On Sat, 05 Mar 2005 23:39:44 GMT, Bob Miller
wrote:

Now that would hurt...

There you go Wes. Do you feel any better now? G


Danny, K6MHE

Wes Stewart wrote:
Some years ago my wife had hand surgery and afterwards was getting
physical therapy. Another patient there had lost a thumb to a
circular saw. They made him a new one out of another finger.

I saw on TV the other day where they made a guy
a new thumb from one of his toes.
--
73, Cecil http://www.qsl.net/w5dxp


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CW wrote:
The answers you get on this group are likely to be far less than
useful. I
would recommend rec.radio.shortwave.

CW, I would suggest you refresh yourself on Signal-to-Noise Ratio, and
what it has to do with antennas. I took a look at the shortwave group,
and found a lot of garbage with little or no technical content. This
thread has had some excellent content, care to explain why it was far
less than useful?

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

On 02/03/2005 8:57 PM, Roy Lewallen wrote:
Try this simple test.

Tune your receiver to a part of the dial where there's no station.
Disconnect the antenna from your receiver. If the noise level drops,
impedance matching won't help your signal/noise ratio, it'll just make
everything louder. You can accomplish the same thing by turning up the
volume control.

Pulling the wire just attenuates the noise. So, a more balanced match
will not help with selectivity or overworked front-ends?

If this is the case, and a balun is most useful for transmitters trying
to manage SWR, then I guess it doesn't matter.

I'm still hoping that keeping all of the antenna outside may help with
household EMI. I sort of though that since I'm bothering to have a
transmission line, I may as well hack together a matching circuit for
efficiency.

On 10/03/2005 12:31 PM, clvrmnky wrote:
On 02/03/2005 8:57 PM, Roy Lewallen wrote:

Try this simple test.

Tune your receiver to a part of the dial where there's no station.
Disconnect the antenna from your receiver. If the noise level drops,
impedance matching won't help your signal/noise ratio, it'll just make
everything louder. You can accomplish the same thing by turning up the
volume control.

Pulling the wire just attenuates the noise. So, a more balanced match
will not help with selectivity or overworked front-ends?

If this is the case, and a balun is most useful for transmitters trying
to manage SWR, then I guess it doesn't matter.

.... in which case my only real choice is to shorten the antenna, or
attenuate the signal coming to my front-end a little ...

Hmmm. More to think about.

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 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:
On 10/03/2005 12:31 PM, clvrmnky wrote:

On 02/03/2005 8:57 PM, Roy Lewallen wrote:

Try this simple test.

Tune your receiver to a part of the dial where there's no station.
Disconnect the antenna from your receiver. If the noise level drops,
impedance matching won't help your signal/noise ratio, it'll just
make everything louder. You can accomplish the same thing by turning
up the volume control.

Pulling the wire just attenuates the noise. So, a more balanced match
will not help with selectivity or overworked front-ends?

If this is the case, and a balun is most useful for transmitters
trying to manage SWR, then I guess it doesn't matter.

... in which case my only real choice is to shorten the antenna, or
attenuate the signal coming to my front-end a little ...

Hmmm. More to think about.

You're on the right track, but more information might help.

Your antenna is picking up signal and noise. When you disconnect your
antenna, the antenna's signal and noise are removed, leaving only the
receiver's internal noise. The fact that the noise dropped means that
the noise being coming into the receiver from the antenna is larger than
the internal receiver noise. This is nearly always the case at HF and
nearly never the case at VHF and higher. As long as the noise from the
antenna dominates over the receiver noise, then improving the impedance
match, which is what the original question and answer were about, will
only make both the signal and noise (both coming from the antenna)
bigger. This is exactly what you get when you increase the volume, and
doesn't help the signal to noise ratio one bit. It therefore doesn't
help you hear signals.

There are other ways to help the signal to noise ratio, though. If a
signficant amount of the noise is originating locally, improving
feedline balance with a balun might help. Horizontal polarization will
often be less sensitive than vertical to moderately local noise sources,
because vertically polarized waves can propagate by surface waves while
horizontally polarized waves can't. Feedline balance also improves
rejection of vertically polarized waves when the antenna is horizontal.
This is because it prevents pickup from the feedline itself, which is
often partially, at least, vertical.

Increased antenna directivity will help if the signal and noise are
coming from different directions. But this requires a mechanically or
electrically rotatable antenna unless you're only interested in
listening in certain directions. Short wave listeners sometimes use a
small rotatable loop, which has sharp nulls which can be pointed toward
a single dominant noise source.

You mention an "overworked" front end. If your front end is getting
overloaded from strong signals, which usually manifests itself as
cross-modulation -- "ghost" signals created from existing signals at
different frequencies -- either a passive preselector or an attenuator
is needed. The former is better only if the loud signals are on
frequencies reasonably removed from the frequency where you're
listening. Adding attenuation is fine, until you add so much that the
receiver noise begins dominating. You can use the antenna-disconnection
test to check for that condition. Another way to attenuate the signal is
to *degrade* the impedance match. That's right, if overload is the
problem, you'll do better with a lousier match.

You also mention selectivity. A preselector can take care of attenuating
strong, out-of-band signals. But nothing you can practically do outside
the receiver will help you separate two signals which are close
together. That requires internal modification to the receiver.

Forget about SWR. It's not of any use in improving your ability to hear
signals at HF where the noise from the antenna dominates.

Roy Lewallen, W7EL

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