Mismatched Zo Connectors
 

At risk of being called a Troll, and having little else to do at
present, I copy from another newsgroup the following text.

"Reg Edwards" wrote -

"The effect of an impedance mis-match at a coaxial connector of
ordinary dimensions is practically zero at frequencies up to UHF.

Regardless of its other dimensions, the primary requirement of a
mismatched connector is that its length should be appreciably less
than 1/4-wavelength at the highest working frequency.

People are unnecessarily worried at VHF and below. Mix up 50 and
75-ohm connectors, and indeed connectors of unknown Zo, and carry on
regardless.

For an analysis of performance, download in a few seconds and run
immediately program CONNECT from website below."

Program CONNECT will calculate the effect on performance of inserting
any relatively short length of line, of Zo different from system Zo,
into the system. It's less than the inexperienced might imagine from
reading frightening magazine and handbook articles about impedance and
conjugate mis-matches.

If you have a short length of coax lying around, of unknown Zo, just
use it!
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

Mismatched Zo Connectors
 

Reg Edwards wrote:
Regardless of its other dimensions, the primary requirement of a
mismatched connector is that its length should be appreciably less
than 1/4-wavelength at the highest working frequency.

Yes, at HF the reflections from one impedance discontinuity
and the reflections from a complimentary impedance discontinuity
3 inches away almost entirely cancel each other.
--
73, Cecil http://www.qsl.net/w5dxp

Mismatched Zo Connectors
 

Some of us are so cheeky as to use CATV, RG-6, Rg-8, R8-11, etc., with
no regard as to the supposed 'surge impedence'..
What is the load impedence of a 50 ohm antenna at any frequency removed
from its resonance point anyway?
If the antenna is 30 ohms or 80 ohms, with some reactance, does the SWR
meter notice the inexpensive run of supposed 70 ohm coax that you
cadged from the cable tv company?
Once in a while I get an antenna that is fed with bits and pieces of
this and that, which swears differently back at the shack than it did
at the antenna feed point... Inserting another 5 or 10 feet of coax
jumper usually cures it...



denny / k8do - antenna monger from way back...

Another fine myth you've gotten us into, Ollie!

Mismatched Zo Connectors
 

Reg Edwards wrote:
Regardless of its other dimensions, the primary requirement of a
mismatched connector is that its length should be appreciably less
than 1/4-wavelength at the highest working frequency.
======================================

Yes, at HF the reflections from one impedance discontinuity
and the reflections from a complimentary impedance discontinuity
3 inches away almost entirely cancel each other.
--
73, Cecil
========================================

Reflections are functions of TIME, not frequency.

Oliver Heaviside had the right idea long before the invention of the
SWR meter.
-----
Reg, G4FGQ.

Mismatched Zo Connectors
 

"Denny" wrote
If the antenna is 30 ohms or 80 ohms, with some reactance, does the
SWR
meter notice the inexpensive run of supposed 70 ohm coax that you
cadged from the cable tv company?
=====================================

Of course it doesn't. But at least it does try.

The meter thinks it indicates SWR on the transmission line, whereas it
actually indicates SWR on a long, imaginary, non-existent, 50-ohm line
between tuner and transmitter.

What sort of mess would Laurel & Hardy have found themselves in when
trying to disentangle forward from reflected power?
===================================

Mismatched Zo Connectors
 

On Tue, 22 Aug 2006 17:28:01 GMT, Cecil Moore
wrote:


and the reflections from a complimentary impedance discontinuity

What is a "complimentary impedance discontinuity", or even a
"complementary impedance discontinuity" if you meant that?

Owen
--

Mismatched Zo Connectors
 

Cecil Moore wrote:
Reg Edwards wrote:

Regardless of its other dimensions, the primary requirement of a
mismatched connector is that its length should be appreciably less
than 1/4-wavelength at the highest working frequency.


Yes, at HF the reflections from one impedance discontinuity
and the reflections from a complimentary impedance discontinuity
3 inches away almost entirely cancel each other.

What's a "complimentary impedance discontinuity," Cecil?
73,
Tom Donaly, KA6RUH

Mismatched Zo Connectors
 

"Owen Duffy" wrote in message
...
On Tue, 22 Aug 2006 17:28:01 GMT, Cecil Moore
wrote:


and the reflections from a complimentary impedance discontinuity

What is a "complimentary impedance discontinuity", or even a
"complementary impedance discontinuity" if you meant that?
=======================================
Owen,
For the benifit of innocent bystanders, he means the same magnitude
discontinuity with the opposite sign. But you knew that of course,
didn't you?

On the other hand, I'm not sure *I* have described it correctly. It
can best be described in terms of the reflection coefficient.

There are two reflections, of opposite signs, which do not occur at
exactly the same instant in TIME.

Whatever it is, Cecil is (im)perfectly correct.
----
Reg.

Mismatched Zo Connectors
 

"Reg Edwards" wrote

Reflections are functions of TIME, not frequency.

Oliver Heaviside had the right idea long before the invention of the
SWR meter.
====================================

For "reflections" also read "Echos".
-----
Reg, G4FGQ.
====================================

Mismatched Zo Connectors
 

On Wed, 23 Aug 2006 00:54:51 +0100, "Reg Edwards"
wrote:


"Reg Edwards" wrote

Reflections are functions of TIME, not frequency.

Oliver Heaviside had the right idea long before the invention of the
SWR meter.
====================================

For "reflections" also read "Echos".

Hi Reggie,

You are in fact wrong in all accounts. Reflections are functions of
distance - as are echoes. This is a phase issue. Time and frequency
are always inseparable as Kelvin would instruct you in first
principles before another hunk of chalk was winged off your noggin.

You may choose to render phase into time, but shift the frequency and
the phase shifts, not the distance. Mismatched Zo connectors do not
shrink or enlarge with frequency - the effects may, but physical
components rarely follow such perturbations.... until an arc-over
that is the classic failure mechanism for such mismatches (obviously,
and deliberately ignored in this thread).

73's
Richard Clark, KB7QHC