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- čas přidán 21. 08. 2024
- Episode 366
Many people have commented about the magnetic mount needing a ground plane. I did use a metal ground plane (top of a metal filing cabinet). Sorry but it was off camera so you couldn't see it. The ground plane reflects the 1/4 wave antenna making it a 1/2 wave dipole
VHF/UHF HT antennas are notoriously difficult to characterise - UNLESS they are attached to the transceiver they were designed for. Reflections from the surrounding room can also shift the design resonance and SWR levels considerably. (But certainly many antennas from China are "bad" - usually due to poor construction methods used to reduce the manufacturing cost of a cloned item)
Your testing method is the prroblem ! Hold the brass base of the antenna and hold it near your head and the resonant frequency will move to the required band. They are designed to be used on hand held! The Nano is fantastic value. M0iiZ
#1 put the VNA in SWR mode for better viewing.
#2 the magnet mount antenna whip is actually two antennas separated with an open air coil.
The top part is the 2m and the bottom part is the 70 cm part of the antenna.
The top was longer than the bottom.
You cut the VHF part down to resonate in the UHF band.
In the video looks like the two elements are the same size.
Now you ended up with two element of 440.
Next time if you try to tune the UHF band cut the bottom of the whip.
You can cut off the coil and you would end up a ¼ --440 antenna it would give you the best SWR and wide range.
If return loss is under -10 dB, that is equivalent to 2:1 SWR.
From my limited experimentation, I found that for both these tests I got better results with a different setup (though I can't see your metal ground plane):
1) For a metal ground plane contact antenna, use varying but mostly just a large metal surface. I often use a large piece of stainless steel from the side of an old microwave. If I'm in the field, I'll use an upside down skillet (especially ones with big copper bottoms. Care to try these?
2) For the other antenna, I found calibrating against the end of a 10 foot (or so) long coax cable and then attaching the antenna to that cable, which was suspended by a tripod up in the middle of the room. I think the idea here is just to get everything away from the near field of the antenna.
If you would let me know if these methods are any different for these measurements you did or not.
Thanks!
I did use a metal ground plane. top of filing cabinet or top of metal tool box.
@@IMSAIGuy please see my comment you are not testing correctly. It is the way you are positioning the antennas on test. You will be surprised at the improvement in performance ! M0IIz
Took mine to ham lunch the other day and guys were interested...even more interested when they heard that RigExpert has a huge sale going on for their analyzers!
I sold mine as soon as I got one of these, it has all the functionality I need at 1/20th the price, And I don't want to kill myself if I drop it. I'm going to buy a few more for extras
Very interesting (and revealing). I can only hope for DC-6Ghz VNA for the holidays. I would love to be part of the solution. Cheers!
To my findings, the Baofeng UV-5R stock turns out to be a performer, against other Japanese counterparts on VX-8DR, ID-51. Not all Chinese whips are crappy.
The first antenna - I have one looking almost identical but it is actually an old cell phone antenna from back when mobile phones had an antenna connector to plug in to an antenna on the roof of your car. The dual band in its name referred to the GSM 900MHz and 1800MHz bands.
The last antenna, I also have a similar one, also meant for 144/430 MHz but when tested it resonated at totally wrong frequencies, 180 and 600 MHz I think, but not sure I remember correctly. It being useless I cut off the covering to see what was inside and see if I could fix it. To my surprise it worked correctly before I even did anything to it (aside from removing the cover). It was probably designed to be without the cover and then someone who doesn't know the first thing about antennas added the cover to make it prettier. What I still cannot fathom though is how the plastic cover increased the resonance frequency whereas by my understanding it should have decreased the resonant frequency. I'm not sure I remember the frequencies correctly but I do distinctly remember my surprise that they decreased instead of increasing further when I took off the cover.
On another note, recently I bought a Chinese 11 element 2400MHz Yagi (for WiFi). Its best SWR was 9:1 at about 4000MHz and what little it radiated went sideways instead of forwards. I have yet to take it apart to see how it achieves such a feat.
interesting, I've bought some "dual band" antenna's and you're correct. SWR was terrible. Don't have a VNA yet (it's in the mail)
but I noticed 2 things. You didn't have it in the swr display
and I didn't see a calibration with open, short and 50 ohm load.
Just wondering
W9DLP
Yes was calibrated. used return loss measurement
The 1st little stubby antenna, what a joke, just stick a 50 ohm resistor in its place and it will also be broad banded LOL
TNX FR THE UPLOAD, 73 N8AUM
If you Santa to test a magnetic antenna for mobile use, you must put it on a metal base or , batter, on a car roof. Without a groundplane it does not work
read the video description. I did use a ground plane
You would probably get a significantly different reading if you used the nanovna coax jumper to the antenna, and don't touch the connectors, instead of connecting directly to the vna and keeping your hand on it. You would also get different reading with proper ground plane as if you were set up to talk, instead of direct connection to vna.
read the video description, ground plane used
@@IMSAIGuy @ the 5 minute mark in your video, you screw the long HT whip directly onto the nanovna and then begin to lament how poorly the antenna is performing. Your claim of poor performance is what I was referring to in my above comment. I did a similar test, this evening, attaching a similar Comet tri-band HT whip antenna directly to my nanovna. With direct connection to the nanovna and my fingers on the fittings, just as you did, the nanovna readings were way off from what they should have been for my HT antenna. Then I attached the HT whip onto an appropriate mount and tested it hands-free with sufficient ground plane under it. The Comet tri-band antenna performed with accurate and useable readings on the nanovna in the second test.
@@craigszwed maybe your antenna is ok. you said it was similar (?). I just know this one was not working well. Other antennas worked just fine even if I touched the connector. I would like to know how antenna designers design for HT applications with no ground plane and relying on the HT and Body to act as a ground. I though the Nano VNA would be a much better tool than a big expensive VNA that is not hand held.
As crappy as many China antennas are, at least test them in the mounting they were designed for. This might be at the top of a metal box (ht) or on top of a large (at least a 1/2 wave) metal plate. Monopole antennas perform very differently without some kind of ground plane.
you didn't read the description. also you might enjoy this: czcams.com/video/wem0DoPe5O0/video.html
@@IMSAIGuy Sorry, I just watched your video.
Very informative video. I have been considering buying the NanoVNA as it seems to be a very handy tool to use for checking antennas. Also, it debunks antennas from China that are branded by well known Antenna makers. Bottom line, it's a good idea to test HT antennas and tune them to something usable if possible.
Thanks for the video. I ordered my VNA and will receive it tomorrow. I think I am a perfectionist so when you tried to show the dip but did not actually move the cursor to the actual bottom, that bothered me. You never actually showed the real dip, just a approximation of it.And you could have easily done so with the scroll wheel! Otherwise a very good video. All the best!
ahahah, yes, you are a bit of a perfectionist :)
I think the Smith chart is important, just to confirm that the impedance is 50Ω, and purely resistive.
Great video. It will be nice if you add the SWR measurements. Dips only not helping much :)
return loss and swr are mathematically related:
www.amphenolrf.com/vswr-conversion-chart/
You get what you pay for I guess. Just for grins I put the antenna from my Yaesu FT-60 on the analyzer and it was resonant at 2m and 70cm. It had the best match at 2m which didn't surprise me considering these fractional wave dual band rubber ducks are a compromise. I also pulled an antenna off of an old ICOM 220MHz brick and wasn't it resonant in that band although, to be honest, the antenna may be damaged. I used to work for an aerospace contractor before I retired and have used all sorts of network analyzers. MY fave was the Agilent PNA-X and have always wanted one. Out of my price range; however, this nanovna really exceeded my expectations for a device under $50. Yeah it has it's shortcomings. The selector switch sucks and the touch pad leaves a lot to be desired but for the use I intend it for it meets the bill.
When I worked at Wavetek we had a 40GHz Wiltron what was very nice. I felt silly measuring my 2m antennas on it when no one was around. The nano is quite good. My friend acutally uses it at work to design fiber optics communication PCBs
@@IMSAIGuy I just wish the software for it worked better. I have v1.03 on my windows 10 machine and the smith chart selection doesn't work. Don't know it it's how my machine is set up or if the software is buggy.
I think Diamond is American. They better not claim it's a Diamond antenna.
take measurements in open space. in your conditions the antenna shows incorrect values
doesn't help. they are bad
If it were 10 Mhz high high, trimming the end would make it higher. What ARE you talking about?
I said short in wavelength, I ment lower in frequency.
@@IMSAIGuy Ah,,,Thanks...Had me puzzled!
@@IMSAIGuy Short in wavelength means *higher* in frequency.
But at 2:57 you literally said: "I kept snipping it off to make it go higher and higher in frequency" which is reasonable because shortening the antenna's active part will increase its resonant frequency.
is there any differences in measurements when we analysing antenna at vertical or horizontal position?
This is a controversial subject. Many believe yes there is a difference no matter what. My experience is that the differences are due to proximity of objects. If the antenna is far away from any object then there should be no difference.
@@IMSAIGuy thanks for your reply. Nice video.
I don't see a metal platform under the antenna))
off camera I put it on a metal tool chest
got to figure an HT antenna isn't to have a metal plate (ground plane)
Mobile antenna, I use a filing cabinet so tool box is the same idea
I bought an FT817ND about 3 years ago and there was a rubber duck with it. I tried it on 2m first: no good, tried 70cm: no good, so I tried it on 6m: no good. The SWR was high on all three frequencies so I don't know what it was.
I was very surprised that Yaesu had put this in. It was no use to me and I threw it away but before I did I took off the connector and soldered a telescopic aerial to it so I could use it for 2m.
I got a NanoVNA a couple of weeks ago and could have measured the frequency of it.
I've used it to check the h/b dipoles in my attic and they are just slightly too long. They work and the SWR is low but now I can get them spot on.
I used it to look at my h/b magnetic loop as I tune it to different frequencies.
I used it yesterday to look at the performance of an LC filter to notch out 9MHz in my h/b tx/rx which I think is amplified by the broadband P.A.
How did I manage before without one?
G4GHB.
The second antenna would be good? for the UK Dab radio frequency bands :-)
Thanks for exposing another China stuff reseller flim-flam. If you must buy made in China, use a reseller that buys sea-land container quanitities and has a good reputation. State side resellers like that are few and far between. The others prey on new amateur radio enthusiasts and others starting out who are looking for good deals to get started in the hobby. Many of the flim-flam operators do not know much about doing legal business in the U.S. They pretty much ignore buyer protection laws.
Yeah, but he's using a Chinese analyzer.
@@bulldogbrower6732 And good antennas read good; bad ones don't.
Look also here czcams.com/video/mvO6frcUDo0/video.html, another antenna.
I had the same mesaventure with a Chinese antenna 433 MHz gain 12dBi announced and bought on Ebay. It resonated at 795 MHz with a VSWR of 1.1. The litigation ended with a loss of 50% of my purchase and 2 antennas on my arms which are of no use to me !
I got my nanovna today. can you let us know which firmware you are running on your unit?
I can't figure out how to view the firmware version. do you know?
@@IMSAIGuy no, i thought maybe you installed a firmware from the internet. does it show any extra info during power-on? one can also dump the firmware with dfu-util with:
dfu-util -a 0 -i 0 -s 0x08000000:leave -U firmware.bin
@@p23q I want to flash the firmware someday. Too chicken right now. Don't want to brick the thing. If I can dump the firmware that will be good. then I have a copy of the original. There is no info on the startup screen.
@@p23q The software does not allow download to save existing firmware. only upload and upgrade (this is what you are told to used).
No way to check revision also
@@IMSAIGuy they are absolutely impossible to brick
They do better with a ground plane
why broadcaster using 50 impedances???not 25 or 100 ohm /z
www.microwaves101.com/encyclopedias/why-fifty-ohms
How do you determine SWR? Read the vertical lines?
see #368 NANOVNA Return Loss vs VSWR
Can you check the gain of the antenna ?
No. antenna gain is a very difficult measurement and requires special equipment and test conditions
czcams.com/video/FeyrQ9yyfTw/video.html
I’m sorry that I had to give you a thumbs down on this one. If I did not view it correctly then I will change that. You have to understand that mag mount antennas only have a quarter wave radiating element and must have a counterpoise. Ordinarily this would be the roof of your car. In the absence of a car roof such as where these videos were taken, you can take two metal rods that are at least 19 inches long laying one perpendicular to the other in the mag mount antenna at the intersection of them and that will serve as a sufficient counterpoise or ground plane. Without that counterpoise the antenna can only function as a half wave radiating element meaning the second part of the advertised a dual band.
It was off camera. I used the top of a metal filing cabinet
Duh...User Error !!!
My swr curve jumps around erratically when i connect an antenna. Any ideas on maybe why this happens?
bad cable or connector
Thankyou
You did not show your calibration and your presentation of all 3 Smith points or even a piece of wire to show resonance i know your demonstration is faulty from many years of professional use of a hp vna. R.T.F.H
Yes I have videos showing calibration just not this one. I'm quite familiar with VNAs working at HP and Wavetek.
None of your measurements were accurate. Each time you turn on the Nano, you must calibrate it, which you did not do. Leave high tech to intelligent people.
I guess that eliminates you
I have a playlist of the NanoVNA that is 90 videos. watch those before commenting next time. I did the cal off camera
You don't provide a proper ground plane when testing the antennas so your results are meaningless
You have to set up a ground plane to test antennas.
read the description
for fun watch this:
czcams.com/video/wem0DoPe5O0/video.html
That's an 443 MHz antenna
For 'stupid American' market.