Hello - Calling R2000SW and Telamon Where Are You ? ?

The Topic has move to the "Impedance of the Transmission Line"

IIRC - If the Matching Transformer is used and the Secondary Side
of the Matching Transformer exhibits a nominal Impedance of 50 Ohm;
and is connected to a 50 Ohm type Coax Cable; that is connected to
a Receiver's 50 Ohm Antenna Input.

The Coax Cable for all practical purposes is not a significant part
of the Impedance Relationship (Ratio) between the Antenna and
the Receiver's Antenna Input.

The Primary of the Matching Transformer 'helps' to smooth-out
the variations in Impedance of the Antenna due to changes in
Frequency with respect to the Receiver's Antenna Input Circuit.

The Impedance Matching improvement is far from perfect :
But the Dynamic Range of the Front-Ends of most Modern
Shortwave Receivers can easily compensate for any signal
lost due to Impedance Miss-Matches between the Antenna
and the Receiver's Antenna Input Circuit.

hey I could be wrong - cause iane ~ RHF

On 27 Dec 2005 20:33:15 -0800, "RHF"
wrote:

Hello - Calling R2000SW and Telamon Where Are You ? ?

The Topic has move to the "Impedance of the Transmission Line"

IIRC - If the Matching Transformer is used and the Secondary Side
of the Matching Transformer exhibits a nominal Impedance of 50 Ohm;
and is connected to a 50 Ohm type Coax Cable; that is connected to
a Receiver's 50 Ohm Antenna Input.

The Coax Cable for all practical purposes is not a significant part
of the Impedance Relationship (Ratio) between the Antenna and
the Receiver's Antenna Input.

The Primary of the Matching Transformer 'helps' to smooth-out
the variations in Impedance of the Antenna due to changes in
Frequency with respect to the Receiver's Antenna Input Circuit.

Only point I was making is the impedance of the antenna could be
anywhere from a few ohms to thousands of ohms. A 9-to-1 balun between
the antenna and a 50 ohm transmission line only helps if the antenna
is in the neighborhood of 450 ohms.

The Impedance Matching improvement is far from perfect :
But the Dynamic Range of the Front-Ends of most Modern
Shortwave Receivers can easily compensate for any signal
lost due to Impedance Miss-Matches between the Antenna
and the Receiver's Antenna Input Circuit.

With that much dynamic range, why use a balun at all?

hey I could be wrong - cause iane ~ RHF

I can be wrong, too. Antennas are complicated beasts :-(

bob
k5qwg
.
.
. .
.

On Wed, 28 Dec 2005 04:56:24 GMT, Bob Miller
wrote:


So you don't put high Z signal into a lower-Z cable. Major faux pas.
500 Ohms is assumed to be about the max for a wire antenna, no?

On Wed, 28 Dec 2005 05:25:49 GMT, David wrote:

On Wed, 28 Dec 2005 04:56:24 GMT, Bob Miller
wrote:


So you don't put high Z signal into a lower-Z cable. Major faux pas.
500 Ohms is assumed to be about the max for a wire antenna, no?

It can be much higher. Looking at the book "Wire Antennas" by William
Cowan, W6SAI, and his chapter on end fed wires:

"In the case of a random length, end-fed antenna, the radiation
resistance at the feed point can vary over a large range, depending on
the operating frequency and the actual length of the antenna. The
measured radiation resistance can be as high as 5000 ohms or as low as
2 or 3 ohms..."

That's why I wonder about the popularity of these 9-to-1 baluns.

One of my antennas is a 20 meter end fed wire, and I tune it with an
old Heathkit AC-1 antenna tuner, which is made especially for random
length, end fed wires. A modern equivalent would be something like the
MFJ-16010 random wire tuner, which at $49.95 doesn't cost much more
than some of the 9-1 baluns I see advertised :-)

It would require bringing the random wire into your residence, and
then running a short length of coax from the tuner to the receiver. I
understand some wouldn't like that because of in-house noise, but
there are always trade-offs to anything.

bob
k5qwg

"Bob Miller" wrote in message ...
[snip]
One of my antennas is a 20 meter end fed wire, and I tune it with an
old Heathkit AC-1 antenna tuner, which is made especially for random
length, end fed wires. A modern equivalent would be something like the
MFJ-16010 random wire tuner, which at $49.95 doesn't cost much more
than some of the 9-1 baluns I see advertised :-)

It would require bringing the random wire into your residence, and
then running a short length of coax from the tuner to the receiver. I
understand some wouldn't like that because of in-house noise, but
there are always trade-offs to anything.

bob
k5qwg


Is there a detailed description, with possible diagrams, explaining how to strip,
connect coax and a random wire... i.e. no balun, direct random wire to coax
connection (coax leading into tuner after that)

On Wed, 28 Dec 2005 14:35:52 GMT, Bob Miller
wrote:


"In the case of a random length, end-fed antenna, the radiation
resistance at the feed point can vary over a large range, depending on
the operating frequency and the actual length of the antenna. The
measured radiation resistance can be as high as 5000 ohms or as low as
2 or 3 ohms..."

I don't think you'll get the kilo-Ohms unless you're under a quarter
wave at the frequency of interest.

Bob [K5QWG],

ABOUT - The "Low Noise" Antenna Design Concepts
that were popularized by John Doty :
http://groups.yahoo.com/group/Shortw...a/message/5178
http://groups.google.com/group/rec.r...38b087b5e89fee


Shortwave Listener (SWL) Longwire Antenna - by John Doty
? WHY Use a Fixed Matching Transformer ?
http://www.anarc.org/naswa/badx/ante..._longwire.html

hope this helps - iane ~ RHF
Shortwave Listener's (SWL) Antenna Group on YAHOO !
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/

The
measured radiation resistance can be as high as 5000 ohms or as low as
2 or 3 ohms..."

yep..

That's why I wonder about the popularity of these 9-to-1 baluns.

generally a waste of money I think... Some bands they might
help, some might hurt... The reason I think it's a waste of time
is rarely are they actually needed to improve the s/n ratio.

One of my antennas is a 20 meter end fed wire, and I tune it with an
old Heathkit AC-1 antenna tuner, which is made especially for random
length, end fed wires. A modern equivalent would be something like the
MFJ-16010 random wire tuner, which at $49.95 doesn't cost much more
than some of the 9-1 baluns I see advertised :-)

I've had one of those 16010's since about 1978. Still works, and I
usually use for a mobile impedance matcher. You can reverse the
leads if you want to match a low z load vs the normal high Z used
with most random wire tuners.

It would require bringing the random wire into your residence, and
then running a short length of coax from the tuner to the receiver. I
understand some wouldn't like that because of in-house noise, but
there are always trade-offs to anything.

Myself, giving that there is usually no increase in s/n ratio
when using a tuner to match a random wire, or other wire
antenna, I'd generally prefer a preselector over a tuner.
The tuner will help reduce out of band signals, but the
preselector will usually do a better job at that.
You can make a simple random wire tuner with a wound
coil that you can tap with a gator clip, and a variable cap.
The 16010 uses a wound tapped toroid inductor instead of the
coil, but otherwise is the same.
When listening on 160m with my IC 706mk2g, I sometimes
get AM-BC interference that puts images across the band.
We have a lot of strong MW stations in this town.
Using my MFJ-989c T match tuner will clean that stuff
right up. So even a tuner will act as a preselector of sorts.
MK

wrote:

The
measured radiation resistance can be as high as 5000 ohms or as low as
2 or 3 ohms..."

yep..

That's why I wonder about the popularity of these 9-to-1 baluns.

generally a waste of money I think... Some bands they might
help, some might hurt... The reason I think it's a waste of time
is rarely are they actually needed to improve the s/n ratio.

Hardly a waste of money, they actually DO work.

Been using them here for a good number of years.

dxAce
Michigan
USA

On Thu, 29 Dec 2005 16:30:58 -0500, dxAce
wrote:



wrote:

The
measured radiation resistance can be as high as 5000 ohms or as low as
2 or 3 ohms..."

yep..

That's why I wonder about the popularity of these 9-to-1 baluns.

generally a waste of money I think... Some bands they might
help, some might hurt... The reason I think it's a waste of time
is rarely are they actually needed to improve the s/n ratio.

Hardly a waste of money, they actually DO work.

Been using them here for a good number of years.

dxAce
Michigan
USA
Wow. Steve and I agree on something. Call Kofi Annan.