Hands Free
First, one very important point. If you plan to operate whilst on the move, remember road safety comes first. Always concentrate on the road ahead and please, use a hands free microphone.
Remember too that not every country permits mobile operation, hands free or otherwise; so before setting out check that mobile operation is within the law.
Hands free mobile operation is clearly the safest and most sensible way to communicate whist on the move. Hands free units, both in kit form and ready built units, are readily available from most amateur radio dealers. They come in many different shapes and sizes so you can chose the one best suited to your station and vehicle. However take a careful note of the specification of anything you are considering purchasing and make sure it is compatible with your radio. Not all units work with every radio!
There are many manufacturers of hands free units including Cool Talk, MyDel and Watson but a friend of mine, Victor GI4LKG, recently came across a neat little unit described as a mono pre-amplifier with an electret microphone. It provides a line level output signal and has an onboard potentiometer for gain adjustment. Operating voltage is 6-18 volts dc.
This unit provides an ideal solution to inject sound into many pieces of equipment including radio transmitters.
I built my hands free unit using one of these modules for less than £20. I fitted the unit into a small box to which was also attached the PTT switch. Four leads (ie. 9 volts, ground, mic and PTT) were wired to an RJ-11 plug which was inserted into the microphone socket and the unit was ready for testing. At this stage the electret was still attached to the pre-amplifier module but it did not perform well so it was removed, placed on the sunvisor, wired back in to the module and the (gain) potentiometer backed right off. This significantly improved performance and I am now happy with my hands free system.
The pre-amplifier module is the PM-3 from Cebek Electronic Circuits. The PTT, housing box, connecting cable and RJ-11 plugs may all be sourced locally.
The PTT box and the microphone are secured by two small self-tapping screws whilst the flat 6-core microphone cable used instead of the thick coiled cable that came with the supplied fist microphone, allows the rig to be fitted further back in the console and the console lid closed when the radio is not in use.
The slide show below shows the components used in this project.
Hands Free
Keep Safe: Use Hands Free
Posted 12 December, 2010 15:34:46 GMT