The diameter is usually not significantly related to the impedance, it
affects Q a lot more.

Impedance is high except at resonance, where it lowers dramatically
(e.g. 500 Ohms to 50 Ohms).

You are asking for trouble with 2 grounds. Any difference in
potential can mean noise. I ground my co-ax on the roof (the mast,
grounded at the bottom) and use the outer conductor for the radio
ground, deep in the bowells of my house.

Technically, I should use a ground lift on the IEC cord, but I don't
unlesss there's a noticeable loop.

On Fri, 11 Jul 2003 21:16:37 GMT, Telamon
wrote:

In article ,
Michalkun wrote:

How does one can determine the impendance of a wire to get the right balun
for it, so it can be hooked up to the coaxial cable?

The impedance of the wire will depend on:

1. The diameter of the wire. The larger the diameter (smaller AWG
number) the lower the impedance will be.

2. The height of the wire above ground. The higher the wire the higher
the impedance will be.

3. The ground conductivity. The more conductive the ground the lower
the impedance will be. Also note here that this is affected by how the
antenna is grounded. If you have just a ground stake or whether you have
radials will make a big difference on how well the wire will perform.
The poorer the ground conductivity the more how you provide grounding
will determine how well the wire will work.

Why grounding is so important is because the wire is just half the
antenna with the ground being the other half. You have to give the RF
some place to go to complete the circuit that is your antenna or it
will not work well.

The coax back to your radio can be that ground but that has the
disadvantage of mixing the antenna currents with the power line noise
at the radios location reducing the signal to noise. One reason why
people are advocates of Baluns is because the antenna can have its own
ground independent of the radio ground.

For a wire antenna one radial run directly under the antenna wire will
do the most good as a minimalist approach.

All that being said a typical wire will be something in the 400 to 600
hundreds of ohms range so the 9 to 1 type of transformer would be the
best type.

In article ,
Dave wrote:

On Fri, 11 Jul 2003 21:16:37 GMT, Telamon
wrote:

In article ,
Michalkun wrote:

How does one can determine the impendance of a wire to get the right balun
for it, so it can be hooked up to the coaxial cable?

The impedance of the wire will depend on:

1. The diameter of the wire. The larger the diameter (smaller AWG
number) the lower the impedance will be.

2. The height of the wire above ground. The higher the wire the higher
the impedance will be.

3. The ground conductivity. The more conductive the ground the lower
the impedance will be. Also note here that this is affected by how the
antenna is grounded. If you have just a ground stake or whether you have
radials will make a big difference on how well the wire will perform.
The poorer the ground conductivity the more how you provide grounding
will determine how well the wire will work.

Why grounding is so important is because the wire is just half the
antenna with the ground being the other half. You have to give the RF
some place to go to complete the circuit that is your antenna or it
will not work well.

The coax back to your radio can be that ground but that has the
disadvantage of mixing the antenna currents with the power line noise
at the radios location reducing the signal to noise. One reason why
people are advocates of Baluns is because the antenna can have its own
ground independent of the radio ground.

For a wire antenna one radial run directly under the antenna wire will
do the most good as a minimalist approach.

All that being said a typical wire will be something in the 400 to 600
hundreds of ohms range so the 9 to 1 type of transformer would be the
best type.

The diameter is usually not significantly related to the impedance, it
affects Q a lot more.

Two AWG wire sizes will change the impedance about 6%. I was trying to
give a sense of how all the parameters of the wire affect the impedance.
The Q of the wire is a complex thing and fairly advanced concept
compared to its impedance. Increasing the wire diameter will reduce the
DC resistance of the wire increasing the Q. Typically this also infers a
narrowing of a resonant peak but other factors conspire to broaden the
peak in this case. Are you concerned with this? I think this is a
non-issue for most receiving antennas.

Impedance is high except at resonance, where it lowers dramatically
(e.g. 500 Ohms to 50 Ohms).

You are confusing the wires intrinsic impedance to its reactance to some
specific frequency of signal energy. This is a common mistake.

You are asking for trouble with 2 grounds. Any difference in
potential can mean noise. I ground my co-ax on the roof (the mast,
grounded at the bottom) and use the outer conductor for the radio
ground, deep in the bowells of my house.

There are two possibilities he

1. You operate the radio on batteries and there is no power line noise
to contend with. From the signal to noise standpoint one or two grounds
are a non-issue.

2. You operate the radio from a AC supply. Here two grounds will reduce
the possibility of power line noise being conducted common mode to the
antenna and then into the radio input. With one ground signal to noise
will be worse if there is any noise on the power line and there always
is some there.

Technically, I should use a ground lift on the IEC cord, but I don't
unlesss there's a noticeable loop.

This is a quick and dirty way to solve a problem. It can be dangerous
and is not recommended. This can also make things worse instead of
better because power supplies in most devices generate some AC noise
currents on the device ground.

Ground loops can cause problems in measurements systems by creating
error voltages and should be avoided. If you don't use two grounds here
a ground loop is formed so noise from the power line, which powers the
radio is added to the measurement and connecting the measurement device
provides the other half of the antenna changing the measurement. Looking
at it this way the radio input is a voltage or power measurement device
that is not floating, which we use to measure the voltage or power from
the antenna. For a single random / long wire antenna the wire is just
half the antenna. The other half is its ground. You don't want your
measurement device ground to influence the measurement so a separate
antenna ground is required. The measurement is the potential difference
between the random wire and its ground terminated in its characteristic
impedance. You then measure the voltage or power across the termination.
The antenna output is some distance from the radio (measurement device)
use coax to convey the signal to it. Here the coax impedance should be
at the antenna output impedance and also the receivers input impedance.
If the antennas output impedance is different then use a transformation
device at the antenna output to change it.

In this way you will get a similar result of signal level whether the
radio is powered from batteries or the AC mains. You can see that if the
antenna does not have its own ground that how the radio is powered will
make a big difference on received signal strength and signal to noise.

--
Telamon
Ventura, California

In article , "Dave"
wrote:

We are not concerned with the characteristic impedance of the wire
antenna. We are concerned with its RF impedance as an antenna, not a
piece of metal.

The characteristic impedance is where the center of the antenna's
impedance spiral is. That's a good choice for a matching impedance if
what you want is a broadband antenna.

See: http://www.anarc.org/naswa/badx/ante..._longwire.html

--
| John Doty "You can't confuse me, that's my job."
| Home:
| Work:

We are not concerned with the characteristic impedance of the wire
antenna. We are concerned with its RF impedance as an antenna, not a
piece of metal.

Resonance is defined as when the reactances neutralize each other, a
very frequency dependant characteristic give a fixed size conductor.

On Sat, 12 Jul 2003 20:39:45 GMT, Telamon
wrote:

Impedance is high except at resonance, where it lowers dramatically
(e.g. 500 Ohms to 50 Ohms).

You are confusing the wires intrinsic impedance to its reactance to some
specific frequency of signal energy. This is a common mistake.

Telamon wrote in message ..
Let me explain that I live in town and have
local noise to compete with any signal I pick up. This noise must be
overcome so I only hear the program material of interest. In other words
the volume can be turned up so the program material is very loud without
any background noise or hiss. Antenna efficiency that generates more
signal energy overcomes the local noise sources. You must be unusually
lucky to live in a location where all you pick up is either broadcast
signal or atmospheric noise. I don¹t think most people are as fortunate.

I assume your noise must be shack generated, and is an ingress
problem. I would think anyway. If the noise was local, but picked up
from the antenna itself
along with the desired station, then adding the transformer would not
change the s/n ratio. The noise would increase along with the station
at an equal rate. Everything would "sound" the same. Only the S meter
would read higher.

If you have a noise ingress problem, feedline decoupling is the
answer, not a better impedance match. Also,feedline decoupling, and
impedance matching, or SWR, are totally unrelated. You can have great
decoupling with an 80 to 1 mismatch. Or you can have a perfect 1:1
match with horrible decoupling. They are totally unrelated. I'm not
lucky. I live in the city of Houston amid all kinds of noise
generating crap. But due to decent feedline decoupling, any noise I
hear is picked up from the antenna. And any attempts to achieve a
better match do not increase my s/n ratio, being as I always have
enough signal level to begin with even with no matching.

Most antennas output impedance is nowhere near the typical 50-ohm coax
and a transformation can remedy that.

But it doesn't matter. You don't have enough loss with the mismatch to
worry about with any decent radio. It's just not enough to knock you
out of the water. I did the math on this a few months ago, and posted
here to demonstrate this. This has been debated before many times. I
used coax feed with wild feedpoint impedances just to ensure a worst
case as far as feeder loss. It doesn't amount to enough to hurt you.
If it does, you have a lame radio. If you used a random wire direct
with no feeder, there is even less loss. For receiving, the mismatch
in that case doesn't matter enough to worry about at all.

Well OK I guess my radios are lame or busted. I must be imagining things
when signals go from ³I can just make it out S1² to ³easy to listen to
S3² on the folded dipole with the transformer. My other loop antennas
must not be working right either.

Is the S1 with the folded dipole fed directly without the transformer,
or another antenna? It sounds like you have or had a noise ingress
problem if the noise does not increase at the same level as the signal
when the transformer is added.
If this is the case, again, this would not be a function of impedance
matching, but a function of better feedline decoupling. The decoupling
is improving the s/n ratio, not the impedance transformation. If the
signal was S1, it should have been solid copy, if it is at S3. If it
wasn't, the overriding noise was not picked up by the antenna. It was
picked up on the outer shield of the coax down in the shack, piped up
to the feedpoint, and then piped back down to the radio on the inner
part of the outer shield. "I assume you used coax"..S1 is plenty of
signal level for solid copy if no shack noise is drowning it out.
What's the problem with the loop? Lots of noise also? MK

In article , "Dave"
wrote:

Is this Smith Chart stuff? (You must forgive me, I am a primitive.)

A Smith chart is a way of graphically relating impedances to reflection
coefficients. The code that made the plots on the web page did the same
sort of calculations numerically. The plots themselves are semilog
Cartesian coordinates, not Smith charts.


On Sun, 13 Jul 2003 12:21:23 +0400, "John Doty" wrote:

In article , "Dave"
wrote:

We are not concerned with the characteristic impedance of the wire
antenna. We are concerned with its RF impedance as an antenna, not a
piece of metal.

The characteristic impedance is where the center of the antenna's
impedance spiral is. That's a good choice for a matching impedance if
what you want is a broadband antenna.

See: http://www.anarc.org/naswa/badx/ante..._longwire.html



--
| John Doty "You can't confuse me, that's my job."
| Home:
| Work:

In article ,
(Mark Keith) wrote:

Telamon wrote in message

..
Let me explain that I live in town and have
local noise to compete with any signal I pick up. This noise must be
overcome so I only hear the program material of interest. In other words
the volume can be turned up so the program material is very loud without
any background noise or hiss. Antenna efficiency that generates more
signal energy overcomes the local noise sources. You must be unusually
lucky to live in a location where all you pick up is either broadcast
signal or atmospheric noise. I don¹t think most people are as fortunate.

I assume your noise must be shack generated, and is an ingress
problem. I would think anyway. If the noise was local, but picked up
from the antenna itself
along with the desired station, then adding the transformer would not
change the s/n ratio. The noise would increase along with the station
at an equal rate. Everything would "sound" the same. Only the S meter
would read higher.

If you have a noise ingress problem, feedline decoupling is the
answer, not a better impedance match. Also,feedline decoupling, and
impedance matching, or SWR, are totally unrelated. You can have great
decoupling with an 80 to 1 mismatch. Or you can have a perfect 1:1
match with horrible decoupling. They are totally unrelated. I'm not
lucky. I live in the city of Houston amid all kinds of noise
generating crap. But due to decent feedline decoupling, any noise I
hear is picked up from the antenna. And any attempts to achieve a
better match do not increase my s/n ratio, being as I always have
enough signal level to begin with even with no matching.

Most antennas output impedance is nowhere near the typical 50-ohm coax
and a transformation can remedy that.

But it doesn't matter. You don't have enough loss with the mismatch to
worry about with any decent radio. It's just not enough to knock you
out of the water. I did the math on this a few months ago, and posted
here to demonstrate this. This has been debated before many times. I
used coax feed with wild feedpoint impedances just to ensure a worst
case as far as feeder loss. It doesn't amount to enough to hurt you.
If it does, you have a lame radio. If you used a random wire direct
with no feeder, there is even less loss. For receiving, the mismatch
in that case doesn't matter enough to worry about at all.

Well OK I guess my radios are lame or busted. I must be imagining things
when signals go from ³I can just make it out S1² to ³easy to listen to
S3² on the folded dipole with the transformer. My other loop antennas
must not be working right either.

Is the S1 with the folded dipole fed directly without the transformer,
or another antenna? It sounds like you have or had a noise ingress
problem if the noise does not increase at the same level as the signal
when the transformer is added.
If this is the case, again, this would not be a function of impedance
matching, but a function of better feedline decoupling. The decoupling
is improving the s/n ratio, not the impedance transformation. If the
signal was S1, it should have been solid copy, if it is at S3. If it
wasn't, the overriding noise was not picked up by the antenna. It was
picked up on the outer shield of the coax down in the shack, piped up
to the feedpoint, and then piped back down to the radio on the inner
part of the outer shield. "I assume you used coax"..S1 is plenty of
signal level for solid copy if no shack noise is drowning it out.
What's the problem with the loop? Lots of noise also? MK

The antenna is a folded dipole cut for 13 meters connected to the radio
with coax.

I evaluated two stations on this band. One had locally generated noise
interference and the other did not.

I tried a repeat today with switching the matching transformer in and
out of the circuit and compared it to a large ferrite toroid in its
place. The coax made one turn through the toroid. The ferrite worked as
well as the transformer on the station with the local noise on it. No
difference found on the station in the clear. In addition the
transformer did not make a difference in the S meter reading either.

It takes me several minutes to change the transformer in or out and we
had a minor geomagnetic storm yesterday so conditions changing must have
been what I saw as a performance difference.

Today conditions are more stable and I switched the transformer and / or
toroid choke in and out several times averaging the results.

So it looks like the only benefit of the transformer was isolation it
provided on the folded dipole.

--
Telamon
Ventura, California

Doesn't loose coupling pinch bandwidth? Q through the roof?

Higher Q = lower noise but not necessarily better overall voice
perfomrance, as I recall.

On 13 Jul 2003 07:40:13 -0700, (Mark Keith) wrote:

Telamon wrote in message ..
Let me explain that I live in town and have
local noise to compete with any signal I pick up. This noise must be
overcome so I only hear the program material of interest. In other words
the volume can be turned up so the program material is very loud without
any background noise or hiss. Antenna efficiency that generates more
signal energy overcomes the local noise sources. You must be unusually
lucky to live in a location where all you pick up is either broadcast
signal or atmospheric noise. I don¹t think most people are as fortunate.

I assume your noise must be shack generated, and is an ingress
problem. I would think anyway. If the noise was local, but picked up
from the antenna itself
along with the desired station, then adding the transformer would not
change the s/n ratio. The noise would increase along with the station
at an equal rate. Everything would "sound" the same. Only the S meter
would read higher.

If you have a noise ingress problem, feedline decoupling is the
answer, not a better impedance match. Also,feedline decoupling, and
impedance matching, or SWR, are totally unrelated. You can have great
decoupling with an 80 to 1 mismatch. Or you can have a perfect 1:1
match with horrible decoupling. They are totally unrelated. I'm not
lucky. I live in the city of Houston amid all kinds of noise
generating crap. But due to decent feedline decoupling, any noise I
hear is picked up from the antenna. And any attempts to achieve a
better match do not increase my s/n ratio, being as I always have
enough signal level to begin with even with no matching.

Most antennas output impedance is nowhere near the typical 50-ohm coax
and a transformation can remedy that.

But it doesn't matter. You don't have enough loss with the mismatch to
worry about with any decent radio. It's just not enough to knock you
out of the water. I did the math on this a few months ago, and posted
here to demonstrate this. This has been debated before many times. I
used coax feed with wild feedpoint impedances just to ensure a worst
case as far as feeder loss. It doesn't amount to enough to hurt you.
If it does, you have a lame radio. If you used a random wire direct
with no feeder, there is even less loss. For receiving, the mismatch
in that case doesn't matter enough to worry about at all.

Well OK I guess my radios are lame or busted. I must be imagining things
when signals go from ³I can just make it out S1² to ³easy to listen to
S3² on the folded dipole with the transformer. My other loop antennas
must not be working right either.

Is the S1 with the folded dipole fed directly without the transformer,
or another antenna? It sounds like you have or had a noise ingress
problem if the noise does not increase at the same level as the signal
when the transformer is added.
If this is the case, again, this would not be a function of impedance
matching, but a function of better feedline decoupling. The decoupling
is improving the s/n ratio, not the impedance transformation. If the
signal was S1, it should have been solid copy, if it is at S3. If it
wasn't, the overriding noise was not picked up by the antenna. It was
picked up on the outer shield of the coax down in the shack, piped up
to the feedpoint, and then piped back down to the radio on the inner
part of the outer shield. "I assume you used coax"..S1 is plenty of
signal level for solid copy if no shack noise is drowning it out.
What's the problem with the loop? Lots of noise also? MK

I used to make folded dipoles out of 300 Ohm TV Twinlead and match the
feedpoint with a TV balun driving RG-6 to the receiver. It worked
pretty well into an R-390A. Including medium wave, even.

On Sun, 13 Jul 2003 18:49:34 GMT, Telamon
wrote:


The antenna is a folded dipole cut for 13 meters connected to the radio
with coax.

I evaluated two stations on this band. One had locally generated noise
interference and the other did not.

I tried a repeat today with switching the matching transformer in and
out of the circuit and compared it to a large ferrite toroid in its
place. The coax made one turn through the toroid. The ferrite worked as
well as the transformer on the station with the local noise on it. No
difference found on the station in the clear. In addition the
transformer did not make a difference in the S meter reading either.

It takes me several minutes to change the transformer in or out and we
had a minor geomagnetic storm yesterday so conditions changing must have
been what I saw as a performance difference.

Today conditions are more stable and I switched the transformer and / or
toroid choke in and out several times averaging the results.

So it looks like the only benefit of the transformer was isolation it
provided on the folded dipole.

Amazing.

I'm going to save this, in case it comes up at a party.

Thanks.

On Sun, 13 Jul 2003 19:58:11 +0400, "John Doty" wrote:

In article , "Dave"
wrote:

Is this Smith Chart stuff? (You must forgive me, I am a primitive.)

A Smith chart is a way of graphically relating impedances to reflection
coefficients. The code that made the plots on the web page did the same
sort of calculations numerically. The plots themselves are semilog
Cartesian coordinates, not Smith charts.


On Sun, 13 Jul 2003 12:21:23 +0400, "John Doty" wrote:

In article , "Dave"
wrote:

We are not concerned with the characteristic impedance of the wire
antenna. We are concerned with its RF impedance as an antenna, not a
piece of metal.

The characteristic impedance is where the center of the antenna's
impedance spiral is. That's a good choice for a matching impedance if
what you want is a broadband antenna.

See: http://www.anarc.org/naswa/badx/ante..._longwire.html