It looks like several radios have built-in "sound cards" that are
available by a USB connection. In principle this should be
essentially the same thing as the Flex flex is doing--no analog audio
line to the radio. I have no idea what the interface is like, what
the quality is, or to what extent you can mess it up, but a bit of
internet searching and browsing through manuals indicates that this
is something that people really haven't looked into very much, even
in the world of PSK31 and other digimodes.
The USB "sound cards" in the current crop of rigs are nothing more than
a standard USB CODEC like one would find in any external USB sound card
fed into the balanced modulator. Some rigs use a switch to select the
mic "chain" or USB sound card, others simply parallel the two inputs
with nothing more than a pair of "summing" resistors.
Using an internal USB sound card is certainly *not* an "add digital"
solution. It is just as important with the built-in sound cards as
with the external interfaces to use good proactive to keep drive
levels to the proper level and avoid external sources of common mode
RF/hum/etc.
73,
... Joe, W4TV
On 1/15/2013 2:02 PM, aflowers@frontiernet.net wrote:
Salvo brings up an interesting point when it comes to generating FSK.
(Incidentally, one of the "narrow" examples on the webpage happens to
be a Flex 5000 and with an Alpha 8410 running about 1000W, using
MMTTY.) To my knowledge, the Flex 1500/3000/5000 architecture has no
on-off keyed FSK line--if you want to send FSK you can do it with
software-defined audio tones and a "virtual audio cable" through the
firewire connection. The interesting thing here is that the "AFSK"
is generated in the radio and there is no analog link between the
software defining the modulation waveform and the conversion to RF.
The entire "audio" chain from PC to RF is digital, so you won't get
RF distortion in the audio and it becomes much harder to "overdrive"
the radio, particularly if the Flex/PowerSDR is smart enough prescale
the levels (I have no idea if it actually does this). In some sense
it's really "faux-AFSK".
I have not been the transceiver market recently, but I decided to
look around to see what has changed in the last 5-10 years as far as
interfacing for digital modes. The Flex architecture is not unique
in having the potential for this "faux-AFSK" model. It looks like
several radios have built-in "sound cards" that are available by a
USB connection. In principle this should be essentially the same
thing as the Flex flex is doing--no analog audio line to the radio.
I have no idea what the interface is like, what the quality is, or to
what extent you can mess it up, but a bit of internet searching and
browsing through manuals indicates that this is something that people
really haven't looked into very much, even in the world of PSK31 and
other digimodes. Perhaps its just so common that nobody mentions it?
The higher-end Icoms even have S/PDIF in and out. Not only can you
not "overdrive" the S/PDIF input on the radio (I don't what is
downstream in the radio that you could still mess up, however), but
the RF isolation on a 3-ft TOSLINK cable is supurb below 300 THz :-)
This is of course in addition to radios that provide filters and
prescalers for (legacy?) analog audio inputs. The K3 and some others
already have features like this specifically for AFSK-RTTY. In any
event, line-level inputs are pretty much standard on every radio in
the last 10 or 15 years. (Why anyone would use a microphone input
when there is a line-level alternative is crazy to me, but it doesn't
help that the manufacturers are currently endorsing this in their
manuals). I guess my realization is that "AFSK", as we tend to call
it, has the potential to be much safer than it used to be five or ten
years ago, at least with some of the more recent inovations. That
said, I'm sure there are definately still some wrong things one can
do.
Anyway, these just some thoughts that Salvo triggered. Is anyone out
there using SPDIF or the radio's internal soundcards for RTTY or
other digital modes? I'd be interested in your experiences, be they
good, bad, or ugly.
Regards,
Andy K0SM/2
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