nanoVNA - Measuring Antenna & Coax Characteristics (Revised Feb 16, 2024)
Ғылым және технология
When building an amateur radio station, it’s good to have the skills and abilities to test your coax and antenna to determine whether they are functioning as expected... In this video, while working on station repairs, I calibrate the nanoVNA to examine my 80 meter NVIS dipole antenna at it's feedpoint while mounted at 35'. Some unexpected discoveries are made!
Subjects: Using the nanoVNA to measure antenna feedpoint SWR, impedance, and resonance. Testing coax cable for loss using the return loss method. Does antenna height effect antenna impedance?
The video wound up running on in time so I was not able to answer all the questions I had originally set out to investigate, so I will have to continue this experiment in a future video.
0:10 - Welcome to my Amateur Radio hobby workbench.
0:45 - Topics for today's video.
1:12 - A surprise package in the mail! Made by KC3UDZ - www.qrz.com/db/KC3UDZ
2:50 - DG0SA 1:1 current balun failure.
4:04 - What was I thinking when I built my NVIS station?
4:48 - Theoretical dipole antenna feedpoint impedance as a function of height above ground.
5:43 - Planning to match the feedpoint impedance of the balanced dipole antenna to the 50 ohm characteristic impedance of unbalanced feedline.
7:06 - Using the nanoVNA to analyze the mounted antenna (35' up in the air) - The "reference plane".
9:53 - Setting up the nanoVNA H4. Calibration for testing the coax cable feed line loss. (This assumes you know the basic calibration steps).
11:14 - Using the "return loss method" of measuring coax cable feed line loss.
12:14 - First reading with end of coax open.
12:21 - The "return loss method" - formula for calculating the feed line loss.
12:55 - Installing the short, taking the second measurement with the nanoVNA.
13:34 - Doing the math and discussing the result.
15:00 - Why keep records of station parameters?
16:13 - Calibrating the nanoVNA to analyze the antenna.
17:17 - Verifying the calibration.
19:04 - Questions I would like to answer.
19:35 - The dipole antenna being used for this test.
19:59 - Initial readings using the nanoVNA.
20:42 - Lowest SWR and antenna resonance.
20:55 - What is resonance? How to find the antenna's resonant frequency.
23:08 - Does "resonance" mean that the SWR of the antenna is 1:1?
23:28 - Dipole antenna feedpoint impedance vs antenna height. Theory vs actual readings.
24:36 - How to tell if your dipole antenna is too long or too short using nanoVNA readings? (Mistake corrected!)
28:03 - Unexpected result for the measured antenna feedpoint impedance and what will the measured impedance be when the antenna is lowered a bit?
28:49 - Another unexpected result after lowering the antenna!
30:18 - The value of taking real readings at your location rather than relying on theory to assume antenna behaviour.
31:03 - More questions for a future video...
31:35 - Final thoughts and closing! 73
VE6WGM (VE6WO)
Пікірлер: 17
Don’t worry you’re not the only one. I Cleaned my work table in the garage only to clutter it back up again.
I have 20m of RG-213 which sat on the floor of my garage for 20 odd years. It seems to be working normally but I’ve since got some RG-58. I have ordered my nanoVNA and will look forward to check if this cable has any loss. At the moment it seems neglible.
Please abandon VSWR and use return loss (in dB). You get so much more information, particularly when you have a good match. And do remember that you are measuringa combination of radiation resistance and loss resistance. You don't want to end up matching into a loss resistance.
Your metallic mast may be interfering with your setup. Generally, a dipole is mounted with non-metallic (dacron etc.) lines or a fiberglass pole.
@ve6wo
4 ай бұрын
Yes, the metal pole will likely have some effect. Also the metal roofing on my garage, and a host of other things unique to my location, all of these things will change how the antenna behaves. For most of us, we cannot control these environmental factors so we should be able to measure and tune and impedance match for each specific location.
Where did you get your "shell" or that green frame for the vna in your video thumbnail?
@ve6wo
6 күн бұрын
KC3UDZ makes them! www.qrz.com/db/KC3UDZ
@philswede
6 күн бұрын
@ve6wo Greetings from Sweden! I appreciate your quick response and also the link. Will check it out now.
If you change the stimulus , you should recalibrate ... every time.
@R50_J0
4 ай бұрын
True that.
@ve6wo
4 ай бұрын
I have done this experiment.. at these low frequencies I observed no benefit. The readings were the same. If a person goes outside of the range of frequencies that were used to calibrate the nanoVNA, then yes, I will re-calibrate.
At least lowering the antenna shifts the resonance down, which makes sense.
You need to know the impedance at the antenna. To do this, the reference plane must be at the antenna feed and not in the shack.
@aWeRCHeli
28 күн бұрын
But he shifted the reference plane to the part of coax, where antenna is connected -e.g. beginning . This should allow the same measurement as it would be directly connected to the antenna.
Just buy a circular polarisation filter for the camera, takes the glare out of anything. en.wikipedia.org/wiki/Polarizing_filter_%28photography%29
@ve6wo
4 ай бұрын
I shoot these videos with an iPhone. I’ll have to see if someone has built a polarization filter for it.
@darylcheshire1618
14 күн бұрын
I got a tiny one for my dashcam to reduce the reflection in the windscreen.