[ARC5] BC-455 IFT - measurements

[Fuqua, Bill L]

  Inductive coupling to the 2mH coil would be useless. The induced voltage in an inductor is in series with the inductor so if you did use magnetic coupling
the inductive capacitance is effectively between the induced voltage source and the grid which would attenuate the signal considerably and not
contribute to the selectivity.
   If they used a tuned secondary at the impedance on the grid would also been increased by the effective turns ratio times the Q. 
It could have been done if they used a tapped tuned secondary. There is room for experimentation here if you want to improve
the selectivity. I still liked the IF feedback (Q-multiplier) approach myself. Simple and improved the selectivity a great deal. High
selectivity is a bit of a problem if you are flying an aircraft and trying to tune in as signal at the same time. These were not always
used in bombers. 
73
Bill wa4lav

________________________________________
From: ARC5 [arc5-bounces at mailman.qth.net] on behalf of kgordon2006 at frontier.com [kgordon2006 at frontier.com]
Sent: Wednesday, October 29, 2014 3:28 PM
To: Dennis Monticelli
Cc: ARC5 at mailman.qth.net
Subject: Re: [ARC5] BC-455 IFT - measurements

On 29 Oct 2014 at 10:58, Dennis Monticelli wrote:

> Perhaps someone can comment upon the degree of coupling between the two
> coils.  If the coupling is tight, then the capacitance's on both sides will
> interact.  Adjusting one side will pull the other side into pretty much a
> single resonant circuit.  Perhaps that was what was intended.

Dennis:

In my opinion, the coupling is pretty loose, but I have no way to quantify that at this
point.

What I will do is to take a close-up photo of my 7277 IFT with the cover removed, and
with a tape-measure along side of it so you can see the distance between and the
orientation of the two coils.

Then if you would give us your opinion of the coupling, I would be grateful.

vy 73,

Ken W7EKB
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