On Jul 10, 2010, at 7/10 2:57 PM, Joe Subich, W4TV wrote: > If one were going to provide digital output, it would be far better > to stream the raw in I/Q data from the DSP's ADC via firewire rather > than push it through two additional A/D and D/A steps and reduce it > to a single channel of audio.
FireWire is not necessarily a great solution either. It will definitely require special drivers at the computer end (viz, the Edirol FA-66 that is common in ham SDR circles). One good connection that I have come across is S/PDIF that is available on the Icom IC-7800. It allows a connection between the radio and the computer that is completely non-galvanic. No ground loops, no RFI, down to -144 dB. S/PDIF provides an audio path with up to 20 bits of resolution (about 120 dB, with 1 bit being 6.02 dB), with 24 bits being an option by using the extra 4 steering bits as data. The standard sampling rate for S/PDIF is 48,000 samples per second stereo, which would support almost 50 kHz of bandwidth on an baseband I/Q channel. S/PDIF provides up to about 30 feet separation between equipment. Both Firewire and S/PDIF lacks a standard way of passing control/ status signals. The Flex-5000 (which uses FireWire) used to hack into the MIDI (Musical Instrument Digital Interface) channel for control/ status; but I have not been following that development and it might have since changed. The Icom IC-7800 goes through its regular CAT path (RS-232 or CI-V, you get to choose, I believe). In any case, if you want a rig like the K3 to support 123 dB of dynamic range I/Q output, it will not come cheap. The Asahi AK-5394A is probably the most expensive component in the front end of the Flex-5000, and you have to be very careful with the circuit layout to get a -125 dB noise floor when mixing analog and digital components. We are definitely not talking about 16-bit codecs like the one in the SignaLink USB -- which by the way, is a TI/Burr-Brown PCM-2902, and it is not the $20 that people have been mentioning, but is $5.85 at DigiKey :-). 73 Chen, W7AY ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
