Howard White wrote:
> I ran parallel testing a while ago with virtually every interface
> then on the market in trying to discover an interface to standardize
> on for our Emcomm Group.
>
> Two different but indentical computers, in parallel, two different
> interfaces, connected to the same radio.
>
> RigExpert and External Sound Cards would decode signal about 6db
> to 10 db better that those using the internal sound cards...we
> could copy signals 100% on RigExpert, etc when devices such as
> RigBlaster no longer copied anthing.
>
> We finally traced it back to the fact that the internal sound cards
> lived inside a very noisy environment inside the computers... even
> using an external sound card, greatly improved the results....
Unfortunately, your test was not properly designed or conducted.
If you simply paralleled the audio feed to the sound cards -
particularly if you were feeding the sound cards from Icom radios
with 100 mV/50K Ohm outputs - you were could not have possibly
provided the proper drive levels to each sound device to guarantee
optimum performance.
Yes, an internal sound card CAN have a higher noise floor than
an external card particularly if, like the DIGI KEYER, the external
sound card uses a properly filtered supply, does not include any
noisy DC to DC converters and uses a high stability voltage
reference for the codec. However, almost every codec on the
market is capable of handling inputs of nearly 5 v p-p. If the
input audio is properly impedance and level matched to use the
full dynamic range of the codec, the noise floor will still be
down some 70 to 80 dB. That will be below the effective (quiet
band) noise level of the receiver ... with AGC in the RF and IF
stages as well as DSP demodulation, the best of today's amateur
receivers have only 50 or 60 dB of variation in their detector
output.
Any quality 16 bit codec will have 87 to 89 dB of dynamic range
(noise floor to clipping) ... the difference in performance is
the way the designer gets the audio to the codec. If the levels
and impedance are matched to take full advantage of the available
dynamic range, the effective dynamic range will be very close to
the maximum available from the chip. If on the other hand the
power supply is noisy and the audio levels are mis-matched (two
devices with different input impedance paralleled with no
attention to insuring equal and proper drive levels), it would
be easy to see only 50 to 55 dB of dynamic range.
> So yes it does matter... and at that time we standardized on the
> RigExpert.
Again, it would not matter if the internal sound card were driven
with the proper level. The 100 mV @ 50K drive of many amateur
radios gives up nearly 25 dB of codec dynamic range right out of
the gate.
> Obviously I am hoping the new microHam device has a 48KHz or
> faster clock and I am intrigued by the statement that it does
> not need special drivers....
Yes, the codec supports 48 KHz for both transmit and receive.
It complies with the USB sound standard and is recognized as
such by WindowsXP, Apple OS 10 and LINUX. Any application
that will work with the native sound capabilities of those
operating systems will be able to use the sound capability
of DIGI KEYER without any special drivers.
microHAM Router provides Virtual Serial port support (for PTT,
CW, and Squelch) in Windows. Macintosh support is build into
MacLoggerDX and an independent third party developer is doing
LINUX support. Cooperative arrangements can be made with
qualified developers who have valid reasons for direct access
to the DIGI KEYER (or microKEYER and CW Keyer) internal MCU.
73,
... Joe Subich, W4TV
microHAM America
www.microHAM-USA.com
Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org
Other areas of interest:
The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/
DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion)
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