what kind of coil symbol is this

Hi!

I recived one document from 1965 and in this document you can see symbol that looks like transformer without core but in description is written... "COIL".

What kind of electronic element is this and what can i use today, as substitute for this old element ?

Max

It could be a transformer if there is coupling between them.

Im sure it's not transformer becuse upper left part of winding is connected to RF antenna and the lower left side of winding is grounded. There is no coupling between them.

It must be some kind of double winding inductor ?

Show more of the circuit so we can see how it is connected to other parts.

It's an air core transformer.

in any case these are coils.
if its Transformer, then these are primary and secondary windings (coils)..

Naveed

The extended schematics....

I dont know... i think it's some kind of crystal radio.
But what kind of coil is he using ?.
There is no meaning to put the transformer in this part.
Like the "brevor" has written, it can be air transformer but again, with what meaning ?

Max

This is a classical crystal set. The diode on the bottom should not be there. The two coils are in close proximity and act like a transformer with low value of coupling factor k.

The two coils are in close proximity and act like a transformer with low value

Click to expand...

OK.
Can you give me more information how to build this low value transformer.
How far should one coil be from the second one and what is the main purpose of putting the transformer in this part of the schematics.

Should i make the transformer on this way :
stick -- first winding -- isolator -- second winding on the isolator ?

If you have some photo of this kind of transformer, please post it.

Max

In the ancient days a paper tube was used for the coil form. The two coils were wound with close wire spacing. Then as part of the process of tuning in a station the separation between the two coils is adjusted.

The secondary inductance is determined by the variable capacitor capacitance range and the frequency range you want to tune in.

The number of turns on the antenna side is found by experimenting. It is usually fewer than on the other side.

OK.

1.) I dont get it why is he using transformer when he can use just one coil and the capacity can be changed thru some variable capasitor.

2.) If i want to expand radio detecting signal on "whole" radio spectrum, what should i do. Or course, based on this design.

3.) Is there possibility to expand this design for use in the rest of the electromagnetic spectrum ( with cat whisker etc ) ?


Max

Crystal sets only work well on AM broadcasting and you will only get local stations.

You do not need the transformer arrangement. You can put the antenna to the tuned coil on the right.

flatulent said:

This is a classical crystal set. The diode on the bottom should not be there. The two coils are in close proximity and act like a transformer with low value of coupling factor k.

Click to expand...

No it is not, IMAO. See link below what a crystal set looks like.
[b]**broken link removed**[/b]

It looks like the coil drawing is an older type where they left out the coil form. As for the coil form, it could be a bifilar wounded coil on a donut ferrite form.

As for the coil form, it could be a bifilar wounded coil on a donut ferrite form.

Click to expand...

Can you give me additional infos or maybe some photo, becuse im trying to make the same one...

Hi,

The coils are part of a typical radio receiver input.
They acts both as an impedance adapter (i.e. a transformer) and a bandpass filter.

- The right side is a parallel LC filter (bandpass) tuned to the receive frequency. This circuit is calculated for one narrow frequency band. Transmission is maximum at the peak resonance frequency (roughly given by the famous Thomson formula ... )

- The left side is the other part of the transformer, "injecting" the antenna signal into the LC filter. The impedence adaptation is function of the turn ratio between the primary and the secondary coils (square of the turn ratio). This choice is however a bit more complicated, but, in this specific application, the antenna side number of turns is usually between 1/4 and 1/20 of the secondary number of turns.

As you see, the physical form and value of the transformer is highly dependent upon the frequency, the bandwdith and the antenna impedance, and even the output circuit charge (the part with the diodes).

It's not possible to give more advice on the construction without knowing at least the operating frequency. A schematic is welcome...

Hope this helps.

its an IF Transformer (air core) used in RF receivers

IF Transformer (air core)

Click to expand...

do you know the label of some european model ?

My biggest problem is frequency range.
In this experiment i need to "cover" range from 500Khz - 2Ghz.

Yes from 500 Khz - 3Ghz :idea:.
Now, for lower freq. i can use this IF transformer but what about higher freq. ?

I know that there in no such IF transformer design, for such range (till 3Ghz), but is there possibility to cover the AM and FM range with one IF transformer ?

it may be transformer or pulse transformer or IFT intermediate frequency transformer

MaxElec said:

The extended schematics....

I dont know... i think it's some kind of crystal radio.
But what kind of coil is he using ?.
There is no meaning to put the transformer in this part.
Like the "brevor" has written, it can be air transformer but again, with what meaning ?

Max

Click to expand...

It is really a RF air core transformer with the ratio of 1:1. It is made of 2 wires twisted together (or 2 coils as 2 layers on each other) and wound on a plastic or paper/wood frame of about several milimeters in diameter. You can easily calculate the number of turns and the length of the coil basing the formula in any RF antenna calculation book, since you can design by yourself for specific resonance frequency needed.

However, to get the higher gain and high-Q for the resonance circuit of this transformer antenna, they always use the ferrite cores, not air core. You can consult any RF antenna design guide for radio amateurs.

nguyennam