Re: USB 2.0 Streaming through SMA

On Jan 30, 11:48 am, "bkama...@xxxxxxxxx" <bkama...@xxxxxxxxx> wrote:

The voltage swing should be about 0.6V. The module does not really
expect a specific protocol, it will just stream any data signals that
are sent through the SMA interface. The module consists of a wireless
transmitter and receiver.

So what you are saying is you have a radio transmitter with a high-
bandwidth analog "modulation in" jack and a radio receiver with a
corresponding "modulation out" jack.

You will still need to answer some questions though - for example, are
you good down to DC, and up to what maximum modulation frequency?
What kinds of distortions can be expected?

At this point, we are just trying to demonstrate a streaming link.
(not really concerned about error checking or data integrity) Is it
possible to bypass the handshaking process and other initialization
procedures associated with the USB protocol and just send out data at
highest data rate. Wouldn't this mean non adherence to the USB
protocol. Are there any other alternatives, or is there some way we
can just use the physical interface of the USB to stream data?

As you've rightly noticed, USB is a bidirectional protocol involving
handhaking. Simply replacing the wires with your radio boxes is not a
very good way of doing things. Yes, I'll admit I once ran S/PDIF
digital audio directly into and out of a pair of video sender boxes,
making only a gain adjustment... but unless the digital signal already
has a fairly robust signaling scheme that's not a good idea.

To do what you want to do right, you need a device on each end which
talks USB to the computer, and then talks a more air-channel-
apropriate one-way signaling scheme that you can run over your
radios. In other words, what you need is a high data rate modem such
as might be used for satellite or microwave communcations.

If I had to do your project in a hurry, with little concern for
getting it right, I'd ditch USB and try hacking up some 100 megabit or
gigabit ethernet cards. You'll want ones with fully open drivers,
because you will be needing to convince the trainsceiver chips to go
right into the high data rate signalling, despite the abscence of any
handshaking to set it up. One way communications on 10 megabit
ethernet is pretty simple, even going through the full operating
system driver and protocol structure. Doing it faster means you have
to persuade the ethernet boards to run at their high speed without
first negotiating their way up form a lower one. Of course you might
run into other unforseen issues.

Really, you need high rate modems... purchased or kludged together.

.

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