I have been running it off 12v or so. I find that it works very well. I built it to use with a Ten Tec Eagle, which (somewhat surprisingly) does not have a spot tone or any other kind of zero beat indicator. My only quibble with this indicator thus far is that it requires a lot of audio gain. In order for it to work, I have to turn up the volume on my Eagle so that it is louder than I am used to.
Click here to download the full size of the above Circuit.
I will see what I can do to make it a little more sensitive. Changing the value of the R1 resistor (currently 470 ohms) might help with this We will see. It`s a handy little circuit though and my thanks to you for making it available. I`m sure it will see a lot of use in my shack! Thanks and 73! Steve KC2SIZ" Another ham has built and used the Zero Beat Ckt described below, and has posted an article about it. He is Allen AE7TG (NAQCC #3947). Take a look at the very informative article including pictures here. The information below has also been supplemented by Elwood WB0OEW who built and uses the unit. The pictures he refers to can be seen at the bottom of this page. Elwood says: "Hello John, I want to thank you for posting the zero beat tuning aid circuit. I have been building it over the past few weeks and I`m now finished. I have attached a few photos. I did not try to miniaturize it very much, the box is about 1x2x3, about as small as I feel comfortable working. It has two connections to the radio, one for audio and one for 12V. I have to say it works very well. I am not confident tuning by ear and this little gem really relieves my worries about not tuning close to a station. " "Calibrate the potentiometer using your built in side tone. Start at one end and turn slowly until it (LED) comes on. Mark that location. Then start at the other extreme and come back the other way until it comes on again. Mark that location...
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