I have to think the frequencies chosen probably give a pretty low
background noise....
On 8/31/22 10:25 AM, Chuck McCown via AF wrote:
3.2.2.4 Telemetry Modulation. The telemetry comes to the telemetry
modulation unit (TMU) separately as a “low-rate” channel and a
“high-rate” channel. Low rate is 40 bps only and its routing through
the TMU is such that it can only be downlinked as uncoded bits. High
rate, one of a set of rates between 10 bps and 115.2 kilobits per
second (kbps), is downlinked as coded symbols. The TMU encodes the
high-rate data stream with a convolutional code having constraint
length of 7 and a symbol rate equal to twice the bit rate (k = 7, r =
1/2). Either modulator can biphase-modulate the telemetry symbols onto
either a 22.5-kilohertz (kHz) or a 360-kHz subcarrier. A subcarrier is
a symmetrical square wave signal derived from a TMU crystal oscillator
that has a nominal frequency of 2.88 MHz. The 360-kHz subcarrier is
required for bit rates greater than 7.2 kbps. The TMU has one
modulator for the S-band downlink and another for X-band downlink. The
modulated subcarrier goes to the S- or X-band exciter.
So, the same as original Canopy.
*From:* Chuck McCown via AF
*Sent:* Wednesday, August 31, 2022 11:13 AM
*To:* [email protected] ; 'AnimalFarm Microwave Users Group'
*Cc:* Chuck McCown
*Subject:* Re: [AFMUG] OT Voyager
I was taught, many years ago, that minority (might have been majority)
charge carrier migration in semiconductors would render them useless
in 20 years. Also solar panels are supposed to wear out in 20 years.
And cosmic rays kill all semiconductors. etc etc Danged good
modulation they are using whatever it is. I think it was some kind of
pseudo random noise code but I may be wrong about that. A professor
in an analog class told me that almost 40 years ago.
*From:* [email protected]
*Sent:* Wednesday, August 31, 2022 11:08 AM
*To:* 'AnimalFarm Microwave Users Group'
*Cc:* 'Chuck McCown'
*Subject:* RE: [AFMUG] OT Voyager
I’d bet a smaller codebase helps. No gigabytes of libraries to debug.
But yeah, if something I built lasted 45 years in outer space I’d pat
myself on the back a bit.
*From:* AF <[email protected]> *On Behalf Of *Chuck McCown via AF
*Sent:* Wednesday, August 31, 2022 11:50 AM
*To:* [email protected]
*Cc:* Chuck McCown <[email protected]>
*Subject:* [AFMUG] OT Voyager
This space vehicle launched 45 years ago started sending garbage
telemetry. The folks running that show figured it was routing the
data through a known defective computer.
So they commanded it to switch to the good computer and they got good
telemetry.
Talk about latency... 16 hours.
So 45 (more likely 55) year old hardware running an OS that old is
still essentially rocks solid. So are the transmitters and receivers
and other RF components allowing communication clear out into deep space.
Damn, those engineers and coders must be proud of the job they did.
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