Small brain teaser

As the result of an error, several coax leads in my house were of 50 ohms
impedance. I recently replaced one of them with modern quality 75 ohm stuff
and the improvement in signal was significant. The remaining cables are
embedded in a way that would require damage for them to be replaced.

I was wondering if they could be terminated in a way that would present a 75
ohms match at both ends and would this improve the signal?

--
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Mageia 2 for x86_64, Kernel: 3.4.13-desktop-1.mga2
KDE version 4.8.4 Running on an AMD 4-core processor

In article , Pinnerite
writes
As the result of an error, several coax leads in my house were of 50 ohms
impedance. I recently replaced one of them with modern quality 75 ohm stuff
and the improvement in signal was significant. The remaining cables are
embedded in a way that would require damage for them to be replaced.

I was wondering if they could be terminated in a way that would present a 75
ohms match at both ends and would this improve the signal?

Transmission line theory suggests source termination with an RF rated
series resistor[1] (of 27ohms) should do the job. I wouldn't bother with
load termination as the input stage probably doesn't look much like
75ohms to start with.

[1] Carbon film/carbon composition?
--
fred
it's a ba-na-na . . . .

In article ,
Pinnerite wrote:
As the result of an error, several coax leads in my house were of 50
ohms impedance. I recently replaced one of them with modern quality 75
ohm stuff and the improvement in signal was significant. The remaining
cables are embedded in a way that would require damage for them to be
replaced.

I was wondering if they could be terminated in a way that would present
a 75 ohms match at both ends and would this improve the signal?

But are those 50 ohm cables designed for the frequency they're being used
at?

--
*I thought I wanted a career. Turns out I just wanted paychecks.

Dave Plowman London SW
To e-mail, change noise into sound.

Pinnerite wrote:
As the result of an error, several coax leads in my house were of 50 ohms
impedance. I recently replaced one of them with modern quality 75 ohm stuff
and the improvement in signal was significant. The remaining cables are
embedded in a way that would require damage for them to be replaced.

I was wondering if they could be terminated in a way that would present a 75
ohms match at both ends and would this improve the signal?

It's the fact that the cable has a solid dielectric that's causing most
of the problem, and you can't do anything about that.

Bill

The aerial itself, if its an aerial and not an amp, could be all over the
place impedance wise as well, byut I suppose a closer coupling of the
reflector might lower the impedence.
Brian

--
From the Sofa of Brian Gaff Reply address is active
"fred" wrote in message ...
In article , Pinnerite
writes
As the result of an error, several coax leads in my house were of 50 ohms
impedance. I recently replaced one of them with modern quality 75 ohm
stuff
and the improvement in signal was significant. The remaining cables are
embedded in a way that would require damage for them to be replaced.

I was wondering if they could be terminated in a way that would present a
75
ohms match at both ends and would this improve the signal?

Transmission line theory suggests source termination with an RF rated
series resistor[1] (of 27ohms) should do the job. I wouldn't bother with
load termination as the input stage probably doesn't look much like 75ohms
to start with.

[1] Carbon film/carbon composition?
--
fred
it's a ba-na-na . . . .

fred wrote:

In article , Pinnerite
writes
As the result of an error, several coax leads in my house were of 50 ohms
impedance. I recently replaced one of them with modern quality 75 ohm
stuff and the improvement in signal was significant. The remaining cables
are embedded in a way that would require damage for them to be replaced.

I was wondering if they could be terminated in a way that would present a
75 ohms match at both ends and would this improve the signal?

Transmission line theory suggests source termination with an RF rated
series resistor[1] (of 27ohms) should do the job. I wouldn't bother with
load termination as the input stage probably doesn't look much like
75ohms to start with.

[1] Carbon film/carbon composition?

I'll give it a try when the weather improves. Thank you.

--
__________________________________________________ _

Mageia 2 for x86_64, Kernel: 3.4.13-desktop-1.mga2
KDE version 4.8.4 Running on an AMD 4-core processor

In article , Dave Plowman (News)
scribeth thus
In article ,
Pinnerite wrote:
As the result of an error, several coax leads in my house were of 50
ohms impedance. I recently replaced one of them with modern quality 75
ohm stuff and the improvement in signal was significant. The remaining
cables are embedded in a way that would require damage for them to be
replaced.

I was wondering if they could be terminated in a way that would present
a 75 ohms match at both ends and would this improve the signal?

But are those 50 ohm cables designed for the frequency they're being used
at?


Usually better then the things that 75 ohm lines are attached to;!...
--
Tony Sayer

Pinnerite wrote:
fred wrote:

In article , Pinnerite
writes
As the result of an error, several coax leads in my house were of 50 ohms
impedance. I recently replaced one of them with modern quality 75 ohm
stuff and the improvement in signal was significant. The remaining cables
are embedded in a way that would require damage for them to be replaced.

I was wondering if they could be terminated in a way that would present a
75 ohms match at both ends and would this improve the signal?

Transmission line theory suggests source termination with an RF rated
series resistor[1] (of 27ohms) should do the job. I wouldn't bother with
load termination as the input stage probably doesn't look much like
75ohms to start with.

[1] Carbon film/carbon composition?

I'll give it a try when the weather improves. Thank you.

I've told you you're wasting your time. The signal loss is caused by the
solid dielectric more than the mismatch.

Why won't people be told?

Bill

Bill Wright wrote:

Pinnerite wrote:
fred wrote:

In article , Pinnerite
writes
As the result of an error, several coax leads in my house were of 50
ohms
impedance. I recently replaced one of them with modern quality 75 ohm
stuff and the improvement in signal was significant. The remaining
cables are embedded in a way that would require damage for them to be
replaced.

I was wondering if they could be terminated in a way that would present
a 75 ohms match at both ends and would this improve the signal?

Transmission line theory suggests source termination with an RF rated
series resistor[1] (of 27ohms) should do the job. I wouldn't bother with
load termination as the input stage probably doesn't look much like
75ohms to start with.

[1] Carbon film/carbon composition?

I'll give it a try when the weather improves. Thank you.

I've told you you're wasting your time. The signal loss is caused by the
solid dielectric more than the mismatch.

Why won't people be told?

Because they like to check what they are told - unless they are brainwashed.

Alan



Bill
--
__________________________________________________ _

Mageia 2 for x86_64, Kernel: 3.4.13-desktop-1.mga2
KDE version 4.8.4 Running on an AMD 4-core processor

Pinnerite wrote:

I've told you you're wasting your time. The signal loss is caused by the
solid dielectric more than the mismatch.

Why won't people be told?

Because they like to check what they are told - unless they are brainwashed.

A healthily sceptical attitude, but on a simple matter like this I would
have thought the simple answer was sufficient.

Bill