Author Topic: 50 ohm Terminator for Oscilloscope Input from Function Generator Ouput  (Read 19144 times)

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Online Electro Fan

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Anyone know what the differences might be between the $25 accessory Rigol sells vs. a $42 Pomona Electronics 4119-50 (other than the $17?)?  The Pomona looks like a straight through BNC connector, the Rigol has some additional packaging around the BNC connector?  Thanks

http://www.alliedelec.com/Search/ProductDetail.aspx?SKU=70198110&mkwid=sT3cWNz3g&pcrid=27420352650&pkw=4119%2050&pmt=e#tab=specs
 
« Last Edit: May 23, 2013, 05:03:47 pm by Electro Fan »
 

Offline edavid

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The plastic box is probably just a snap-on... it actually has some value in keeping the thing from rolling off your bench.

I wouldn't buy either of these, though... look for a Tektronix 011-0049-XX or something from a quality microwave parts vendor like MiniCircuits.
 

Offline Rufus

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Anyone know what the differences might be between the $25 accessory Rigol sells vs. a $42 Pomona Electronics 4119-50 (other than the $17?)?  The Pomona looks like a straight through BNC connector, the Rigol has some additional packaging around the BNC connector?

Terminators (through or otherwise) are defined by their power handling capability and high frequency performance. High frequency performance usually being specified as maximum VSWR over a frequency range.

Compare specifications, lower VSWR = better.
 

Offline EV

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Your Rigol part looks like attenuator. The Rigol feedthru terminator which I bought looked like that one in the attached picture.
 

Online Electro Fan

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Anyone know what the differences might be between the $25 accessory Rigol sells vs. a $42 Pomona Electronics 4119-50 (other than the $17?)?  The Pomona looks like a straight through BNC connector, the Rigol has some additional packaging around the BNC connector?

Terminators (through or otherwise) are defined by their power handling capability and high frequency performance. High frequency performance usually being specified as maximum VSWR over a frequency range.

Compare specifications, lower VSWR = better.

Thanks for the tip on VSWR:

Here is the VSWR spec info (and some other specs) on the Pomona:

MATERIALS:
Body and Fittings: Brass, Alloy 360, ½ Hard.
Center Contact: Male – Brass, Alloy 360, ½ Hard.
Female – Beryllium Copper per Cond. Ht.
Outer Contact: Beryllium Copper, Cond. Ht.
Dielectric: Teflon per L-P-403.
Gasket/Seals: Silicone rubber per zz-r-765, Class 11a, Grade 50.
Finish:
Body and Fittings: Tarnish Resistant.
Center Contact: Male – Gold plated.
Outer Contact: Tarnish Resistant.
Marking: “Pomona Elect. 4119-*” and resistance value marked on label.
Specifications: 2%, 2 Watt, Carbon-film resistor deposited over Ceramic Core.
VSWR: 1.1 Max. from D.C. to 250 MHz.
1.2 Max. from 250 MHz to 500 MHz.

RATINGS:
Operating Temperature: +102°C (+216°F) Max.
ORDERING INFORMATION: Model 4119-*


It looks like a low VSWR is easier to achieve from DC to lower frequencies (I have a 100 MHz scope).  What is a reasonable VSWR spec (how much below 1.1 is desirable and what would types of performance improvement would a tenth or a few tenths bring)?

What is an acceptable spec for VSWR? 
 

Online Electro Fan

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Anyone know what the differences might be between the $25 accessory Rigol sells vs. a $42 Pomona Electronics 4119-50 (other than the $17?)?  The Pomona looks like a straight through BNC connector, the Rigol has some additional packaging around the BNC connector?

Terminators (through or otherwise) are defined by their power handling capability and high frequency performance. High frequency performance usually being specified as maximum VSWR over a frequency range.

Compare specifications, lower VSWR = better.

Thanks for the tip on VSWR:

Here is the VSWR spec info (and some other specs) on the Pomona:

MATERIALS:
Body and Fittings: Brass, Alloy 360, ½ Hard.
Center Contact: Male – Brass, Alloy 360, ½ Hard.
Female – Beryllium Copper per Cond. Ht.
Outer Contact: Beryllium Copper, Cond. Ht.
Dielectric: Teflon per L-P-403.
Gasket/Seals: Silicone rubber per zz-r-765, Class 11a, Grade 50.
Finish:
Body and Fittings: Tarnish Resistant.
Center Contact: Male – Gold plated.
Outer Contact: Tarnish Resistant.
Marking: “Pomona Elect. 4119-*” and resistance value marked on label.
Specifications: 2%, 2 Watt, Carbon-film resistor deposited over Ceramic Core.
VSWR: 1.1 Max. from D.C. to 250 MHz.
1.2 Max. from 250 MHz to 500 MHz.

RATINGS:
Operating Temperature: +102°C (+216°F) Max.
ORDERING INFORMATION: Model 4119-*


It looks like a low VSWR is easier to achieve from DC to lower frequencies (I have a 100 MHz scope).  What is a reasonable VSWR spec (how much below 1.1 is desirable and what would types of performance improvement would a tenth or a few tenths bring)?

What is an acceptable spec for VSWR?

Here is a link to a Tektronix spec sheet:

http://www.alliedelec.com/images/products/datasheets/bm/TEKTRONIX/70136817.pdf

It indicates the 011-0049-02 has a Max. VSWR of 1.2 (DC to 1 GHz).  These seem to sell for about $140 new (about 1/3 of a Rigol 1102!) and maybe $25-$60 used.  Any chance this would really enable a cleaner square wave than the Pomona product on a 100MHz analog Tektronix scope?  Or is the benefit of the 011-0049-02 only likely to be seen on higher bandwidth scopes?  (Or is there something fundamentally better about the quality of the Tektronix part than the Pomona part that will show up in some way other than the VSWR and associated bandwidth spec?)  Maybe it's a better investment to just buy a used Tek 011-0049-02 than a new Pomona 4119-50?  My guess is that 100MHz and below it would be unlikely these two parts would yield any difference but I'd be happy to learn otherwise.  Thanks again
« Last Edit: May 23, 2013, 06:10:07 pm by Electro Fan »
 

Offline KedasProbe

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The Rigol "PL-50" feed-through termination  (20 Euro without VAT)
has these specs (according to Rigol)
50 ohm  (I measured DC: 50.29 ohm and 50.17 ohm on the second one)
Z-tol: 0.5 ohm  (1%)
freq BW: DC-1GHz
Size: 46mm, 16mm
Max. Power: 2 Watt
Weight: 25 gram

edit pictures: http://www.circuitsonline.net/forum/view/107920/30
« Last Edit: May 23, 2013, 06:33:19 pm by KedasProbe »
Not everything that counts can be measured. Not everything that can be measured counts.
[W. Bruce Cameron]
 

Offline BravoV

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It looks like a low VSWR is easier to achieve from DC to lower frequencies (I have a 100 MHz scope).  What is a reasonable VSWR spec (how much below 1.1 is desirable and what would types of performance improvement would a tenth or a few tenths bring)?

What is an acceptable spec for VSWR?
As other mentioned, lower is better, but how low is "good enough" ? Do we really need a 1.01 VSWR but will cost your arm & leg ? or say at 1.3 but cost you only few bucks ?

Made a thread asking this VSWR figure in the measurement context instead of RF transmission, at this thread -> HERE, with a lot helps from other helpful experienced members here, and also finally I sort of summarized it my self at post #19 with 2 pictures from external references that really helped me a lot.

Hope this helps.
« Last Edit: May 23, 2013, 06:10:29 pm by BravoV »
 

Offline edavid

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Here is a link to a Tektronix spec sheet:

http://www.alliedelec.com/images/products/datasheets/bm/TEKTRONIX/70136817.pdf

It indicates the 011-0049-02 has a Max. VSWR of 1.2 (DC to 1 GHz).  These seem to sell for about $140 new and maybe $60 used.  Any chance this would really enable a cleaner square wave than the Pomona product on a 100MHz analog Tektronix scope?  Or is the benefit of the 011-0049-02 only likely to be seen on higher bandwidth scopes?  (Or is there something fundamentally better about the quality of the Tektronix part than the Pomona part that will show up in some way other than the VSWR and associated bandwidth spec?)  Maybe it's a better investment to just buy a used Tek 011-0049-02 than a new Pomona 4119-50?  My guess is that 100MHz and below it would be unlikely these two parts would yield any difference but I'd be happy to learn otherwise.  Thanks again

Check the eBay sold listings, you can get used 011-0049-01s for much less than that.  Better quality than Pomona for less money.
« Last Edit: May 23, 2013, 06:20:21 pm by edavid »
 

Online Electro Fan

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It looks like a low VSWR is easier to achieve from DC to lower frequencies (I have a 100 MHz scope).  What is a reasonable VSWR spec (how much below 1.1 is desirable and what would types of performance improvement would a tenth or a few tenths bring)?

What is an acceptable spec for VSWR?
As other mentioned, lower is better, but how low is "good enough" ? Do we really need a 1.01 VSWR but will cost your arm & leg ? or say at 1.3 but cost you only few bucks ?

Made a thread asking this VSWR figure in the measurement context instead of RF transmission, at this thread -> HERE, with a lot helps from other helpful experienced members here, and also finally I sort of summarized it my self at post #19 with 2 pictures from external references that really helped me a lot.

Hope this helps.

BravoV - wow, great links to great post(s).  Thanks!!
 

Online Electro Fan

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Here is a link to a Tektronix spec sheet:

http://www.alliedelec.com/images/products/datasheets/bm/TEKTRONIX/70136817.pdf

It indicates the 011-0049-02 has a Max. VSWR of 1.2 (DC to 1 GHz).  These seem to sell for about $140 new and maybe $60 used.  Any chance this would really enable a cleaner square wave than the Pomona product on a 100MHz analog Tektronix scope?  Or is the benefit of the 011-0049-02 only likely to be seen on higher bandwidth scopes?  (Or is there something fundamentally better about the quality of the Tektronix part than the Pomona part that will show up in some way other than the VSWR and associated bandwidth spec?)  Maybe it's a better investment to just buy a used Tek 011-0049-02 than a new Pomona 4119-50?  My guess is that 100MHz and below it would be unlikely these two parts would yield any difference but I'd be happy to learn otherwise.  Thanks again

Check the eBay sold listings, you can get used 011-0049-01s for much less than that.  Better quality for less money.

Hi edavid, Thanks - I had just come to that same conclusion after looking at not just the current asking prices but also the previous sell prices on eBay.  Looks like it should be easy enough to get a good used Tek product at a reasonable price.  (I modified my post to show the $25 to $60 used range so as not to propagate less than accurate info.)
« Last Edit: May 23, 2013, 06:24:10 pm by Electro Fan »
 

Offline jahonen

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I wouldn't worry about VSWR too much since this kind of termination is always a compromise (but much better than no termination at all), since there is significant length of unterminated stub behind the terminator when connected to a typical scope, so I doubt if it makes any difference at all if VSWR is 1.01 (return loss 46 dB) or 1.3 (return loss 17.7 dB) for the terminator itself. For this reason, higher bandwidth scopes have a terminator resistor built in, so that the unterminated stub length is greatly reduced.

Regards,
Janne
 

Online Electro Fan

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011-0049-01 vs 011-0049-02 ?
« Reply #12 on: May 23, 2013, 06:45:26 pm »
Ok, I think we've pretty well knocked out most of the questions on this (Thanks to Everyone Here!).

Just one last question:  what's the difference between a 011-0049-01 and a 011-0049-02?  Thx

(All? the ones on eBay are 01, but the Tektronix spec sheet says 02)??
« Last Edit: May 23, 2013, 06:49:38 pm by Electro Fan »
 

Online Electro Fan

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Waves and SWR
« Reply #13 on: May 23, 2013, 08:03:32 pm »
This was/is an excellent video:



- explains SWR and a lot more
 

Offline Martin72

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Re: 50 ohm Terminator for Oscilloscope Input from Function Generator Ouput
« Reply #14 on: March 15, 2019, 09:11:01 pm »
Hi there,

Let me pull this thing up after years…

Done measurements with an external 50 \$\Omega\$ Termination resistor :

https://www.eevblog.com/forum/blog/new-rigol-scope/msg2270838/#msg2270838

The risetime decreases remarkable against 1M \$\Omega\$ Input - but there are massive overshoots..
Causing by the resistor, as you can see that two scopes reproduces the same Signal, while the one with integraded 50 \$\Omega\$ reproduce no overshoots.

Question:
Could the overshoots be avoiding ( by taking a "better" resistor) or ist it a common thing when using such an external termination ?

Martin


Offline TheSteve

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Re: 50 ohm Terminator for Oscilloscope Input from Function Generator Ouput
« Reply #15 on: March 15, 2019, 10:29:37 pm »
From what I have seen a better 50 ohm terminator can help a little but the real problem is the non 50 ohm path internal to the oscilloscope. An external 50 ohm feed-thru will generally never match a good 50 ohm internal path in a scope. That doesn't mean it isn't just fine to use the external feed-thru when required, you just need to understand its limitations.
VE7FM
 

Online tautech

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Re: 50 ohm Terminator for Oscilloscope Input from Function Generator Ouput
« Reply #16 on: March 15, 2019, 10:35:02 pm »
Yep, there are some quite bad 50 ohm feed through terminations available.  :(

On the other hand quite reasonable ones aren't that dear, this $22 PL-50N from Pintek compares very well against my Tek feed throughs.

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Offline David Hess

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Re: 50 ohm Terminator for Oscilloscope Input from Function Generator Ouput
« Reply #17 on: March 16, 2019, 09:07:35 pm »
It comes down to some feed-through attenuators are better than others and all are compromised by the length between the termination and load.  Up to 200MHz they are fine but above that they are increasingly marginal and an internal termination is required for good performance.
 

Offline gf

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Re: 50 ohm Terminator for Oscilloscope Input from Function Generator Ouput
« Reply #18 on: March 16, 2019, 09:54:34 pm »
I guess that one limiting factor of external 50 Ohm termination on 1M scopes is also the input capacitance of the scope?
RC low pass 50 Ohm and say 20 pF gives a cut-off frequency of ~160 MHz.

EDIT: Forgot to consider the source impedance, so the low pass is rather formed by 25 Ohm and Cin, doubling the mentioned cut-off frequency.
« Last Edit: March 17, 2019, 10:14:26 am by gf »
 
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Offline Martin72

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Re: 50 ohm Terminator for Oscilloscope Input from Function Generator Ouput
« Reply #19 on: March 16, 2019, 10:14:26 pm »
A forum colleague ( we´re both working as administrators there) which is in hf-technique told me, I need a pass-through termination in fully coaxial method of construction with at least an bandwith of 3Ghz or more to get a clean signal.

Offline Mortymore

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Re: 50 ohm Terminator for Oscilloscope Input from Function Generator Ouput
« Reply #20 on: March 16, 2019, 10:38:16 pm »
I guess that one limiting factor of external 50 Ohm termination on 1M scopes is also the input capacitance of the scope?
RC low pass 50 Ohm and say 20 pF gives a cut-off frequency of ~160 MHz.

The 50 Ohm resistor of the feed-through terminator is not placed in series with the input of the scope, it's in parallel.

... this $22 PL-50N from Pintek ...

Where can the PL-50N be found for that price, please?
 

Online tautech

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Re: 50 ohm Terminator for Oscilloscope Input from Function Generator Ouput
« Reply #21 on: March 16, 2019, 10:49:54 pm »
... this $22 PL-50N from Pintek ...

Where can the PL-50N be found for that price, please?
Only directly from Pintek and they have a min order of $500 IIRC. I just got one with another order I placed and just so see if it was any good compared to the Tek 1x and 10x I have.
Otherwise it's available on Aliexpress from AideTek:
https://www.aliexpress.com/item/PL-50N-Oscillscope-Scope-to-Function-Genarator-Converter-impedance-match/32227714382.html?spm=2114.search0604.3.2.a38afca59Qed6q&ws_ab_test=searchweb0_0,searchweb201602_1_10065_10068_10547_319_10059_10884_317_10548_10887_10696_321_322_10084_453_10083_454_10103_10618_10307_537_536_10902,searchweb201603_70,ppcSwitch_0&algo_expid=8b68d4e7-1717-4c02-871b-b4d3e9dcb718-0&algo_pvid=8b68d4e7-1717-4c02-871b-b4d3e9dcb718&transAbTest=ae803_4

And somewhere on a Google search I saw them for $40.....let your fingers do the walking.  ;)
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Offline gf

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Re: 50 ohm Terminator for Oscilloscope Input from Function Generator Ouput
« Reply #22 on: March 16, 2019, 10:52:10 pm »
The 50 Ohm resistor of the feed-through terminator is not placed in series with the input of the scope, it's in parallel.

There is, however, the 50 Ohm source impedance in series, but agreed, the low-pass is eventually formed by only 25 Ohm and Cin, doubling the cut-off frequency.
The capacitive component of the load also leads to a mis-termination of the cable, IMO, leading to reflexions.
 

Offline Mortymore

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Re: 50 ohm Terminator for Oscilloscope Input from Function Generator Ouput
« Reply #23 on: March 16, 2019, 10:53:13 pm »
Thanks tautech

I google them, but found non for that price. I now understand why.  :'(

@gf

As I see it, the only resistance in series in a connection between two devices terminated with the 50 ohm, is the resistance of the cable that connects them. Simply put, the input/output capacitance of the devices involved (and C of the cable) and the resistance of the cable that connects them, is what can be considered a low pass filter. In order to minimise the cut-off frequency, the cable must be kept as short as possible.
Sorry if I'm not explaining myself very well.
« Last Edit: March 16, 2019, 11:08:48 pm by Mortymore »
 

Offline gf

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Re: 50 ohm Terminator for Oscilloscope Input from Function Generator Ouput
« Reply #24 on: March 16, 2019, 11:46:49 pm »
As I see it, the only resistance in series in a connection between two devices terminated with the 50 ohm, is the resistance of the cable that connects them. Simply put, the input/output capacitance of the devices involved (and C of the cable) and the resistance of the cable that connects them, is what can be considered a low pass filter. In order to minimise the cut-off frequency, the cable must be kept as short as possible.

The AWG usually has an output impedance of 50 Ohm as well, which is in series with the voltage source. And at higher frequencies, the cable basically acts as transmission line (no longer as capacitor), therefore the remote end of the cable still looks to the terminator as if it were a voltage source with 50 Ohm impedance (but with delayed signal).

[ If the cable were very short and the generator had an output impedance of zero, then a 50 Ohm termination wouldn't make a difference either. The 50 Ohm termination at the scope is considered, because the scope is supposed to be driven via a 50 Ohm transmission line in this prticular use case. ]
« Last Edit: March 17, 2019, 10:31:47 am by gf »
 


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