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<div dir="ltr" data-setdir="false">NOPE!!!!! Do some research on Class C amplifiers vs Class A linear amps.</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">Kent WA5VJB</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">Well ...... if the transmitter is only running a fraction of a watt, then the bent pipe would</div><div dir="ltr" data-setdir="false"> be more energy efficient.</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false"><br></div><div><br></div>
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On Wednesday, February 12, 2020, 1:35:13 PM CST, KC9SGV via Ground-Station <ground-station@lists.openresearch.institute> wrote:
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<div><div dir="ltr">Interesting requirements.<br clear="none">I would imagine that a pure "bent pipe" transponder would require less power consumption than an on-board digitizer and multiplexer add-on.<br clear="none"><br clear="none">Bernard,<br clear="none">KC9SGV<br clear="none"><br clear="none"><br clear="none">Sent from my iPad<br clear="none"><div class="ydpbce07fddyqt5663056437" id="ydpbce07fddyqtfd01610"><br clear="none">> On Feb 12, 2020, at 12:56 PM, Phil Karn via Ground-Station <<a shape="rect" href="mailto:ground-station@lists.openresearch.institute" rel="nofollow" target="_blank">ground-station@lists.openresearch.institute</a>> wrote:<br clear="none">> <br clear="none">>> On 2/12/20 09:54, Wally Ritchie via Ground-Station wrote:<br clear="none">>> At Hamcation, G4KLX and others expressed some very valid concerns that<br clear="none">>> Digital Multiplexed Transponders will not provide the opportunities<br clear="none">>> for experimentation with analog modes that are available through<br clear="none">>> QO-100's analog bent-pipe transponder. While we haven't been talking<br clear="none">>> much about this subject, the DMT can actually provide even greater<br clear="none">>> opportunities for such analog experimentation while still taking<br clear="none">>> advantage of all of the advantages of a pure digital design. How<br clear="none">>> exactly can that be?<br clear="none">> As you know, I really like this idea too. It could even be used for<br clear="none">> *digital* experimentation with different modulation and coding schemes<br clear="none">> not implemented on the spacecraft itself. But it's a rather inefficient<br clear="none">> use of downlink capacity so it should be enabled only when it is<br clear="none">> actually used.<br clear="none">>> <br clear="none">>> Using a standard 4K voice channel as an example, we can filter to<br clear="none">>> 3400Hz wide, and nyquist sample with 16 bits at 8KHz, and we end up<br clear="none">>> with a synchronous stream of 32K Bytes per second or 256kbps. Such raw<br clear="none">>> IQ channels can then be relayed in real time through the standard<br clear="none">>> quasi-error-free DMT downlink using GSE encapulation of a UDP or RTP<br clear="none">>> stream.<br clear="none">> <br clear="none">> 16 bits seems a bit (!) excessive, especially if a user wants a wider<br clear="none">> "transponder" than just 4 KHz. What's a typical uplink SNR, and what SNR<br clear="none">> is actually needed by the user?<br clear="none">> <br clear="none">> There's also my idea of having some number of uplink channels that can<br clear="none">> demodulate and digitize analog FM, compress it onboard using a decent<br clear="none">> codec (e.g., Opus) and multiplex that into the downlink stream. This<br clear="none">> would not be as flexible as a digital uplink (e.g., the downlink<br clear="none">> metadata could only identify the uplink channel frequency, not the<br clear="none">> callsign of the user) but it might appeal to people who still want to<br clear="none">> keep an analog "feel" in the system, like a squelch tail. Maybe an<br clear="none">> analog FM uplink transmitter on 5 GHz would be easier to construct than<br clear="none">> a digital transmitter, though it would probably require more uplink<br clear="none">> power to close the link.<br clear="none">> <br clear="none">> The same thing (digitization with Opus before inclusion in the downlink)<br clear="none">> could be done for *any* analog voice mode uplink, including linear SSB<br clear="none">> for anyone still crazy enough to insist on it for that wonderful "analog<br clear="none">> experience". And there probably will be some challenges like frequency<br clear="none">> stability. This would be more economical than a pure uncompressed "bent<br clear="none">> pipe" mode, but it would be an attribute of the virtual transponder<br clear="none">> instance when it is created.<br clear="none">> <br clear="none">> But as far as the downlink is concerned, we're two decades into the 21st<br clear="none">> century. It should be 100% digital, period.<br clear="none">> <br clear="none">> Phil<br clear="none">> <br clear="none">> <br clear="none">> <br clear="none">> <br clear="none">> <br clear="none"></div></div></div>
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