The basic system in configured around a interface circuit board sold by WB2REM. I purchased this unit in a kit for the amount of $4Ø with $6 shipping.

In order to make a compact interface system, I mounted the board, and audio circuits, inside of a Astron 12 amp. power supply, and I mounted a Yaesu FT-51ØØ radio to the top. The only cables connected to the radio/power supply, is the antenna, computer serial cable, sound card mike, speaker cables, and the computer sound amplifier input cable. I have installed controls on the power supply to switch the radio speaker, and the computer speakers on or off, as well as to set the audio input level to the radio.

I wanted to minimize cables and equipment parts in my QTH, so I decided to built the interface and radio all in one unit. I purchased an Astron 12 amp. desk top power supply with built-in speaker.

The reason for the internal speaker is that I wanted to be able to switch the Yaesu and the computer speakers on and off from the power supply without making mods to the radio.

I connected 2 shielded cables to the mike and PTT connections on a 8 pin din plug to interface to the Yaesu mike socket. These cables, as well as the Yaesu external speaker cable, were routed into the Astron through the grommet the internal speaker wires originally came through.

After removing all the connectors and LED's from the interface board I mounted it at the rear of the Astron using the serial connector as a mount. I had to remove about 1/16 of an inch of PC material from the board in order for it to mount square.

Cutting the serial connector hole was probably the biggest part of the whole job. Using a small drill, and many holes later, and cleaning it up with a box file did a nice job of it.

I opened the Yaesu radio and disconnected the internal speaker. I installed a toggle switch on the power supply to disable the Astron internal speaker and connected that speaker lead and the Yaesu external speaker cable lead to the interface card.

I installed two 1/8 inch stereo, and one mono audio connectors on the Astron rear panel and a 5K ohm pot and a DPST toggle switch on the Astron front panel.

The mono connector is for connecting to the PC mike input cable lead, it is connected to a single shield wire which runs to the interface board PC mike input.

The first stereo connector has 2 shielded wires, and they are connected to the PC Speaker toggle switch, and also, connected in to each lead, are 2 each 68ØØ ohm resistors, the other side of which go together on the hot side of the 5 K level pot. The shields connect to the low side of the pot, but not ground.

The other side of the PC Speaker switch connects to 2 more shielded wires that go back to the other stereo connector on the rear. This connector is for the computer speaker amp. input cable. Be careful not to ground any shields except at the stereo connectors.

I had some problems with AC hum, because of the proximity of the power transformer. To solve this I added a Radio Shack 6ØØ ohm, 1 to 1 ratio, audio transformer in the mic line. No grounds on this either. The output winding is connected directly to the mic line of the Yaesu.

The input side of the transformer connects to the Mod Level pot. center arm and cold side. Using shielded wire, No grounds.

I mounted the audio transformer by inclosing it inside of copper straps, one with a tab to mount to a speaker bolt, and soldiering it all together to completely shield it. I mounted a small section of perfboard on top as a tie strip. This transformer was mounted as far away from the power transformer as possible.