Saturday, October 1, 2011

Interface (Computer-to-Radio Cables)

Interface (Computer-to-Radio Cables)

Getting Started

To connect your radio to the sound card, you'll need an interface consisting of three (3) cables, one each to handle the RX (receiver audio), TX (transmit audio), and PTT (transmit) functions. If you want to use your sound card with 2 radios, you'll need a more complicated interface. See cable2radio.htm

The basic AGWPE radio-to-computer interface is the same as one as would be used for other sound card digital programs such as PSK31 or Slow Scan TV. So, if you already have such an interface, you probably can just use that for AGWPE. (Warning: This may not always be true. For example, the standard RASCAL interface for a Kenwood TS-2000 will work for the Main band but not the Sub Band. That's because there are different RX pins for each band on the radio's ACC jack.)

You can either build your own interface or you can also purchase kits and pre-assembled interfaces.

Note for 9600 baud operations: kits or pre-assembled interfaces usually have isolation transformers on the TX and RX audio lines that do not have the correct frequency response range for 9600 baud FSK operations.

Actually, I know of no isolation transformers that will work. So for 9600 baud operations, you may be better building your own interface and omit the isolation transformers, understanding the risk involved in directly coupling two devices that may be at different voltage potentials, i.e. ground loop noise and conceivably damage to your radio or computer.
If you build your own:

Make sure you build the interface long enough to reach from your radio to your computer sound card jacks, especially for fixed position radios and computers! .. yet as short as possible to reduce the chance of picking up stray RF (radio frequencies ) or EMI ( Electro Magnetic Interference ).

Be sure to use cables with a shield in them to help prevent stray RF from entering the cables.

Use isolation transformers in the Receive (RX) and Transmit (TX) Audio cables (except for 9600 baud packet ) and an opto-coupler/photo-transistor in the PTT cable to break the ground path between the radio and computer.

At least two of the cables will need small circuits. You'll find other variations at WM2U's PSK31 site. Circuit components should be readily available at local electronics store or online. For example, you'll find some very attractive prices for components at Buck's online store.
Going beyond my simple circuits, you'll find instructions for home-brewing the "Cadillac of sound card interfaces" in the March 2002 QST, p 31. Bob Lewis describes how to build an interface for ICOM HF rigs with many deluxe features.

Also, take a look at Skip KH6YT's TX audio-triggered (VOX) PTT interface which was featured in a QST article in June 2009 (p.30): The beauty of Skip's design is that you won't need a serial, parallel or USB port for triggering the radio's PTT circuit; the TX audio will trigger it.

Special Tip: If you want the flexibility of easily switching your interface between different radios, you might be interested in this cable construction trick.

No comments: