Jimmie,

Thank you for your comments.

On Wed, 18 Feb 2009 13:19:12 -0800 (PST), JIMMIE wrote:
On Feb 18, 3:12*pm, Richard Clark wrote:
On Wed, 18 Feb 2009 12:06:09 -0600, Frnak McKenney

wrote:
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".

Hi Frank,

Matching provokes heated debates that in times past ran to 600+
postings - few knew what they were arguing (but enjoyed arguing
nonetheless) and little was offered.

A JFET at these frequencies does satisfy the naive requirements of
"matching," but that giving you a reception solution doesn't always
follow.
--snip--
Its not uncommon to have a high impedance input into a preamp.
This is the one-size- fits-all approach. While its not good
engineering for the purist it works quite well to make a casual user
happy and may be the practical solution for even the professional
installation..

Well, I think of myself as a "casual user", and _I'd_ like to be
happy. grin!

I don't mind throwing in a high-impedance (JFET) front end to my
antenna simply on the basis that (a) people who seem to know what
they're talking about recommend it and (b) I associate "high
impedance" with "sensitive" (which seems like a desirable quality
when you're working with microvolts). Someday, though, I'd like to
have build up a framework in which _I_ can see why it's appropriate,
or at least "does no harm". grin!

My brother Bruce is working on the same problem from a slightly
different angle; his experience is in software and digital stuff,
and I find myself unintentionally assuming the role of "RF expert"
without an EE degree or years of circuit design to back it up. Left
to myself, I'm perfectly capable of pushing stuff around on the
breadboard until it seems to work, but when I'm offering advice to
someone else I'd prefer a better response to his questions than
"someone else said so". grin!

Ive had some experience limited working with VLF and it always
seemed the thing that made the difference between a good and bad VLF
antenna was the quality of the ground network

Thanks for the suggestion. Do you think that my current "ground", a
30x60' 4-way pipe-loop network (mixed copper and cast iron) with
thermal radiation elements might be... um, "less than
satisfactory"? grin!


Frank
--
"What one writer can make in the solitude of one room is something
no power can easily destroy." -- Salman Rushdie
--
Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all)