54 - Building A Return Loss Bridge

Nick M0NTV shows how to build and test a Return Loss Bridge. This video was originally recorded in June 2023 exclusively for the FRARS Hamfest lecture stream.
** ERRATUM **
Apologies for a mistake I make in the calculations section towards the end. I claim that the Magnitude of the Reflection Coefficient is measured in volts! Whilst the loaded voltage and open circuit voltage are clearly both measured in volts, the Magnitude of the Reflection Coefficient is simply the RATIO of these two figures and as such is dimensionless. Apologies again for any confusion.
*****************
Hope you enjoy!
73,
Nick
M0NTV

[@leroymay8156]

Thank you very much. I will build me such a Return Loss Bridge.
It seems kind of redundant to my NanoVNA, but IMHO it is important to know and understand the basics behind the measuring.
Also it is nice to have a fallback solution.
Hope you hafe great holydays. 73

[@M0NTVHomebrewing]

Thanks very much Leroy! 73, Nick

[@ornithopterindia]

👍Thank you sir.

[@M0NTVHomebrewing]

You are very welcome. 73, Nick

[@alanmacdonald65]

Great to get to see the Hamfest special edition at last Nick! look forward to this years one too. Enjoy your holiday mate!

[@M0NTVHomebrewing]

Thanks Al. I'm going to the Club tonight (that's twice in 2 weeks!!!) to deliver said video to Dave. Hope you had a good time away yourself. See you soon. 73, Nick

[@paulswift700]

Hi Nick
Very good love your explanation of the calculations.
I cheat a bit here as I use a HP networkx analyser to do it but sometimes I do go back to basics and working it just you have here in this video.
Well do keep up you good work.
73's.
Paul. De HS0ZLQ, G0MIH.

[@M0NTVHomebrewing]

Thanks very much Paul! 73, Nick

[@juanmanuelmartorell6859]

Excellent!! as always! Have a happy holiday!

[@M0NTVHomebrewing]

Thank you Juan! 73, Nick

[@mechmania8450]

Great video, you can sometimes use the cores which come on power leads in computers.

[@M0NTVHomebrewing]

Thanks very much. Absolutely - if you can reuse something then all the better! 73, Nick

[@andye2005]

nice description of the RLB well done
Andy

[@M0NTVHomebrewing]

Thanks Andy 👍 73, Nick

[@MegaCadr]

Love your videos!

[@M0NTVHomebrewing]

Thanks so much! 73, Nick

[@M0UAW_IO83]

Have a great holiday Nick.

[@M0NTVHomebrewing]

Thanks very much Clint! 73, Nick

[@shean4]

Nice video thanks.

[@M0NTVHomebrewing]

Thank for watching! 73, Nick

[@borisj4054]

Never ever seen premade bifila wire in 50 years of being in the industry. We just twist two enamel coated wires together. Sometimes we put extra thick insulation on one strand to form a particular characteristic impedance.

[@M0NTVHomebrewing]

That's an interesting idea which I've thought about before (using different gauge wire to get different results). Is it the width of copper or the width of insulation that helps to form a particular characteristic impedance? I've been doing some study of transmission line transformers recently and I imagine thicker insulation will decrease the distributed capacitance of the windings (as they'll be slightly further apart)? Thanks for sharing that interesting idea! 73, Nick

[@borisj4054]

138log of the ratio between the wire diameter and distance between them. You can make 35, 50, 65 Ohm etc line to put on ferrite cores for driving solid state amplifiers etc.

[@haraldlonn898]

I noticed the two tabs on the BNC connectors are not soldered to ground. Am I missing something? Thanks for a great video.

[@M0NTVHomebrewing]

Hi Harald, the two lugs you see are electrically isolated from ground, centre pin and even from each other. Their purpose is purely mechanical - to fix the connector to a PCB. I choose to invert the connectors, ignore the lugs and make my connections to the separate centre pin and ground wires. The BNCs are superglued down to the board. If you are building Manhattan style then it works pretty well. 73, Nick

[@ghlscitel6714]

This is true HAM spirit. Tinkering until the doctor comes.
(By the way, the magnitude rho is dimensionless)

[@M0NTVHomebrewing]

Thanks very much indeed. 73, Nick

[@M0NTVHomebrewing]

I've now corrected this in the comments. Thanks again. 73, Nick

[@drstrangelove09]

How did you connect those connectors to the board? Soldered down somehow?

[@M0NTVHomebrewing]

Hi there! They are the ones with the two lugs on one side which are intended to be attached to a PCB. But the opposite side is flat so I turn them upside down and superglue them in. I bought a huge bag of them from AliExpress or somewhere similar. They seem to be fine. 73, Nick

[@drstrangelove09]

@@M0NTVHomebrewing Aha!!! Thanks, Nick! (I did not think of superglue.)

[@romanescu_misha]

Happy holiday, take a break from the internets, enjoy analog!

[@M0NTVHomebrewing]

Thanks very much! 73, Nick

[@louiskatzclay]

If you divide volts by volts you get a ratio with no units. No? Its a coefficent, not a voltage. Thanks, love the videos, I learn a lot and am mostly dense with AC concepts.

[@M0NTVHomebrewing]

Hi Louis, you are absolutely correct! My bad! Thanks for pointing this out. I must have had a bit of a brain freeze when I recorded this. I've now corrected it in the comments. 73, Nick