# Replacing coils (Plese)

[Someone Electro]

I found a simple AM transmiter(yeey ):

**broken link removed**


I have all the parts but i dont have a stick of ferite.

How many thurns wod i need around a air core coil or a coil around a screw and what diameter

 

[john1]

Hi,

you can't use a screw,
or anything conductive.

cannibalise a piece of ferrite from an old radio.

i would be interested to hear how you get on,
Regards, John

 

[Someone Electro]

I think i have one somvare but its not round

Its like two half cicles whith 1 cm betven it

And I think its diameter is biger than 8 mm

How cod i caculate how meany thurns?

I have a 15 year (its a transistor tipe) old radio but i listen to it wean i work.I scavegd some things from it but only the LED UV meter and the casete player, I had to let a eqolizer i pece becose it controles the volume. all rest is on one circuit bord(radio reciver,amplefier...),

 

[Someone Electro]

O and what abaot to coacutate it to air core

 

[Someone Electro]

Why isent anyone replying ?

Or are evrybody out ther idiots on coils (like me).

 

[Sebi]

For MW You need a coil on ferrite rod. What You actually have is a wawe-trap for cable mounting. (maybe from VGA, printer, or supply cable. This have very different permeability as ferrite rod, so unuseable for this purpose.
The air coil is phiscally too big for application, this is the reason of ferrite application.
Search the old MW pocket-radio and canibalize it, if cannot foud another source.

 

[Russlk]

What is the capacitor that will tune the coil? What frequency are you trying to recieve? I can calculate an air core coil for you with that information.
OH! never mind, I looked at your link. The coil can be wound on a quaker oats box or corn meal box (3.85 inches diameter). 135 turns of #22 enameled wire should do it. The turns should be neatly wound close together. If the wires are spaced, it will tune higher in frequency. The wire size is not critical.

 

[Someone Electro]

135 Thurns around what?

Ow:
The alomst whole MW band is free(3-5 weak stations)

The coil can have to much inductivi but not to litle (you can get to the right inducticity with stecing the inductir)

 

[Someone Electro]

IT WORKS !!!

Its i bit unstable but im going to fix that.

Whith a 110 pF cap and a inductor whith 66 thurns it transmits at 810 kHz

 

[Someone Electro]

oops

The contact of the tunung cap had some resistance and it gave the right freq.

Hey if i wod put in a potencimeter serial whith the tuning cap i cod change the freq.Right?

 

[Someone Electro]

Its stable now and i built in a potencimeter for tunung.

This thing isnt only a trasmiter its also a RF remudulator becose i get some stations and some data streams wean its on.

Anyway im hapy whith it