#593 SMA Load Improved and NanoVNA Measurements of Several Loads

Episode 593
Using the VNA to test 50 ohm loads. Then using the VNA to fix one with an unwanted resonance. S11 s-parameter measurements tell the story
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[barrykery]

Great video. Thanks for posting.
Barry

[gorba]

Good morning IMSAI Guy! The experiment is really cool. A suggestion, as you have a TAP RF connected in a capacitive way over the load resistor, try placing a 50 ohm load on the TAP as well, I believe it can stabilize the circuit, since the clamp insertion brought the ground closer to the housing to the TAP probe. Congratulations!!!

[lmamakos]

I have a small 50 ohm BNC terminator that started life decades ago as a terminator for "thin" Ethernet. I was shocked and dismayed when I put it on the NanoVNA to see that it wasn't really all that great beyond HF. To be fair, 10 Mbit ethernet with it's manchester encoding is a 20MHz signaling rate, so I suppose the terminator was "Good Enough". Next I'll have to check the yellow-snake thick ethernet N terminators to see how they will disappoint me. ..and the answer is better than I thought, about 20 dB return loss to 275 MHz, so not too bad!

[subramanianr]

Yet another cool demo of the significance of RF construction techniques. I believe you didn't ensure electrical continuity between the flange of the thick film resistor and body of the box and hence with the shell of the sma connector. And yesterday I had thought that you had the small wire just to ensure additional ground connection. Now I Justice can see some kind of adhesive (some insulating material) cynoacrylate/araldite kind of material between the round lid and the body of the square box. Or is it something else!?. I don't know.

[PapasDino]

That weird resonance almost looks like a crystal with a resonance/anti-resonance response.

[markoller]

Thank you for the very informative videos! I'm fairly uneducated when it comes to Rf but I'm learning. I'm slowly acquiring test equipment but I'm needing some advice for a budget friendly (if that exists) service monitor. I mostly work on am/ssb transceivers. Thanks again!

[subramanianr]

Yes, now I remember in a previous video of intending to make use of the eBay surplus 70 MHz bandpass filters's square metallic enclosure, you mentioned that you had to force open lid as it had been glued together. So, here too after screw fixing the dummy load resistor you have used some glue and that's why there's no electrical continuity.
And your homebrew 250w dummy load must be having a coaxial cable between the connector and the resistor; I think that is the limiting factor of the highest frequency to which it can be used. I mean the cable (PTFE?) (exactly 50 ohm!?) and it's attachment may be contributing some reactance.

[DRC_]

That resonance is likely because at that frequency the line is 1/2 wavelength long, at at 1/2 a wavelength Zin = ZL. So any line discrepancies in Z0 that make the return loss bottom out at around only -30dB at other frequencies drops away.

[RC-Heli]

Wow! I thought I was doing something just building my 1st small oil cooled dummy load with 8 - 100 ohm 5 watt metal oxide film resistors.
I didn't realize one needs so many dummy loads!🤯

So I have a Nano VNA and was watching your video trying to figure out how to test and see what I actually have.
The multimeter shows 49.6 ohms and I was wondering if it can be tuned for a perfect 50 ohms?

[vidasvv]

It's becomes VOODOO after 50MHz lol The 40ohm could have been 50 at 1 time until too much power was applied. I also have a high quality load thats marked 50 but also measures 40 ohms at DC. Have you looked at the response if you put a shield on the bottom? Could have near by FM broadcast blasting into it? Where did you find those enclosures? 73 N8AUM

[galileo_rs]

If you calibrated your VNA with that 18GHz load the measurement of that same load is more or less meaningless. BTW update your firmware, many new useful features in newer versions.