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 FT-51ии dual band radio and disconnected the internal speaker.

I connected 2 shielded cables for the mike, and PTT, connections to a 8 pin din plug to connect to the Yaesu mike socket. This cable, as well as the Yaesu external speaker cable, were routed into the Astron power supply through the grommet the original internal speaker wires came through.

I installed a toggle switch on the power supply front panel to disable the Astron internal speaker from the Yaesu external speaker cable, and to the interface card radio audio input.

I installed two 1/8 inch stereo, and one mono audio connectors on the Astron rear panel.

One stereo connector is for the computer audio output, one is for the external PC speakers input.

The mono connector is for the Yaesy FT-51ии external speaker output.

The mono connector is connecting internally to a single shield wire which runs to the interface board radio audio input.

The first stereo connector has 2 shielded wires, and they are connected to the PC Speaker toggle switch, and also, connected on to each lead, are 2 each 68ии ohm resistors, the other side of which go together to the hot side of the 5K level pot.

The shields connect to the low side of the pot, but not ground. The center arm of the 5K ohm pot. connects to a shielded wire to the computer audio input of the interface board.

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 6ии 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.

Two 1/8 inch red LED's were mounted to the front panel. They connect to the interface board to indicate power on the board and Echo Link connectivity.