This TV transmitter will handle frequencies up to about 250MHz, so it will work perfectly if you have
on your telly. In principle, the transmitter should work up to 500MHz or more, using the BF959 bipolar transistor. You should be able to generate a signal on UHF channel 21, but I have not (yet) tried this with the first rats-nest version.
TR2 and TR3 may be difficult to get, but you need to select a small-signal transistor with an ft=1.1GHz (1100MHz). For 50/200MHz bands you may be able to get away with 2N2369, but I have found this to be a little temperamental. It seems to “blow”, whereas the BF959 is a lot more tolerant to overloads.
The first prototype transmitter was built on a bit of copper-clad board, just to prove the principle. Due to pressure from visitors to the homepages I have published what I have done, instead of finishing the project. I want to complete the project with a PCB, but you will have to wait for that. No idea as to when that will be – Sorry!
The coil in the collector of TR2 determins the operating frequency. Using a 4 – 20pf trimmer capacitor I could cover 150MHz to 240MHz. For this the coil is 4 turns of 0.3mm Dia. magnet wire wound on a 6mm drill bit, close-wound, with 5mm wire ends. The tapping to the amplifier is one turn from the +ve supply rail.
I have used a larger coil as an experiment and the frequency went down to cover 40MHz to 75MHz, so it more than covers Band-I. I have no coil data that you could duplicate, but it was about 10 turns with a tapping at 2 turns. I will update this when I know more, but before then you can consider this a rough start for your own experimentation.
TV transmitter VHF Bands I, II, or band III
This TV transmitter will handle frequencies up to about 250MHz, so it will work perfectly if you have
on your telly. In principle, the transmitter should work up to 500MHz or more, using the BF959 bipolar transistor. You should be able to generate a signal on UHF channel 21, but I have not (yet) tried this with the first rats-nest version.
TR2 and TR3 may be difficult to get, but you need to select a small-signal transistor with an ft=1.1GHz (1100MHz). For 50/200MHz bands you may be able to get away with 2N2369, but I have found this to be a little temperamental. It seems to “blow”, whereas the BF959 is a lot more tolerant to overloads.
The first prototype transmitter was built on a bit of copper-clad board, just to prove the principle. Due to pressure from visitors to the homepages I have published what I have done, instead of finishing the project. I want to complete the project with a PCB, but you will have to wait for that. No idea as to when that will be – Sorry!
The coil in the collector of TR2 determins the operating frequency. Using a 4 – 20pf trimmer capacitor I could cover 150MHz to 240MHz. For this the coil is 4 turns of 0.3mm Dia. magnet wire wound on a 6mm drill bit, close-wound, with 5mm wire ends. The tapping to the amplifier is one turn from the +ve supply rail.
I have used a larger coil as an experiment and the frequency went down to cover 40MHz to 75MHz, so it more than covers Band-I. I have no coil data that you could duplicate, but it was about 10 turns with a tapping at 2 turns. I will update this when I know more, but before then you can consider this a rough start for your own experimentation.