Homebrew PWR/SWR Meter: Part 3 - Tandem Coupler Experiments

Video looking at the some experiments with a Tandem style SWR coupler. The coupler uses two FT50-37 toroid cores, each with 10T.
Details at: zl2ctm.blogspo...

[@ae0ai358]

this is very cool! Interesting to see what a low frequency directional coupler looks like!

[@CharlieMorrisZL2CTM]

Hi. I don't have 160m in the shack, but it seemed to work well using the sig gen. Charlie

[@moustaphamuhammad7013]

I love When it comes to the pigtail of coaxial cables terminals. And also your pin and paper explanation.good keep up the good work.

[@CharlieMorrisZL2CTM]

Thanks Moustapha. Hopefully, the log amps will arrive soon and I can continue.

[@moustaphamuhammad7013]

Charlie Morris we'll be waiting for the latest 😀

[@bundylovess]

Good progress mate its looking good big thumbs up 👍

[@CharlieMorrisZL2CTM]

Thanks Allan. I'm debating about trying a log op amp again as I wait for the AD8307s to arrive. That or work on the SNA.

[@32cdromcz]

tnx bravo since the libraries from you fit me to my arduin now only a mustek and and I can have you thank you

[@christinamarks6349]

Hi Charlie! Just a question/observation (because it wasn't clear in the video).... In almost every rendition I have seen with directional couplers, the forward and reflected sense ports, in this video going to the oscilloscope, are typically terminated with resistors (respectively) matching the transmission line impedance, the obviously most common being 50 ohms. I didn't know if your oscilloscope has input terminations and, other than the discussion about padding, you didn't mention it in the video. I would think that the lack of, in this case, 50 ohm terminations on the respective sense ports could impact your measurements. Again, just a question/observation. 73 :)

[@CharlieMorrisZL2CTM]

Hi Christina. Yes, you are quite right. Both the FWD and REV ports do have 50 ohm terminations. You can see the 2 parallel 100 ohm resistors that I used for each port on the video banner picture. I also understand that these are important to minimize high voltages across the transformer windings.Charlie

[@christinamarks6349]

Yep. totally missed that! LOL!

[@CharlieMorrisZL2CTM]

No worries Christina, I do it all the time. Apparently, I have 'boys eyes'... :o)

[@watsok]

Great video as always. With many hams rig being 100 w, could you discuss the pad values needed at 150 watt?

[@CharlieMorrisZL2CTM]

Hi Kenneth. I could, but the problem is I don't know what the FWD port will produce at 100W input. I'll see what i can do.

[@angeldelvax7219]

Looking at the coupler box; does it make a difference for the measurements on what side of the coax you connect the ground?

[@CharlieMorrisZL2CTM]

Hi Ronald. I must admit I struggled a little with the same question. In the end I went with the configuration in the original article. If you have the time, try both options and see how it works.

[@raafatalheety826]

Good morning The is box is very large

[@CharlieMorrisZL2CTM]

Yes it is. Probably an overkill, but i did want to keep the transformers away from the sides (increase d-distance) to reduce capacitance.

[@ashave9100]

Hi Charlie -Thank you for the over my head video -Hi Hi !!! It will take me a week to try and unravel the maths !! Can I ask you- where do you find the 10 Log power numbers from ? (It is the only bit that stumps me) ! If it is not to much trouble(and your valuable time ), would it be possable to do a short run though the 10 Log power calculations on your next video please ? I am sure there must be someone else out there confused by them ! Thank you again -M

[@CharlieMorrisZL2CTM]

Sure thing. I'll add that into the next video. In the mean time, this may be of help: en.wikipedia.org/wiki/DBm Charlie

[@CharlieMorrisZL2CTM]

I'll aim to put up another short video tonight that looks specifically at the calculations. Hopefully, that will be of use.Charlie

[@ashave9100]

@@CharlieMorrisZL2CTM Hi Charlie-Thank You, that would be brilliant, I would then have a great reference point to work back though all of the sums you have completed since your very first video. Thank you again for you time and patience -M

[@CharlieMorrisZL2CTM]

Gidday. I've just put up a video. No doubt there will be some errors, but hopefully, you will find it useful. Charlie