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

clvrmnky wrote:
The lack of good RF ground is going to be a challenge, and may preclude
any of this.

If you use a balanced antenna system, you don't need
an RF ground for the receive function.
--
73, Cecil, W5DXP


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On 10/03/2005 1:04 PM, Cecil Moore wrote:
clvrmnky wrote:

The lack of good RF ground is going to be a challenge, and may
preclude any of this.


If you use a balanced antenna system, you don't need
an RF ground for the receive function.

Hmmm. I can probably make a decent-sized folded dipole out on the
patio. It will have to turn a corner, but I can probably get a
fair-sized loop out there.

On 10/03/2005 4:15 PM, clvrmnky wrote:
On 10/03/2005 1:04 PM, Cecil Moore wrote:

clvrmnky wrote:

The lack of good RF ground is going to be a challenge, and may
preclude any of this.



If you use a balanced antenna system, you don't need
an RF ground for the receive function.


Hmmm. I can probably make a decent-sized folded dipole out on the
patio. It will have to turn a corner, but I can probably get a
fair-sized loop out there.

Ok, further to this. Even if I'm not to care about impedance matching
or choking, my receiver has an unbalanced antenna input. One side of
the antenna connection simply goes to "chassis" ground.

This implies that I should use a traditional BalUn to make the balance
connection work for me. Otherwise, one side of a dipole or looped
longwire is just going to go straight to ground (such as it is.)

I built myself a reasonably stealthy random-wire running along the top
of my wooden balcony railing (which turns a 90-deg corner around the
building) for a total length of around 25-30 ft. I was considering
simply looping the wire to make a bent, untuned, "folded dipole" (the
wires would be 5-6 inches apart) just to get more wire into the wind.

To realize this, I am supposing I'll have to use a true BalUn to get the
signal into my unbalanced front-end somehow. Since most designs for a
true BalUn assumes I have a decent ground, I'm a bit stumped by your
comment. Perhaps the ground of the BalUn can just go to the coax sleeve?

Thanks for all your suggestions.

On Mon, 14 Mar 2005 13:02:20 -0500, clvrmnky
wrote:
This implies that I should use a traditional BalUn to make the balance
connection work for me. Otherwise, one side of a dipole or looped
longwire is just going to go straight to ground (such as it is.)

Hi OM,

You reject the BalUn (matching/choking) to only presume the
implication (one wire goes to ground) forces you to use it for another
reason?

Wrong implication, even if the solution works. The one side of any
dipole/loop antenna design going "straight to ground" (ground a
euphemism for Hell?) is not a loss in any sense of the design. The
receiver is sharing the same path - unless it is strictly battery
operated without a charger connection.

Your radio wants to see a signal potential applied across its input
and chassis (as you put it, which is suitable enough). With a
monopole the input is satisfied, but you need either a ground or
counterpoise connected to the chassis. With a dipole or loop, the two
returning wires meet the radio's needs at the input/chassis
connection. A ground connection or counterpoise for the dipole/loop
would be benign in the practical sense. You won't need it (unless you
have lightning phobias); and with the common specie of radio you will
have it, somewhere, anyway (it will then simply be uncontrolled and
variable).

Perhaps the ground of the BalUn can just go to the coax sleeve?

That will work fine.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote

A ground connection or counterpoise for the dipole/loop
would be benign in the practical sense. You won't need it (unless you
have lightning phobias);

Well said. And most of us who get anywhere near as much rain as Richard
does (in WA) unfortunately have a LOT more lightning to deal with in the
summer. In that case, shield-grounding the coax of a dipole should happen as
soon as the feedline is down at ground-level, and again at the station
entrance/single point ground, where it should connect to a coax
surge/lightning arrestor.

Perhaps the ground of the BalUn can just go to the coax sleeve?

That will work fine.

73's
Richard Clark, KB7QHC

Indeed, matching transformers such as Industrial Communications Engineers
make, insist the metal xfmr case be grounded for safe and proper operation.
I ground long wires on both an I.C.E. xfmr and a current-type Balun,
directly to ground rods that the equipment is mounted on. This is also the
connection point for ground radials for the long wire, if used.

Best regards,

Jack Painter
Virginia Beach, Virginia

On Mon, 14 Mar 2005 16:53:57 -0500, "Jack Painter"
wrote:
And most of us who get anywhere near as much rain as Richard
does (in WA) unfortunately have a LOT more lightning to deal with in the
summer.

Hi Jack,

In all actuality, Seattle sees the least lightning nationwide. If
you drew a line from Seattle to Miami, you would find that the
incidence of lightning grows roughly ten-fold as you progressed along
that line.

73's
Richard Clark, KB7QHC

On Thu, 10 Mar 2005 12:24:15 -0500, clvrmnky
wrote:
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.

Hi OM,

I am sure that is the gospel in rec.radio.shortwave. There is little
there that qualifies as dependable information - except what station
was being heard (and then, this information is obviously iffy).

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.

No, no tuner is going to have that much Q unless you get a very small
loop to go with it. Then, you are better off tuning the loop instead.
All-in-all you need to twist a knob somewhere. There are several
merits of using tuners with longwires. The chief among them is that a
tuner will depress the strenght of local AM stations that will desense
your receiver (even if you are not even tuned anywhere near that AM
station's frequency - such is its power and the weakness of receiver
front ends).

In this regard, homebrew is good because it allows me to experiment for
cheap.

By all means, do it.

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.

This is all true, but bears very little on your needs.

All the designs for homebrew longwire X:1 baluns I've seen are step-down
transformers using specific types of ferrite material.

Those are conventional transformers, not chokes, not BalUns (or
UnUns).

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.

May as well divorce yourself from those explanations. A tuner will do
the job of transforming AND filter out the crap. A tuner is a
variable transformer. If you have a single wire coming in to the
tuner, add a hank of wire to the tuner's ground connection [hank = 20'
±6dB].

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?

Matching at the antenna, or matching at the receiver? Unless you have
long arms, or many antennas for each band, it is simpler to match at
the receiver.

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.

Returning to the need for a BalUn, properly a choke, for your
application. It is useful for reducing house noise from getting mixed
with your signal. Conventional transformers won't do that (unless you
add a choke at their output on the signal downstream).

73's
Richard Clark, KB7QHC

clvrmnky wrote:
. . .

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.


No, that's not correct. Balun is a contraction of "balanced-unbalanced".
A balun is sometimes combined with a transformer or made to transform
impedance, and sometimes it isn't. Its function is to balance the
currents on the two feedline conductors (either coax or parallel wire
line) to prevent radiation from the line when transmitting and pickup
from the line when receiving. The impedance transformation is a separate
function for a different purpose.

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.

A typical 1:1 "current" or "choke" balun, which does what I described
above, does not require any external "ground" or other connection. If
fact, such a connection provides a path for imbalance current and can
actually degrade balance. There are a number of ways of providing this
function, with and without ferrite cores.

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?

There's no reason not to experiment. Improving the match won't help your
signal-to-noise ratio. After your experiments show that this is so, you
can go back and learn why not.


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.

There's no need for an RF ground if you use a well-balanced antenna.

Roy Lewallen, W7EL