Byonics TT4: Kenwood vs Icom vs Wouxun and JP8

I received an interesting ham-radio-related query from Chuck Burton, K9CBX:

I have a new Wouxun KG-UV6D and a TinyTrak4. My TT4 is setup to work with my Yaesu FT-8800 radio. Can you tell me how your TT4 JP8 jumper is setup to work with your Wouxun HT? Just need to determine if my JP8 needs to change when I use my TT4 with my Wouxun for APRS on search and rescue missions.

I’ve never paid any attention to JP8, to tell you the truth. My TT4 just works with everything I’ve tried it with. So I got it out and did some testing this evening. First some specifics: My TT4 hardware is the pre-built version with surface-mount technology (v7.1). JP8 has a jumper on it, meaning it’s closed (it came that way). JP8 is the PTT control. The manual says this:

This jumper adds the resistor R15 (2.2K) to the radio mic line to allow PTT via the mic audio connector. It should be closed (shorted) for use with handhelds other than Kenwood. For mobile radios and Kenwood radios, J[P]8 should be open.

Most radios key via a separate PTT line, but the Kenwood is a little different. I have two cables: HT2P (Icom) and HTKP (Kenwood). (Byonics has a big chart here that describes which cable to use with which radio.)

Anyway,the table below shows the results I got. Note that the Wouxun uses the Kenwood cable, and the Icom uses a separate cable specific for the Icom. The Kenwood keys differently from other radios, and requires a capacitor in series with the audio source fed to the mic input line, as does the Wouxun, but note that in the TT4, there’s already a capacitor in series with the audio line to the radio. The Icom has a separate PTT lead and is keyed by bringing the PTT lead to ground.

Radio Jumper 8 open (disconnected) Jumper 8 closed (connected)
Kenwood TH-22A handheld Transmits normally Transmits normally
Wouxun KG-UV3D handheld Transmits normally Transmits normally
Icom IC-T7H handheld Does not transmit Transmits normally

No wonder I’ve never had any trouble. My TT4 came with JP8 closed (jumper in place). These are the only three radios I’ve used with the TT4. My results show that the manual is not wrong, but I do get satisfactory results with all the handhelds with the jumper closed. I guess the bottom line is that experimentation is required to see what works.

You can see my previous posts on using the Byonics TT4 APRS unit and the Byonics PicCon unit here, which takes you to a list of the posts. The connection of radios for packet (APRS is a form of packet) is a subject unto itself. Sufficient to say that my APRS base station uses an Icom IC-2100H mobile rig, and I ended up putting in an audio isolation transformer for the transmit audio. I hope this helps.

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