by Joe Otten WD8PNH  
> MARC December 1993/February 1994 

This project was originally disclosed to Dick Hughes, W6CCD in 1993. At the time, MARC members were looking for the ideal interface, and this looked like it might be it. Joe also provided a follow-up to the original data to clarify some points. This, along with an article by Gary Haynes, N0VPN follow the nuts and bolts of the circuit. The articles have been modified somewhat to bring them up to date.  

Full integration has not proven popular with most MARC members for a variety of reasons. An examination of Joe's circuit, however, may provide ideas for use in your own application. The following was the original circuit diagram provided to Dick by Joe.  

The interface is really quite simple. It parallels the signals the CB uses at the harness plug on the rear of the CB radio. The key is knowing "what pins do what." Here is an attempt to draw the connector. This is the front view of the connector as it plugs into the rear of the radio. With the locking lever on top, the connections are as follows:

Now, let me explain this a bit further. The power connections on the left are mentioned for reference. It isn't needed for the interface, and certainly should NOT be used to power the HAM radio. If your radio has any appreciable output power you need to wire it directly to the battery. The 2nd wire from the right on TOP is the "first stage" output of the intercom. You should see a shielded cable here. (Bottom is the shield) This is the audio signal that will feed the mic input on your HAM radio. This MUST be done via a 600 ohm isolator xfmr. The HAM radio side of the xfmr should be run ACROSS a 10K pot, with the wiper feeding the mike input to the radio. This of course allows you to set the TX audio level. The 3rd wire from the right on TOP is the "input" to the sound system audio amp. The speaker output of your HAM radio will feed into this wire via your isolation xfmr (and routing switch.) The 3rd wire from the right on the BOTTOM is the 2nd stage "input" to the intercom. This is the amp that delivers audio to the headsets. The speaker output of your HAM radio will feed into this wire via your isolation xfmr (and routing switch.) Now for the schematic.....

As you can see it really is very simple, and there are no active components (chips or transistors) to worry about. The isolation transformers are absolutely mandatory to keep out the alternator whine. I originally had a separate PTT SW for the HAM radio, but the SCAN control depends on the UP/DN buttons on the mic, so I decided to port the CB controls to either radio via the 4PDT Switch. It is also MANDATORY to switch the common GND for the control switches. You must maintain total GND isolation to keep out the alternator whine.  

The connections for the control switches are half way up the handle bar. I mounted the interface board near the CB, and remoted the switches to the panel between the handle bars. I am using a Yaesu 5200. Using the optional remote mount, I mounted the head just behind the "hump" that houses the optional HONDALINE fader control for the rear speakers. This really worked out SUPER nice because, not only does the "hump" hide the bracket for the Yaesu, it gives it a more symmetrical look with the bike. It really looks Like the Yaesu belongs there. This "hump" also provides a wonderful mounting place for a touch tone pad! It's real handy being able to "patch" from the bike!  

The antenna is a Diamond NR-770RA. I was told the "NR" meant "non radial and the "A" is for "American." It folds just above the base. A friend had some "L" brackets fabricated for me, and I mounted it at the peak of the trunk lid between the backrest cushion and trunk lid. This centers the antenna between the other two, again giving it a nice symmetrical look. The antenna rises only a few inches above the other two, and provides the height and much needed gain that is lacking in a situation where there is little ground plane.  

The body of the radio is small enough to fit in the faring just in front of the pocket, although one of my friends has mounted his in one of the side compartments. His thoughts are that the moisture of the outside air might affect the radio since the radio has "vented" covers. My concern is the lack of ventilation in the side compartment. The radio will get warm! I reminded him that the CB is also located in the faring. Well, I think I covered everything!  

Joe - W8PNH   
  

Jan 7, 1994  

Hi Dave and Ray. I've been meaning to send a letter to the club, and the December newsletter showed up in my mailbox. The holidays and other projects took a higher priority of course. I was quite surprised to see a reprint of my letter to Dick Hughes (W7LVA) in the newsletter.  

First of all, the reprint expressed my efforts as an "IDEA", as though it had never been tried. Rest assured that there are a number of 1500's in the Cincinnati area using this circuit. As simple as this circuit appears to be, it indeed took some time and patience to "boil it down" to this design. The two biggest problems were to figure out the actual wire connections to the bike, and then to eliminate the alternator noise.  

The schematics for the sound system are virtually "un-obtainable" from Honda, so after many hours with the O'scope, and a fair amount of experimentation, BINGO! It's simple and works quite well, with no active components to fail on the road! This circuit is not without its drawbacks however. The main drawback with this design is that both the driver's and passenger's mikes are "live." This is due to the fact that this design borrows the intercom circuit to drive the mike input on the HAM gear. (Both mikes are always live on the intercom.) On the other hand, if the co-rider is interested in participating in over the air communications, it's pretty handy. My wife has her general ticket, so it's not a problem for us. She even has her own PTT switch for it. The other drawback is that it also feeds the intercom circuit with audio FROM the Ham radio. Depending on what the co-rider wants to listen to, it could be a problem. Then again, the situation is the same for the CB radio!  

There have been variations on this interface, some of which employ relays and additional switches to reroute the audio to the driver's helmet ONLY when desired, thus solving this problem. Another future enhancement to this interface was to be a VOX circuit to drive the "MUTE" control in the sound system. This would allow the HAM gear to MUTE the stereo the same way the CB does. I later decided it simply wasn't worth the effort. Whenever I'm engaged in conversation on the radio, the stereo is usually turned down or off anyway!  

There is also a considerable amount of interest in how to go about interfacing to a GW-1200. I wish I could be more helpful to those interested, but I have no experience with the sound system on the 1200. I understand it is quite complex, and I simply do not have the time or incentive to get involved with it. I do believe however, that the same interface would work if the proper connection points could be identified. As I pointed out in the letter, on the 1500, the isolation transformers are MANDATORY to keep out the alternator noise. I assume the same might be true for the 1200.  

Joe 
  

Joe, Dave, Ray and the rest of the MARC gang...  

I just finished the installation of the Audio/Ham interface that was diagramed by Joe Otten, WD8PNH. Here's some added information on how I did the job.  

The parts are really simple to get. Just hit Radio Shack. Here's the parts list:

You also need a small piece of perf board to mount the components on.  

I did not use the SPDT switch because I only wanted the audio from the ham radio to go to my headset. If you want to switch the audio you will need the switch. I mounted the components to the perf board and used some small hookup wire from the component side for leads.  

Removing the left fairing pocket is easy and you can see the connector on the CB. It has a plastic boot over it. Slide the boot back and you can press the release pin to pull the connector out. I then slid the boot back and scraped a small area off each of the hook up wires. I used some small hookup wire, tinned the ends, wrapped it around the bare area, and soldered it on. Then electrical tape the splice and you can put the connector back on and replace the boot.  

The spliced wire is connected to the short leads off of the PC board. I use a Kenwood TM-741A and had already run the mike extension cable from the trunk of the bike where the radio is mounted. Using a piece of telephone wire with the appropriate RJ connector on the end, I hooked in a remote PTT and the 741 mike audio-in connections. The 741 speaker output is on a separate jack on the radio, and that was wired to the connectors on the PC board.  

Since the PC board is only about 1 inch by 1-1/2 inches, I just covered the bottom with some duct tape to keep the exposed connections from shorting out, and tucked it back into the fairing pocket. Then I reinstalled the pocket.  

The system works fine. The only complaints that I get are that the audio sounds muffled, and there is a small whine. I plan to talk with Joe to see if there is a way to improve the audio, but since it is going through an audio transformer I don't know if it will get better.

Total time on the project was about 3 hours. An hour to make the board, and a couple of hours putting it on the bike.  

Hope this helps, and I would like to hear feedback from anyone else who has tried the install. It sure is much nicer this way rather than my previous way which only let me use the 741, and not be tied into the rest of the audio system. Too bad that J&M couldn't come up with a small device that would do all of this a little easier.  

73, Gary Haynes N0VPN