50 ohm Terminator for Oscilloscope Input from Function Generator Ouput - Page 1
Forum section: electronics / testgear

author: Electro Fan
author_rank: Super Contributor
timestamp: May 23, 2013, 05:02:05 pm
content: 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? Thankshttp://www.alliedelec.com/Search/ProductDetail.aspx?SKU=70198110&mkwid=sT3cWNz3g&pcrid=27420352650&pkw=4119%2050&pmt=e#tab=specs

author: edavid
author_rank: Super Contributor
timestamp: May 23, 2013, 05:19:29 pm
content: 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.

author: Rufus
author_rank: Super Contributor
timestamp: May 23, 2013, 05:22:15 pm
content: Quote from: Electro Fan on May 23, 2013, 05:02:05 pmTerminators (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.

author: EV
author_rank: Frequent Contributor
timestamp: May 23, 2013, 05:24:47 pm
content: Your Rigol part looks like attenuator. The Rigol feedthru terminator which I bought looked like that one in the attached picture.

author: Electro Fan
author_rank: Super Contributor
timestamp: May 23, 2013, 05:34:00 pm
content: Quote from: Rufus on May 23, 2013, 05:22:15 pmThanks 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?

author: Electro Fan
author_rank: Super Contributor
timestamp: May 23, 2013, 05:49:32 pm
content: Quote from: Electro Fan on May 23, 2013, 05:34:00 pmHere is a link to a Tektronix spec sheet:http://www.alliedelec.com/images/products/datasheets/bm/TEKTRONIX/70136817.pdfIt 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

author: KedasProbe
author_rank: Frequent Contributor
timestamp: May 23, 2013, 05:57:37 pm
content: 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-1GHzSize: 46mm, 16mmMax. Power: 2 WattWeight: 25 gramedit pictures:http://www.circuitsonline.net/forum/view/107920/30

author: BravoV
author_rank: Super Contributor
timestamp: May 23, 2013, 06:06:52 pm
content: Quote from: Electro Fan on May 23, 2013, 05:34:00 pmAs 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 figurein the measurement contextinstead 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.

author: edavid
author_rank: Super Contributor
timestamp: May 23, 2013, 06:11:02 pm
content: Quote from: Electro Fan on May 23, 2013, 05:49:32 pmCheck the eBay sold listings, you can get used 011-0049-01s for much less than that. Better quality than Pomona for less money.

author: Electro Fan
author_rank: Super Contributor
timestamp: May 23, 2013, 06:17:22 pm
content: Quote from: BravoV on May 23, 2013, 06:06:52 pmBravoV - wow, great links to great post(s). Thanks!!

author: Electro Fan
author_rank: Super Contributor
timestamp: May 23, 2013, 06:22:29 pm
content: Quote from: edavid on May 23, 2013, 06:11:02 pmHi 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.)

author: jahonen
author_rank: Super Contributor
timestamp: May 23, 2013, 06:29:16 pm
content: 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

author: Electro Fan
author_rank: Super Contributor
timestamp: May 23, 2013, 06:45:26 pm
content: 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)??

author: Electro Fan
author_rank: Super Contributor
timestamp: May 23, 2013, 08:03:32 pm
content: This was/is an excellent video:- explains SWR and a lot more

author: Martin72
author_rank: Super Contributor
timestamp: March 15, 2019, 09:11:01 pm
content: Hi there,Let me pull this thing up after years…Done measurements with an external 50Termination resistor :https://www.eevblog.com/forum/blog/new-rigol-scope/msg2270838/#msg2270838The risetime decreases remarkable against 1MInput - 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 50reproduce 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

author: TheSteve
author_rank: Unknown
timestamp: March 15, 2019, 10:29:37 pm
content: 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.

author: tautech
author_rank: Super Contributor
timestamp: March 15, 2019, 10:35:02 pm
content: 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.

author: David Hess
author_rank: Super Contributor
timestamp: March 16, 2019, 09:07:35 pm
content: 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.

author: gf
author_rank: Super Contributor
timestamp: March 16, 2019, 09:54:34 pm
content: 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.

author: Martin72
author_rank: Super Contributor
timestamp: March 16, 2019, 10:14:26 pm
content: 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.

author: Mortymore
author_rank: Frequent Contributor
timestamp: March 16, 2019, 10:38:16 pm
content: Quote from: gf on March 16, 2019, 09:54:34 pmThe 50 Ohm resistor of the feed-through terminator is not placed in series with the input of the scope, it's in parallel.Quote from: tautech on March 15, 2019, 10:35:02 pmWhere can the PL-50N be found for that price, please?

author: tautech
author_rank: Super Contributor
timestamp: March 16, 2019, 10:49:54 pm
content: Quote from: Mortymore on March 16, 2019, 10:38:16 pmOnly 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_4And somewhere on a Google search I saw them for $40.....let your fingers do the walking.

author: gf
author_rank: Super Contributor
timestamp: March 16, 2019, 10:52:10 pm
content: Quote from: Mortymore on March 16, 2019, 10:38:16 pmThere 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.

author: Mortymore
author_rank: Frequent Contributor
timestamp: March 16, 2019, 10:53:13 pm
content: Thanks tautechI google them, but found non for that price. I now understand why.@gfAs 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.

author: gf
author_rank: Super Contributor
timestamp: March 16, 2019, 11:46:49 pm
content: Quote from: Mortymore on March 16, 2019, 10:53:13 pmThe 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. ]

author: gf
author_rank: Super Contributor
timestamp: March 17, 2019, 10:46:34 am
content: I got these ones for just a hand-full of bucks:https://www.ebay.com/itm/50-Ohm-Feed-Through-Terminator-BNC-to-BNC-50KY-Device-Q9-Adapter-Black/312248423345Seem to work pretty well up to the BW limit of my scope.Would be interesting how well they work up to the specified 1GHz.I can't measure that, though, with my equipment.

author: WhichEnt2
author_rank: Regular Contributor
timestamp: March 17, 2019, 11:26:51 am
content: Quote from: tautech on March 16, 2019, 10:49:54 pmHow do you find it?It has a rather unusual non-search-optimized title. I searched previously for feedthrough bnc terminator and aliexpress is just full of those Cleqee P57 black box based ones and nothing more.

author: gf
author_rank: Super Contributor
timestamp: March 17, 2019, 11:32:25 am
content: I simply searched for "feed-through terminator 50 ohm" at eBayThis model is obvioulsy available from several sellers, and at different prices.EDIT: Retracted answer - the question did refer to a different model.

author: David Hess
author_rank: Super Contributor
timestamp: March 17, 2019, 03:10:47 pm
content: Quote from: gf on March 16, 2019, 10:52:10 pmExactly, the cable impedance and 50 ohm termination mean that the oscilloscope input is driven by the parallel combination of 25 ohms and that combined with the lumped input capacitance produces an upper limit on the input bandwidth which is why higher bandwidth high impedance inputs have lower input capacitance; some are below 10 picofarads.Incidentally, the same applies to how oscilloscope probes are specified including active probes. A special probe tip adapter is used which has the feedthrough termination at the probe tip so the probe is also driven by a 25 ohm source. The probe delivers less bandwidth when attached to an impedance greater than 25 ohms.

author: gf
author_rank: Super Contributor
timestamp: March 17, 2019, 04:56:06 pm
content: Quote from: David Hess on March 17, 2019, 03:10:47 pmSo the obvious step to the next level would be to terminate the cable at the scope end not with 50 Ohm, but with a (say) 40:10 Ohm or 45:5 Ohm divider, reducing the impedance seen by the scope input even further to < 10 or < 5 OhmOverkill?

author: tautech
author_rank: Super Contributor
timestamp: March 17, 2019, 06:40:10 pm
content: Quote from: WhichEnt2 on March 17, 2019, 11:26:51 amBy its Pintek part #: PL-50NCheck this thread for further info:https://www.eevblog.com/forum/rf-microwave/inexpensive-50-ohm-attenuator-tests/

author: David Hess
author_rank: Super Contributor
timestamp: March 17, 2019, 07:35:50 pm
content: Quote from: gf on March 17, 2019, 04:56:06 pmThat will work and some probes effectively do that but most of the attenuation will be at the probe end to reduce the capacitance from the probe's cable.

author: Roger Need
author_rank: Regular Contributor
timestamp: March 18, 2019, 12:17:22 am
content: Quote from: gf on March 17, 2019, 10:46:34 amI bought a couple of those inexpensive P57 50-Ohm-Feed-Through-Terminators from eBay. They work better than a T with a 50 ohm terminator. AT DC they measure exactly 50 ohms and when I measured the return loss it was at least 25 dB (SWR 1.1 or less) up to 170 MHz. The BNC connectors have good contacts and the center pin is the same diameter as my scope probes..

author: Roger Need
author_rank: Regular Contributor
timestamp: December 13, 2019, 03:52:16 am
content: I just got a VNA so I re-tested the P57 50-Ohm-Feed-Through-Terminators in my post above. I was quite surprised at how good the return loss was up to 750 MHz. RL better than 25 dB (VSWR < 1.1) at all frequencies.

author: jonpaul
author_rank: Super Contributor
timestamp: December 14, 2019, 12:19:01 pm
content: Hello thereI have all of these termination types.je, mostly the Tektronix, EGG, and HP.The Chinese knockoffs are poor quality mechanical in the connectors.I very highly recommend the Mini-circuits parts for terms or attenuatorsVery nice service on small orders.Paid $10-15 each.VERY well specified and VSWR ~ 1.2 up to 1-2 GHzJust the ramblings of an old retired EE !Jon

author: Martin72
author_rank: Super Contributor
timestamp: December 14, 2019, 01:03:46 pm
content: A few weeks ago, I´ve bought my own 50Ohm Terminator due to a auction on eBay - A Huber&Suhner 6701.01.B, with about 120 bucks not really cheap ( got it for 25...).The overshoots using this one instead the former terminator from work are signifiant less (but of course still avaible).

author: Mortymore
author_rank: Frequent Contributor
timestamp: December 14, 2019, 02:24:08 pm
content: Quote from: jonpaul on December 14, 2019, 12:19:01 pmIs it possible to provide a reference for a feed trough 50BNC terminator (similar to the Rigol P57)?Appreciated

author: tv84
author_rank: Super Contributor
timestamp: December 18, 2019, 09:30:39 am
content: Follow jonpaul's advice:https://www.minicircuits.com/WebStore/terminations.html

author: Mortymore
author_rank: Frequent Contributor
timestamp: December 18, 2019, 01:37:14 pm
content: Quote from: tv84 on December 18, 2019, 09:30:39 amI've been there, but was unable to find a BNC feedthroug 50terminator. Only the "regular" ones to use with the T's.Or could be the case I'm not looking hard enought

author: David Hess
author_rank: Super Contributor
timestamp: December 18, 2019, 03:12:24 pm
content: Quote from: Mortymore on December 18, 2019, 01:37:14 pmI could not find any either. I do not think Mini-circuits makes feedthrough terminators.