- Intercom between two bikes -

(By René Dame) - This is about a means of communicating between two motorcycles. You can buy systems from Baehr but these are expensive. For two sets from Baehr, one for each bike, you'll easily pay NLG 1800,00. A cheaper solution is the one from Henk Oskam for about NLG 1300,00. For a lot of people that is still a lot of money. I won't say that thes systems are to expensive. They will most likely be worth the money.

I started doing things my way. The main thought was to keep it as cheap as possible. Second thought was to keep it simple. So for about NLG 250,00 per bike you should be set to go. And even for an electronics-no-no like me it is easy to assemble.

My idea is that the system is not mounted permanently on the bike, but it is put in a tank bag or something similar. The CB takes up little space and it may even fit in the card holder of your tank bag. I think that you only have a need for communication if you prepare for a day- or weekend-trip. When you finished packing, putting the CB on the bike only takes minutes extra. If you prefer a permanently mounted system please feel free to find a solution. Following is the description of how I did it.

What you need
philips screwdriver solder iron + solder
needle nose, cutter, stripper ohmmeter
spanners glue
hobby knife drill
fret-saw McGyver-instincts
Material: (from CONRAD mailorder)
CB radio 20.05.30-11 119,00
CB antenna 26.07.70-11 70,00
switch 3-contact 70.31.33-11 7,00
microphone holder MD33 30.21.39-11 14,00
3,5 mm. mono jackplug/cable 73.44.54-11 1,50
3,5 mm. stereo contra-jackplug 2,00
90 degree antenna plug 74.10.60-11 4,00
enclosure 52.23.33-11 1,75
Material: (bv. from model-shop)
AMP conector (male + female)
Aluminum plate/hoeklijn (for antenna and box)
M5 bolt, nut and wing-nut
Total 10,00
Material: (from audio-shop)
headphone 3,5 mm jackplug (no earplugs) 25,00
Total cost estimate (NLG) 250,00

So, I started with a standard CB radio (in Holland that means 40 channels and a 4 Watt maximum output power). That is by the way no different from what Baehr and Henk Oskam use. So as long as it is standard CB you're OK. You could of course use an older CB from the dusty corners of your attic but that will most likely be bigger and bulkier and maybe not have the same output power as the CONRAD CB. And the price will not be the problem here. I assume that everybody knows how to operate a CB radio.

You can also go for a cheaper/other antenna but that will most likely be longer and heavier. The antenna mentioned is only 33 cm long, featherlite and mounts easy on a bike. And it can be unscrewed from the bottom.

In general it goes like this:
From the CB you have the curly cord (without the hand mike) and a cable for the external speakerset (on the rear) to a switchbox that is mounted on the steer handle. From the switchbox you run a cable with a 3.5 mm jack plug (male) to your helmet to a 3.5 mm jack plug (female). The female plug is connected to a microphone and two walkman-headset-speakers that are build-in, in your helmet. You also need a power cable from the battery and an antenna cable from the CB to the antenna.

We'll start with putting the microphone and the speakers in the helmet. I assume the use of an full-face helmet. If you have another model you have to change things as you seem fit. You need to disconnect the speakers from the headset. Leave the plastic enclosure intact because it protects the speaker membranes. So you have two speakers, couple centimeters diameter, less than one centimeter thick that will easily mount inside your helmet. Put them in the foam or glue them onto it. Depends on your helmet and your ears. Make sure that they are centered before your ears. Test this with a walkman. Run the wires to one side of your helmet. Cut the wires at about 10 cm under the helmet. You need the 70/80 cm cable with the jack plug later so don't throw it away.

The microphone I picked, is very good for human voice. It reaches up to 8000 Hz and pickes up little high frequency wind noise. You could use the microphone from the hand mike and save some money but I think that the other microphone is better. Cut about 20 cm from the wire with the mono jack plug and solder this on the microphone. Red = plus, white = minus.

Cut a hole of the size of the microphone in the foam of your helmet right in front of your mouth. Tape or glue the microphone in it. Run the wire out of sight to where the speaker wires come out. Cut the three wires to one length and strip them. They should stick out under your helmet. Then twist and solder the three minus wires together. The speaker wires will have a core with insulation and a shield around it. The shield is the minus. Twist and solder the two plus wires of the speakers together. This leaves you with three wires total. (1) the shared minus, (2) the speaker plus and (3) the microphone plus. Take the 3.5 mm female stereo jackplug and solder the wires to the three contacts. Figure out first which is which. Use the left-over 3.5 mm walkman original together with the ohmmeter to find that out.Usually the tip is minus and the ring is plus. See Figure 1 ...

Don't forget to put the hood over the wires first and then solder the three wires to the female jack plug. Find a way to put a strain relief in. Maybe tie a knot in the wires and glue that to your helmet. This prevents you from pulling the wires from the speaker(s) or microphone whe you get of your bike without disconnecting the cable first. (You can drill two little holes next to each other near the edge of your helmet and use a cable tie to secure the cable. That works for me - HdW). Your helmet is done now and all you see is a short cable with a 3.5 mm female stereo jack plug on it. While you're at it figure out the wiring for the mono jack plug as well. It should look like Figure 2 .

Now the switchbox. I picked a very small enclosure so everything fits very neat. Be carefull when assembling. This design is intended to be attached to the clutch handle of your TA or AT. You may have to modify for another bike. Open the box and drill, file and saw the holes as outlined in the drawing. The 9 mm hole on the right must be sawed open to put the ferrule (?) for the curly cord in. Put it back after you took it out. Make an aluminum strip of 1 by 4 cm and dril the 5 mm hole on one side. Glue it to the box. See Figure 3 .

Then take the 3 cm M5 bolt, M5 nut and an M5 wing-nut. Saw the head of the bolt and saw a groove on one side. To use with a screwdriver later. The clutch handle is closed with a philips screw. Take it out and use the sawed-off bolt as a replacement. Twist the M5 bolt on and secure the whole thing. Now you have a handle to put the switchbox on. It is perfectly located for thumb-operation.

The CB is next. Open de handmike and you'll find a small printed circuit board with 4 wires (one of which is shield) of the curly cord solderd to it. The 4 wires and the 2 wires from the microphone are connected on the PCB through a switch. Un-solder the wires from the print after documenting their original order.

See Figure 4 for the original wiring scheme.

We will use another switch because of an extra circuit. When switching from receiving to transmitting you have to disconnect the speakers. Tests have shown that the system will resonate. So put the new switch in front of you with the contacts towards you and the button/lever to the left, as in Figure 5 . This will give you the same view as the original switch.

Put the cable with the mono jack plug through one of the 2.5 mm holes and put the cable with the stereo jack plug through the other. Tie a knot in both cables, inside the box, a couple of centimeters from the jack. This will serve as a strain relief.

Strip all wires and solder them to the switch as in Figure 5 . Strip the plus of the microphone a little more and put it through contact 4 and 5 simultaneously. That makes for an easy jumper. Start from the middle because it's difficult to get to the middle if you start from the outside. After finishing, put the switch through the 6 mm hole on the left and secure it. Make sure that the switch points up when set for receiving,unless you think that down suits you better. Put the ferrule and the curly cord in the 9 mm hole and put the sawed-out part back in. Maybe you want to test first, before closing the hole.

To make it easy to mount you want a plug-connection between battery and CB. Cut the 12Vdc wires (red/black) so you can use them to connect to where you want to put the power connection on your bike. Solder one of the AMP plugs to the CB power cord. Wire the battery to where you want to connect it to the CB power cord. You need to wire directly from the battery because if you take 12Vdc from somewhere else it may not be fully rectified and cause noise. Solder the other AMP connector to the battery wire. Make sure you don't switch the plus and minus. The CB has a fuse in the power cord. Do not remove that fuse.

Finally we need a place for the antenna. Put it where you think it is best. Try to put it close to the CB. I used a 90 degree aluminum piece of about 4 x 4 x 4 cm with one 13 hole for the antenna and one 8 mm hole for screwing it to the bike. By keeping the distance short you can use a standard antenna cable and take that with you when you take the CB off. It is better than having a length of antenna cable on your TA that is not used normally. Cut the antenna cable to the desired length and put the antenna plug on. Solder it to the cable.

Testing. Before closing everything test the installation. If you work for two bikes, then leave one CB unmodified and use it for testing. After you found that the first works OK, start with the second one. I used a couple of times and it works up to about 100 kmph. Quality goes down fast if you go faster. This also depends on your helmet, your wind shield and the strength of the wind. But during those limited-speed tours it works like it should and it is worth the money.

CONRAD is a mail-order company for electronics and the like. Delivery time is usually within a week. They can be reached in Holland on 053 - 285444. They have a catalogue so you can have a look first before ordering. They also have a store in Rotterdam where you can get the parts. You can of course walk to your local electronics shop and get equivalent parts.

PS The antenna is sold-out, go for another one.