At 03:18 PM 6/17/2007 -0700, you wrote:
It looks as though adding more wire, either in the form of a coil or
additional turn(s) on the loop itself would have the effect of lowering
the top and bottom freqs thus altering the freq range of the loop. VE7AFN.
noswadplease <<mailto:ewdawso_1%40verizon.net>ewdawso_1@...>
wrote: Hi Group,
In the photo section under passin_thru2 ther is a loop antenna, 3rd
and 4th photo that shows an octagon loop antenna. In the photo it
shows a coil, just looks like heavy gauge wire coiled, that is between
the antenna and the variable capacitor. Does anyone know what this
loop is for or what it could possibly be used for? I am currently in
the final stages of building a loop from pvc for am dxing. Ever since
I saw that picture it has intrigued me. If anyone knows the purpose
please respond. Apparently passin_thru2 didn't know either.
Ed Dawson
Hi Ed,
Well the loop and coil are in series which will create a combined (A + B)
inductance. Adding or shorting turns on the small inductor would have the
effect of adding or subtracting a partial turn on the loop .... how much
will depend on the ratio of the inductors. I would guess that the
inductance of the loop is much greater than the 'side' coil inductor and
thus it's effect would be rather small in affecting the tuning range of the
overall circuit. A direct response to your question is: The side coil in
the photo provides an interesting conversation piece.
As a side light, it is possible to adjust the inductive reactance of a coil
by putting a capacitive reactance (capacitor) in parallel with it. Of
course when they equal each other they are said to be 'resonant'. If you
put a capacitor and inductor in series and adjust the capacitor to
resonance at a particular frequency as in an 'L network', the ratio of the
capacitance to inductance can provide impedance transformation (commonly
used in antenna tuners). Since it is much easier to obtain variable
capacitors than variable inductors an old trick is put a variable capacitor
in parallel with the inductor. This second capacitor cancels some of the
inductive reactance of the coil giving the effect of a variable inductor
.... common in the Z-match antenna tuner.
Jim, VE3CI
