48 mhz fm reciever

[grendal]

I'm looking for a schematic for a 48 mhz fm reciever. I've been looking for days but I ain't found anything that would work. Usually it's just photo's of crude drawings on a napkin, or something that would say tuner ->converter->tv reciever, wich I find very very vauge. Think one of you find gentlemen could help with this?

 

[mneary]

To change the schematic of a 100 MHz receiver to the schematic of a 48 MHz receiver, change the resonant frequency of the Local Oscillator from 89.3 MHz to 47.3 MHz. Change the resonant frequency of the RF stage from 100 MHz to 48 MHz. That's how to do it on paper.

You probably also need to change the sensitivity of the detector, perhaps it will be 5 or 15 kHz, but given the principles you should be able to easily change the schematic.

In actual construction, the 100 MHz receiver will probably be designed for 88-108 MHz and you can dispense with the wide frequency range, making the LO and RF stages easier.

 

[grendal]

so basically all I need to do is change the crystals? (thinking about just using a baby monitor, not sure if you can just change the crystals in the circuit already or not)

 

[mneary]

You have a baby monitor, or are you looking for a schematic?

There would be an LC circuit in the RF front end, and the LO might need some adjustment too.

 

[grendal]

You have a baby monitor, or are you looking for a schematic?

There would be an LC circuit in the RF front end, and the LO might need some adjustment too.

both would be quite useful, I originally wanted to figure out how to get the baby monitor off such a commonly used frequency, but after taking it apart I realized I was over my head. So wondered if there was a schematic already out there, or if there were schematics for 48 mhz. It's been ages since I played with electronics, going on 5 years now. So it's like learning all over again. Either way would work, schematic would kinda force some memory, but tweaking an existing object would work good too.

 

[mneary]

I would believe that hacking an existing receiver would be a lot easier than building from a schematic. But, without a schematic of the existing receiver you are working in the dark. You would learn a lot if you have the time to draw a schematic of it (reverse engineer it).

A schematic of any receiver between 40MHz to maybe 200MHz would tell you generally what components to expect.

When changing a 'license free' device away from its original frequency, be sure to move it to another 'license free' frequency. If you start using a frequency belonging to someone else, they will be sure annoyed. If it belongs to law enforcement, the military, or aviation you could be in big trouble.

(If you use a ham radio frequency, we will track you down more quickly than the others would.)

 

[grendal]

here from my research it's a unlicened frequency. Then again that might of changed, it's about a 6 month old list, I know local military bands are higher generally the c band and up. Local law enforcement uses 3.2 ghz, and aviation uses 60.3 ghz.

Got any recommendations on how I can find a more up to date list?

 

[mneary]

I have no idea where to find an up to date list for your country because you have not revealed which country you are in.

In the U.S. we have the FCC (Federal Communications Commission (FCC) Home Page).

 

[mneary]

World wide, aviation uses many frequencies. Some of the main communications frequencies are just above 108 MHz. GigaHertz frequencies are not reliable in places where physical barriers exist. I would bet that local law enforcement only uses 3.2gHz for speed enforcement (RADAR) and uses something in the 120-174 MHz range for primary communication.

 

[grendal]

Thanks, I'll blip back if I got any other questions.