balun spec depending on coax impedance
 

On Wed, 01 Mar 2006 20:37:16 GMT, David wrote:

On Wed, 01 Mar 2006 20:00:22 GMT, Bob Miller
wrote:

On Wed, 01 Mar 2006 18:20:29 +0100, Charly wrote:


Dear all,

Usualy, people use 9:1 balun to connect a wire or dipole antenna to a 50 ohm coax.

A resonant dipole, I believe, is about 72 ohms. Connecting it through
75 ohm TV coax to a 50 ohm receiver input should be a near ideal
match.

On non-resonant frequencies, the dipole will present different
matches. That shouldn't be a problem, though, just for listening on a
sensitive receiver.

A balun won't give you a decent match except on the single frequency
it is designed for. That's one problem you run into, putting a balun
on a multi-band or multi-frequency antenna.

That's not the point.

One of the big rules in impedance matching is that the load (gozinta)
have equal or higher impedance than the source (gozowta). You never
go from a HiZ generator into a LoZ cable. Major faux pas.

If the antenna's highest impedance is 450 Ohms, and it's going through
a 9:1 matcher it will never be choked by a 50 (or 75) Ohm cable.

Why do you think an antenna for multi-frequency use has an impedance
no higher than 450 ohms? As an example, check the impedances of the
all band doublet at http://www.cebik.com/wire/abd.html

bob
k5qwg



Think of impedance as hose diameter and the signal as a solid stream
of water.

balun spec depending on coax impedance
 

On Wed, 01 Mar 2006 22:48:03 GMT, Bob Miller
wrote:


Why do you think an antenna for multi-frequency use has an impedance
no higher than 450 ohms? As an example, check the impedances of the
all band doublet at http://www.cebik.com/wire/abd.html

'cause Steve is my lord and saviour.

http://www.hard-core-dx.com/nordicdx.../magbalun.html

balun spec depending on coax impedance
 

David wrote:

On Wed, 01 Mar 2006 22:48:03 GMT, Bob Miller
wrote:

Why do you think an antenna for multi-frequency use has an impedance
no higher than 450 ohms? As an example, check the impedances of the
all band doublet at http://www.cebik.com/wire/abd.html

'cause Steve is my lord and saviour.

http://www.hard-core-dx.com/nordicdx.../magbalun.html

Please note that I no longer offer the matching transformers for sale.

Why?, one might ask. Well, I sold between 400 and 500 of them and quite frankly
I got tired of winding the darn things up.

I still get the occasional inquiry.

dxAce
Michigan
USA

balun spec depending on coax impedance
 

On Wed, 01 Mar 2006 18:15:07 -0500, dxAce
wrote:



David wrote:

On Wed, 01 Mar 2006 22:48:03 GMT, Bob Miller
wrote:

Why do you think an antenna for multi-frequency use has an impedance
no higher than 450 ohms? As an example, check the impedances of the
all band doublet at http://www.cebik.com/wire/abd.html

'cause Steve is my lord and saviour.

http://www.hard-core-dx.com/nordicdx.../magbalun.html

Please note that I no longer offer the matching transformers for sale.

Why?, one might ask. Well, I sold between 400 and 500 of them and quite frankly
I got tired of winding the darn things up.

I still get the occasional inquiry.

dxAce
Michigan
USA

I wish these were around back in '97 when I drove to Escondildo to get
a Palomar MLB for $40 for my 120' all steel random wi

http://www.geocities.com/qrp_baluns/E-LMZ-50-640.gif

balun spec depending on coax impedance
 

In article ,
Bob Miller wrote:

On Wed, 01 Mar 2006 15:09:12 -0500, dxAce
wrote:



Bob Miller wrote:

A balun won't give you a decent match except on the single
frequency it is designed for. That's one problem you run into,
putting a balun on a multi-band or multi-frequency antenna.

Single frequency?

dxAce Michigan USA


At different frequencies the antenna will have different impedances
and the balun may or may not match.

Antenna reactance and impedance are two different things. The antenna
impedance in this case is a characteristic of the single wire or a
dipole. The first case is hundreds of ohms and the second about 72
ohms. And like you stated in another post in the thread he does not
need a BALUN for the dipole.

The purpose of a BALUN, UNUN or other types of impedance matching
device is to match the characteristic impedance of the antenna to the
transmission line, which in this case is the coax.

The impedance transformers do not tune the antenna and don't deal with
antenna reactance to a certain frequency.

It seems people make this mistake all the time.

--
Telamon
Ventura, California

balun spec depending on coax impedance
 

In article ,
Bob Miller wrote:
Why do you think an antenna for multi-frequency use has an impedance
no higher than 450 ohms? As an example, check the impedances of the
all band doublet at http://www.cebik.com/wire/abd.html

You don't understand. We're not transmitting.

The goal in not some absolute effiency for raditating RF energy or babying
the RF final amplifier, but maximising the signal to noise ratio of the
signal fed into the receiver.

At low cost.

There's great improvment with these transformers because you can
stick some random hunk of hookup wire out in weeds, far enough away
from the computers, light dimmers and other modern electronic crap.

And if your receiver doesn't have high impedance input, you'll get
even more signal off a random wire, with either the transformer remotely
located or at the receiver.

With receivers, it's all relative.

Mark Zenier
Googleproofaddress(account:mzenier provider:eskimo domain:com)

balun spec depending on coax impedance
 

On Thu, 02 Mar 2006 14:00:41 GMT, David wrote:

On Thu, 02 Mar 2006 13:39:00 GMT, Bob Miller
wrote:

On Thu, 02 Mar 2006 00:28:43 GMT, Telamon
wrote:


I guess I'm missing something here. If the impedance of a 1/2 wave
dipole at its resonant frequency is about 72 ohms, and at twice that
frequency is about 5000 ohms, how is any single balun going to work
for a multi-frequency listening or transmitting setup? How does the
popular 9-1 balun used by so many swl-ers work for multi frequency
listening? Would it be to simply get the impedance within yelling
distance of the receiver input, or is it really needed at all, given
the pretty good sensitivity of most modern receivers?

Who uses 1/2 wave dipoles for receive only?

9:1 baluns are for random wire monopoles.

The purpose of the dingus is to more properly mate the random wire
with the shielded transmission line. It keeps noise pickup down and
bleeds static electricity away from the receiver.

Thanks for clarifying, but the question remains the same. Why would a
random length wire monopole at assorted listening frequencies always
be at nine times the impedance of the coax feed? If it is not, why the
fixed 9 to 1 ratio of the balun? Would not a variable device, such as
an L-circuit antenna tuner work better?

bob
k5qwg

balun spec depending on coax impedance
 

On Thu, 02 Mar 2006 18:56:08 GMT, Bob Miller
wrote:


Thanks for clarifying, but the question remains the same. Why would a
random length wire monopole at assorted listening frequencies always
be at nine times the impedance of the coax feed? If it is not, why the
fixed 9 to 1 ratio of the balun? Would not a variable device, such as
an L-circuit antenna tuner work better?

The device prevents the generator impedance from exceeding the load
impedance, which is a major no-no.

Rule of thumb is a high impedance source cannot be connected to a low
impedance input, but a low impedance source can be connected to a high
impedance input.

For maximum current transfer a perfect match is desired (like for
transmitting) but for receiving there's a little more latitude.

balun spec depending on coax impedance
 

Bob Miller wrote:

On Thu, 02 Mar 2006 14:00:41 GMT, David wrote:

On Thu, 02 Mar 2006 13:39:00 GMT, Bob Miller
wrote:

On Thu, 02 Mar 2006 00:28:43 GMT, Telamon
wrote:


I guess I'm missing something here. If the impedance of a 1/2 wave
dipole at its resonant frequency is about 72 ohms, and at twice that
frequency is about 5000 ohms, how is any single balun going to work
for a multi-frequency listening or transmitting setup? How does the
popular 9-1 balun used by so many swl-ers work for multi frequency
listening? Would it be to simply get the impedance within yelling
distance of the receiver input, or is it really needed at all, given
the pretty good sensitivity of most modern receivers?

Who uses 1/2 wave dipoles for receive only?

9:1 baluns are for random wire monopoles.

The purpose of the dingus is to more properly mate the random wire
with the shielded transmission line. It keeps noise pickup down and
bleeds static electricity away from the receiver.

Thanks for clarifying, but the question remains the same. Why would a
random length wire monopole at assorted listening frequencies always
be at nine times the impedance of the coax feed? If it is not, why the
fixed 9 to 1 ratio of the balun? Would not a variable device, such as
an L-circuit antenna tuner work better?

Of course it would, but that involves a lot of fiddling everytime one makes a
big frequency change whilst the balun approach offers a good compromise in
evening out the impedence mismatch, without the hassle.

http://members.aol.com/DXerCapeCod/z_transformers.pdf

http://www.dxing.info/equipment/impe...ing_bryant.pdf

dxAce
Michigan
USA

balun spec depending on coax impedance
 

Bob Miller wrote:
On Thu, 02 Mar 2006 14:00:41 GMT, David wrote:


On Thu, 02 Mar 2006 13:39:00 GMT, Bob Miller
wrote:


On Thu, 02 Mar 2006 00:28:43 GMT, Telamon
wrote:


I guess I'm missing something here. If the impedance of a 1/2 wave
dipole at its resonant frequency is about 72 ohms, and at twice that
frequency is about 5000 ohms, how is any single balun going to work
for a multi-frequency listening or transmitting setup? How does the
popular 9-1 balun used by so many swl-ers work for multi frequency
listening? Would it be to simply get the impedance within yelling
distance of the receiver input, or is it really needed at all, given
the pretty good sensitivity of most modern receivers?


Who uses 1/2 wave dipoles for receive only?

9:1 baluns are for random wire monopoles.

The purpose of the dingus is to more properly mate the random wire
with the shielded transmission line. It keeps noise pickup down and
bleeds static electricity away from the receiver.


Thanks for clarifying, but the question remains the same. Why would a
random length wire monopole at assorted listening frequencies always
be at nine times the impedance of the coax feed? If it is not, why the
fixed 9 to 1 ratio of the balun? Would not a variable device, such as
an L-circuit antenna tuner work better?

bob
k5qwg

I use an MFJ-986 tuner. Overkill for sure on a reciever, but you can
adjust the cap and inductor to "peak" any signal on any frequency (HF).
Easily possible to get 2 or 3 S units improvement. My current antenna
is 182 foot dipole, fed with 450 ohm ladderline. A 4:1 balun is in the
tuner.
I agree with Bob, a variable tuner will give greater results than just
picking one particular frequency and balun.

PJ in NJ