[HBR] HR-67

[Eddy Swynar]

Hi Helm...

Nice tip! I'll keep that in mind...

I think a lot of guys look at basic stuff like coil spacing as some sort of
black magic---it's a science, true, but also a bit of an art, as you just
described...

Thanks again, Helm...

~73~ Eddy VE3CUI - VE3XZ



----- Original Message -----
From: "Helmut Usbeck" <vze2gmp4@verizon.net>
To: "Diane Swynar" <gswynar@durham.net>; <hbr@mailman.qth.net>
Cc: <vze2gmp4@verizon.net>; <N2EY@aol.com>
Sent: Friday, April 12, 2002 3:09 PM
Subject: Re: [HBR] HR-67


>
> > One little caveat to receiver builders who, like me, wind their own
coils
> > in RF amplifiers, etc., and that is this: do NOT place your link coil
too
> > close to the main tuning coil. I did just that with my version of the
Mate
> > For The Mighty Midget receiver, hoping to maximize sensitivity of the
final
> > product, above all...
> >
> > The coils are over-coupled: when I'm trying to listen to AM on 1885-KHz
> > with an SSB or CW contest down the band, I can hear the junk all over
the
> > dial! Now, I agree this receiver isn't the last word in complexity &
all,
> > but I know if I had separated the two coils up to a maximum of 3/8"
apart
> > (as suggested by Rocky in his regen books), the set-up would have had a
LOT
> > more up-front selectivity, where it really counts.
> >
>
> Coupling coils used to drive me nuts.  The way I do my RF coils now is to
get
> them on frequency (or about) and then instead of using a coupling coil I
> start making temporary taps up from the ground end of the RF coil while
> monitoring (with a scope or a meter) a very low level RF input ( signal
> generator or such).  Go for maximum and then tap back down 1/2 of of the
> signal level being monitored.  You could do pretty much the same with a
> coupling coil by adding or subtracting turns and/or spacing.  It usually
> turns out to be the best compromise between sensitivity and selectivity.
For
> me it's a bit more of a sane cut and try method.
>
> Regards,
> Helm.  WB2ADT