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CB Radio Communications

This project is currently under construction!

This is s simple project to enable me to use a CB radio whilst on track or in a convoy on the road. It uses in-ear headphones and a separate electret microphone installed inside the helmet. This idea was suggested after I had initially built a similar unit around a PMR466 radio. Interfacing to a CB radio is even easier though. The primary advantage over this appraoch is that the higher power of a CB radio (~4W) is more than that of a PMR radio (~500mW) and thus the range is much greater. Typically a CB radio can easily transmit over a distance of 5 miles and in favourable conditions can reach 50+ miles.

Time for a bit of nostalgia. CB radio was in the UK, long before it was actually legal. In my teenage years I used to mess about with the illegal AM rigs, mainly chatting to truckers passing through Somerset and and other school mates. At the age of about 15, CB radio was legalised in the UK and I bought my first 'rig', a Cybernet Beta 1000. It was a very good bit of kit and it is still working today, now that I'm in my 40's. Much of my teenage days playing with electronics was messing about building CB aerials and stuff to see how far we could communicate. Searching for stuff on the Internet found me a few pictures of my CB rig in the 'CB Museum'!

Headphones

As with my PMR radio project I'm using my Sennheiser CX 500

headphones. These are simply brilliant at passive external noise attenuation because they come with different sized rubber surrounds to seal the ear canal. They have a relatively low impedance of 16 Ohms but my CB radio has a 3.5mm socket for an external speaker. All that was required to interface the two was a 3.5mm stereo to mono jack plug adaptor (Maplin part no. FK14Q).

Microphone

The microphone is a little bit more problematic as a typical CB handset uses a moving coil microphone, which a relatively insensitive when compared to the electret microphone I have installed in my helmet. The electret microphone also requires a power supply.

First thing to do is to find out the microphone connections and I found the required information on this page

. My CB radio is type 1 and the pins are:

= Audio
= Ground / Common
= Receive
= Transmit

CB Wiring

This section needs to be completed.

Wiring this lot up is fairly simple because only a microphone and switch are required to put the unit into transmit mode.

Circuit Design

This will appear soon.

Packaging

I'm planing on doing something pretty similar to my PMR466 radio solution.