On 10/9/2019 17:29, Ronald G. Parsons via AMSAT-BB wrote:

WY7AA I believe that it should be in L Band for 48 hours during the week for a period (say 3 months) and then 24 hours on the weekend for the same. Everyone gets some time with it then, and people can complain when they forget it changed.

WD9EWK With AO-51 in the past & its different configurations, it was usually left in something like V(USB)/U(FM), V/S, or L/S for a week at a time. Not just one day at a time. Made it easier to try the different configurations when they were available

If I may, this seems a good opportunity to present a little background on Fox-1 L band.

The L band uplink capability on AO-92 and AO-95 (sobsob) are in fact, an experiment called DOWNSHIFTER.  Just as we fly partner experiments in the "top" four PCB positions of the Fox-1 avionics stack, DOWNSHIFTER occupies the EXP4 slot in Fox-1C and Fox-1D.

When Fox-1C/D were assembled, the EXP4 was available as it had been on Fox-1A.  Fox-1A was of course the first flight, and it had a minimal payload because of the inherent uncertainty in any first flight.  Fox-1C consists of the flight spare Vanderbilt University radiation experiment from Fox-1A and one of the two Virginia Tech camera experiments.  Fox-1D consists of the University of Iowa HERCI experiment and the other Virginia Tech camera experiment.  In both cases, although the VT camera "peeks through" a slot in the EXP4 PCB, the EXP4 was vacant.

We were kicking around the idea of maybe flying our own (AMSAT or AMSAT Engineering) experiment of some sort in order to populate the EXP4 slot on C and/or D, after the completion of Fox-1A.  With the purchased launch of Fox-1C and D (at that time) coming up in short order we did not have a lot of time to spend looking around for ideas.  John Klingelhoeffer WB4LNM came up with the design idea for an L band uplink capability made possible by down converting the 1267.x MHz uplink signal to the 435.x assigned UHF uplink for the bird and passing it to the receiver input.  It fit the bill of the smaller real estate available due to the camera notch, the mechanical limitations of EXP4 volume (less than the other three EXP slots because of the +Z solar panel right above), the need to function with the existing standard Fox-1 antennas, and the slim power budget of the Fox-1 birds "fully loaded".  John dubbed it "DOWNSHIFTER" and we went for it.

Being less complex than an entire repeater or transponder made for somewhat faster fabrication to make the C/D deadline (C/D were originally booked to launch together on the same LV) and both birds were outfitted with a DOWNSHIFTER.

DOWNSHIFTER was/is an experiment, given the new (to the 1U CubeSat form factor) design and uncertainty of the performance of the UHF antenna at 12xx MHz among other things.  As such it was treated as all experiments are, with an overruling control by IHU and hardware that protects the bird from a runaway experiment.  Pretty much, it's called an experiment and not a system (like the rest of the avionics stack) for a reason.

For that reason we assigned a 24 hour timer to the activation of L band mode in order to protect against the bird being in L band and deaf, whether due to the antenna not being so hot at 1267.x MHz or DOWNSHIFTER failing to shift down, any malfunction that would prevent the UHF receiver/transponder from hearing a command station.  By use of the timer, if all was well then 24 hours was a good period of operation for ops around the globe and in the worst case if it didn't work, the bird would be back in UHF mode and under command control within 24 hours.  The 24 hours is required as part of the imaging device license and an FCC order to cease transmission.

We are blessed and I was totally jazzed that the DOWNSHIFTER worked quite well in commissioning on AO-92 and continues to do so.  We took DOWNSHIFTER into consideration as a point of failure in AO-95's woes and did tests exploring that.  While -95 is deaf in any of its assigned bands the 24 hour timer would protect if we were able to command it to L band which offered the designed comfort to be able to try that if it was a possible path in troubleshooting.

I will not enter into any discussion of the scheduling of L band mode or the use of any of the satellites as that is entirely up to Ops when the leave Engineering's hands at commissioning.  I did think it might be useful to give some history on the why and how of L band on AO-92 and AO-95 (sobsob) for your discussion.  Have fun with the birds whatever their mode and your style of operating, that's what makes my day!

Jerry Buxton, NØJY