Alignment meter
Hi,
So there are several ways of hooking up some kind of meter, mainly to the output, when aligning a radio. Indeed, the sister site to this forum has a simple project idea for exactly that, and I have indeed built and used this method.
Personally I like to hear the modulation tone when aligning, as it gives confidence that you are adjusting the correct signal, as it is possible to go off frequency and end up with noise which will also be able to be 'peaked' on your output meter. The problem therefore is connecting a meter that is sensitive enough to provide a useful reading while hearing the output without having the tone loud enough to annoy.
My solution has been to modify a sound level meter. There are plenty of cheap 2nd hand analogue units on ebay, and I picked up mine for £15 delivered. In my case it was a YF-20, but any similar unit should do. These meters just use a microphone to provide a sound level, and are ideal for modifying.
The modification itself is really simple. I removed the microphone and installed a BNC socket in its place, connected via a 100nF capacitor. I then adjusted the calibration preset to lower the sensitivity of the unit. Of course actual calibration is not needed as you are only after an indication of relative level. That is it.
In use, I connect the unit across the speaker and can now have a nice low level of hearing the tone, while having a sensitive meter to peak the adjustments on. The YF-20 is a particularly nice unit for the task as a) the BNC socket fits nicely in place of the mic and b) it has two sensitivity levels, ideal for working across a range of sets.
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