But at 120 MHz, there are two difficulties. One is getting enough energy without a beam antenna. The other is if it is FM, (vice AM) that is difficult to demodulate with conventional crystal set approaches.

But certainly possible, an interesting challenge.

This can be handy when a transmitter gets a "stuck mic". That is, someone's mic transmit button gets stuck in the transmit position and the user does not realize it. Communication can often proceed on top of the stuck mic, but often with difficulty.

Listening with an FM receiver would cause the strongest signal to be "captured" and the other one would not be heard. (Or maybe heard much less well, I'm no expert on this part.) So a nearby plane with a stuck mic on FM might block all communications.

When I was about 14 I had a Remco Radio which was a crystal set with a one transistor audio amp. Compared to my modern well built crystal sets, it was not such a hot performer, thinking back, despite the transistor amp.

But, I could pick up the Hartford, CT VOR (VHF navigation station) on it when using my long wire and ground. It was not supposed to tune to that frequency, but because it was not very selective with only the single tuned RF stage, the signal managed to get in somehow. I was probably 5-10 miles from the transmitter and the terrain was a bit hilly with lots of forest.

So if you are close to the transmitter, I think you stand a chance of picking up aircraft VHF, but you may find that you hear multiple frequencies at once, depending on what is close by and strong. I think it would be difficult to get selectivity out of one stage at VHF.

There are a number of FM Crystal set designs on the net. Because the Air band is just above the FM BC band, and because aircraft use AM instead of FM, these sets should work well with a little tweeking. The only problem would be that aircraft transmissions are much lower power than FM Broadcast, so you will need to be quite close to the transmitter.

Incidently, another form of Aircraft transmissions are the NDB beacons which are just below the AM broadcast band. When I was a kid, the local NDB was about the only thing I could hear on my first crystal set.

Have fun........ Zim

What are the specs on the litz you ordered? Most folks use #44, #46 or #48 size wire with the strand count varying according to desired performance and coins in the piggy bank.

Were you going to start with a MW set?

Frequencies that high do not propagate well as "ground waves", as do BCB stations. They would be "direct waves" and subject to attenuation from objects between the transmit and receive antennas.

Aircraft might be more line-of-site (direct waves), and I think the transmitters might be more powerful, but I am not sure. The ground stations would suffer the same problems as CB sigs, but might have their antennas on a tower, improving the situation.

In both cases, a single stage set would likely receive multiple frequencies at once. I think selectivity would be a problem at higher frequencies, but I cannot explain why . . . .

Did someone say that a CB crystal set could not be done? I think that it might yield a poor result.

A regen might be worthwhile, even a single stage one. But it would have to be well designed and built because the L and C for the CB band is quite low. Any tiny movement of components would shift the frequency. Hand capacitance could drive you nuts.

Commercial broadcast transmitters (MW or SW) by contrast are very powerful and they can skip, and their waves can have a lot of energy. FM Broadcast (FM) is high power too, but don't skip much and it is hard to collect power from their waves because they are so short. Aircraft transmitters are not much stronger than CB, and they are also very short. Hope that helps?

I wonder if you could clarify "strength of wave" and "shortness of wave". I'm not following whether you are indicating that the low power of the transmitter causes CB and VHF to be difficult to receive on a crystal set or whether it has to do with the shorter wave lengths (compared to BCB). Or both?

Thank you,

A crystal set has a tuned circuit which is intended the accept the wanted station and reject all others.

If you didn't have this tuned circuit you would (in theory) be able to hear many hundreds of different AM transmitters all jumbled up together (Medium Wave Broadcast, CB, Aircraft, NDB's, mobile phones, etc). However, because a crystal set is not very sensitive, you would only be able to hear the stronger ones (eg those nearby).

So to receive CB (for instance) on a crystal set it is only necessary to re-tune your Tuned Circuit to the necessary frequency (eg 27 MHz).

Of course if you have a CB'er next door, you probably will be able to hear him even on a normal crystal set. This is because the single tuned circuit in a crystal set has very poor selectivity.

So the bottom line is this: To hear any AM transmitter, you only (1) need to tune the circuit (including the antenna) to the appropriate frequency and (2) be close enough.

You can build a simple "un-tuned" crystal set (just a diode without any tuned circuit). But as before, you will only hear strong local signals.

have fun ......... Zim