On Sep 3, 10:49*am, dave wrote:
RHF wrote:
On Sep 2, 10:41 pm, wrote:
On Sep 2, 5:21 pm, "Brian Gregory *wrote:

*wrote in message

....

- - - Palomar's currently sold 9:1 transformer
- - - is good only for a longwire, but not for T2FD.

- - How can that be?

Your Way ! - iane ~ RHF
* .

You can use 450 Ohm ladder line to feed your T2FD

Very true,but the interference won't allow appropriate low-noise
reception at my location. I have to use coax.

On Sep 3, 11:03*am, "Brian Gregory [UK]" wrote:
wrote in message

...

Because the presently made MLB-1 by Palomar Engineersis a UNUN for a
longwire. The older transformer which I used (may have the original
instruction paper somewhere) was a true BALUN. To build a T2FD we must
use a balun, since it is a broadband dipole.

A long wire balun should not assume you want a common ground connection on
the input and output.

But I've look at the picture and description of the MLB-1 on the web and I
agree it's far from clear what connections are provided.

However if I bought it and found it did have the grounds joined I'd return
it as unacceptable because when using a long wire you want to use a separate
good quality earth which is not joined to your receiver's earth which may
have RF noise on it.

--

Brian Gregory. (In the UK)

To email me remove the letter vee.

MLB-1 from Palomar is probably (I would rate that at 99%) their answer
to the MLB from RF Systems in the Netherlands. I still have the
latter and it has only one connection for the antenna on the top. P.S.
Just checked back Palomar's website and a true 9:1 balun kit is still
available,but it is made for transmitting up to 250W,not for SWL and
does not have any enclosure box. And it is certainly much bigger and
heavier than the old one I originally used for T2FD.

On Sep 3, 9:15*pm, dave wrote:
Brian Gregory [UK] wrote:
*wrote in message
...
Because the presently made MLB-1 by Palomar Engineersis a UNUN for a
longwire. The older transformer which I used (may have the original
instruction paper somewhere) was a true BALUN. To build a T2FD we must
use a balun, since it is a broadband dipole.

A long wire balun should not assume you want a common ground connection on
the input and output.

But I've look at the picture and description of the MLB-1 on the web and I
agree it's far from clear what connections are provided.

However if I bought it and found it did have the grounds joined I'd return
it as unacceptable because when using a long wire you want to use a separate
good quality earth which is not joined to your receiver's earth which may
have RF noise on it.

I disagree. Use on an UnUn (autotransformer) puts all points of the
system at ground, provided you ground per electrical code. *"Noise" from
the radio chassis (?) flows to ground through the IEC cable. Static
charges from the antenna system flow to ground at the transmission line
point of entry.- Hide quoted text -

- Show quoted text -

My own cell-phone generates more noise than some of the cold war era
jammers,sometimes! That is another reason for using coax. And
grounding may bring more problems,sometimes it is better not to
ground. Static usually is not a major issue over here at my lattitude
(40* N).

On 9/3/2010 10:01 PM, dave wrote:

...
Common mode rejection of noise happens in a truly balanced configuration.

That is the worst suggestive BS I have ever seen, no antenna knows the
difference between "RF noise" and a desirable RF signal ...

Regards,
JS

wrote:
On Sep 3, 10:49 am, wrote:
RHF wrote:
On Sep 2, 10:41 pm, wrote:
On Sep 2, 5:21 pm, "Brian Gregory wrote:

wrote in message

...

- - - Palomar's currently sold 9:1 transformer
- - - is good only for a longwire, but not for T2FD.

- - How can that be?

Your Way ! - iane ~ RHF
.

You can use 450 Ohm ladder line to feed your T2FD

Very true,but the interference won't allow appropriate low-noise
reception at my location. I have to use coax.

Common mode rejection of noise happens in a truly balanced configuration.

wrote:


Brian Gregory. (In the UK)

To email me remove the letter vee.

MLB-1 from Palomar is probably (I would rate that at 99%) their answer
to the MLB from RF Systems in the Netherlands. I still have the
latter and it has only one connection for the antenna on the top. P.S.
Just checked back Palomar's website and a true 9:1 balun kit is still
available,but it is made for transmitting up to 250W,not for SWL and
does not have any enclosure box. And it is certainly much bigger and
heavier than the old one I originally used for T2FD.

I'm pretty sure the Palomar's been out longer. I've had one for 14
years, drove to Escondido and bought it at the factory.

http://www.qrp.pops.net/images/before 2008/UNUN-1.JPG

"dave" wrote in message
. ..
Brian Gregory [UK] wrote:
wrote in message
...
Because the presently made MLB-1 by Palomar Engineersis a UNUN for a
longwire. The older transformer which I used (may have the original
instruction paper somewhere) was a true BALUN. To build a T2FD we must
use a balun, since it is a broadband dipole.

A long wire balun should not assume you want a common ground connection
on
the input and output.

But I've look at the picture and description of the MLB-1 on the web and
I
agree it's far from clear what connections are provided.

However if I bought it and found it did have the grounds joined I'd
return
it as unacceptable because when using a long wire you want to use a
separate
good quality earth which is not joined to your receiver's earth which may
have RF noise on it.


I disagree. Use on an UnUn (autotransformer) puts all points of the system
at ground, provided you ground per electrical code. "Noise" from the
radio chassis (?) flows to ground through the IEC cable. Static charges
from the antenna system flow to ground at the transmission line point of
entry.

All I ccan suggest is that you try it.

If I comapre reception on the lower bands between using my own earth made
from a copper pipe hammered into the ground somewhat away from the house to
that using the mains earth I find there is way more noise using the mains
earth and using both earths is almost as bad.

--

Brian Gregory. (In the UK)

To email me remove the letter vee.

John Smith wrote:
On 9/3/2010 10:01 PM, dave wrote:

...
Common mode rejection of noise happens in a truly balanced configuration.

That is the worst suggestive BS I have ever seen, no antenna knows the
difference between "RF noise" and a desirable RF signal ...

Regards,
JS



I think what Dave was saying is that open wire feeders will not pick
up noise (or signals, for that matter) if they are truly balanced,
because of common mode rejection. Which is true.


With all good wishes,


Kevin, WB4AIO.
--
http://kevinalfredstrom.com/

wrote:

- Show quoted text -

My own cell-phone generates more noise than some of the cold war era
jammers,sometimes! That is another reason for using coax. And
grounding may bring more problems,sometimes it is better not to
ground. Static usually is not a major issue over here at my lattitude
(40* N).

GMS phones seem to get into everything. I'd look for an audio path, not
via HF radio circuitry.

Snow blowing across a wire antenna generates static electricity.
Grounding the transmission line where it enters a structure is
consistent with good operating practice. My radio floats on a 13 VDC
switch mode power supply. The only ground is the coaxial cable from the
feedthru.

John Smith wrote:
On 9/3/2010 10:01 PM, dave wrote:

...
Common mode rejection of noise happens in a truly balanced configuration.

That is the worst suggestive BS I have ever seen, no antenna knows the
difference between "RF noise" and a desirable RF signal ...

Regards,
JS

The noise is in-phase and cancels when the transmission line is
terminated in a "differential" input. The desired signal is + on one leg
and - on the other. The desired signal remains after differential summation.

John, lo:

http://en.wikipedia.org/wiki/Balanced

Any external signal sources tend to induce only a common mode signal on
the line and the balanced impedances to ground minimizes differential
pickup due to stray electric fields. The conductors are sometimes
twisted together to ensure that each conductor is equally exposed to any
external magnetic fields that could induce unwanted noise.

Some balanced lines also have electromagnetic shielding to reduce the
amount of noise introduced.

A balanced line allows a differential receiver to reduce the noise on a
connection by rejecting common-mode interference. The lines have the
same impedance to ground, so the interfering fields or currents induce
the same voltage in both wires. Since the receiver responds only to the
difference between the wires, it is not influenced by the induced noise
voltage. If twisted pair becomes unbalanced, for example due to
insulation failure, noise will be induced. Examples of twisted pairs
include Cat-3 Ethernet cables or telephone wires.

Compared to unbalanced circuits, balanced lines reduce the amount of
noise per distance, allowing a longer cable run to be practical. This is
because electromagnetic interference will affect both signals the same
way. Similarities between the two signals are automatically removed at
the end of the transmission path when one signal is subtracted from the
other.
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