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
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 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
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
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
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
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:
||Radio Shack Part No.
||1997 Cat. Page No.
|10 mfd Capacitor
You also need a small piece of perf board to mount the
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
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