Richard,

Thank you for posting back.

On Mon, 16 Feb 2009 23:07:37 -0800, Richard Clark wrote:
On Mon, 16 Feb 2009 22:22:20 -0600, Frnak McKenney
wrote:

First, the need for impedance matching between an antenna and a
receiver.
--snip complaint about the size/cost of 60kHz h-w diploes grin!--

So any non-loop antenna I can construct will necessarily be a "short
wire" or "electrically small" antenna (two useful search terms).
But how does one go about calculating the impedance of a coat hanger
or an extension cord ("short piece of wire")?

One doesn't try.

So Yoda was right: "Do, or do not. There is no 'try'." grin!

What has puzzled me is that I have run across designs that use
(e.g.) a JFET isolation amplifier hooked to a whip or hunk-o-wire
with the statement (or implication) that this is done to ",atch the
antenna's impedance". So I;ve been trying to figure out how to
calculate/estimate what it would be, without much success.

The simple solution is the conventional one - you use a tuner.

The tuner provides the matching (providing it has sufficient
inductance and capacitance - you will have to investigate designs) and
adjacent signal rejection (which could seriously de-sense your
received signals).

I imagine that the inductance of a 6' extension cord (not plugged
in, just dangling from a planter hook grin!) is down in the
uH-or-less range, which would mean that most of the "tuning"
inductance would have to be supplied to achieve 60kHz. I have this
image of a big (tens of mH) inductor in series with a moderate
capacitor and my (electrically) short wire; all of the surrounding
EM sets the electroncs in the wire to dancing, but the series RC
blocks those which are wiggling "off-key" (e.g. not dancing at the
"proper" rate of 60kHz).

Your antenna doesn't need to be very big, but it might help to have it
very remote, if there are noise sources nearby (like motors, aquarium
heaters, bottle style TVs, ...); and the line sufficiently choked. A
good ground too, tying into the service ground through a separate wire
to reduce coupling of noise from shared grounds.

Well, there's no question that I have EM in the area. I hooked my
DVM -- set to ACV -- between the radiator and my 6' extension cord;
would you believe 8-10V??!! Not much current, though: feed it
through a 1k resistor and measure the voltage across it, suddenly
it's down in the mV range. grin!

... This last may
introduce a ground loop if your Mohican is so vintage as to have had
relaxed design standards. A little research online reveals it is
battery operable. You may want to fully exercise that option.

The Mohican came with two 12V power "modules" which plug into the
back of the unit. The AC power module has a transformer with a
12V-12V center-tapped secondary, which is good, but then they run
the line voltage out of the module and down into the receiver's
volume control's on/off switch. The module's 12V power and 120V
switching connections are done through a 9-pin tube socket with
mating connector/cable; remember those? grin!

73's

Thanks for the hepl.


Frank
--
There is one thing even more vital to science than intelligent
methods; and that is, the sincere desire to find out the truth,
whatever that may be. -- Charles Sanders Pierce
--
Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all)