Disqus - Latest Comments for rpspeck

Re: CHANGES

rpspeck — Wed, 15 Jul 2009 11:50:45 -0000

If you are locked into NASA thinking, the idea of WALKING up Mount Everest is very "Unrealistic". Yet for at least 55 years, that was the only way its peak was reached!

Re: Control and Telemetry in a Phase Locked RF System (1)

rpspeck — Mon, 27 Apr 2009 16:33:45 -0000

Software has the ability to hide many things in systems - without really changing the underlying physics. Yes, I use a lot of embedded software systems, and the results are often impressive. But software is also good at hiding what is going on when things aren't working.

"Phase Coherent" 4, 8 and 16 channel UHF receivers, like those we have been building for our own use, aren't really easy to buy or inexpensive. Nor are the dynamic mixers to optimize a signal with changing polarization and phase relationships (approaching AESA performance).

In this series of notes I have been introducing the physics beyond advanced applications, and the AWESOME navigational performance which can be obtained in a good system.

In addition, I am describing performance that can be achieved in a few grams of pico-sat subsystem.

Re: More Navigational Uses of RF Phase Shift

rpspeck — Fri, 24 Apr 2009 17:45:25 -0000

I have personally observed 10 nanovolt 50 Ohm RF signals with a 0.5 dB noise figure preamp in "single sideband" CW mode (0.01 microvolt). This is not unreasonable with <1 nanovolt/sqrt(Hz) noise level for the front end (300K source temperature), but implies about 100 Hz bandwidth for my ear at the optimum tone frequency. The 50 Ohm 0.01 Microvolt RF would be -147 dBm.

Few people are talking about 100 Hz bandwidth, but I have achieved signaling with much lower bandwidth using synchronous detection - which is inherent in the phase locked modes. Data rates would be limited, but 100 Baud actually requires less bandwidth than this. SMAD (Wiley J. Larson) lists 300K, 100 baud, 0.01 uV RF with an OK (10^-3) Bit Error Rate, even without error correction.
(Eb/No = 6.8 dB)

I did not suggest that this would be accomplished with a dipole receiving antenna. I was just looking at a 14.4 dBd, 70 cm Ham antenna. Four of these would provide a very nice tracking array. Using dynamic mixing to combine these signals, a net gain of >20dBd would be available. If each was modified to Cross Element configuration, and the resulting 8 RF signals properly amplified and processed, dynamic mixing of the cross components would accommodate Faraday and mechanical rotation with little loss. These antennas might also approach 30K “Galactic Noise”, and see an additional 20dB S/N improvement as a result.

This is 20 dB better than the signal you computed (which I agree with, except for <100% antenna efficiency – possible 50%), and 40 to 60 dB actual Signal/Noise. (With a 10 milliwatt transmitter, we could be talking about communication from the Moon.) My Phase Accuracy assumes a good S/N, but averaged to 1 Hz bandwidth. One degree phase accuracy (1/60 radian) needs S/N Voltage = 60x in its effective bandwidth, = 36 dB with 1 Hz, or 16 dB S/N with 100Hz bw.

No, this is not a simple receiver system. Yes, this is exactly the kind of hardware I have been building, and to an extent using for our rocket flights.