In article ,
Joel Koltner wrote:

2) I can readily see why you'd want a center-tapped primary, or a primary
with, say, a tap 10% "up" as a small feedback winding, but why do you get such
things as an IF transformer with 103 and 50 turns on the primary (on either
side of the tap) and then 27 turns on the secondary? (E.g.,
http://www.mouser.com/catalog/specsheets/XC-600014.pdf ). None of my books
address this, and the only thing that looks close on the web is this article:
http://hem.passagen.se/communication/ifcan.html . Is his conclusion, "by
tapping the transformer the Q value increases" the main reason?

Tranformers from the 1960's vintage for bipolar transistors were
tapped in strange ways. I don't remember any special use of taps
on tube era stuff.

3) Sticking a parallel capacitor on the primary to resonate out the
magnetizing inductance makes sense to me. I'm a little less clear on parallel
capacitors on both the primary and secondary -- a double-tuned arrangement.
Hagen's "Radio Frequency Electronics" assigns leakage inductance to the
secondary and then converts the resonating capacitor in parallel with your
load resistance back into a series circuit and, voila!, you now have a series
RLC circuit so clearly bandpass behavior... but this approach implies that you
could just use a *series* resonating capacitor on the secondary instead. Is
that correct? (I am aware that there are a handful of commonly used
transformer equivalent circuit models, you can transform magnetizing or
leakage inductances and losses from primary to secondary or vice versa at
will, etc.)

There's a discussion older ARRL handbooks about getting broad bandwidth
with dual tuned over-coupled IF transformers.

4) Anyone have pointers to good books or articles that ideally discuss some
actual design examples of the more complicated cases (weird primary turns
ratios, double-tuned circuits, etc.)? -- The ones I've found so far as the
simpler single-tuned case, just center-tapped, etc.

Digging out an copy of Terman's _Radio Engineer's Handbook_ (that I
bought at a used bookstore and never got around to reading), it has
a discussion of point 3 in the section on "tuned amplifiers", (which
appears to be what the ARRL was cribbing from).

Mark Zenier
Googleproofaddress(account:mzenier provider:eskimo domain:com)