[Elecraft] Good Low Cost Audio to USB Interfaces For Digital Modes

[Jim Brown]

in the last few days I've been evaluating a couple of low cost audio to 
USB interfaces for use primarily with digital modes -- RTTY, PSK, JT65, 
FSK441. My primary objective is to improve decode performance at low 
signal levels. I studied the catalogs and chose two low cost units that 
looked like they would do the job and would not have RF problems.

Here's a link to a little Numark adapter that I bought for $33.  t's as 
cute and easy as it looks.  Power from the computer, a couple of RCA to 
1/8-in cables for gozinata and gozouta.

http://www.bhphotovideo.com/c/product/639303-REG/Numark_STEREO|IO_Stereo_iO_USB.html 


The other one I bought is this Tascam unit.  A bit larger, more 
mechanically robust, mostly metal enclosure, more flexible with respect 
to levels.  The 1/4-in jacks for guitar and mic have more gain, so will 
work with lower signal levels.  $70

http://www.bhphotovideo.com/c/product/648495-REG/Tascam_US_100_US_100_USB_2_0_Computer.html 


To evaluate them I hooked them to different Thinkpads running JT65-HF 
and fed both of them from the line of a K3, then compared their decode 
performance, and also compared them with the Thinkpads' internal sound 
card.  The two new adapters performed equally well, and often produced 
almost twice as many decodes on a given pass as the the internal cards. 
Next I transmitted through them and looked at their spectrum on a P3 
hooked up to a second K3. Distortion products look minimal on both units.

I also pulled them apart and studied their construction.  Both use 
proper construction that avoids the Pin One Problems that cause RFI 
issues. Now that I'm sure that they work well, I'm rewiring my station 
to use them in place of the sound cards built into my Thinkpads for SO2R 
contesting and everyday digital operation on both HF and VHF.

Both of these units are a real bargain from well known audio vendors. 
Their interface to the K3 (and other rigs) is really simple. They don't 
do any control functions, so you still need a serial or USB to serial 
for that. I use VOX to key the K3.

Both are available from other vendors, but B&H had the best prices I 
found, and shipping by UPS Ground was free.

73, Jim K9YC