19 June 2018

A cheap hands-free solution: the idea

One of the many drawbacks of driving and talking on the radio is that the microphone is usually physically wired to the transceiver. Let alone that it is illegal in many parts of the world. Very few RTX's have a hands-free solution out-of-the-box and even in 2018 too few support some form of [Bluetooth] detached earphone-microphone. Last but not least, all off-the-shelf solutions can be expensive.

Obviously I looked for a DIY alternative. To simplify things a bit I assumed that an RTX for mobile use has enough audio power in the speaker so that an earphone or an audio amplifier is not needed. This means we need to transmit audio one-way only: from the mouth to the TX.

Now our feared Chinese fellows come very handy. Head to any of their portal and look for "Wireless microphone 2.4 GHz" (they have some that operate in UHF too). Be prepared to dig through many products until you land on something advertised for touristic guides. These products have a boom mic with transmitter and a simple receiver that is supposed to plug into an amplified speaker or other form of audio amplification.

I bought the product from NEWGOOD for 19€ (in 2017). It's still a bit more expensive that my desiderata since I hoped for 10-12€, but definitely cheaper than other solutions.

Both parts have an on-off switch, a microUSB socket for charging and the transmitter has volume control buttons. They are not Bluetooth so there's no need of pairing. I have no idea whether two similar units would interfere or could be swapped, but it's not a popular product I'd say and the risk is low even if the advertised range is 50 metres!

In its intended use, so with an amplified speaker on the other side, it works right. The audio quality is also very good.
How to interface with the transceiver then? Just feed the receiver output into the microphone input through a bypass capacitor, think of a way to handle the PTT: pushbutton, lever switch, VOX, .... and hope that signal levels & impedances match!

My current mobile RTX is the Baofeng UV-82 handheld, so it will be my test platform.

No comments: