radio

hi

i want to modify a radio i bought ( a cheap one ). i don't know what is the type of the circuit.
i want it to receive frequencies other than the default range e.g. 400 - 500 MHz..
how can i calculate the capacitance of the tuning capacitor ? or if there is another way todo so..

thank you

Hello , i have no clue , but if you could tell us the type of radio that you want to modify , maybe somone could help..

hi
sry i forgot to add that.. i want to modify the FM band..
the radio is FM only ..
thx

IDon'tGetCircuits said:

hi
sry i forgot to add that.. i want to modify the FM band..
the radio is FM only ..
thx

Click to expand...

You have to modify both the local oscillator, and the input tuning circuits, it's unlikely (VERY unlikely) that you can do this by altering the capacitance across the tuning circuits. You will more probably have to alter the inductance - however, the move from VHF to UHF usually involves moving from coils to 'lecher lines', and your variable capacitor is probably going to be far too large.

Probably a better way would be to use a down converter, a simple mixer/oscillator stage (with tuned inputs and outputs) that would shift down a few hundred MHz. These are commonly used to receive 70cm transmissions on 2m receivers.

What are you actually trying to receive?, 400-500MHz seems a strange band to be wanting?.

Not only what Nigel said, but the transistors/ICs are not very likely to work up at the 400-500MHZ range.

And the digital (syntheser) tuner work only as Nigel said.

Nigel Goodwin= said:

Probably a better way would be to use a down converter, a simple mixer/oscillator stage (with tuned inputs and outputs) that would shift down a few hundred MHz. These are commonly used to receive 70cm transmissions on 2m receivers.

Click to expand...

you mean heterodyning right???

There isn't any wideband FM at 400MHz to 500MHz. Do you have a buddy who transmits wideband FM up there?

There is some narrowband FM, but the radio's wideband IF and detector are unsuitable. You could make a dual-conversion with an oscillator/mixer and a 455KHz narrow-band IF and detector.

pike said:

Nigel Goodwin= said:

Probably a better way would be to use a down converter, a simple mixer/oscillator stage (with tuned inputs and outputs) that would shift down a few hundred MHz. These are commonly used to receive 70cm transmissions on 2m receivers.

Click to expand...

you mean heterodyning right???

Click to expand...

Yes!.

thank u all for replying..

i said "E.G. 400-500 MHz" so i don't really mean that range.. i mean any other range greater than the regular one.

would be trying to receive 108-130 MHz simpler ?..

i'm sry but i don't understand very good cuz i didn't study this with these names (my original language isn't English) but its no problem..

thanks alot for ur help..
and if there is any other way to do it.. like if i were going to build a radio from 0 is it going to be easier..

P.S. u can see from my name and writing that i don't get circuits really good ..

thx again
regards