Thanks for all the history and information Jerry. It is very interesting and I am sure others appreciate it as well.
It is funny you mention interference as that is one of the reasons I was a little surprised the uplink is on VHF. I was told there was more interference from things like cordless phones and taxis on 2 meters than there is on UHF. Obviously it is more of a problem on a single channel FM sat than a linear sat with room to move around.
Would love to hear more about why V/u was chosen.
73, John Brier KG4AKV
On Fri, Jan 31, 2020, 14:02 Jerry Buxton via AMSAT-BB amsat-bb@amsat.org wrote:
On 1/30/2020 11:52, John Brier via AMSAT-BB wrote:
Can someone explain why V/u was chosen for the linear Fox (they are all
Fox
right?) Over U/v that all the FM Foxes are?
Hi John,
While RadFxSat-2/Fox-1E is a Fox-1 series CubeSat in much of its design, it is also an "extra" Fox-1 in that only four Fox-1 were originally planned, the four FM birds.
The intent to build a 5th Fox-1 was first determined in late summer 2014, when I was contacted by Columbus High School asking to partner with us as a STEM payload on a Fox-1 satellite. After we determined feasibility they submitted a CSLI in November 2014. Unfortunately, their CSLI was not selected in that round and they chose not to go for another (at least in 2015).
The economics of ordering components in larger quantities basically created leftovers, especially PCBs, from the construction of the Fox-1 FM birds. Too, many of the components of the FM repeater had gone defunct in the years of design, development, and construction of the first four so another FM bird was not possible without a redesign of the RF system. For Fox-1E, we faced choices in how to proceed with the RF system. Drew had been suggesting a linear transponder, I took that to the team for consideration, and John Klingelhoeffer, WB4LNM, came up with the linear transponder design. Originally intended to be U/v as the others, as things progressed and we wound up having "extra time" since the Columbus CSLI was not selected, it was subsequently determined that V/u was a better choice for this bird.
The specifics of that choice of mode are best addressed by Drew as he was the protagonist on that choice.
The choice was not arbitrary, there were user input and other considerations, and the link analysis worked. I recall that urban RFI was a factor, my trip to Colombia back when (2013?) made 2m useful for about 30 degrees of the pass and it had to be above 60 degrees so I was familiar with 2m interference. I worked Hector a lot, but things got pretty bad by the time a bird got to the U.S. Signal quality was a reason as well, if I recall correctly. UHF sounds better. I was in the midst of getting Fox-1A to launch so without searching for emails, beyond those I don't have any more worthwhile recollection.
The decision to go with a linear transponder was driven by two simple facts: We needed to redesign the RF system, the (linear) reasoning was solid, and the Engineering team was capable and interested. There was enough member interest in a linear transponder to get a good ROI.
Jerry Buxton, NØJY
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