Dave wrote:

Okay, I'll try to keep you posted. Here's what I asked on Yahoo!

OKAY, here are the new questions and clarifications...

Thanks for clearing up for me why it is called a random wire. I
thought that was just what they called it when it wasn't 1/4 or 1/2
wavelength.

I realized something today- I think I am actually talking about
installing a HALF-WAVE dipole, not a 1/4 wave. Since it is twin-lead
I am talking about, and since it is going to be joined at the far
end, each leg would be twice the 1/4 wavelength of the physical
cable. Am I right here?

It sounds like you're thinking about making a folded dipole. The total
length of the twinlead folded dipole should still be a half wavelength
but the impedance at the connection point (middle) for the downlead
changes from about 50-ohms for a simple dipole to 300-ohms for the
folded type. This means a 50 or 75-ohm coax lead would not be suitable
without a 6:1 impedance matching transformer. The higher impedance side
of the transformer connects to the middle of the dipole and the low side
goes to the coax.

Correct me if I am wrong, but you do ground one side of a dipole,
right? So one leg would be grounded along with the shield of the
coax, right?

It's not necessary to ground the coax shield from a dipole because it's
a balanced antenna design. However you may want to ground the chassis of
the receiver itself. The coax should be connnected to a balanced antenna
input on the receiver. This means the coax shield is not directly
connected (grounded) to the receiver's chassis. You should be aware that
some receiver's don't have the proper input connection for a balanced
antenna like a dipole. In that case you would just connect the coax to
whatever external antenna input there is and not be concerned whether
the coax shield is grounded to the chassis or not. It's not the ideal
way to do it, but sometimes you don't have any choice. I forgot what
receiver you're using.

What I am visualizing is two pieces of twin-lead, one called A (left)
and the other called B (right.) A would have one side of one end
soldered to the ground rod (call this the "near" end) with the other
side of that end hanging out in space. The rest of that piece of
twin-lead (side A) would go up the side of my house to the eaves and
over several meters. The far end of A would have the two conductors
soldered together. B would have one side of the "near" end attached
to the appropriate lead of a 300/75 ohm matching transformer, which
has it's other lead soldered to the grounding rod and goes to 75 ohm
coax. The other side of the "near" end of B hangs out in space. B
would then go up the side of the house to the eaves, just like A, but
would then stretch several meters in the other direction. The "far"
end of B would also have the two conductors soldered together. Each
leg is a little over 15 meters long (counting the part that goes up
as well as the part that goes over), which would make the whole
dipole a half-wavelength for some frequency slightly below 10 MHz.
(Have I got this right?)

The coax would travel approx. 4 meters to my window, where it would
go through another matching transformer and into the external antenna
input of the radio.

Wouldn't that be a half-wave dipole?

A folded dipole is made from twinlead by first cutting it to a half
wavelength long (total length) for the frequency you want. The two wires
in each end are connected together. Then you open (strip) an inch or so
of the insulation for one wire *only* (either wire), at the middle of
the twinlead. Cut the exposed wire and pull two short lengths of it
(pigtails) out of the twinlead. Connect each of those wires to the
matching transformer on it's high impedance side.

Would it matter that the side of the house is covered in steel
siding, against which it would be lying?

Yes it would. You want to get the twinlead section out in the open, like
between two trees, and as high as possible. The coax would run from the
middle of the twinlead dipole (matching transformer) to the receiver.
The dipole should be orientated so it runs at a right angle to the two
directions you want to hear the best. If you wanted to hear signals from
the east and west, you would run the dipole (twinlead) north to south.

Would this work, or would an inverted L still be better (or
quieter)? I could put the grounding rod immediately outside my
window, which might enable me to make the long leg of the L somewhat
longer than the combined 30 meters of the dipole. That would make
for a shorter run of coax, but the soil would be drier thereby making
for a poorer ground (where it is now, the grounding rod sits next to
the output of a downspout.)

It's not clear to me why you are thinking of making a folded dipole when
a simple dipole would be easier. The latter doesn't require any matching
transformer for the coax and uses just one wire (split in the middle)
for the dipole element. A dipole responds best to the frequency for
which it is designed and it's bi-directional. The inverted-L is a
broadband antenna and usually non-directional if it's not too long. I
suggest you build a low noise inverted-L. See the following website:

http://www.anarc.org/naswa/badx/ante...e_antenna.html

If I went with the inverted L (with joined conducters on the far end
to make a loop) would I still ground one side of the twin-lead? Do
you ground one side of a loop?

If you join the ends, you no longer have an inverted-L design. It's
become a horizontal loop antenna. You wouldn't use twinlead to make an
inverted-L, just a single horizontal wire with either a single lead wire
from one end or coax. The website I gave you (above) shows the best way
to connect a coax lead to an inverted-L.

Okay, I've written War and Peace. Sorry for the great number of
questions, I'm just trying to understand the fundamentals of
installing an antenna. I hope I am not trying your patience.

Thanks,

Dave

No problem with the questions. It's nice to see an interesting on topic
thread for a change.


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Hey Starman,

Thanks for the answers. Following are replies interspersed.


"starman" wrote in message
...
Dave wrote:

Okay, I'll try to keep you posted. Here's what I asked on Yahoo!

OKAY, here are the new questions and clarifications...

Thanks for clearing up for me why it is called a random wire. I
thought that was just what they called it when it wasn't 1/4 or 1/2
wavelength.

I realized something today- I think I am actually talking about
installing a HALF-WAVE dipole, not a 1/4 wave. Since it is twin-lead
I am talking about, and since it is going to be joined at the far
end, each leg would be twice the 1/4 wavelength of the physical
cable. Am I right here?

It sounds like you're thinking about making a folded dipole. The total
length of the twinlead folded dipole should still be a half wavelength
but the impedance at the connection point (middle) for the downlead
changes from about 50-ohms for a simple dipole to 300-ohms for the
folded type. This means a 50 or 75-ohm coax lead would not be suitable
without a 6:1 impedance matching transformer. The higher impedance side
of the transformer connects to the middle of the dipole and the low side
goes to the coax.


Yes, I saw a diagram of a folded dipole today in an old Amateur Radio
Handbook, and it looks like what I am talking about, more or less. I also
found out that a half-wave dipole does not need to be grounded.

Correct me if I am wrong, but you do ground one side of a dipole,
right? So one leg would be grounded along with the shield of the
coax, right?

It's not necessary to ground the coax shield from a dipole because it's
a balanced antenna design. However you may want to ground the chassis of
the receiver itself. The coax should be connnected to a balanced antenna
input on the receiver. This means the coax shield is not directly
connected (grounded) to the receiver's chassis. You should be aware that
some receiver's don't have the proper input connection for a balanced
antenna like a dipole. In that case you would just connect the coax to
whatever external antenna input there is and not be concerned whether
the coax shield is grounded to the chassis or not. It's not the ideal
way to do it, but sometimes you don't have any choice. I forgot what
receiver you're using.


I am using a DX-402 (aka Sangean ATS 505). I would be surprised if it had a
balanced antenna input, and have been thinking about just clipping the
external antenna to my whip after all. I hooked 20 feet of 300 ohm twinlead
to a 300/75 ohm transformer and miniplug last night and plugged it in, but
the signal strength was about half of what my whip gives me. Therefore, the
change in plans.


What I am visualizing is two pieces of twin-lead, one called A (left)
and the other called B (right.) A would have one side of one end
soldered to the ground rod (call this the "near" end) with the other
side of that end hanging out in space. The rest of that piece of
twin-lead (side A) would go up the side of my house to the eaves and
over several meters. The far end of A would have the two conductors
soldered together. B would have one side of the "near" end attached
to the appropriate lead of a 300/75 ohm matching transformer, which
has it's other lead soldered to the grounding rod and goes to 75 ohm
coax. The other side of the "near" end of B hangs out in space. B
would then go up the side of the house to the eaves, just like A, but
would then stretch several meters in the other direction. The "far"
end of B would also have the two conductors soldered together. Each
leg is a little over 15 meters long (counting the part that goes up
as well as the part that goes over), which would make the whole
dipole a half-wavelength for some frequency slightly below 10 MHz.
(Have I got this right?)

The coax would travel approx. 4 meters to my window, where it would
go through another matching transformer and into the external antenna
input of the radio.

Wouldn't that be a half-wave dipole?

A folded dipole is made from twinlead by first cutting it to a half
wavelength long (total length) for the frequency you want. The two wires
in each end are connected together. Then you open (strip) an inch or so
of the insulation for one wire *only* (either wire), at the middle of
the twinlead. Cut the exposed wire and pull two short lengths of it
(pigtails) out of the twinlead. Connect each of those wires to the
matching transformer on it's high impedance side.


Gotcha. Saw a diagram like that today in that book, so I understand what
you are talking about. This would be easy.

Would it matter that the side of the house is covered in steel
siding, against which it would be lying?

Yes it would. You want to get the twinlead section out in the open, like
between two trees, and as high as possible. The coax would run from the
middle of the twinlead dipole (matching transformer) to the receiver.
The dipole should be orientated so it runs at a right angle to the two
directions you want to hear the best. If you wanted to hear signals from
the east and west, you would run the dipole (twinlead) north to south.


Gotcha. I was planning on running the vertical portion of twinlead that
went from ground level/grounding rod/coax up to the eaves over the steel
siding, but I could just as easily run the coax up the side of the house,
which would put all of the twinlead above the steel siding. Still not "out
in the open" but probably the best I can do. Wifey doesn't want anything
that obviously says "Hi there, I'm an antenna!" I am beginning to consider
running the coax around to the end of the house and up that side, and laying
the twinlead along the ridge of the roof from one end to the other. That
would be a up a lot higher and a lot more "out in the open."

Would this work, or would an inverted L still be better (or
quieter)? I could put the grounding rod immediately outside my
window, which might enable me to make the long leg of the L somewhat
longer than the combined 30 meters of the dipole. That would make
for a shorter run of coax, but the soil would be drier thereby making
for a poorer ground (where it is now, the grounding rod sits next to
the output of a downspout.)

It's not clear to me why you are thinking of making a folded dipole when
a simple dipole would be easier. The latter doesn't require any matching
transformer for the coax and uses just one wire (split in the middle)
for the dipole element. A dipole responds best to the frequency for
which it is designed and it's bi-directional. The inverted-L is a
broadband antenna and usually non-directional if it's not too long. I
suggest you build a low noise inverted-L. See the following website:

http://www.anarc.org/naswa/badx/ante...e_antenna.html


I will check this out. I was thinking of a folded dipole just because I
already have 50' of twinlead sitting around. Of course, I have plenty of
regular wire sitting around too.

If I went with the inverted L (with joined conducters on the far end
to make a loop) would I still ground one side of the twin-lead? Do
you ground one side of a loop?

If you join the ends, you no longer have an inverted-L design. It's
become a horizontal loop antenna. You wouldn't use twinlead to make an
inverted-L, just a single horizontal wire with either a single lead wire
from one end or coax. The website I gave you (above) shows the best way
to connect a coax lead to an inverted-L.


Gotcha. I'll look at it and sleep on it.


Okay, I've written War and Peace. Sorry for the great number of
questions, I'm just trying to understand the fundamentals of
installing an antenna. I hope I am not trying your patience.

Thanks,

Dave

No problem with the questions. It's nice to see an interesting on topic
thread for a change.

Thanks for the encouragement. I'm not yet sure what I will end up doing,
but I want to make the best decision possible.

Dave

Dave wrote:

I am using a DX-402 (aka Sangean ATS 505). I would be surprised if it had a balanced antenna input, and have been thinking about just clipping the external antenna to my whip after all. I hooked 20 feet of 300 ohm twinlead to a 300/75 ohm transformer and miniplug last night and plugged it in, but the signal strength was about half of what my whip gives me. Therefore, the change in plans.

It would be a mistake to connect a good external antenna directly to the
whip. The receiver will almost certainly overload. You know the symptoms
for overloading now. If you build the low noise inverted-L, the coax can
be connected to the external antenna jack with a mini plug.

I was planning on running the vertical portion of twinlead that went from ground level/grounding rod/coax up to the eaves over the steel siding, but I could just as easily run the coax up the side of the house, which would put all of the twinlead above the steel siding. Still not "out in the open" but probably the best I can do. Wifey doesn't want anything that obviously says "Hi there, I'm an antenna!"

It's funny how women have an aversion to antennas. Must be an esthetic
thing. :-)

I am beginning to consider running the coax around to the end of the house and up that side, and laying the twinlead along the ridge of the roof from one end to the other. That would be a up a lot higher and a lot more "out in the open."

The horizontal section (single wire) of an inverted-L could also run
along the roof ridge. The vertical downlead wire would connect to one
end of the horizontal section and run down the end wall of the house to
the ground. The balun would be located near the ground next to a ground
rod. The coax would go from the balun to the receiver. That's the design
of the low noise inverted-L except it's better to locate the antenna
away from the house when you can.

No problem with the questions. It's nice to see an interesting on topic
thread for a change.

Thanks for the encouragement. I'm not yet sure what I will end up doing,
but I want to make the best decision possible.


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Replies interspersed.


"starman" wrote in message
...
Dave wrote:

I am using a DX-402 (aka Sangean ATS 505). I would be surprised if it
had a balanced antenna input, and have been thinking about just clipping
the external antenna to my whip after all. I hooked 20 feet of 300 ohm
twinlead to a 300/75 ohm transformer and miniplug last night and plugged
it in, but the signal strength was about half of what my whip gives me.
Therefore, the change in plans.

It would be a mistake to connect a good external antenna directly to the
whip. The receiver will almost certainly overload. You know the symptoms
for overloading now. If you build the low noise inverted-L, the coax can
be connected to the external antenna jack with a mini plug.


If it wasn't much worse than what I am dealing with right now, I can live
with it. Especially if I buy or build an antenna tuner, which I am planning
to add in one way or another. Let me ask you this, what makes the inverted
L so good for noise? I am taking what you say seriously, but if I install
the antenna on top of the roof and run it down the other side of the house
it will be quite close to our A/C compressor, which I expect to become a
significant source of EMI. What if I just ran it along the ridge of the
house and attached it to coax up *there*, before running the coax down the
side of the house and grounding the shield to the grounding rod? Seems like
that would eliminate a great deal of EMI from the A/C compressor, which I
cannot move.


I was planning on running the vertical portion of twinlead that went
from ground level/grounding rod/coax up to the eaves over the steel
siding, but I could just as easily run the coax up the side of the house,
which would put all of the twinlead above the steel siding. Still not "out
in the open" but probably the best I can do. Wifey doesn't want anything
that obviously says "Hi there, I'm an antenna!"

It's funny how women have an aversion to antennas. Must be an esthetic
thing. :-)

Wife read your comments and laughed. She says that if women designed
antennas they would be a lot prettier. Probably Modern Art, if I know her.




I am beginning to consider running the coax around to the end of the
house and up that side, and laying the twinlead along the ridge of the
roof from one end to the other. That would be a up a lot higher and a lot
more "out in the open."

The horizontal section (single wire) of an inverted-L could also run
along the roof ridge. The vertical downlead wire would connect to one
end of the horizontal section and run down the end wall of the house to
the ground. The balun would be located near the ground next to a ground
rod. The coax would go from the balun to the receiver. That's the design
of the low noise inverted-L except it's better to locate the antenna
away from the house when you can.

Away from the house is not possible. Even if it was, that would put it near
the power lines. How would I build a balun? (Websites/links?)

No problem with the questions. It's nice to see an interesting on
topic
thread for a change.

Thanks for the encouragement. I'm not yet sure what I will end up
doing,
but I want to make the best decision possible.

Gotta go. Wife has to get up at 5:00 and I am supposed to get up first and
fix breakfast. Long day tomorrow. I pulled up the grounding rod today
(using a car jack to lift it out) and then told my wife what I had done.
She asked what it was there for, and why didn't we still need it. Told her
the TV antenna used to be connected to it, but since we moved that it wasn't
being used. Now I need to install another grounding rod for the TV antenna
in it's new location. Wasn't thinking when I put it there and didn't ground
it. It's not hooked up anyway. We haven't even watched any broadcast
programs on that TV in years, using the small one with an independant
antenna in the bedroom instead. The big one is just used for watching
DVD's.

Thanks for the help.

Dave

The word balun to describe this device, while quite common, is incorrect. Go
he www.kc7nod.20m.com
Look for matching transformer.

"Dave" wrote in message
...
Away from the house is not possible. Even if it was, that would put it
near
the power lines. How would I build a balun? (Websites/links?)

It's an impedance matching transformer or unun. I use the word 'balun'
because most people haven't heard the term 'unun'.

CW wrote:

The word balun to describe this device, while quite common, is incorrect. Go
he www.kc7nod.20m.com
Look for matching transformer.

"Dave" wrote in message
...
Away from the house is not possible. Even if it was, that would put it
near
the power lines. How would I build a balun? (Websites/links?)


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We knew that you knew the difference. I was just insuring that Dave new
the difference.

"starman" wrote in message
...
It's an impedance matching transformer or unun. I use the word 'balun'
because most people haven't heard the term 'unun'.

CW wrote:

The word balun to describe this device, while quite common, is
incorrect. Go
he www.kc7nod.20m.com
Look for matching transformer.

"Dave" wrote in message
...
Away from the house is not possible. Even if it was, that would put
it
near
the power lines. How would I build a balun? (Websites/links?)


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So, a matching transformer is all I need? I have pretty much decided to use
300 ohm twinlead along the rood ridge with a 300/75 ohm matching transformer
to connect it to the coax, and more as needed between the coax and radio.
Will that honestly work?

Thanks,

Dave


"starman" wrote in message
...
It's an impedance matching transformer or unun. I use the word 'balun'
because most people haven't heard the term 'unun'.

CW wrote:

The word balun to describe this device, while quite common, is
incorrect. Go
he www.kc7nod.20m.com
Look for matching transformer.

"Dave" wrote in message
...
Away from the house is not possible. Even if it was, that would put
it
near
the power lines. How would I build a balun? (Websites/links?)


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THANK YOU for this link! I especially like the schematic for the MFJ-956.
I'm definetly going to build that.

Dave


"CW" wrote in message
...
The word balun to describe this device, while quite common, is incorrect.
Go
he www.kc7nod.20m.com
Look for matching transformer.

"Dave" wrote in message
...
Away from the house is not possible. Even if it was, that would put it
near
the power lines. How would I build a balun? (Websites/links?)

starman wrote in message ...
Dave wrote:

I am using a DX-402 (aka Sangean ATS 505). I would be surprised if
it had a balanced antenna input, and have been thinking about just
clipping the external antenna to my whip after all. I hooked 20 feet
of 300 ohm twinlead to a 300/75 ohm transformer and miniplug last
night and plugged it in, but the signal strength was about half of
what my whip gives me. Therefore, the change in plans.

It would be a mistake to connect a good external antenna directly to the
whip. The receiver will almost certainly overload. You know the symptoms
for overloading now. If you build the low noise inverted-L, the coax can
be connected to the external antenna jack with a mini plug.

I was planning on running the vertical portion of twinlead that
went from ground level/grounding rod/coax up to the eaves over the
steel siding, but I could just as easily run the coax up the side of
the house, which would put all of the twinlead above the steel
siding. Still not "out in the open" but probably the best I can do.
Wifey doesn't want anything that obviously says "Hi there, I'm an
antenna!"

It's funny how women have an aversion to antennas. Must be an esthetic
thing. :-)

I am beginning to consider running the coax around to the end of the house and up that side, and laying the twinlead along the ridge of the roof from one end to the other. That would be a up a lot higher and a lot more "out in the open."


DAVE & STARMAN,

- - - - - - - - - - This would be my recommendation - - - - - - - - -
-

The horizontal section (single wire) of an inverted-L could also run
along the roof ridge. The vertical downlead wire would connect to one
end of the horizontal section and run down the end wall of the house to
the ground. The balun would be located near the ground next to a ground
rod. The coax would go from the balun to the receiver. That's the design
of the low noise inverted-L except it's better to locate the antenna
away from the house when you can.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-

Unless you have a Target Frequency and Country (Direction)
I do not recommend Dipole Antennas for general all around
broadband 500kHz to 30MHz Shortwave Listener "SWL" Antennas.

iane ~ RHF


No problem with the questions. It's nice to see an interesting on topic
thread for a change.

Thanks for the encouragement. I'm not yet sure what I will end up doing,
but I want to make the best decision possible.


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