Comments from technical review

Added by Skylar Hoffert about 2 years ago

Review was performed based on revision 74 found here: https://opendesignengine.net/projects/groundsphere3/repository/revisions/74

Updated version is revision 76 found here: https://opendesignengine.net/projects/groundsphere3/repository/revisions/76

Notes from review with Zach Leffke on December 5, 2017
Participants: Sky Hoffert, Monty Noblezada, Zach Leffke
Date: December 5, 2017
Time: 1:30 p.m.

Shoutout for an additional antenna design
- Quadrafiler Helical Antenna (QFHA) (SRQFHA)
- > Closer to circular polarization at low elevation angles (less loss)
- > Polarization harness (exotic coax impedance) is not needed compared to eggbeater
- > though this antenna is very narrowband

Comments:
Implementation loss should be in the receiver, not the transmitter

Assumed values
Receiver antenna gain should be better referenced (include "Reasonable Assumption")
- M^2 has a site
- > model # EB144
- Same for required ebno
- Same for system noise figure

Maybe define noise bandwidth a little better

Maybe another section for specific notes on values in the first test case docs

Add a reference section
- Zach (as a hobbyist) is interested in references

Equation for required ebno
- Should be minus a negative value - modify above


Replies (1)

RE: Comments from technical review - Added by Aaron Harper about 2 years ago

You are correct, but the tradeoff was that a quadrafilar (QFHA) antenna has a dip in the gain at the top (top blind), and while the antenna does have better performance at lower elevations, the free space propagation loss (FSPL) made reception at this angle largely impossible.

If a better LNA was available, such as a 2 stage unit at +30dB a piece with a sufficiently low noise figure, the dip in antenna gain at zenith would offset the reduction of FSPL, while the higher preamp gain would allow the QFHA to pull in the signals at low elevation angles. This equipment is available at 2.4GHz or higher, but at the 915MHz ISM band, which Skycube used, the preamps available were the limiting factor, as was the cost.

Anyone who wants the 90 ohm cable, email me at with the desired length. I have 442 feet available, all you need to do is cover postage.

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