Wednesday, 16 January 2019

More on Es’Hail-2 sat.

After seeing today’s excellent test signals in the satellite amateur transponder passband I was motivated to dig out my 13cm SG Labs transvreter and fire it up. It hasn’t been touched in two years and never previously fired up on 2400.050MHz. That’s the start of the 250kHz narrowband uplink range, extending to 2400.300MHz.
After initial tests, using my FT817 on 432MHz, and checking all was well on my spectrum analyser I thought it might be interesting to see just what 432MHz drive levels I could use and still get useful output from the transverter. The reasoning being I wanted to use an Iceni 70cm transverter with my K3 as the drive source. I wanted, if possible, to use the Iceni barefoot i.e. no add on 70cm linear amplifier. The SG Labs transverter can stand several watts of 70cm drive, but the barefoot Iceni only generates 50mW.
I first tested with various levels with my SMG Signal generator set to 0dBm, transverter input attenuator set to minimum loss. The transverter gave +7.5dBm output. The RF Vox did not operate. As I don’t require this facility, no problem. Increasing the drive to +10dBm gave +18dBm transverter output. Finally, with +16dBm drive, the SG Labs gave +25dBm output. RF Vox worked from +10dBm upwards.
The transverter will be mounted in the shack and a coax cable will connect to the 25W output GaAs FET PA out by the transmit antenna.  The  power amplifier requires about +10dBm at 2401MHz (wideband PA) for full (saturated) output and that gives lots of room for both coax loss and an attenuator at the PA input!
It looks feasible to use the Iceni barefoot  in this application.
Of course, underdriving the transverter will result in the spurious outputs (image and any Residual LO) as well as the transmitted composite noise being effectively 10dB below spec. However with a 432MHz IF these are a long way down.
Now to box the transverter and arrange for somewhere for it to mount in the rack.


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