help building a cheap fm vhf receiver

[awright]

VHF FM receiver

Hey, Guys:

There's something very fishy going on here, and I'm not feeling very comfortable about helping mrfamilia with his radio projects.

Look at his post, Tue Jul 12, 2005 8:17 am "Post subject: if you transmit at wideband frequency will narrow band frequ." Basically, in that discussion it developed that mrfamilia wanted to come up with "broadband" transmitter that would allow him to override many other's communication channels with his own transmission, "just as a joke."

Now he wants to come up with a narrow band "receiver" to add into a conventional broadcast band FM receiver in what sound like another technically bizarre scheme. He also claims to be knowledgable about transmitter design, but not receiver design, yet his questions about flooding the airwaves with RF don't seem to reveal much knowledge about transmitters.

Is this guy really interested in learning about practical transmitter and receiver design for legitimate purposes, or is he either pulling our leg or up to something else? I think we are all interested in supporting newbies who are sincerely interested in learning about electronics, but this thread is looking strange to me.

How about telling us what you are up to, mrfamilia?

awright

 

[JimB]

My sentiments exactly.

JimB

 

[BravoKilo]

MRFAMILIA:If all u need is a cheap receiver to pick up a community radio you said, just convert a regular FM radio which can pick up 88 to 108 mhz. Actually, you do not convert radio itself. You convert your incoming signa on the 152 mhz range. Best bet is a car FM radio which has high selectivity and shileding. Find a 50 mz crytal (any) and set up an oscillator. i don'tknow your skilbut if do a little research on mixing, you could set up a mixex (FET) would be nice. Inject the loca oscillator on its base via a small capacitor or run the emitter leg through a secondary on the RFchoke to power the oscillator. You have to make the 152 mhz input coil. What will you have? the two frequencies and their sum and difference. Your input signal of 152 MHZ will be down converted to 102mhz if you have a 50 mhz xtal in there. Now that is within the FM band! Tune your FM radio to you community transmitter. It's need because you do not have to tune the input or the Local Oscillator.
Got it? Now if that FM radio is digital and can scan, once you picked up your community transmitter, store it and bingo! u have it "locked" as a channel. Sometimes, the obvious escapes us. i do not have the exacty schema but I once build a SW receiver like this and the mixed frequency was fed inot a car AM radio which had the mechanical memory by pulling the button (remember this, anyone?). i do a lot of RC projects and I do have diagrams for oscillators and mixers from 27 mhz to 75 mhz. So, the 50 MHZ is within my experience.


Send a private message at : rcdevices@yahoo.com.ph since I don open the forum daily.

BravoKilo

 

[JimB]

Woh, hold on there BK.

This thread is 15 months old. I dont think that Mr Familia will see your reply, he went off in a huff shortly after this this thread stopped. He was trying to do something very silly/anti-social/illegal and got all upset when he was told so.

I must also point out that your down-converter scheme has a few flaws.
Look at the frequencies.
The oscillator 50Mhz, the IF 100Mhz (very near), the RF 150Mhz (very near), all harmonically related, a recipe for spurious responses if ever there was.
To convert 150Mhz to 100Mhz, it would be far better to use a Local Oscillator at 250Mhz, so that 250-150=100Mhz. Of course, then you have the problem of generating 250Mhz, I see lots of multiplier stages.

However, all this is waffle because the thread is dead and the OP is not likely to return.

JimB