Video: Oscilloscope Balanced Antenna System Tuner Performance Test

The currents need to be equal but out of phase. You can't measure phase with an RF ammeter

 

You don't need to constantly have two current meters in the circuit. You only need one meter to verify that the currents are equal to check for risk of feedline radiation once you install a new antenna. Measure one conductor, then the other. The tuner will address any matching required to transform the impedance as seen at the shack-end of the feedline. You should not be tuning for a particular current or voltage value. This is why a current balun on the output of the tuner is so important with open-wire; you let the current balun force the currents to be equal. A simple MFJ-853 is all you need. Measure the currents only when required. Once the currents are equal, the voltage to ground on each conductor will vary, as needed, based on the antenna imbalance. Any voltage imbalance we saw in Tyler’s video would be expected if his antenna (i.e.: the load at the far end of the open-wire line) was not balanced to ground equally on both sides.


I know this seems like nit-picking, but it truly is important when trying to understand the subject matter of: tuners, transmission lines, and antennas. We’re in a rather technical hobby, and we can all learn more about the science of radio.

And Wes, you are correct. I did neglect to go into the aspect of current phase. I was focused on the magnitude of the curent vector. Point well taken. However the video was focused on voltage ballance, and that's not what matters.

 

Thanks for noting that in the 'Antenna Tuner Test' second part in the video while the ant was disconnected and I had the balanced load hooked up. Very good to demo these kind of things maybe others can try them out and gain a better understanding of their scopes and possibly even use the scope that is collecting dust.
Mine is in good use, along with a fun NIXIE tube counter I have netted to WWV at 25MHz! Who does not love NIXIEs for real? Yes, there is a video for that too along with a fun phase meter detector to net you in on frequency!!!

 

The question has been asked but not answered as to why a balun on the input of an unbalanced tuner is a good idea. It actually isn't as Kevin, W9CF, points out here: http://fermi.la.asu.edu/w9cf/articles/balun/ and Tom, W8JI points out here: http://www.w8ji.com/tuner_baluns.htm

I'm just the messenger.

 

Keep making videos

 

That's why I and one other ham asked Ty the question: Why is it a good idea? (Hint: It is not, and never has been.)

Tyler has yet to give his opion why he feels it was good. I myself know why w/o reading the links. Yet we see no answer from Tyler.

There also must be a reason why he felt he had to replace the original balun with another. Why might that be I wonder? Many questions, just no answers from him. I can only guess Ty's been busy running an AC-circuit simulation in Keysight EEsof ADS or maybe QUCS and working on a new video to show us how it's done. I'm really looking forward to see that one too. Can't wait.

But back to the unun on the input, do tell us Tyler. Why was it a good idea?

 

duplicate post deleted

 

Thanks for the post, I will be posting in regular intervals on all kinds of topics related to RF in general you can subscribe to my youtube channel directly to see them first!

 

Hope to work you on 40M again maybe this weekend, let me know all about the experiments!!!

 

Keep making videos, but PLEASE PLEASE ditch the music!!! As an earlier post says this isn't a dance club! I would like to see it had say 100 watts? A KW?

 

Thanks, ya well do, many of them are completed now, I will have music in them but as you, I think said on my youtube channel comments I will try to lessen the main tracks, prob only include it in the end where I choreographed the still photos with the music! Remember this was my first video creation!
I will try to show topics to me, that are rare to non-existent that people would really benefit from! I did hook up a voltage divider I made to the balanced line and ran legal limit, I could add that into some addition possibly... no difference in my system!

 

Tyler, why is voltage balance important?

 

Remember, a scope in its native form is only a volt and time indicator, there this is actually a complex three part AC signal [Xc; Xl; R] summed to [ Z ] where the point of termination on the feedline is maintaining a static phase and amplitude when F1 is also static. Both [ V ] and [ I ] are separated in phase on the feed line, but maintain a proportional relationship under these static conditions.

We can then look at the relationship of AC voltage and phase to measure what I would call destructive interference or constructive interference, this is the simple summing of both amplitude and phase.

When a line (or system) is balanced, the respective separation in voltage and current will maintain a 180 degrees destructive relationship between the two lines, this ideal situation is then how one part of the antenna system works to get you on the air!

On the second half of the video I use the ‘add’ button to bring both CH1 and CH2 summed together to demonstrate this, hopefully bringing something more to the demo... Great question, I hope this simple explanation helped a bit!

 

Thanks. Is it possible for the signal on each line to be balanced in amplitude and phase and the current to be unbalanced? For example; let's say the antenna is actually unbalanced for some reason. Maybe one side is closer to ground or other objects. If the voltage is balanced and in phase, could the current be out of whack?

 

Well, think of all the TV shows that have program music during the main action (NCIS) and some that don't but have it during the transitions (BlueBloods). Both have music during the intro and the outtro. Remember, too, that this is amateur radio and not amateur video, so I doubt more than 0.05% of the respondents have produced a serious video of even 15 minutes or longer. The textbook for the broadcast school here insists on program music. And, I gotta tell ya, I doze off without it.
Some just hate music, don't understand it, and refuse to change. Others of us who are musicians for over 50 years live otherwise.
Bottom line: It's YOUR video. Do what you want. Listen to your inner artist.