[AMRadio] HD-15 PSK Interface

Bob Macklin macklinbob at msn.com
Thu Feb 17 12:12:38 EST 2005

I was asked about this yesterday but I did not see my response show up.

I used to operate TTY back in the 60s witha real TTY machine. A Model 15.

After returning to ham radio after a 30 year absense I heard about PSK31. I
downloades WinPSK and gave it a try. I also read about making an interface
with isolation transformers.

I am a Heath collector. I decieded I could make a decent PSK interface using
a Heath HD-15 phone patch. But I knew very little about the phone patch at
the time I started. I bought a pair of small 500ohm to 8ohm audio
transformers from Ocean States Electronics.

I pulled the original transformers made to work with a phone line out and
replaced them with the small audio tranformers. I removed the nulling
circuit as it is not needed. I commected the Rx transformer with the 8ohm
winding to the speaker and the 500ohm winding going to the sound card LINE
IN. I used the switch on the HD-15 to connect the Tx output to either the
speaker or the audio transformer. I connected the second transformer with
the 8ohm winding connected to the computer speaker output. The secondary was
connected to the Hi-Z and Lo-Z outputs to the Tx. Since I have a SB-401 I
used the Hi-Z connected to the phone patch input on the SB-401. I don't like
messing with the mic input.

The HD-15 switch and level controls were connected pretty much like the
original circuit. I have the VU meter connected to the output of the Tx
level control.

I can copy PSK QSOs that I cannot even hear. I am very impressed with this
technology. It does not take much bandwidth and the cost of the software is

Bob Macklin
Seattle, Wa.


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