[HBR] transformers or capacitors

[Helmut Usbeck]

>Some questions. What are the pros and cons of IF
>transformer coupling vs capacitor coupling (2-3pf)
>of tuned circuits ? Ray N3XZV pointed me towards
>an article in a mid 50s ARRL Handbook which touts
>some pretty sharp passbands using the latter (several
>stages).
>
>I think it's great to read an article which discusses
>"L1" .... with inductance, number of turns, and coil "Q".
>That's doing it right.
>
>73s  Kees K5BCQ
>************************************
>Visit the HBR Receiver Web Site with over 100 pictures of=
 receivers
>and
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>
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To me, the first thing about using shunt inductors with coupling=
 caps 
was always, seems to be easier to build one own's coils and IF 
strips.  Also changing the coupling cap value is one way of=
 varying 
the selectivity.  I don't think there's a selectivity advantage=
 of 
one over the other.  I built a 50 khz IF strip once using 3=
 inductors 
which then fed an LM-1350 ic.  It worked on the bench and had a 
bandwidth about 2 khz.  The coupling capacitor between the coils=
 was 
a 3 gang variable capacitor.  Increasing the capacitance (and 
coupling) between the coils brought the selectivity out to 12 khz=
 or 
so.  Never used this thing in a receiver.  The inductors were 300=
 
turns of #28 on 1 inch toroids I pulled out of a switching power=
 
supply.  It took about a week and a half to wind the coils.  I=
 hate 
winding toroids now.
Chapter 26 in the Radiotron book has a lot about if transformers=
 
along with the math, Q, selectivity and such.  Only thing it =
 about 
shunt inductors is that they're not used too much.
-- 
Helmut Usbeck, WB2ADT vze2gmp4@verizon.net on 04/24/2002
"You mean you can build something like that!?"