I made a 300 ohm twinlead folded dipole that is resonant at around 15mHz.
It was cut because I wanted to try some 20m operation with an indoor antenna
and that fit exactly the space.

The ham I wanted to reach was km away, across a valley. I figured with a
tuner and a few watts, I could reach him.

I never used it for that, he moved before we ever got together.

I put the antenna up outside to use for an SWL antenna. It is fed with
about 6 feet of twinlead and then 75 ohm coax. It worked best at 15mHz,
and slowly degraded as frequencies got lower. It was useable at 7mHz for
reception.

At MW frequencies it's basicly a noise pickup and no signals could be
received.

I made a balun from 9 trifilar turns of wire that I had (.5mm plastic
insulated). The instructions I was following said to use 10 turns of
#14 enamel on a wider core, but 9 were all that fit on the core I had.
The core is 8mmx80mm with a permeability of 400.

When I hooked it up to the antenna, I found that the resonant frequency
shifted to 14mHz. My guess is that the feedline now is part of the antenna.
However at 7Mhz it is totally dead. So dead that a signal that reads S5 on
my receiver using a 2m JPole hung from the near end of the folded dipole
as an antenna does not move the s-meter at all. The null extends from
around 6950 kHz up to around 7300.

The question is why and what can I do to improve it?

Is it because there is null in the system because it is resonant at 14mHz and
it is unresonant at 1/2 of that? Is it because the balun acts as a 7mHz trap?

I now have some cores that are 8x140 and 10x200. If I make a balun using the
same wire (enamled wire is not available to me) with a different number of
turns, will it behave differently? For example, if I make a balun with a few
more turns, will the null move down?

My guestimate is that I can get 15 turns on a 140mm rod, and 22 slightly larger
ones on a 200mm rod.

How far down can I go? Will moving it down affect upper frequency response?
Can I move it down far enough that the balun will do something useful
at AM broadcast frequencies?

Some of the 10mm rods were broken into pieces in shipping. Does that affect
their performance? Can I just use the pieces as they are?

Thanks in advance,

Geoff.

--
Geoffrey S. Mendelson N3OWJ/4X1GM
Those who cannot remember the past are condemned to misquote it.

On Thu, 2 Dec 2010 12:24:04 +0000 (UTC), "Geoffrey S. Mendelson"
wrote:

Hi Geoff,

This is a pretty busy agenda:

I made a 300 ohm twinlead folded dipole that is resonant at around 15mHz.
It was cut because I wanted to try some 20m operation with an indoor antenna
and that fit exactly the space.

This should have been foreboding (resonance so near by?).

I put the antenna up outside to use for an SWL antenna. It is fed with
about 6 feet of twinlead and then 75 ohm coax. It worked best at 15mHz,
and slowly degraded as frequencies got lower. It was useable at 7mHz for
reception.

At MW frequencies it's basicly a noise pickup and no signals could be
received.

These signal reports sound more like issues of propagation than issues
of the antenna. In other words: normal.

I made a balun from 9 trifilar turns of wire that I had (.5mm plastic
insulated). The instructions I was following said to use 10 turns of
#14 enamel on a wider core, but 9 were all that fit on the core I had.
The core is 8mmx80mm with a permeability of 400.

You say instructions, but instructions for what (to what end, to what
purpose)? Why trifilar? This is suggestive of a voltage BalUn, which
is not going to give you the choking action you need to reduce noise
problems.

Keep your BalUn as is (I don't think it is going to materially improve
anything) and add a W2DU style to its input.

When I hooked it up to the antenna, I found that the resonant frequency
shifted to 14mHz. My guess is that the feedline now is part of the antenna.
However at 7Mhz it is totally dead. So dead that a signal that reads S5 on
my receiver using a 2m JPole hung from the near end of the folded dipole
as an antenna does not move the s-meter at all. The null extends from
around 6950 kHz up to around 7300.

This still sounds like the vagaries of propagation. Do you keep logs?

The question is why and what can I do to improve it?

Your lead out to the antenna could have a short/open in it. I presume
you use your tuner, however of late I have been given the impression
that SWLers of this generation sneer at it in favor of the magic
BalUns they chase on the Internet (given you are a frequent poster
here, I give you the benefit of the doubt).

Is it because there is null in the system because it is resonant at 14mHz and
it is unresonant at 1/2 of that? Is it because the balun acts as a 7mHz trap?

The electrical properties are unrelated to the pattern properties. We
speak of nulls in a pattern.

If you are referencing a null in tuning, then that would occur at
either resonance, or anti-resonance (broadly speaking). If this is
your intent, then, yes, "nulls" would represent impedance matching
issues which in turn would put a block to signals. A tuner is a
design tool for this situation.

I now have some cores that are 8x140 and 10x200. If I make a balun using the
same wire (enamled wire is not available to me) with a different number of
turns, will it behave differently? For example, if I make a balun with a few
more turns, will the null move down?

Uhhhh. We need to decouple "null" somehow, from the discussion, or
give it a more descriptive treatment.

You describe a problem that is binary:
I used to have signals
I don't have signals
what you describe in fumbling with turns ratios is a continuum:
I used to have booming signals
I have weak signals

BalUns are not used to offset/fill/sharpen nulls of any type.

My guestimate is that I can get 15 turns on a 140mm rod, and 22 slightly larger
ones on a 200mm rod.

How far down can I go? Will moving it down affect upper frequency response?
Can I move it down far enough that the balun will do something useful
at AM broadcast frequencies?

Solve your problems one at a time.

Some of the 10mm rods were broken into pieces in shipping. Does that affect
their performance? Can I just use the pieces as they are?

Magnetic performance is impacted by air gaps. In some situation this
is an asset where saturation is an issue. Super glue the pieces for
the closest fit.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
This should have been foreboding (resonance so near by?).

Well, it stretched from one end of my apartment to the other. It just happend
to be slightly short of a 20m folded dipole.


You say instructions, but instructions for what (to what end, to what
purpose)? Why trifilar? This is suggestive of a voltage BalUn, which
is not going to give you the choking action you need to reduce noise
problems.

It from a book "Simple, Low-Cost Wire Antennas for Radio Amateurs" by
Coan and Orr.


When I hooked it up to the antenna, I found that the resonant frequency
shifted to 14mHz. My guess is that the feedline now is part of the antenna.
However at 7Mhz it is totally dead. So dead that a signal that reads S5 on
my receiver using a 2m JPole hung from the near end of the folded dipole
as an antenna does not move the s-meter at all. The null extends from
around 6950 kHz up to around 7300.

This still sounds like the vagaries of propagation. Do you keep logs?

It's not needed. I have two coaxes going outside, one to the folded dipole,
one to the J-Pole. If I tune in a station in the "dead" range (7.0-7.3mHz),
using the J-Pole as my antenna that reads s-5, when I switch to the folded
dipole, it barely moves the s-meter at all.

Your lead out to the antenna could have a short/open in it.

Possible, but at 14mHz, it comes in great, far better than the J-Pole.

I presume
you use your tuner, however of late I have been given the impression
that SWLers of this generation sneer at it in favor of the magic
BalUns they chase on the Internet (given you are a frequent poster
here, I give you the benefit of the doubt).

It was an experiment. I was hoping to use the antenna to transmit too, and
can't run twinlead out to it. So the compromise was the Balun at the far
end of a coax. I can't say if it worked at all, I never got far enough to
try.


The electrical properties are unrelated to the pattern properties. We
speak of nulls in a pattern.

My bad, I was speaking of a null, as in a frequency range with zero
(or close to it) signal.

If you are referencing a null in tuning, then that would occur at
either resonance, or anti-resonance (broadly speaking). If this is
your intent, then, yes, "nulls" would represent impedance matching
issues which in turn would put a block to signals. A tuner is a
design tool for this situation.

Thanks, that's easy to try. Would it work on the near end of the system?
radio - tuner - 10 meters of coax - balun - 300 ohm feedline - 300 ohm
folded dipole.


Solve your problems one at a time.

Thanks. that's a good idea.

Some of the 10mm rods were broken into pieces in shipping. Does that affect
their performance? Can I just use the pieces as they are?

Magnetic performance is impacted by air gaps. In some situation this
is an asset where saturation is an issue. Super glue the pieces for
the closest fit.

Sorry, I wasn't clear. Someone on another mailing list said that breaking
a ferite rod could magnetize it. I don't want to glue them together
again, I would use the pieces as they are.

Maybe a better question would of been to start from the begining and ask "I
have a 300 ohm twinlead folded dipole resonant at 15mHz, with an aprox 6 foot
twinlead feed line. I need to feed that with 10-15 meters of 75 ohm coax.
How do I get that to appear resonant to my transmitter on 14 mHz, and hopefully
7 and 28 mHz and get some signals in and out?".

Thanks and 73,

Geoff.

--
Geoffrey S. Mendelson N3OWJ/4X1GM
Those who cannot remember the past are condemned to misquote it.

On Dec 2, 2:34*pm, "Geoffrey S. Mendelson" wrote:

Maybe a better question would of been to start from the begining and ask "I
have a 300 ohm twinlead folded dipole resonant at 15mHz, with an aprox 6 foot
twinlead feed line. I need to feed that with 10-15 meters of 75 ohm coax.
How do I get that to appear resonant to my transmitter on 14 mHz, and hopefully
7 and 28 mHz and get some signals in and out?".


You are trying to get a lot from a 20m dipole. And that feed line
setup just complicates things and adds undue loss.
Myself, I would start over from scratch if you really want to
transmit on all three bands. Are you limited to the size of
the dipole? Do you have to use coax?
As far as receiving lower bands, I'd try unhooking one leg
of the feed line. Just feed the center conductor. That
should cure the dead antenna problem as far as just
listening on the lower bands.

"Geoffrey S. Mendelson" wrote in message
...
I made a 300 ohm twinlead folded dipole that is resonant at around 15mHz.
It was cut because I wanted to try some 20m operation with an indoor
antenna
and that fit exactly the space.

The ham I wanted to reach was km away, across a valley. I figured with a
tuner and a few watts, I could reach him.

I never used it for that, he moved before we ever got together.

I put the antenna up outside to use for an SWL antenna. It is fed with
about 6 feet of twinlead and then 75 ohm coax. It worked best at 15mHz,
and slowly degraded as frequencies got lower. It was useable at 7mHz for
reception.

At MW frequencies it's basicly a noise pickup and no signals could be
received.

I made a balun from 9 trifilar turns of wire that I had (.5mm plastic
insulated). The instructions I was following said to use 10 turns of
#14 enamel on a wider core, but 9 were all that fit on the core I had.
The core is 8mmx80mm with a permeability of 400.

When I hooked it up to the antenna, I found that the resonant frequency
shifted to 14mHz. My guess is that the feedline now is part of the
antenna.
However at 7Mhz it is totally dead. So dead that a signal that reads S5 on
my receiver using a 2m JPole hung from the near end of the folded dipole
as an antenna does not move the s-meter at all. The null extends from
around 6950 kHz up to around 7300.

The question is why and what can I do to improve it?


I think I would not go with a folded dipole and balun. Especially if you
want to use it to transmitt with.

If you do not have enough space for a full size antenna you may want to try
what is called an inverted U antenna. YOu run the horizontal elements as
far as you can and drop the ends down. Somewhere I saw a way to stack
several like this for multibands. It is difficult to make a dipole operate
on a much lower frequency. That is if you cut one for 20 meters, it is
difficult to make it opwerate on 40 meters.

On 2 dic, 13:24, "Geoffrey S. Mendelson" wrote:
I made a 300 ohm twinlead folded dipole that is resonant at around 15mHz.
It was cut because I wanted to try some 20m operation with an indoor antenna
and that fit exactly the space.

The ham I wanted to reach was km away, across a valley. I figured with a
tuner and a few watts, I could reach him.

I never used it for that, he moved before we ever got together.

I put the antenna up outside to use for an SWL antenna. It is fed with
about 6 feet of twinlead and then 75 ohm coax. It worked best at 15mHz,
and slowly degraded as frequencies got lower. It was useable at 7mHz for
reception.

At MW frequencies it's basicly a noise pickup and no signals could be
received.

I made a balun from 9 trifilar turns of wire that I had (.5mm plastic
insulated). The instructions I was following said to use 10 turns of
#14 enamel on a wider core, but 9 were all that fit on the core I had.
The core is 8mmx80mm with a permeability of 400.

When I hooked it up to the antenna, I found that the resonant frequency
shifted to 14mHz. My guess is that the feedline now is part of the antenna.
However at 7Mhz it is totally dead. So dead that a signal that reads S5 on
my receiver using a 2m JPole hung from the near end of the folded dipole
as an antenna does not move the s-meter at all. The null extends from
around 6950 kHz up to around 7300.

The question is why and what can I do to improve it?

Is it because there is null in the system because it is resonant at 14mHz and
it is unresonant at 1/2 of that? Is it because the balun acts as a 7mHz trap?

I now have some cores that are 8x140 and 10x200. If I make a balun using the
same wire (enamled wire is not available to me) with a different number of
turns, will it behave differently? For example, if I make a balun with a few
more turns, will the null move down?

My guestimate is that I can get 15 turns on a 140mm rod, and 22 slightly larger
ones on a 200mm rod. *

How far down can I go? Will moving it down affect upper frequency response?
Can I move it down far enough that the balun will do something useful
at AM broadcast frequencies?

Some of the 10mm rods were broken into pieces in shipping. Does that affect
their performance? Can I just use the pieces as they are?

Thanks in advance,

Geoff.

--
Geoffrey S. Mendelson N3OWJ/4X1GM
Those who cannot remember the past are condemned to misquote it.

Hello Geoffrey.

I think the problem is in the folded dipole. It works as long as it is
in resonance (so that current in all wires is in phase). At half the
frequency, it will behave more like a halve wave loop with very small
loop area (as the wires are in parallel). This is not an effective
arrangement. Maybe you can try to cut the short (so it becomes an
open dipole with non-straight halves).

When you live in a quiet environment, a 4:1 or 9:1 balun will increase
both signal and noise for frequencies below resonance (so that antenna
noise exceeds your receiver's noise).

Regarding the feedline between antenna and balun. If the balun does
function well, the feedline will not contribute to the radiation
pattern (current are opposite), but it will provide impedance
transformation, so it becomes part of the tuning (hence resonant
frequencies).

From your balun description, I can't figure out what you have in your
hands Maybe you have link to a description you followed. I prefer
baluns that provide common mode suppression so that when there is some
asymmetry in the system, the coaxial feeder doesn't become part of the
radiating/receiving antenna structure. A guanella type balun wound on
two magnetically separate cores/rods does provide common mode
suppression.

Regarding ferrite rods (for a 4:1 guanella balun for example), if the
broken surfaces still mate closely, just use some liquid adhesive and
join them. As most of the field lines go to air, effective
permeability doesn't change practically.

For making a really wide band balun, you need the right ferrite
material. For wide band applications I use, for example, fairrite
material 43 [ur=800] (material 31 [ur=1500] would be better). You need
a material that has high permeability at low frequency and also
reasonable permeability at high frequency. Many power ferrites have
good permeability at low frequency, but it drops rapidly at increasing
frequency.

If your choice is limited, try to get ferrite material indicated for
HF (1.. 100 MHz) EMI suppression. As it is for reception only, I would
not go for rods, but toroids. Toroids provide higher inductance at low
frequency because of the closed magnetic path (so you need less
turns).

Regarding MW broadcast reception. I get best results with vertical
polarized antennas, so your dipole may not be good for this.

Best regards,

Wim
PA3DJS
www.tetech.nl

On Thu, 2 Dec 2010 20:34:09 +0000 (UTC), "Geoffrey S. Mendelson"
wrote:

This still sounds like the vagaries of propagation. Do you keep logs?

It's not needed. I have two coaxes going outside, one to the folded dipole,
one to the J-Pole. If I tune in a station in the "dead" range (7.0-7.3mHz),
using the J-Pole as my antenna that reads s-5, when I switch to the folded
dipole, it barely moves the s-meter at all.

Hi Geoff,

That confirms propagation - more a matter of polarization. We keep a
variety of antennas to suit just situations. Polarization diversity
is what that is called.

Your lead out to the antenna could have a short/open in it.

Possible, but at 14mHz, it comes in great, far better than the J-Pole.

I presume by this response, your antenna/line being "dead" at 15 MHz
(it should be a busy band) is quite alive at 14 MHz (which, too,
should be a busy band).

My bad, I was speaking of a null, as in a frequency range with zero
(or close to it) signal.

The following is pedantic for its own sake:
Null in engineering denotes the indication offered in a balanced
situation - the meter indication in a bridge - where two potentials
are equal (no current flows in the meter). As you adjust the arm on
one side of the bridge, the approach of equality reduces the potential
between both side of the meter, and its indication "nulls."

If you are referencing a null in tuning, then that would occur at
either resonance, or anti-resonance (broadly speaking). If this is
your intent, then, yes, "nulls" would represent impedance matching
issues which in turn would put a block to signals. A tuner is a
design tool for this situation.

Thanks, that's easy to try. Would it work on the near end of the system?
radio - tuner - 10 meters of coax - balun - 300 ohm feedline - 300 ohm
folded dipole.

That is good solution; the perfect topology would have the tuner at
the 300 Ohm folded dipole with coax back to the radio.

Some of the 10mm rods were broken into pieces in shipping. Does that affect
their performance? Can I just use the pieces as they are?

Magnetic performance is impacted by air gaps. In some situation this
is an asset where saturation is an issue. Super glue the pieces for
the closest fit.

Sorry, I wasn't clear. Someone on another mailing list said that breaking
a ferite rod could magnetize it. I don't want to glue them together
again, I would use the pieces as they are.

Someone on another mailing list has mixed priorities. So what? (Not
to say I buy their guff.)

Feel fine to use them as they are, but if you were to use them as
stock for choking purposes, more bulk ferrite offers more bulk
isolation.

Maybe a better question would of been to start from the begining and ask "I
have a 300 ohm twinlead folded dipole resonant at 15mHz, with an aprox 6 foot
twinlead feed line. I need to feed that with 10-15 meters of 75 ohm coax.
How do I get that to appear resonant to my transmitter on 14 mHz, and hopefully
7 and 28 mHz and get some signals in and out?".

The fold in the dipole, the approx 6 foot twinlead feed line, the 75
Ohm coax, and the BalUn are unnecessary elaborations. The combination
of all sounds like complexity squared to achieve a goal by applying
nebulous charms.

Resonance is resonance and the rest is unnecessary. You put up an
ordinary dipole, connect an ordinary line to it (OK, so it can be 75
Ohm line if that is what is handy) THROUGH a choke (AKA 1:1 BalUn),
and to a tuner at your radio. The tuner solves resonance. Sometimes
a tuner cannot cope with extreme natural resonances such as a fullwave
dipole presents you on the band you want. Cut the size of the dipole
and move on.

The combination of folded dipole, odd twinlead line, and high ratio
BalUn (almost always of the wrong construction) suggests the desire
for an "all band antenna." That and unicorn horns for aphrodisiacs
are sought by many and claimed real by liars or fools. Marrying the
term "resonate" or seeking resonance from these antennas compounds the
lie or the foolishness.

The usual (and inverted wish from seeking resonance) is that this
solution of dipole/tuner dashes the SWLer's desire for frequency
agility (no time to tune an optimal signal when chasing the bands).
The simple solution is the Fan Dipole. This new solution being too
easy and lacking the mystique of charms, amulets, and complexity to
fuss over, SWLer's quickly reject simple success to cozy up to the
oddities of their failure in contrast to the glowing (lying or
foolish) reports of others (liars or fools) using the (presumably)
same contorted design.

It's not like any of these contorted designs bring any gain to the
table. And the gain differences between them and a simple dipole
wouldn't move the S-Meter more than a needle's width!

The reason why I am quick to dismiss "frequency agile" requirements is
that I know full well that SWLing demands your full attention on one
frequency to pick up that interval ID signal, or just recognize the
style of programming if you are going to catch that DX. The agility
race is won by the patient listener.

However, if you really want an "all band" antenna that is "frequency
agile" then the Fan Dipole will do that on every band you cut an
element for. All it takes is wire (and it would seem you, and others,
made that investment with the fold).

73's
Richard Clark, KB7QHC