Long/random-wire balun and grounding Q (longish)
 

I've got a little shortwave receiver that has a decent amount of gain in
it's antenna input. I've been experimenting with different lengths and
placements of the wire, and seen some interesting homebrew antennas I
might try once the snow melts.

I know that receivers are less demanding of impedance matching in
general, but my readings suggest that I should have a balun (unun) of
some sort to match the impedance better, since I'm pretty much stuck
with end-fed longwires. This should get more signal to my front-end,
and a proper shielded connection to my receiver should help minimize
stray RF noise.

I'm a renter, so I'm going to experiment with running a wire along the
eaves on the balcony, which is open to two sides of the house (wooden
two-story.) That is, I do not have the luxury of using the yard, trees
or anything.

So, my idea is to have a long wire (or folded longwire made from a
length of twin-lead) go to a balun (or unun, since this is really
unbalanced-to-unbalanced) and then run a downwire from there to my
receiver through a window.

I'm guessing the real advantage would be realized if I had a good RF
ground at the receiver and/or balun. This will be sort of tricky. I
don't even think I have copper cold-water pipes anywhere, and running
copper braid over the balcony, down the side of the building and into
6-foot rod just ain't going to happen. I've heard of people using
houseplants for poor grounds when no other was available, and I have
many kilos of wet earth on the balcony.

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?

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? Sorry if this is stupid question, but I've got
most of the math figured out (i.e., no. of turns and such) but since
I've never seen a balun... my assumption (right or wrong) is that it is
just a special transformer.

Thanks for your comments.

-- cm

On Wed, 02 Mar 2005 13:04:50 -0500, clvrmnky
wrote:

I know that receivers are less demanding of impedance matching in
general, but my readings suggest that I should have a balun (unun) of
some sort to match the impedance better, since I'm pretty much stuck
with end-fed longwires.

Hi OM,

This match, as you speak of, is probably remote from any probability
you are likely to encounter with the antenna options you describe in
your posting. However, there are other merits:

a proper shielded connection to my receiver should help minimize
stray RF noise.

Presuming you mean to terminate the far end shield connection to
ground.

I'm guessing the real advantage would be realized if I had a good RF
ground at the receiver and/or balun. This will be sort of tricky. I
don't even think I have copper cold-water pipes anywhere, and running
copper braid over the balcony, down the side of the building and into
6-foot rod just ain't going to happen.

OK, so we strike out those as options not available to you.

I've heard of people using
houseplants for poor grounds when no other was available, and I have
many kilos of wet earth on the balcony.

Don't even think of it. Ground does not mean wet mud.

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.

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).

73's
Richard Clark, KB7QHC

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.

Roy Lewallen, W7EL

clvrmnky wrote:
I've got a little shortwave receiver that has a decent amount of gain in
it's antenna input. I've been experimenting with different lengths and
placements of the wire, and seen some interesting homebrew antennas I
might try once the snow melts.

I know that receivers are less demanding of impedance matching in
general, but my readings suggest that I should have a balun (unun) of
some sort to match the impedance better, since I'm pretty much stuck
with end-fed longwires. This should get more signal to my front-end,
and a proper shielded connection to my receiver should help minimize
stray RF noise.

I'm a renter, so I'm going to experiment with running a wire along the
eaves on the balcony, which is open to two sides of the house (wooden
two-story.) That is, I do not have the luxury of using the yard, trees
or anything.

So, my idea is to have a long wire (or folded longwire made from a
length of twin-lead) go to a balun (or unun, since this is really
unbalanced-to-unbalanced) and then run a downwire from there to my
receiver through a window.

I'm guessing the real advantage would be realized if I had a good RF
ground at the receiver and/or balun. This will be sort of tricky. I
don't even think I have copper cold-water pipes anywhere, and running
copper braid over the balcony, down the side of the building and into
6-foot rod just ain't going to happen. I've heard of people using
houseplants for poor grounds when no other was available, and I have
many kilos of wet earth on the balcony.

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?

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? Sorry if this is stupid question, but I've got
most of the math figured out (i.e., no. of turns and such) but since
I've never seen a balun... my assumption (right or wrong) is that it is
just a special transformer.

Thanks for your comments.

-- cm

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

"clvrmnky" wrote in message
...
I've got a little shortwave receiver that has a decent amount of gain in
it's antenna input. I've been experimenting with different lengths and
placements of the wire, and seen some interesting homebrew antennas I
might try once the snow melts.

I know that receivers are less demanding of impedance matching in
general, but my readings suggest that I should have a balun (unun) of
some sort to match the impedance better, since I'm pretty much stuck
with end-fed longwires. This should get more signal to my front-end,
and a proper shielded connection to my receiver should help minimize
stray RF noise.

I'm a renter, so I'm going to experiment with running a wire along the
eaves on the balcony, which is open to two sides of the house (wooden
two-story.) That is, I do not have the luxury of using the yard, trees
or anything.

So, my idea is to have a long wire (or folded longwire made from a
length of twin-lead) go to a balun (or unun, since this is really
unbalanced-to-unbalanced) and then run a downwire from there to my
receiver through a window.

I'm guessing the real advantage would be realized if I had a good RF
ground at the receiver and/or balun. This will be sort of tricky. I
don't even think I have copper cold-water pipes anywhere, and running
copper braid over the balcony, down the side of the building and into
6-foot rod just ain't going to happen. I've heard of people using
houseplants for poor grounds when no other was available, and I have
many kilos of wet earth on the balcony.

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?

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? Sorry if this is stupid question, but I've got
most of the math figured out (i.e., no. of turns and such) but since
I've never seen a balun... my assumption (right or wrong) is that it is
just a special transformer.

Thanks for your comments.

-- cm

Classic. I new someone would come up with the "stick a coat hanger in your
antenna socket and be happy" line.

"Roy Lewallen" wrote in message
...
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.

Roy Lewallen, W7EL

clvrmnky wrote:
I've got a little shortwave receiver that has a decent amount of gain in
it's antenna input. I've been experimenting with different lengths and
placements of the wire, and seen some interesting homebrew antennas I
might try once the snow melts.

I know that receivers are less demanding of impedance matching in
general, but my readings suggest that I should have a balun (unun) of
some sort to match the impedance better, since I'm pretty much stuck
with end-fed longwires. This should get more signal to my front-end,
and a proper shielded connection to my receiver should help minimize
stray RF noise.

I'm a renter, so I'm going to experiment with running a wire along the
eaves on the balcony, which is open to two sides of the house (wooden
two-story.) That is, I do not have the luxury of using the yard, trees
or anything.

So, my idea is to have a long wire (or folded longwire made from a
length of twin-lead) go to a balun (or unun, since this is really
unbalanced-to-unbalanced) and then run a downwire from there to my
receiver through a window.

I'm guessing the real advantage would be realized if I had a good RF
ground at the receiver and/or balun. This will be sort of tricky. I
don't even think I have copper cold-water pipes anywhere, and running
copper braid over the balcony, down the side of the building and into
6-foot rod just ain't going to happen. I've heard of people using
houseplants for poor grounds when no other was available, and I have
many kilos of wet earth on the balcony.

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?

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? Sorry if this is stupid question, but I've got
most of the math figured out (i.e., no. of turns and such) but since
I've never seen a balun... my assumption (right or wrong) is that it is
just a special transformer.

Thanks for your comments.

-- cm

Do you believe that what I posted isn't true, or do you just wish it
isn't true?

Roy Lewallen, W7EL

CW wrote:
Classic. I new someone would come up with the "stick a coat hanger in your
antenna socket and be happy" line.

"Roy Lewallen" wrote in message
...

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.

Roy Lewallen, W7EL

On Fri, 4 Mar 2005 21:30:40 -0800, "CW" wrote:

Classic. I new someone would come up with the "stick a coat hanger in your
antenna socket and be happy" line.

As a rule I subscribe to the school that says every antenna should be
well-matched, in the clear and fed with low loss line, even those used
for receiving. Must come from my VHF/DXing background.

That said, I know my friend Roy is correct and I am wrong when he
gives this advice. Generally speaking, the SNR is set at the antenna
and nothing done after that will make much difference. This isn't
always the case if there are noise sources that can nulled or reduced
by phasing or other directive techniques that don't reduce the signal
simultaneously.

Roy did not mention this at all. He spoke to "impedance matching."

Wes N7WS

ps. You have no idea how hard it is to type with one (the "wrong")
hand while doing drugs. I had 2 1/2 hours of surgery putting my rt.
shoulder together on Thursday. Just in time to keep me out of the DX
contest---good planning :(



"Roy Lewallen" wrote in message
...
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.

Roy Lewallen, W7EL
[snip]

On Sat, 05 Mar 2005 06:18:45 -0700, Wes Stewart
wrote:

ps. You have no idea how hard it is to type with one (the "wrong")
hand while doing drugs. I had 2 1/2 hours of surgery putting my rt.
shoulder together on Thursday. Just in time to keep me out of the DX
contest---good planning :(


Hi Wes,

I don't think this will boost your spirits by more than one S-Unit,
but in today's NYT there was a report of a fellow that chopped off
both hands, and had them sewn back on.
graphic:
http://graphics8.nytimes.com/images/...n/05hands2.jpg
story:
http://www.nytimes.com/2005/03/05/nyregion/05hands.html

73's
Richard Clark, KB7QHC

On Sat, 05 Mar 2005 11:48:01 -0800, Richard Clark
wrote:

On Sat, 05 Mar 2005 06:18:45 -0700, Wes Stewart
wrote:

ps. You have no idea how hard it is to type with one (the "wrong")
hand while doing drugs. I had 2 1/2 hours of surgery putting my rt.
shoulder together on Thursday. Just in time to keep me out of the DX
contest---good planning :(


Hi Wes,

I don't think this will boost your spirits by more than one S-Unit,
but in today's NYT there was a report of a fellow that chopped off
both hands, and had them sewn back on.
graphic:
http://graphics8.nytimes.com/images/...n/05hands2.jpg
story:
http://www.nytimes.com/2005/03/05/nyregion/05hands.html

Oh my, that's gotta hurt.

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.

On Sat, 05 Mar 2005 13:19:40 -0700, Wes Stewart
wrote:

On Sat, 05 Mar 2005 11:48:01 -0800, Richard Clark
wrote:

On Sat, 05 Mar 2005 06:18:45 -0700, Wes Stewart
wrote:

ps. You have no idea how hard it is to type with one (the "wrong")
hand while doing drugs. I had 2 1/2 hours of surgery putting my rt.
shoulder together on Thursday. Just in time to keep me out of the DX
contest---good planning :(


Hi Wes,

I don't think this will boost your spirits by more than one S-Unit,
but in today's NYT there was a report of a fellow that chopped off
both hands, and had them sewn back on.
graphic:
http://graphics8.nytimes.com/images/...n/05hands2.jpg
story:
http://www.nytimes.com/2005/03/05/nyregion/05hands.html

Oh my, that's gotta hurt.

Last week in the news some lady got mad at her man and cut his
ying-yang off and flushed down the toilet. It was later recovered,
taken to the hospital, cleaned up and sewn back on the man.

Now that would hurt...

Bob
k5qwg



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.