[ARC5] Easy selectivity improvement....Mutual coupling measurement

[Bruce Long]

If you have a way to accurately measure inductance there is a fairly simple  way to measure mutual inductance between two coils

In order to use this to measure ARC-5 receiver IF coil mutual coupling you would ahve to disconnect the resonanting and tuning capacitances from both the primary and the secondary.

The procedure is
Measure primary side (self) inductance---secondary side open circuited 

Measure secondary ( side) inductance--- primary side open circuited
Measure inductance of primary and secondary sides connected in series aiding

Measure inductance of primary and secondary side connected in series opposing

do some simple algebra


If there is interest i will provide better information on this procedure.  I use it often at work.

I have good impedance measurement equipment available to me at work.  If some one wants to send me one or  more ARC-5 IF transformer cans with suitable modes already made i woudl be happy to make the inductance/ mutual inductance measurements and return both


You know at some point it is possible to mix the arc-5 IF frequency to some other common IF frequency such as 455kHz or 9 MHz, pass the signal through a commercial narrow fileter and then use the same stable LC or xtal 2nd LO to heterodoxy the filtered signal back up to the ARC 5 IF frequency.


bruce


________________________________
 From: Kenneth G. Gordon <kgordon2006 at frontier.com>
To: Richard Knoppow <1oldlens1 at ix.netcom.com> 
Cc: Arc5 at mailman.qth.net 
Sent: Tuesday, May 7, 2013 9:45 AM
Subject: Re: [ARC5] Easy selectivity improvement....isn't...
 

On 6 May 2013 at 18:06, Richard Knoppow wrote:

>      There are several old text books though I can't cite 
> one off the top of my head, with "universal selectivity 
> curves" in them that show the shape of the curves of coupled 
> transformers with various degrees of mutual inductance 
> coupling.

Yes. I have Terman's here, among others. But how do you easily measure 
that mutual coupling?

The only way I have here to do that is to connect a100 K resistor in series 
between my sweep generator and the input of the IF transformer, then my 
scope to the output, and manually adjust the spacing to see what I get.

Given the way the transformers are built and the "tight quarters" this is not 
going to be a short-term job.

>      The optimum spacing of the ARC transformers could be 
> found by using a sweeper and indicator or a spectrum 
> analyser with coupled tracking generator.

I don't have that fancy equipment. I have a B&K sweep/function generator 
with a sawtooth or ramp output which will drive the horizontal input of my 
scope, and which covers the necessary frequency range, and I have a 
couple of good scopes. I also have a good HP-8640B. Those will have to do.

>      Its sometimes possible to broaden out a normal IF 
> transformer by adding an auxilliary winding to increase 
> mutual inductance. Theoretically, such a winding with 
> opposing couping would serve to decrease coupling but I've 
> not seen anything practical on this.

That would be too much work for me. I want to use what is there.

Thanks for the info.

Ken
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