Impedanc Matching Problem

[James Meyer]

On Fri, 25 Mar 2005 02:39:56 +0000, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wroth:

Openhiemer wrote:

Hello,

I have a impedance matching problem that I need help with.

I have a 1Mb data transmission system that is designed to work with 100-150
ohm cable, We would like to use it on 55 ohm cable.

Isn't it traditional at this point to suggest the use of 2 lengths of 55 ohm
cable in series ? ;-)


Graham

No. Historically, the most popular suggestion for this news group would
be to replace the cable with a PIC.

Jim

 

[Fred Bloggs]

I have a impedance matching problem that I need help with.

I have a 1Mb data transmission system that is designed to work with 100-150
ohm cable, We would like to use it on 55 ohm cable.

You do know that every single device that puts data on the line will
have the same problem- requiring that whatever so-called matching you
use will have to be applied to each and every device, and at low
impedance this will load the hell out of everything since (duh) they are
all in parallel.

 

[John Woodgate]

I read in sci.electronics.design that Openhiemer <openhamer@dot.dot>
wrote (in <Xns9622C01FD9184openhamermicrosoftco@158.152.254.254&gt about
'Impedanc Matching Problem', on Wed, 23 Mar 2005:

I have a impedance matching problem that I need help with.

I have a 1Mb data transmission system that is designed to work with
100-150 ohm cable, We would like to use it on 55 ohm cable.

If anyone thas has a good understanding of transmission line theory and
would like to help out (I can probably pay for time of the problem is
solvable) please e-mail me.

Do you have enough signal to use L-pads at each end of the 55 ohm cable?
Just two resistors in series, designed to look like 100 ohms one way and
55 ohms the other.

Use Courier font:


+----[R1]----+-----o o-----[R1]----+----+
| | | |
[100] [R2] <--55 ohms 100 ohms--> [R2] [55]
| | | |
+------------+-----o o-------------+----+

The calculation of R1 and R2 will keep you out of mischief for a few
seconds/ minutes/hours and will be a valuable addition to your little
black book of useful cribs.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Openhiemer]

bigcat@meeow.co.uk wrote in news:1111717318.128063.17300
@z14g2000cwz.googlegroups.com:

Openhiemer wrote:
Gareth <me@privacy.net> wrote in
news:qL6dneQSXZJXY9zfRVnygg@brightview.com:
John Woodgate wrote:
Do you have enough signal to use L-pads at each end of the 55 ohm
cable? Just two resistors in series, designed to look like 100
ohms
one way and 55 ohms the other.

I make R1 68 Ohms and R2 82 Ohms (nearest E12 preferred values),
which
will give you just over 7 dB of loss at each end. Can you afford
that
much attenuation?


You must have a very good reason to spend all this time trying to work
with a non compatible cable.

NT

Usual thing - Salesman agrees, engineer has to fix


-----------------------------------------------------------
To e-mail me please change the z characters to o characters
and the hat symbol to a at symbol. itmaster2001^yahzz.cz.uk
(hopfully mailbots are not that bright yet)