⭐ Inexpensive 50 ohm Feed Through Terminations
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- čas přidán 14. 07. 2019
- I cover why you need to use a feed-through termination with an example. I review a new inexpensive model available on Amazon and eBay. I compare it to ones from Tektronix and HP. I show them in use on an oscilloscope, measure the input match, show how to improve the match, and discuss why you would or would not choose one over the other.
You can download the data and graphs in excel format and find a copy of the slides here:
chrisgrossman.com/yt/0007/ - Věda a technologie
When I saw the ringing, the I loudly said 'Yoooo...!'
Excellent demonstration! Keep up the good work!
Chris, thank you so much for producing this excellent video. I learned so much thanks to your thorough evaluation and tests. keep it up. I will be following you from now on.
EXCELLENT video Chris, TNX 4 the upload !
Thanks, the details of reading a Smith Chart are still difficult for me but you spelled things out well here and the key takeways were simple enough without the nitty gritty details :) Learning about the attenuator part was something I'd not considered.
Thank you! I ran into this video by accident. I had already bought exactly the same things you showed. I am taking Mr Carlson's Lab fix anything series and I was confused about him using a 47 ohm resistor for termination. Then I realized 47 meant 50. Your explanation was fantastic. Thanks, I subscribed.
Thanks Chris: I was looking for a good alternative to those $45 feedthroughs and it looks like you gave me exactly what I was looking for!
You prolly dont give a shit but does someone know of a trick to log back into an instagram account?
I stupidly forgot the password. I would love any tips you can give me!
You should give the black plastic ones a shake. My best load is one of those. It's rated DC-1Ghz but works very well up until 2.25Ghz, according to my libreVNA.
Great Chris, thank you very much. I just wrote an article (5/2010) in the german Ham magazine about a Zo-probe with a 50 Ohm feedthrough. So your measurements fits perfectly to that. //DK9ZY//
Sorry, wrong date of the article, it's 5/2020. Maybe it can be found in www " DARC CQ-DL". And another one will probably follow similar to your topic here.BR
Amazing and straight to the point. Now I gotta redo some PSU noise measurements I made with 50ohm terminated coax. I wonder if there is a practical way to get reasonable return loss at 200mhz while maintaining 500uV sensitivity without an expensive and finicky differential amplifier
Found your channel by pure accident! Thanks for the great comparison, very informative! You've got a new subscriber...
Are you a ham by any chance?
Not since I had a novice license when I was in high school. I am planning to get a license when I retire in a few years. For work I design III-V RF and mixed signal circuits including the design of the transistor layouts and MBE profiles.
@@Chris_Grossman
Hopefully you can join the fray sooner rather than later; I started out as a Novice in HS 50 years ago this month...life is busy I know, been there, done that, got the T-shirt.
Great video. It really illustrates the need for termination. Is it possible to make a precision 50 ohm bnc cable at home? I see the Tek ones for $350-$450. Crazy price
I really think it is a thing that should have more echo, (the attenuator + load one) and the channel too.
I tried to perform this myself but couldn't. What exactly and how is the un-shown 'wire' inductance added?
Hi Tony, wondering if you can help..i have an old Marconi 100db STEP attenuator..unfortunately it has 75ohm input and output..since i would like to use for the 27mhz cb band can you please suggest how i might convert its input and output to 50ohm.?
Regards
Andrew
This is a very interesting video. Thank you for sharing, especially the impact of placing an attenuator just upstream of the 50 ohm terminator. I am wondering how well a BNC tee with a 50 ohm BNC terminator works? It is also a low budget approach. It is my usual approach when using scopes that do not have a built-in 50 ohm termination.
I have not measured the capacitance of a BNC Tee, but I suspect it will add couple of pF to the input capacitance of the scope. Thus I would expect a tee with a termination have a just slightly degraded input match vs. a feed through termination.
I use BNC T and 50 ohm terminators, and I get slightly worst performance that shown in the video, but once I add a 20 db attenuator, I get very similar results (an almost flat -39.5 dB for S11). Hope it's useful.
Hi, I'm absolute beginner and I have a OWON HDS2102S 100Mhz oscilloscope and a LiteVNA 6ghz , I have good attenuators and 50ohm loads and cables everything rated 18ghz.
I could reproduce with almost your exact values and behaviour on my VNA and Scope than in yours up to 150Mhz.
The thing is that I can see reduced the signal amplitude to /2 or /10 with the attenuators but I can not see any benefit apart of better return loss reading, no in the max readable speed I can get,150mhz from 100mhz spec, and maximum visible of 200mhz, this one is reduced in clarity by the attenuators. The attenuators doesn't improve the noise, spikes, and like a parasite reflection that is still there with the attenuators, I think VNA's RX/TX crosstalking but I'm beginner and no way I can be sure.
With this I mean that apart of the better s11 reading (I improve 8db) in practice are all disadvantages at the moment.
So my real question is you added uses cases, but what the use of attenuators improve exactly in them and in what conditions (i.e. bad cables, higher amplitud that I use).
It looks helps my s11 but not to me and what I can to do.
Thanks I had a great day reproducing you video in my very first day with a oscilloscope
Thanks!
You should get your ham license! 73
Crap, my old scope has 28pf input capacitance!
Great video Chris. I just ordered two of those terminations on Amazon. Do you think it would be feasible to replace the two 1/8 watt resistors with two 1/4 watt resistors? It they would fit, one could double the power handling capabilities.
The clearance for the diameter of the resistor is tight, so I don't think ¼W resistors will fit. However I had a thought that it might be possible to use four 1/8W 200 Ohm resistors to get to the ½W total power level.
"Im not interested in those plastic "Chinese" ones." - this statement though LOL
I haven't checked but those are probably metal shielded and plastic isolated.
Too bad they were not actually used in comparison.
Is it possible to replace the resistors inside with ones that have a higher power rating?
There is not room for resistors that are larger diameter. You might be able to replace the two 100 Ohm resistors with four 200 Ohm resistors and double the power handling.
10 V peak sine wave has power 1 W into 50 Ohm...
Are there any inexpensive 6db/20db attenuators you know of to pair with this? Thanks!
I buy them when I see good deals online or ham swap meets. I have a good collection, but I have acquired them over 45 years.
Is there any significant difference to using a pass-through termination like this versus using a T adapter on the scope with a 50ohm termination on one end and your DUT on the other?
It depends on the frequencies and/or rise time of the signals being tested. My guess is that at 50 MHz or below the T will work, it might even be ok higher, but I have not tried it.
@@Chris_Grossman Thanks!
Surprised that you slag off the P57 just because of what the label says. The only way to know how good/bad it is, is to actually test it. Don't judge a book by it's cover.
I just make my own with a "T" connector.
Couldn't you solder on your own higher power resistors?
There is not room for much larger diameter resistors because the ground/shield screws over these with very little clearance.
If you could find something to fit you might be able to increase the power handling capability a bit, however at 0.25W you are getting plenty of signal so there is no reason not to use a attenuator in front of the termination and get a better match as well.
Of course, every scope will be different even if it is the same model.
Really BS spec for those plastic Chinese ones!
Great video, thx!
11:38 why is something breathing aggressively into the mic?
What are you, cinema critic?
If we come to the conclusion that in-use, as long as its basic design is functional as a 50 ohm path to ground, almost all devices function the same, does that then mean the "crappy black chinese ones" should also be fine? As always, simply divide all chinese specs by 2 or 3 and disregard all translated text 🤣