ribbon cable's characteristic impedance?

[funster]

ribbon cable impedance

hello, all friends:

how much is the normal ribbon cable's characteristic impedance,

can I measure it useing a simple method?

best regards

 

[FoxyRick]

characteristic impedance ribbon

Simple, flat 0.05" IDC ribbon is generally around 95Ω to 110Ω. Some can go as high as 210Ω. I have seen jacketed cables down to 62Ω

The manufacturers' datasheets will tell you, if you are using surplus cable it might be hard to identify though.

Cheers,
FoxyRick.

 

[xxargs]

cable impedance calculator

hello, all friends:

how much is the normal ribbon cable's characteristic impedance,

can I measure it useing a simple method?

best regards

measure inductanse on shorted piece of cable
and measure capacitance opened same piece of cable


for low frequences ( 0-20 kHz) is also interest of resistanse of shorted pieces of cables

and for high frequency is loss tangent of insulation of cables and convert to 'g'


--------------------------------------------------

alpha = loss constant in Neper

(1 neper = 8.686 dB)


beta = phase constant in Radians

f = frequency in Hz

j => j^2 = -1, imaginary number, normaly 'i' but here in 'j'

w = 2*PI*f

r = resistance Ohm

c = capacitance Farad

l = inductance Henry

g = conductance Siemens


----------------------------------------------

Simplified equation to calculate for low fequency 0 - 20 KHz on cable:


alpha = sqr( wrc / 2) Neper

beta = sqr (r/(jwc)) Radian

Z = sqr(r/(jwc)) Ohm

impedances is always complex value and
current is 45 degree phaseshift before voltage
and result high frequency attenuate more than low frequency


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simplified calculation for high frequencys >> 200 KHz on cable

alpha = (r/2 * sqr(c/l)) + (g/2 * sqr(l/c)) Neper

beta = w*sqr(lc) Radian

Z = sqr(l/c) Ohm

impedances is are real and attenuate depends of 'r' and 'g' and more or less same for all frequency, but give slowly higher attenuate of frequency depend increase of skin effect of conduct and dielecric loss of insulator between cords. This effect is not included in simplified formula above or full telegraph equation.


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if working in range 20 KHz to 2 MHz on cable, is tricky part make simplified equations like above and need calculate with whole 'telegraph equation' to estimate cable character on actual frequency - And in old transsissions theory books marks this part is not intresting depend of more complicate math for students - but if works with ADSL, RS-485 etc. is _very_ intresting parts...


gamma = alpha + jbeta


gamma = sqr((r+jwl) * (g + jwc))

and

Z = sqr((r+jwl)/(g + jwc))


---

simplified formula for low and high frequecy is maked to calculate with
paper and pencil, but if using complex capable calculator is it easy to handle
with full 'telegraph equation' in all situation for more accurate value

I using hp42s on many year and now finding free GPL software version
on http://home.planet.nl/~demun000/thomas_projects/free42/

and show her input example for this calculator on equation 'sqr( (r+jwl)/(g + jwc) )':



OK, first make, first time installed/started free42 calculator to store complex values in registers:

2nd modes -> select RECT ; make view and input to reqtangular mode
0
<Enter>
0
2nd complex ; make this zero to complex zero
STO
+
select 'REGS' in dispaly ; make all store registe to handle complex numbers now and need this moment only one time (to next machine reset)


ok, calculate equation 'sqr( (r+jwl)/(g + jwc) )':


'r' value ; resistans 'r' value
<ENTER>
2 ; calculate 'w' from frequency now
<ENTER>
2nd PI
*
frequency ; frequecy in Hz
*
STO 00 ; copy and store 'w' value to later using
'l' value ; inductance 'l' value
* ; calculate for 'wl' and have now value 'r' and 'wl' on stack
2nd complex ; make complex value 'r + jwl'

'g' value ; conductace 'g' value
RCL 00 ; recall stored 'w'-value
'c' value ; capacitance 'c' value
* ; calculate 'wc' value
2nd complex ; make complex value 'g + jwc'

;now, stack has 'r + jwl' value on Y and 'g + jwc' value on X positions

/ ; fraction of 'r + jwl' / 'g + jwc', result in complex value

; and lastest step

SQR ;Square root of result

and answer impedances Z in complex value.

if you want polar view:

2nd modes -> select POLAR

and present answer on display in result resistance value and angle

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OK, this can easly solve on Mathematica or Mathcad, but for 'quick an dirty - thinking' calc, hp42s or simular calculator with complex support is very useful...

---


hp42s is very useful to handle 'simple' but complex valued formula as above
and can also handle complex matrices and matrice operation like eigenvector
and cross products etc. and need bigger caculator like hp48 and better or TI 86 and better (possible TI 83??) to find same functionality....

hp33s cannot handle this directly depend miss of handling square root with complex value (but working with work around y^x, ie y^0.5) and cannot handle and store complex value in store registers - hp33s is hard to work with complex values IMHO.