Hardline Coax RF Power Divider
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- Опубліковано 12 вер 2024
- This video is a kind of, "Here's what I'm working on" - I don't explain everything, but "let's hang out and make something while we all have cabin fever". Now, I'm no RF expert, but I've been dabbling in amateur radio for quite some time. The latest effort is setting up an EME (moonbounce) station. I need to make a power divider to split the RF between two stacked yagi antennas. In this video I try to make a proper power divider with some brass tubing and extruded aluminum. Some strange measurements are taken - maybe self-resonance? Help out in the comments!
Link to AppCAD: www.hp.woodshot...
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@tcurrentsource
www.thecurrentsource.com
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I am an RF engineer. In the simplest terms, calibrate your VNA with the exact load you are using for your experiment. Your loads more than likely won't work at that high a frequency.
Derek, I've made many of these over the years a long time agon, and needed a refresher. Great video, thank you.
I'd like to learn how you would solve the resonance issue. I teed this up to w2eaw here on youtube. I think this is up his alley.
This was really fun to watch. Thank you!
Marr hope to follow up later this week
Check your dummy loads. If your resistors were wire-wound, you may have accidentally added a reactive load.
I did one that came out perfect for 2 meters and looking to do another for 4 antennas.
check it again when you get the other matching load , that resister might be the problem
Might be the velocity factor causing the error
Validate your test setup with a cheap and simple quarter wave coaxial trap. Try with a open end 50 ohm cable of known length and propagation constant and measure S11 dip value (quarter wave length impedance inverter). Confirm it by measuring value at short circuit of other end to interpret the result.
This was an AWESOME video and exactly what I was looking for. I'm looking to phase a couple of 50mhz antennas. Can't wait to play with this. De K9KJ
Hi Thomas. 50Mhz may be more forgiving. What I ultimately learned from this experience is that I was better off just ordering one from HRO. It was fun to play with though!
Would love to see what you are doing with 432 some time
Nicely done thanks for sharing
Man I honestly love these type of videos that exponentially become more complicated lol. Tbh I trust the nanovna to get you close to the ballpark of your actual swr readings. If I had to guess, it seems that you might have some stray capacitive impedance messing with your inductive impedance, throwing off the resonant frequency of it. I would consider making it longer and shortening it it depending on your readings.
Hi, Derek. Probable explanation IMO would be that all the formulae you used (explicitly or in calculator) are applicable only in the case of quasi-infinite wave guide (which translates into the L>>d , where d would be some characteristic outer shield dimension ). This means that near that cutoff plane, where spliter is installed, wave guide is not a wave guide anymore -- geometry is different etc. You could probably estimate effective length of your section as something like L > L_eff > (L - d) which would give your higher resonant frequency then calculated.
Another way you could look at it (physics is the same, off course) is that expressions that you used for capacitance and inductance of unit length of coax are expressions for _infinite_ coaxial cylinders. For finite section you need to subtract some length near the end(s) with the length in the order of lateral size of a coax where field would be disturbed by edge effects.
I simmed a quarter wavelength segment with wave ports on HFSS and it seemed to work okay.
thank you Derk for such a great video and explanation,i would like to ask if i want to make a 2 ways power divider for the FM band but i need it wide band cause i do not know on wich is the broadcasting frequency , where i should be consider the working frequency , Center bandeg :98.00 mhz
Thanks Derek for the clarification.
Hi current source, thank you for the nice video.
epsilon_r is in fact is the permittivity.
The unexpected dip frequency is likely caused by the neglect of the additional inductance due to the N connector pin connections. How much did you alter the length during your experiments? Did you also try to connect the inner conductor to the N connector pins with reduced inductivity (e.g. via an end plate)? At 432 MHz and the design you showed, a correction of approx. -11mm seems necessary (see details and suggestions at):
dg7ybn.de/Splitters/coax_online_calc.htm
I cut it exactly to 1/4 wavelength. I lengthened by ~5mm but couldn't "stretch" it more than that physically. I did run across that site, and he points out x nH per connector - unfortunately I put mine together before reading it. I think I'll use one of his calculators and see what kind of results I get.
I can see that the abrupt change in propagation mode from the coax to the square waveguide might have some issues.
Not sure how centered the inner conductor is. That will have a small impact.
The additional capacitance at the launch site will also have an impact.
If it is an exact quarter wave length then it should show open circuit when shorted and vice versa
Great work! Thank you for sharing!
A nano vna (hobby grade) may not have the dynamic range to verify the individual pieces. Without spending thousands on a high end VNA, using only quality brand connectors with verified values will greatly reduce the unknown variables. I used 75ohm pl259 amphenol connectors with RG59 coax to make a matching section work, for example. Velocity factor needs to be considered also. I do like the do it yourself efforts, we all learn something.
the pic in the thumb is like a filter wee use to do for seing hbo on the cable in romania :)
Hey Current Source - Nice video. Regarding the incorrect frequency of the notch: Are there notches at any lower frequencies? I couldn't tell from the video. The propagation velocity in coax is typically slower than in free space. In regular RG223, it's about 55% of the speed of light; which makes the wavelength shorter in coax than it would be in air. If you used the free space wavelength to calculate your quarter wavelength distance, that would make the tube too long and the notch would appear below your desired 400 MHz. However, the 600 MHz notch could be the coax resonating at 3/4 wavelength and your quarter wave notch would show up at around 250 MHz (I think).
Sounds like my type of outcome. I did like your presentation though. Thanks, John
No experience with that software you used. Does it specify or take into account the velocity factor of the coax you are making? That +/-690mm wavelength you used sounds like a velocity of 1, like in air. For any real coax, this is
Cool. Good work. Is your quarter wave length calculated correctly?
Far as I know, I obeyed the laws of physics ;)
@@AmRadPodcast you did not factor in the velocity factor of an open air conductor
Extra capacitance at the termination or inductance at the launch will cause this effect I believe.
You actually need to build the line to the impedance specified.. You don't get to fudge the figures.
By the way. I would make the line 3/4 wave long, the errors in measurements will add up against you fast.
You need a larger center conductor.
Would assume that apcad calculates with perfect values, infinite conductivity, infinite thin-ness of the sleeve and a solid core? UHF is a tricky business, a millimeter more or less, a blob of solder and everything is different. No wonder they charge so much for this stuff.
nanovna needs to be calibrated in a narrow band width to have decent resolution
I'm no expert here but I would guess that since you are using 2 different materials which have different propagation times you would get different travelling waves setup in the materials hence the E/H fields won't interact at the same points. This is defo an FEA simulation thing.
I want to know specification power divider for 144 Mhz please
Sir can i have your diagram about 4 bay power divider.73
Did you cal out the N connector? Maybe try putting cabling on each end and deembedding?
If you give me more detailed plans I can put it in HFSS and show you the results.
Actually let me sim out the square waveguide. I suspect maybe the formula is off...
Yep, Cal’d out
@@AmRadPodcast weird. Do you know the thickness of the inner and outer conductors?
HFSS looks pretty slick. Outer is 1/8” and inner is 0.014”
@@AmRadPodcast thanks, will update
You’ve got all the tools there, meter all the ports. See what the real world values are on all the ports
sorry....boleh gak minta desain devider 2 way 144 mhz
Where can I find a link to download appcad?
design assistant for RF.
Sure... www.hp.woodshot.com/
Next build with coaxial feeder
I would suspect the terminations you have used. One side of port You may have high quality and other side port really poor quality. Put them on your VNA and test both of them. See this article it may qualify the differences you see.
www.element14.com/community/groups/test-and-measurement/blog/2018/05/12/which-50-ohm-loads-are-any-good-finding-out-with-the-fpc1500-vector-network-analyzer
Otherwise put some real world loads on it and measure again.
One More video on AC source. please
Asif Arshad ordered the proper size center conductor, it’ll be in next week - I’ll cover the source and measurements more in depth in the next vid. Thanks!
@@AmRadPodcast Thanks
No Idea what you talking about, but watch the whole video and have to say, Loved your music and find the glasses shadow on your face super distracting ;)
Al Armandi that’s dedication! I know, it’s distracting during editing too. Actually I’ll touch on the new lighting and improvements in the next FAQ
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