alioth wrote:
I’m kind of surprised that no one in the homebuilt/experimental scene has built an SDR based avionics tester, based on something like the LimeSDR or Ettus USRP.
That’s more or less what SunAvionics tester is.
In addition to that, someone here on EuroGA built a tiny (~ 6×6 cm) VOR signal generator and was showing it at one of the first fly-ins. @Peter, do you remember who did it?
Yes; it was Tomjnx (he wrote the original Autorouter code) but he vanished along with Achim a few years ago 
I still have it here. It was quite useful, although the output level was indeterminate.
As I posted earlier, it is easy to make a basic transmitter. The challenge is to do an attenuator well, because at high attenuation ratios the leakage from the input to the output is bigger than the output. So you have to build different stages in separately shielded compartments. The simple testers are useless for picking up things like bad cabling or bad connections.
Generating the waveform is trivial. There are loads of DDS chips out there.
The other thing is that “nobody” will buy it unless it is calibrated, and that is a whole new dimension.
Then there is the view, relevant if you want to build a commercial product IMHO, that not many will buy it unless it also does DME, transponder (incl. Mode S) and ADS-B and that is a whole load more work than just generating some RF signals. My feeling is that the main market for a DIY tester is in the American homebuilder community (the European one is almost entirely VFR and doing short local flights) and they are having to comply with ADS-B so at least you would have to do that one.
@Peter, yes, but even an uncalibrated basic widget may be used as a supplement to the SunAvionics box for testing the glideslope indication on EHSI: you first test the LOC with the calibrated box, then use this board to keep supplying the LOC signal when you switch the main box to GS.
I can’t disagree, but my experience in business in general is that most people look for “convergence” and they are willing to pay extra for it.
And “convergence” in this case is a whole load of work
The parts cost in an IFR4000 (list price say 15k) is probably a few hundred. The rest is a premium for the hassle which a competitor would take on to make something similar. The original IFR4000 was done by a firm which had all the technology in-house (signal generators, etc).
Ultranomad wrote:
@Peter, yes, but even an uncalibrated basic widget may be used as a supplement to the SunAvionics box for testing the glideslope indication on EHSI: you first test the LOC with the calibrated box, then use this board to keep supplying the LOC signal when you switch the main box to GS.
This is what I’m going to do. Buy sun and keep 401 (uncalibrated) for loc/gs testing. Anyway 401 seems to be nice unit – I start to like it and it will be nearly always possible to fix it..
Ha, simultaneous loc+gs alive :)
