That is a thought, Chris. I kind of like the idea of CW, but it would still require the modulator. So would fsk for that matter. I don't think there is anything I can do in software to generate a carrier without using the modulator.
As I understand it, the transmitter does not really generate a carrier for CW or FSK. It shifts the frequency of whatever comes into the mixer to the downlink frequency band and boosts that with the PA. So we would need the modulator chip to generate the (lower frequency) carrier to be mixed up to the downlink frequency for either CW or FSK.
RF experts, do I have that right? Is there any other way to generate some sort of downlink without changing the design? We can't afford the time to design the RxTx differently. Of course the 5599 is far from the only chip that is a single point of failure.
73,
Burns Fisher, WB1FJ *AMSAT(R) Flight Software*
On Wed, Feb 3, 2021 at 12:27 PM Chris Thompson [email protected] wrote:
Burns,
Thanks for the detailed update. One item we might want to review is the modulator. It is currently a single point of failure for the telemetry. While it seems unlikely it is the cause of the issues on Fox1E, given the low transponder power, it would be nice to know that it is not in some way preventing telemetry being sent.
Could it fail over to another format if we detect an issue? If the transponder is off we could send fsk or cw without the modulator for example. That would allow some housekeeping information in the event of a failure. We would make it command able and not have some sort of clever detection circuit. Just a power down the modulator and send cw status instead.
73 Chris
On Wed, Feb 3, 2021, 11:02 Burns Fisher (AMSAT) [email protected] wrote:
It's been a long time since there was anything on this list, largely because there is a LOT in common between LTM-1 and the legacy side of Golf-TEE. But things are warming up, so here is a quick status report, partly to remind you that LTM-1 is still in play and partly to remind you that many of the Golf projects you are working on have another destination and deadline as well.
First regarding "customers". AMSAT has signed a letter of agreement with The University of Maine (Eric Skoog's alma mater, and the state university of my home state) to provide an LTM-1 for their MESAT. They recently told us that they have been assigned to a launch with a delivery deadline for the completed satellite early next year. Obviously, this puts some additional pressure on us, since they will need flatsat-level hardware shortly. There is also at least one additional potential customer waiting for us.
CURRENT STATUS
As you no doubt recall, the LTM-1 consists of three boards: The RxTx, the ICR, and the LIHU. All of these are nearly identical to what we will use on Golf-TEE (the LIHU can be one rev earlier, but probably will not be for flight). In addition, there is software for the LIHU and customers will expect documentation. Here is where we are on these pieces:
LIHU: We have two of the latest rev LIHUs populated and undergoing testing. There will be another rev for a Golf-only function, but the existing design should work for LTM-1 unless the testing finds design problems.
RxTx: There is a new design that replaces Husky/1E obsolete parts, has more and switchable RF power, and which we intend to test far more thoroughly in an attempt to reduce the risk of HuskySat-type issues. (We don't yet know if the RxTx is related to 1E's issues). Two of these boards are under construction and Eric and I are anxiously awaiting one while the other will undergo thermal testing.
ICR: There are no functional changes on the ICR compared to Husky and 1E, so existing ICRs can be used for bench testing. However, an updated design is required to replace obsolete components. This is in work.
Software: The software for LTM-1 will be a branch off the Golf-TEE software with the RTIHU coordination code removed and with a more generalized telemetry collection scheme and downlink format. As the software person, I have avoided splitting off the new branch to reduce the amount of merging required as bug fixes are made (and minor features added) to the Golf-TEE code. That will include testing the support for the new RxTx and the new LIHU.
Documentation: We will need thorough documentation (schematic, BOMs, gerbers, masks, etc etc for hardware, functional specs for software) for our customers and also because we will likely have the flight units commercially built. I assume the documentation has been done for devices that are in build, but we will want that documentation in SVN or Redmine soon.
A fair bit of software documentation is in Redmine for Golf-TEE but more is required . It will be written as part of the design for what software gets changed as we split off from the Golf-TEE branch. My current thought is to use UMe as reviewers for some of this since they are our first guinea pigs (HuskySat uses the same basic software as LTM-1 and Golf-TEE, but much of the intercommunication with their satellite was custom designed).
Continued thanks to everyone involved for all the work you are doing!
73,
Burns Fisher, WB1FJ *AMSAT(R) Flight Software* *LTM-1 Engineering Contact and Annoyer-in-chief* (Jerry feel free to give me a better title!)
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