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> Has anyone tried using modded (down to 10GHz) 11GHz Satellite TV RX & 10GHz
> ATV TX for hooking up 10Mbit ethernet ports? - that's another one for you to
> think about...
I have been studying this idea for a while now (like intermittantly for a
couple of years) and have arrived at the following conclusions:
1) Direct use of the 10base5 (the coax ethernet) is not appropriate, both
transmit and receive data paths are on the same piece of wire and the
actual signal is somewhat untidy.
2) Using the AUI interface (the 15 pin ethernet connector) is a better point
to pick, the transmit and receive data paths are separate and the signal
is cleaner.
3) Or use a 10baseT/10base5 chipset to reduce the signal to clock & data.
4) There is no need to reduce the data stream to clock and data, just modulate
the existing manchester data stream.
5) When modulating the data stream attempt to create sinusoidal transitions
rather than filtering the datastream. This is to avoid the effects of the
group delay characteristics of the filter.
Where have I got to:
1) hand wired boards that accept AUI on one side and are joined by
separate data paths, in my case short sections of twisted pair wire.
2) I use either 10base5 (coax) or 10baseT (UTP) as the mood takes me by
just changing the transciever on the AUI.
The next step:
1) build the section that produces the sinusoidal modulation signal, this
could be 1v pk output for use in an ATV transmitter.
2) build the slicer to recover the data stream from a sinusoidal signal.
3) get it working at 6" over two bits of coax.
4) get it working over a link consisting of ATV transceivers or some other
form of 10GHz link.
Why have I not done it:
1) young family,
2) changing jobs,
3) lack of test equipment.
The fun and other bits:
1) creating the sinusoidal modulation signal, the data stream is 10Mbit/sec
to get a good enough sine wave I estimate that 8 samples per transition
are needed. This indicates a clock of 160MHz.
2) It may be possible to use a lower clock rate by using both edges of the
clock wave form but it still needs 160MHz to obtain a 50% duty cycle,
but the bulk of the logic is then running at 80MHz.
3) It may be that 4 or 6 samples per transition is sufficient, again
reducing the clock requirement.
4) Most of the 10baseT/5 chipsets use clock & data at the input/output,
so synchronising the transition smoothing to the data clock is going to
be an interestign exercise.
5) Achieving the UK id requirement will disrupt the data flow. However when
I informally asked the question of the UK Radiocommunication Agency the
response was "when you are ready come and talk, there may be a compromise"
6) With some ethernet boards it is possible to change the Ethernet address
(MAC address) this could be changed to be your callsign in ascii,
provided your callsign is 6 or less chars in length.
All the above assumes 1 bit per symbol and my guessitmate of bandwidth is
about 50MHz i.e. carrier +/- 25MHz.
Long term the signalling rate needs to be brought done, i.e. keep the bit
rate up and bring the symbol rate down (more bits per symbol).
Basically I lack test equipment and time. If someone can use the ideas then
all I ask is to be credited with the bits I have had a hand in.
Given time I hope to produce a design that could be built by an amateur,
but it is going to take me years.
> You need an ethernet adaptor with BNC o/p. The o/p levels will need to be
> converted to 1v peak to peak (as per Composite Video). Feed this into your
> ATV TX (with no pre-emphasis or filtering), and at the RX, pick up "baseband
> video o/p" from the "SCART" connector. Convert that back to normal levels
> (which I think are around the TTL area), and feed that back into your
> ethernet adaptor. A T-piece is needed at each end, or you can spilt it at
> your level converter.
> Sounds simple. Should work. Anyone got the time to give it a go?
>
> Back to reality....
Never left it.
> How does this 300bd modem work????
slowly :-)
What a screed. Anybody biting, the bait hasn't got a hook in it, honest.
--
Regards
Richard
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Amateur radio callsign: G1SOG Home BBS: G1SOG@GB7SDN.#49.GBR.EU
Amprnet co-ordinator for Wiltshire
My opinions are mine, all mine. None to spare for unopinionated masses.
This message comes from a WinTel free zone. CPU = Cyrix, OS = Linux.
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