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) Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/