[RTTY] Digital Mode Interface Design

Fri Apr 23 14:55:33 EDT 2004

Les G3NFP Said:

Are you going to share the details of your well designed interface?
By the way most PSK operation in Europe takes place around 1838.15 as we  
have no access to frequencies below 1810.

Presuming that you mean me here's the deal with my homebrewed digital interface. I used the circuits found on WM2U's excellent PSK31 website at: http://www.qsl.net/wm2u/psk31.html .

First of all I used real RG-174 for the cabling and soldered on metal cased connector plugs and jacks. All the cabling goes through three split beads on each end of the cable. All components are soldered onto a circuit board and placed in an shielded aluminum enclosure. The components themselves came from Mouser Electronics, not the Radio Shack junk. Between the fixed audio out from my Yaesu FT-840 to computer soundcard input I used a 1:1 isolation transformer and variable potentiometer, same with soundcard output to rig mic input. My FT-840 does not have VOX so I also had to build a PTT circuit between the 9 pin serial port on the computer and mic input plug. In this circuit I used an opto-coupler. 

This interface works very well on PSK31, MFSK16 and RTTY. I'm able to run 100 watts with a very narrow clean PSK31 signal, better then a -30 IMD and good on air reports.

Also my radio station and computer are well grounded to prevent stray RF problems. The ground system consists of four one inch diameter ten foot long copper water pipes spaced 12 feet apart, plus thirty two sixty four foot radials on the ground, plus one 1/4 wave radial for every band between 160 and 10 meters. The antenna is a switchable 160-10 meter doublet/tee vertical up at 40 feet and fed with 450 ohm window line to a balanced antenna tuner.

As far as digital DXing on 160 meters I realize that many other countries can't operate below 1810 kc, so operate around 1838 kc. But with the recent tensions on 160 meters here in the U.S. over failed band plans, I would not want to operate around 1838 kc. Split would be the way to go, plus it's probably to late now for any reliable across the pond PSK31 operation until next winter due to rapidly building QRN levels. However MFSK16 and the new mode PSKFEC31 might work?!

73 & GUD DX,
Thomas F. Giella, KN4LF
Retired Space & Atmospheric Weather Forecaster
Plant City, FL, USA
Grid Square EL87WX

SKYWARN Observer # HIL-249
SWFWMD Observer #574
PODX 070 PSK31 Member #349

Yaesu FT-840 & PSK31 News Group http://groups.yahoo.com/group/yaesu_ft840
10 & 6 Meter Propagation Beacon Network http://www.PropNET.org 
Solar Space Weather & Geomagnetic Data Archive http://www.kn4lf.com/kn4lf5.htm
HF/MF Radio Propagation Theory Notes http://www.kn4lf.com/kn4lf8.htm
160-10 Meter Amateur Radio Resources & More http://www.kn4lf.com
Florida Space & Atmospheric Weather Institute http://www.kn4lf.com/fsawi.htm

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