[hpsdr] HERMES schedule question

[Ray Page]

Thank you, Phil.

I'll be on TeamSpeak tonight, but in listen mode. I have a lot of catching
up to do. I realize it's a little early to be thinking about derivatives of
HERMES, but an idea struck me as I was reviewing the HERMES design. Unless
there is a major flaw in the concept, I am willing to peruse it and fund the
project myself with the work donated to the HPSDR community.

The core of the idea is to have the option to locate the RX and TX functions
at the antenna using fiber-optic cable. The HERMES design is the perfect
starting point. It would be partitioned at the FPGA/ADC and FPGA/DAC
connections. A full-duplex 3.125Gb fiber-optic link  will carry raw ADC and
DAC (or P/E) data. There will also be dedicated control/monitoring data
paths as well. The fiber can loop through multiple RX and TX modules as
desired with only one-each selected at any given time. Otherwise, one could
populate more than one fiber-optic transceiver on the main processing board
to realize multiple concurrent RX/TX modes as needed. Both RX and TX
functions can also be integrated onto a single FO board to reduce cost.

I am very comfortable with designing custom FO data transmission systems, as
I have quite a bit of experience in this area. I already have (and own) IP
that  uses a pseudo-random, self-synchronous polynomial to guarantee DC
balance and a Gaussian noise profile. I believe that the likelihood of
interference will be greatly reduced due to the fact that the sensitive
circuits are isolated from each other by links that will have their
uncorrelated noise contribution spread over a very large bandwidth. The link
exhibits around 200ns pipeline delay plus propagation delay of the FO cable
itself. In other words, the data paths are real-time---not packet based. It
will be nearly trivial to transmit contiguous 16-bit x 130MHz sampling data
over the fiber. In effect, the fiber becomes a virtual full-duplex parallel
bus. That is exactly how the interface is presented inside the FPGAs.

The FPGA on the main board will need to be changed to a Cyclone IV -GX.
Smaller Cyclone GX's are required on RX and TX modules.

PROS
====
- Shack can be located up to 200m away from the antennas using low-cost
multi-mode fiber exhibiting the equivalent of 0dB loss. Note that the 200m
limitation is per FO hop, so a single FO pair can loop from one tower to
another if someone is so fortunate to have this problem.
- Single FO pair can select any arbitrary combination of an RX and TX module
in the chain. ie: RX on one band and TX on another.
- For those wanting to operate more than one TX or RX module concurrently,
then more FO pairs can be added back to the base unit.
- Lightning protection for the shack. Only the RX, TX, and power supplies at
the antenna are at danger.
- The FO cable itself is immune to RFI/EMI, so routing of the cable is
simplified.
- FO cable is far cheaper than large copper RF coax.
- RX and TX modules can be plug-n-play, since the control/monitoring
channels can identify their capabilities automatically.
- Monitoring includes status of each FO connection in addition to RF module
status for easy troubleshooting and performance monitoring.
- This topology is extremely flexible. Start simple, and then expand to your
hearts content (never).
- Each RX and TX module contains everything needed to connect to the
antenna. RX modules will have any required filters, attenuators, etc. TX
modules will include power amps and output filters as needed.

CONS
====
- More expensive than HERMES for a simple setup.
- More complex than HERMES for a simple setup.
- RX/TX modules exposed to weather/temperature extremes if mounted on the
tower.
- It doesn't appear that SERDES-enabled FPGAs (at least not Altera) are
available in leaded packages---only BGA.
- My bias and lack of experience as a HAM may prevent me from thinking of
another CON.

Finally, as you may be aware from an earlier post, I am testing for the
first time tomorrow for my Technician license along with my son, Carson. So,
I do not have the real-world experience of operators like yourself. My idea
is based on what I imagine my needs will be. Please feel free to temper my
ideas.

Thank you,

Ray Page
Georgetown, TX
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