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.

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

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.

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

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

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)