[ARC5] Selectivity improvement in ARC-5 receivers - another question.

[Ian Wilson]

My understanding is that the stray capacitive coupling worsens the
performance on the high frequency side. For this reason, the grounded
ends of the coils forming the IF transformer are usually positioned
adjacent to each other. Addition of a metal plate reduces any residual
capacitive coupling still further.

I have to say that opening up some of the more inventive IF transformer
designs is a real pleasure. Sometimes there are several extra components
lurking in there; sometimes (as in the ARC-5 IFTs) there are unsuspected
ground connections (other than through the pins); and sometimes the
intended function is too complex to figure out (e.g. any FM discriminator
transformer that I have attempted to decode).

73, ian K3IMW


On Mon, Jun 2, 2014 at 5:47 PM, Kenneth G. Gordon <kgordon2006 at frontier.com>
wrote:

> On 2 Jun 2014 at 16:54, Dennis Monticelli wrote:
>
> > Ken,
> >
> > I have not done any measurements but I'm pretty sure the plates only
> affect the
> > electrostatic coupling not the magnetic coupling. The two coils are in
> the near
> > field of each other so magnetic coupling is probably dominant. The
> designer must
> > have had a reason to isolate the two coils from a capacitive coupling
> > standpoint.
>
> That makes sense, Dennis. Thank you. I agree that the designers must have
> had a reason. As far as I am concerned, all those folks who were involved
> in
> the design of the ARC-5 were sheer geniuses.
>
> Ken W7EKB
>
> > Dennis AE6C
> >
> >     Another question (to which you may not have the answer): in the ARC-5
> >     IFTs
> >     there is often a small circular grounded metal plate between the two
> coils.
> >     My first impression on finding one of these was that its purpose was
> to
> >     reduce the magnetic coupling between the two coils.
> >
> >     However, after further investigation, and thinking about it, I am
> not at all
> >     sure that is its real or only purpose.
> >
> >     Moving the coils further apart, rather than adding a second "plate"
> does far
> >     more to improve the selectivity of those IFTs than adding that
> second plate,
> >     spacing those plates so that one is nearer one coil, and the other
> nearer
> >     the other coil.
> >
> >     In fact, it seems that removing that metal plate entirely while in
> the
> >     process of moving the coils further apart results in no apparent ill
> >     effects.
> >
> >     This apparent result, however, may be simply because my limited test
> >     equipment did not show the effect.
> >
> >     In any case, not knowing whether or not my removing the plate had any
> >     effect, I put it back in, but centered it between the two coils.
> >
> >     I have yet to complete my own "research" on this selectivity
> improvement
> >     idea. I am FAR behind Jeep's work on it.
> >
> >     Your thoughts?
> >
> >     Ken W7EKB
> >     _____________________________________________________________
> >     _
> >     ARC5 mailing list
> >     Home: http://mailman.qth.net/mailman/listinfo/arc5
> >     Help: http://mailman.qth.net/mmfaq.htm
> >     Post: mailto:ARC5 at mailman.qth.net
> >
> >     This list hosted by: http://www.qsl.net
> >     Please help support this email list: http://www.qsl.net/donate.html
> >
>
>
>
> Kenneth G. Gordon W7EKB
>
> "Courage is being scared to death but saddling up anyway."--- John   Wayne
>
> ______________________________________________________________
> ARC5 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/arc5
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:ARC5 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>