Banggood 50 ohm BNC feed-through terminator - a quick review

[stj]

i actually thought if anything, the T-piece would be the problem by causing reflections.

[alm]

Not if the terminator has terrible VSWR above 50 MHz (I have not verified it, but 10baseT does not require it, and I trust TheSteve's assertion). The short stub from the terminator (assuming you connect it directly to a high-impedance input) will not become an issue until much higher frequencies.

Has anyone observed a difference between the cheap 10base2 tees and proper RF ones? I would expect the construction to be quite similar, but I have never used the 10base2 ones for critical work.

[edpalmer42]

I've bought various terminators over the years.  Most of my work is at 10 MHz or less so just about anything will work.  But I've measured some terminators that are likely 10base2 at higher frequencies so I'd know which ones to grab if I needed to.  At 100 MHz, they all had a return loss > 30 dB (VSWR < 1.06).  At 1 GHz, they varied from < 8 dB (>2.3) to > 18 dB (< 1.3).  I've also measured various unmarked SMA terminators.  They all measured > 28 dB @ 1 GHz.  To make the measurements, I used a signal generator, directional coupler, and RF power meter.  Calibration is questionable so take the actual numbers with a grain of salt.

I suspect that if you tore apart a name-brand multi-GHz rated terminator, you'd find a very special style of resistor.  Maybe a circular resistor that would be comparable to an infinite number of resistors in parallel instead of two or three resistors.  Continuous soldered ground around the outside, no discontinuities anywhere, etc.

Bottom line, if you can measure your terminators, or you work at low frequencies, 10Base2 might be all you need.

Ed

[TheSteve]

This is a standard low cost BNC 50 ohm terminator - nothing special, it likely represents what you can expect from one.
Good enough to use to 200 MHz +

[CJay]

This is a standard low cost BNC 50 ohm terminator - nothing special, it likely represents what you can expect from one.
Good enough to use to 200 MHz +

That's nice to see, it's satisfying to see my simplistic measurement was on the money.

Have you a 10B2 T-Piece and would you mind throwing it into the mix to see how that performs?

[TheSteve]

I also tried it with a BNC T, it doesn't change it too much. Sorry I didn't grab a screen capture.

[bjcuizon]

I also wonder why tek/hp feedthru terminators can cost much. Are we paying for the name brand it has? Or does it have really really high quality parts used?

You are paying to avoid wasting your valuable time, by avoiding "surprises". The surprise in the first message is easy to spot, but you can waste a lot of time/effort with more subtle and/or intermittent faults.

"No DP manager lost their job because they bought IBM", and "no EE lost their job because they bought HP/Agilent/Keysight/Tek"

I wonder how a feed through terminator from a high brand will be constructed.
If you look at this picture
https://www.eevblog.com/forum/testgear/banggood-50-ohm-bnc-feed-through-terminator-a-quick-review/?action=dlattach;attach=329772;image
it is easy to see: you just have to accidentally drop it once (maybe it already was during shipping) and you can never be sure if each of the fragile resistors will have survived this, or if -due to the mechanical shock- there are micro cracks somewhere which will result in unpredictable results ... now or in a year from now.
Are Fluke, Tektronix or Keysight feed-through terminators using the same construction? Any volunteer with a jab saw?
Though I remember that a Hameg (=Rohde & Schwarz) terminator was not much different  (https://www.mikrocontroller.net/attachment/98198/HZ22.jpg)

Will tiny cracks in smd resistors cause increase/decrease of the resistor's performance over time? I have this 100R 2512 with a tiny crack which can be seen using a magnifying glass...does this matter?

[tautech]

Will tiny cracks in smd resistors cause increase/decrease of the resistor's performance over time?

With any compromise of a component's envelope you can be assured the the outcome will be terminal but you never know when.

I have this 100R 2512 with a tiny crack which can be seen using a magnifying glass...does this matter?

If you can remember exactly where it is in the years to come and the part is not mission critical, it might not matter much. If you want to forget all about it and ensure reliability.......replace it.
Sometimes this old saying serves and guides us well:
First cost = last cost.

[bjcuizon]

If you can remember exactly where it is in the years to come and the part is not mission critical, it might not matter much. If you want to forget all about it and ensure reliability.......replace it.
Sometimes this old saying serves and guides us well:
First cost = last cost.

Alright, good point right there!

Well, it was a thick film resistor. I researched about its construction and composition and the top layer is glass, so maybe the tiny crack was just on the glass/primary coating.

[tautech]

If you can remember exactly where it is in the years to come and the part is not mission critical, it might not matter much. If you want to forget all about it and ensure reliability.......replace it.
Sometimes this old saying serves and guides us well:
First cost = last cost.

Alright, good point right there!

Well, it was a thick film resistor. I researched about its construction and composition and the top layer is glass, so maybe the tiny crack was just on the glass/primary coating.

Which has likely compromised the envelope. 

[alm]

Got a pair to have some extra around. One of them came apart while disconnecting a BNC cable. Guess they ran low on both thread locker and 100 Ohm resistors .

[Gyro]

More likely, the assembly instructions called for three 150R resistors spaced at 60' and the poor, underpaid, assembler realised that he/she could save a few seconds by stacking two of them.

[CJay]

At least they filed through the nickel or chrome to get to the brass underneath for soldering

[Gyro]

Hence the time saving - and probably the loosening too. Less burrs on the threads to make it tight.

[alm]

More likely, the assembly instructions called for three 150R resistors spaced at 60' and the poor, underpaid, assembler realised that he/she could save a few seconds by stacking two of them.

Unlikely in my opinion, given the earlier pictures that showed two 100 Ohm resistors at 180° spacing.

[rf-loop]

How it looks when terminator other end is connected to ecample 1M/18pF real scope input.  How scope internal circuit see it and how external signal see it when this spaghetti circuit say hello to coming signal. Also we need care higher frequencies even if scilloscope nameplate freq BW is 200MHz. Many times these may have real -3dB point far over 200MHz and many times -6db well over 300 or even 400. With fast risetime signals we then can see all wonderland miracles what we have seen in many places and in this forum many times.  Terminator itself may be more or less ok but is measurenment system ok if yhink 50 ohm termination. I have seen so much terrible and horrible results, also in my self made tests. Best what I have seen was in some old HP digital oscilloscope internal 50 ohm termination what can say it is 50 ohm impedance over wide freq range. Real RF guys developed and designed. Very very different what we can see in cheap oscilloscopes where these 50ohm input are just like 50ohm  DC/audio loading resistors.

But, how is feed thru terminator connected to oscilloscope input spaghetti circuit.
50 ohm terminator connected to scope input using T is more bad. Acceptable with DC and LF but also bit higher if measurement quality is first what can push to garbage collection. Still can see wonderland images.

[SeanB]

150R reel was less than half the price of the 100R reel that morning. so they used that, despite needing an extra resistor to make up the right value. Hate to think of the guy who gets the change over ones, with either resistor value being used and either 2 or 3 as well.

[BravoV]

So how can we improve this terminator say just desolder all the current resistors, and then probably replace with new and better ones, better placement of the resistors and etc ?

Or there is not so much to expect from this BNC metal bodies to make a good terminator say up to 500 MHz ? or even 1 GHz ?

Actually I've been thinking to order more and make myself various attenuators. 

[Specmaster]

I did a quick check with a DMM and found one was near 50 ohms, the other though is 100 ohms - so quality control may be an issue.

Even so, 100 ohms is way better than 1,000,000 ohms

[Diabolo]

Hello,

2 resistors 1/4W of 100 ohms in // give 1/2W of "power", 3 resistors 1/4W of 150 ohms give 3/4 W of "power" !

Diabolo

[Hydron]

I bought four and changed one to 4*200R, mostly for added power handling. Not worried about use over a few hundred MHz so parasitics aren't likely to be a problem.

Just a warning - be careful not to heat them up too much, the plastic softens easily.

If anyone decides that they want something nicer, then RS has some own-brand ones for about £10 which are silver plated and much better made (at least externally).

[bjcuizon]

Yeah, just but be careful with the RS one. I've bought one of those and the male bnc's locking mechanism went loose right away after mating it once with a bnc jack. And also, they specified the VSWR on its online datasheet to be 1.7:1 @ 300MHz ...Oh well, it should work to maybe around a couple of hundred megahertz.

[MF-jockey]

On 18.Dez.2018 I have ordered two of this feed-through terminators:
https://www.ebay.de/itm/2PCS-P7001-BNC-Device-Q9-Adapter-Feed-Through-Terminator-Wholesale/312203578748
On 28.Dez.2018 I received it, but both were broken. From center to shell both have infinitely resistance.
I told the seller and ask for good parts, but he wants to give me a refund.

[exe]

I bought similar terminators, one had 50Ohms, another one was 75. I open the latter, it was made of three 150Ohms resistos. Apparently one didn't make a contact, but visual inspection didn't find any problems at all. Soldering looked good, it's still a mystery what happened. Occasionally the broken part was measuring 50 Ohms. So, I suspect there is an internal crack or something. If/when I have time, I'll try to inspect it with a microscope (I don't remember if I did that before).

[Microcheap]

I got a pair of these feed through terminators https://www.aliexpress.com/item/P7001-2PCS-High-quality-BNC-to-BNC-Female-seat-50KY-50-ohm-matching-device-Q9-adapter/32661228102.html

It has 3x 150 ohms resistors. You may note the wrong footprints on the PCB, that's because they are reusing the PCB from another product (20:1 attenuator)