our FPAC switches which
use Motorola Radius radios, and these radios do not like anything much
beyond 2.5khz with 2.7 being about as high as I will go to talk to such
a unit.
We also have TEKK radios, these units can go the full 4-5 with no problem
but since we also have other radios we keep it down to 3 khz except those
links where we have a Radius on one end, in which case we throttle back
to 2.7.
As always it is the RX filters that cause the grief, (got pretty good at swapping
filters in the TEKK radios, setting them up for 19k2. The TX will go much
higher, seems I tried something back years ago when I worked at PacComm
where I pulled the filters out and ran 38k4 thru two radios but they were as
broad as barn doors.
Really the higher the speed the easier it is to modulate the radio, it is on the
RX end where the problems appear, the higher speeds do not have such low
freq components as do the lower speeds, i.e. 9k6 has a 23hz component, 4k8
19k2 is about 46 or there abouts, getting that low freq part through some TX
particularly those that are synthesized can be a test of patience,
I have even taken wireless mic TX and made short haul high speed (well
after 1k2 and 9k6 b/s 64 and 128 ARE high speed B-b) links out of these
devices...
On Sun, 30 Jan 2000 19:05:48 +0000 (GMT), Ing. Jose A. Amador wrote:
>
>This is not exactly Linux, but more of a hardware related comment.
>
>I wonder if it would help to point the interested to
>www.febo.com/layer-one, or sort of it, I am typing by heart. John has put
>together a number of advices and experimental/measurement reports that is
>really interesting to read, since without layer one support we could not
>make our software to communicate via radio.
>
>I picked my Radio Shack handheld scanner and tapped the FM detector
>output. Then I calibrated it with my 2 m radio, looking at the scope and
>moving it 5 up and down. Then I adjusted my 2 meter radio deviation to 10
>KHz pk-pk (limiter setting) and adjusted the mic gain a bit BELOW the
>threshold of clipping and the results have been excellent, specially with
>some rebel cases of users with soundcard modems that could not copy 1200
>baud packet reliably before. Clipping was destroying preemphasis, after
>the repair and "readjustment for voice" of the 2m radio. TNC levels are
>obviously different to microphone levels.
>
>I hope this works for 9600 too. I have no EASY (at will) access to recent
>comms lab instrumentation, and this fills the gap.
>
>After this, I have been playing with a couple of programs dealing with
>Carson's Rule, and I believe that 7 KHz pk-pk deviation would be OK for
>9K6. I have not done this for 9k6 yet myself, I just have played with a
>little math, and comparing it with practical results at 1k2, and they
>have been pretty illustrative.
>
>73 de Jose, CO2JA
>
>---
>
>Ing. Jose A. Amador Fundora | Tel : (537) 20-7814
>Dept. de Telecomunicaciones | E-Mail : [EMAIL PROTECTED]
>Facultad de Ing. Electrica |
>ISPJAE |
>
Chuck Hast e-mail [EMAIL PROTECTED]
---- FPAC ----
www.fpac.qth.net
