FM Transmitter

[audioguru2]

Make a simple FM transmitter and receive it on an FM radio.

 

[crivoli]

Well, I guess I set myself up for that one!!

I have already made the amplifier circuit I wish to send the audio too. I was looking for a simple transmitter/receiver for this project but I am not finding anything.

I guess a 49Mhz walkie talkie schematic may do the trick but they seem impossible to find. Just my luck

 

[MNA]

Hi, Audioguru,
u said,
"The toy car transmitter and receiver just makes the toy car go and stop."
So,it acts as a switch......How much range is this transmitter supposed to cover????

 

[audioguru2]

My son had a cheap radio controlled toy car. Its range was about 10 metres.
Then I bought a good one for him with a range of about 100 metres.
The radio systems for model airplanes have a range of about 1km.
Look how far NASA can remotely control things!

 

[MNA]

Oh!yeah!I forgot to refer  http://jap.hu/electronic/rf.html .......27Mhz.....
Thanx

 

[crivoli]

audioguru:

I found an AM transmitter and AM receiver on the project page:

http://www.electronics-lab.com/projects/rf/006/index.html  -- Receiver
http://www.electronics-lab.com/projects/rf/011/index.html  -- Transmitter


Would this work in my scenario to send audio through a mic across my house to the speaker?

I thought it looked promising so I figured I would ask.

Thanks again for the help

 

[audioguru2]

The projects don't say how much range they have.
Make them and let us know.

 

[crivoli]

I agree it does not specify the range, but this 'should' work in my scenario correct?

I don't want to try them if they are not useful to me. If you think they will work for my project I will give them a shot.

I would builf the receiver first to see if I could get AM stations on it.
Why doesn;t the receiver have an antenna? Is this normal?

Thanks

 

[audioguru2]

Why doesn;t the receiver have an antenna? Is this normal?

AM radios don't have an external antenna. They use a ferrite rod which has the coil wound arround it. The transmitter might need a very long wire for an antenna for it to have any range.

 

[crivoli]

audioguru:

I appreciate your patience with me.

Would this work for the am receiver as the 220uH component?
http://cgi.ebay.com/Ferrite-Loopstick-Antenna-Coil-Crystal-Radio-Radios_W0QQitemZ6619389741QQcategoryZ7275QQssPageNameZWD1VQQrdZ1QQcmdZViewItem

also I can not seem to find any good variable capacitors..... any suggestions?

thanks man

 

[audioguru2]

The article for making the radio says to get a loopstick antenna and tuning capacitor from an old AM radio.
The E-Bay loopstick antenna coil is fine. Also get the guy's tuning capacitor or the kit AM crystal radio that has both.

 

[crivoli]

The AM receiver schematic specifies a 500pf variable capacitor.

The one  on E-bay is 60/160pf. Do you think that will work, or will I need to change values of other coponents on the schematic? 

Thanks

 

[audioguru2]

Crivoli,
Don't you realise that the variable capacitor has to match the value of the ferrite loop coil antenna?

 

[crivoli]

audioguru,

No I didn't realize that. How then on that schematic is the antenna a 220uH and the resistor is a 500pf? Do you have to tune the capacitor until it reaches the matching value?

 

[audioguru2]

The value of the E-Bay ferrite loop antenna coil isn't listed but it could be calculated since the value of its tuning capacitor is known and also the tuning frequency range.
The 220uH coil has a low value so it needs a high value tuning capacitor to tune the AM tradio band.

 

[crivoli]

So, I could be safe in replacing those components of the schematic with those I found on e-Bay. Does that sound right?

Also, on the transmitter schematic it is not clear of what L1 is:
http://www.electronics-lab.com/projects/rf/011/index.html

Is it another ferrite coil, or magnet copper wire? I assume it is another ferrite coil since this is AM and it's tuning cap is the same value as the other.

thanks again

 

[audioguru2]

The transmitter and receiver both use the same ferrite rod loop antenna coil and tuning capacitor.

 

[crivoli]

So am I able to replace the coil and tunning capacitor in the schematic with any coil and tunning capacitor I find that are compatable with each other?

Thanks

 

[audioguru2]

So am I able to replace the coil and tunning capacitor in the schematic with any coil and tunning capacitor I find that are compatable with each other?

Correct. Then the radio can tune in the entire AM broadcast band.

 

[crivoli]

The designer of the AM ciruit said he built this on a breadboard.

Any idea how to hook up a variable cap on a breadborad since the connectors don't fit?