[amsat-bb] Re: 67 Hz PL Frequency Tolerance?
Wed Aug 23 02:48:33 PDT 2006
I don't know the answer about the tolerance of AO-51's tone decoder, but
if the purpose is to make a tone encoder I can tell how I designed and built
two working encoders for all PL (38 if I remember correctly) tones.
My problem was total lack of test instruments at that time, so I had to
use a no tune approach. The only thing I could think of was to make a
"poor man's" dds with a microcontroller and an R/2R 8 bit DAC followed
by a low pass active filter. The only frequency reference is the
microcontroller external crystal oscillator. The only tuning I needed was
on the output level and I just used a multi-turn trimmer and moving it to the
point that the tone squelch on a TH-D7 receiver opened.
The first unit built is an external one for the TR-9130 vhf radio (it's
a little box with an lcd display and two buttons to chose tone frequency). I use it
for AO-51 and SO-50. I've never had problems getting into those two sats.
The second unit I built is for the TR-851 and it's internal, using the little
space of the original kenwood board. I just had to reverse engineer the signals
that the radio generated for the original board (I've never seen one). This
second unit has only been tested with the TH-D7, since I don't think we have
a working satellite with FM tone squelched uplink on the 70 cm band.
Hope it helps.
73 de IS0FKQ
> ----- Original Message -----
> From: "Bill Ress" <firstname.lastname@example.org>
> To: <email@example.com>
> Sent: Tuesday, August 22, 2006 7:59 PM
> Subject: [amsat-bb] 67 Hz PL Frequency Tolerance?
> > I've looked through the AMSAT web site and the AO-51 book but can't any
> > information about the frequency tolerance of the satellite receive
> > system to the 67 Hz PL tone.
> > I believe someone way back when actually did some measurements after it
> > was launched but I can't find it either. Does +/- 2 Hz sound right? What
> > about the level (deviation) require? Is it the same for the Mode V and L
> > receivers?
> > Regards and thanks...Bill - N6GHz
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