[ARC5] BC-455 IFT - measurements

[J Mcvey via ARC5]

The primary is the only resonant part there and probably approx 17 uh in parallel with the 180 pf.
The low reactance of the 180 pf coupling to the grid dominates the input circuit because the Xl  of the secondary L7 is on the order of 35K.
The circuit would probably work if L7 was not there and  replaced with a resistor.  However I think they are using the transformer turns ratio for voltage augmentation, so there would be less gain from the first IF. 

Analysis of that simple circuit can get reasonably complicated if the coupling interaction and mutual inductance is considered. 
So, to raise the Q, improving  the L6-C12 combo with something better ( higher Q components?) would be the way to do it. Otherwise, it's back to "regen".

Does that make sense?



On Wednesday, October 29, 2014 8:35 PM, Kenneth G. Gordon <kgordon2006 at frontier.com> wrote:
 


On 30 Oct 2014 at 9:24, AKLDGUY . wrote:

> This is a confusing thread to follow because some are talking of a dual
> winding, others of a single winding. If there's a single winding with an
> inductance that seems too high to some, perhaps the following will 
> help.

Neil:

To help get things straight, the IFT has two "coils" in it, both wound on 
the same form. 

The top coil, which is the secondary, is a pie-wound type coil, about 
1/16" thick. It measures around 2+ mH (millihenries).

It appears to NOT be resonant at the IF frequency. There is no fixed 
capacitor anywhere near it.

The lower coil, which is the primary, and is in parallel with a nominally 
"180 pfd" capacitor, is a single-layer coil which covers the bottom 3/4 
of the coil form, and is spaced about 3/16" below the pie-wound coil.

That combo is resonant at about 2830 Khz. Its inductance is about 17 uH 
(microhenries).

Does that make it a bit clearer?

I can send you a photo and a schematic if you would like to see them.

Ken W7EKB
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