Hi Gurus.

I've been looking for an explanation on coils for a simple FM transmitter, and FM receiver.

Once I bought a FM receiver kit, one of the parts, were a steel wire I was supposed to wind up to form a coil. The kit didn't work well. All I heard was "flopp-flopp-flopp" sound. So I put that away.

On the Net, I've seen explainations (correct spelling?) on how to make good coils. See the attached files: complete turns & L3_2. This looks like copper-wire to me.

In the attached file t7000-2, you see a coil, etched in the PCB.

And here's my question:

What is the best way to make a coil? Is it using a screw with the proper diameter and follow the threads with copper - wire? Or steel - wire? Or do you get the same result by etching it in the PCB?


Jens

 

Hello,

Do you have the schematics and description of your kit?
Coils are usualy made of (enamel) copper wire.
Some even use copper wire with a silver layer.
(Take care the windings do not touch).

Here is some info on making coils:
http://info.ee.surrey.ac.uk/Workshop/advice/coils/air_coils.html

Greetings,
Bertus

 

Hi.

Thanks for the link. I will read it this evening.

This is the link to my kit:

http://www.kemo-electronic.de/product_info/B156-FM-Receiver.php

Jens

 

Hello,

In the description they talk about siver coated wire.

As told the windings may not make contact with eachother.

Also take care of the correct mounting of D1 (the varicap).

I also attached the datasheet and aplication notes of the TDA7000 recieverchip.

Greetings,
Bertus

 

Thank you, Bertus.

I will inspect my soldering, again.

You have been most helpful.

Jens

 

The usual way I wind small coils is to close-wind on an appropriate diameter item such as the shank of a twist drill or bit of plastic tubing.

Form the 'legs' before taking the coil off the 'former' so as not to distort the coil.

Remove the former and gently stretch the coil to the correct length by gripping the legs and/or end turns.

That should give even spacing between turns over the length of the coil.

 

Hi,

my bits holder for my drill makes exactly 10mm diameter air coils, and I've also had success with winding them in the threads of a 10mm screw. This makes perfect space between the turns.

I have also used this link for calculating:

http://208.94.242.202/~sm0vpo/begin/calc-00.htm

Thanks for reply.


Happy new year to all. Let's hope 2010 brings money and joy.

Jens

 

The TDA7000 is not made anymore. It was replaced by the TDA7088 that scans for tuning.
Both have very poor performance as an FM radio and the entire radio with a battery and earphones is sold in The Dollar Store for only $1.00.

 

Hi,

I know that it is not made anymore. Do you know if there is a substitute or similar kind of chip?

Jens

 

Hi,

I know that it is not made anymore. Do you know if there is a substitute or similar kind of chip?

I said that the newer TDA7088 replaces the old TDA7000. The TDA7088 is in the poor quality scanning FM radios sold for only $1.00. I think it is made only in a tiny surface-mount package.

 

Yes, you did. My fault. I'm sorry...

 

Here's an interesting project for an FM receiver... use an MPF-102 FET.
I found this "Radio Shack Special" on the web somewhere. It works, although not very well. Just google 'radio shack special' and you'll find it.

 

The Radio shack Special is a super-regenerative "radio".
It is overloaded by strong local stations.

It detects AM, not FM but if you tune it to one side of an FM station it "slope-detects" by changing the frequency changes into amplitude changes.

It "squelches" which is it turns itself on and off at an ultrasonic frequency so it is very sensitive but that beats with the 19kHz and 23kHz to 53kHz of stereo FM which causes whistles.