Help modifying an FM transmitter circuit

[draco_james]

Like this?

**broken link removed**

 

[audioguru]

Hi Draco,
In my FM mod4 transmitter circuit's schematic, the voltage rating of the capacitors must be at least equal to the 9V supply.
The pF caps are all ceramic, 10%, and are about 50V. C12 and C14 don't have to be 30pF and 22pf, that's what I had. They could be 20pF to 47pF.
The nF caps are metalized plastic, 5%, and are 50V.
The uF caps are polarised electrolytic, about 20%, and are 16V.

The trimmer capacitors could be plastic type or ceramic. I used tiny ceramic ones that were probably made for a pocket watch.

The resistors are carbon film, 1/4W and 5%. 1/8W would also be fine. :lol:

 

[audioguru]

Hi again,
A JPG file type makes a fuzzy schematic but is good for a photograph. GIF or PNG file types are much clearer for schematics.

You have stuff shorted out. It should be like this:

 

[draco_james]

k, thanks for the info and the diagram... oh, and for the sites to buy components from, I was having trouble finding sites for Canada, thank you very much for those aswell

are the coils store bought, or are they home made? I know that some projects call for you to wrap a certain wire type a certain number of times around a specified diametre...

 

[audioguru]

I was having trouble finding sites for Canada

On those suppliers' sites, click on the Canadian flag and all pages will have Canadian dollars. If you order before 8:00PM than your order is delivered the next morning.

are the coils store bought, or are they home made?

I took some 1mm diameter enameled copper wire from a transformer and wound 8 close together turns around a 3mm object then scraped the enamel from the ends for soldering. :lol:

 

[draco_james]

thank you muchly

 

[audioguru]

You're welcomely! :lol: :lol:

 

[draco_james]

so just to make sure i don't buy parts that won't work, the resistors that don't have a k after the number, are just in ohms rather than kohms, right? and the voltage rating can be anything as longs as its over 9V (so like 50 is actually higher than needed, but its doesn't matter as long as its high enough...) also, do the nF caps have to be the metalized ones, cause I can't find a great deal of them... will the polyester kind work?

(just curious also, aside from the pF caps(that are ceramic), does the type matter? or is that just what you ended up using?)

Thanks again

 

[audioguru]

so just to make sure i don't buy parts that won't work, the resistors that don't have a k after the number, are just in ohms rather than kohms, right?

Correct. The "k" means thousands. 47k is 47,000 ohms.

the voltage rating can be anything as longs as its over 9V (so like 50 is actually higher than needed, but its doesn't matter as long as its high enough...)

Correct. It is good to use capacitors with a voltage rating higher than required for a likelyhood of long life. Too high a voltage rating makes caps very large and expensive.

do the nF caps have to be the metalized ones, cause I can't find a great deal of them... will the polyester kind work?

Polyester caps are metalized plastic which is what is needed.

just curious also, aside from the pF caps(that are ceramic), does the type matter? or is that just what you ended up using?

Electrolytic caps can have high values (uF) but poor tolerance, small size and low cost. Metalized plastic caps can have medium values (nF), tight tolerance, small size and low cost. Ceramic caps are good at very high frequencies and are usually very low values (pF).
1uF is 1000nf, and 1nF is 1000pF.

I used values of ceramic caps that I had. The circuit will work fine if the 30pF cap is 22pF, 27pF, 33pF or 39pF. :lol:

 

[draco_james]

k, thanks yet again

 

[mstechca]

so just to make sure i don't buy parts that won't work, the resistors that don't have a k after the number, are just in ohms rather than kohms, right?

Correct. The "k" means thousands. 47k is 47,000 ohms.

It is correct to a point. The resistor value is in ohms only if there is nothing after the number, just the ohm symbol, or the word ohms.

If there is no k, but you see an M after the number, it means megaohms (millions of ohms).

the voltage rating can be anything as longs as its over 9V (so like 50 is actually higher than needed, but its doesn't matter as long as its high enough...)

Correct. It is good to use capacitors with a voltage rating higher than required for a likelyhood of long life. Too high a voltage rating makes caps very large and expensive.

For optimal capacitor performance, I recommend using a capacitor that has a voltage rating that exceeds or meets double the supply voltage.

do the nF caps have to be the metalized ones, cause I can't find a great deal of them... will the polyester kind work?

Polyester caps are metalized plastic which is what is needed.

I use ceramic disk radial capacitors for RF work.

just curious also, aside from the pF caps(that are ceramic), does the type matter? or is that just what you ended up using?

Electrolytic caps can have high values (uF) but poor tolerance, small size and low cost. Metalized plastic caps can have medium values (nF), tight tolerance, small size and low cost. Ceramic caps are good at very high frequencies and are usually very low values (pF).
1uF is 1000nf, and 1nF is 1000pF.

I used values of ceramic caps that I had. The circuit will work fine if the 30pF cap is 22pF, 27pF, 33pF or 39pF. :lol:

The best and most truthful capacitor :lol: will have the lowest tolerance rating, a higher voltage rating, and material that is immune to temperature changes and other factors which can affect the capacitor.

I think mica (is that what ya call them?) capacitors are the best, but they are more expensive. Personally, I go with ceramic disk capacitors.