[amsat-bb] ANS 321 AMSAT NEWS SERVICE SPECIAL BULLETIN - AO-85 Commissioned, Handed Over To AMSAT-NA Operations

Phil Karn karn at philkarn.net
Wed Nov 18 23:28:28 UTC 2015

> ANS-321

> Downlink audio is 5 kHz deviation, as expected. Many will perceive
> that the audio is "low." This is an effect of the filtering below 300
> Hz, which provides for the DUV telemetry, coupled with any noise on
> the uplink signal resulting from lack of full quieting or being off
> frequency. That makes for less fidelity than a typical receiver in
> terms of audio frequencies passed.

> It is important to remember that science is the reason behind the
> Fox-1 satellites. Not only does science help with the launch cost, it
> provides a great amount of educational value both from the science
> payload and in amateur radio itself. The data-under-voice (DUV)
> telemetry is an excellent way to provide the science without
> sacrificing the use of the satellite for communications, which would
> be the case if higher speed downlinks were needed. DUV provides
> constant science as long as the repeater is in use, which in turn
> provides more downlink data for the science - a mutually beneficial
> combination.

I designed the DUV telemetry system on Fox-1, with an important
suggestion (use 8b10b coding for spectral shaping) from Tony, AA2TX.
It's important to remember the severe design compromises imposed by the
requirement that the satellite itself be an analog FM repeater,
confining the telemetry to modulating frequencies below 300 Hz.

These design compromises would have been unnecessary with a fully
digital communications payload, like those on every non-amateur
satellite launched in at least the past decade or two. I've made it
clear that this is my last telemetry design for an analog spacecraft.
It's past time for AMSAT to move into the all-digital era.

--Phil, KA9Q

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