On 02/03/2005 6:25 PM, Richard Clark wrote:
On Wed, 02 Mar 2005 13:04:50 -0500, clvrmnky
wrote:
[...]
I've seen a neat artificial ground/antenna tuner from MFJ (I think)
which seems to offer a lot of bang for the buck. It even has multiple
inputs for high-Z single wires. Would this be useful for SW?

Certainly, but you would achieve just as much with a simple tuner
(cheap one without the transmitter meters). In fact, this tuner is
generally very necessary to keep local AM stations from desensitizing
your receiver. This is a common plight suffered by many who would
otherwise think they were doing pretty well, but just need more
antenna to get those signals others are reporting.

I've been looking more seriously at the balun/tuner/ground offerings out
there. Seems to be a fair amount of contention out there about whether
antenna tuners work for SW.

If I can lessen the abuse my otherwise sensitive front-end is taking
from the wire, then maybe it's worth a try. That is, I'm
hoping/guessing that such a device will help my radio not hear a strong
signal 10-15kHz on either side of the mark, swamping out stuff I might
otherwise hear near these stations.

In this regard, homebrew is good because it allows me to experiment for
cheap. Even the cheapest MFJ equipment is a bit steep shipped to my
door in Canada.


Finally, I'm probably just going to wind my own balun out of a ferrite
core. I just can't seem to find the details on how to wind the copper.
Do I wind the primary first around the whole core, and then the
secondary on top of it?

What you are describing is a conventional power transformer - NOT the
same thing as a Transmission Line Transformer. What you should really
concentrate on is what is called a Transmission Line Choke (perfectly
accomplished using a 1:1 Current BalUn/UnUn).

Hmmm. I understand that a balun is really a type of matching
transformer, and that the specific nomenclature used is really just to
distinguish the various use, application and materials of the transformer.

All the designs for homebrew longwire X:1 baluns I've seen are step-down
transformers using specific types of ferrite material. Of course,
typical use often has one side of the primary and secondary going to a
good RF ground (for balanced application, anyway), which I do not have.

My thinking is that since I'm going to be experimenting with different
wire antennas this summer, why not try a few different matching
techniques as well?

The lack of good RF ground is going to be a challenge, and may preclude
any of this. I've got lots of wire, however, so I'm willing to give a
weekends up to try different things.

-- cm