A bit of a steal from the pound shop - a transmitter and receiver set operating on the FM 88 - 108MHz frequency band. Once I get it up and running, I put my OWON 60MHz oscilloscope on it and look at some signals.
By Julian
Youtuber, shed dweller, solar charge controller aficionado
Umm – what about the legality of transmitting on 87.2 and 88.5 MHz ?
just bend contact with screwdriver
This may be a European thing since an FM frequency here in the US, could not tune to an even even number
of 87.2 Here in the US, it would have to be 87.1 or 87.3
I was also going to suggest that you use a Cheapo RTL8232 dongle as a spectrum analyser. It would show the frequency drift before it goes into 'power save' nicely. I've got four of the little beasties and use them for all sorts of things, from spectrum analysis to ADSB and data-radio decoding.
The oscillo is limited at 60MHz and the FM freq is at 88Mhz? Can that actually work ? (real noob question)
Another thing, i noticed when u turn off the sound the led gets dimmer and dimmer (and on the oscillo the wave dies out — as you noticed ) can it be a "feature" ? No transmission if no input?
The deviation for broadcast FM is about +-75kHz which is too small a fraction of 88Mhz to see much on the scope.
could it be rds
Did anybody notice how when the AGC flatlined, the TX's LED went out, and went back on when Julian started the music?
Yes, a scope artifact — it's called aliasing.
+w2aew Alan Wolke, are you watching? Your expertise is needed!
That clipped wave on the other side of that diode is probably the trigger source for activating the transmitter when audio is available, and turns off when there's no audio.
You could take a look at the emitted spectrum using a 12-dollar SDR dongle. The cheapest ones come with a surprising bandwidth (50-1600MHz) and software like SDR# can give you a good idea of what you are working with. It could definitely let you confirm the frequency drift of the carrier when the audio is muted, as well as the quality of the carrier itself. It also lets you tune in to various radio communication, although probably not the police.
Well if it doesn't work then maybe its with less than a quid 😉
Hey, that was interesting! As I have mentioned that I'm still new to the oscilloscope, watching you use your scope of various points of an FM transmitter, was pretty educational to watch. I'm think I may try that myself. 🙂
whenever i have a device that has that battery contact problem, tin foil to the rescue! just fold up a little piece into a little square and jam it in there. perfect!
You could try the FFT function to display the frequency domain. Probably not real time on such a basic scope but an indication at least.