SWR Measurements using a Bird 43, AIM-4170C, Siglent 3021X SA, & Agilent 8712ES VNA
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- Опубліковано 23 сер 2024
- A demonstration of SWR measurement differences using four different instruments on a 2m antenna. In particular is the use of the new Siglent reflection bridge for the SSA 3021X spectrum analyzer.
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First... Thank you for taking your time to make this excellent video! Like you, I also have a SA/TG by Rigol and a HP 8711A VNA, A Bird 43 and finally a MFJ 259B Analyzer. Having a small look at your lab, and your 2 Towers, you are very well equipped for a Ham Shack! The one thing I would like to mention is that I worked for Bird for 12 years as a Element Calibration Tech. You measured 40 Watts Forward and I think 2 Watts in the Reverse with the 43 at the Transmitter end. For the sake of this discussion, IF your Heliax had 3 dB loss/100' and you had a 100' run, then you would of course be loosing 1/2 of your Transmitter power, but more important is that the 2 Watts of Reverse power shown is actually 4 Watts at the Antenna. At the Antenna the 43 would show 20 Watts Forward and 4 Watts Reflected. Since SWR= 1+SQR (4/20) / 1-SQR(4/20) or a VSWR of 2.61. Return loss = 10log (20/4) = 6.98 dB. My email is. k8kem@aol.com would enjoy hearing from you since our interests are quite similar. 73's. David. K8KEM btw.. I thought $ 600 was a bit pricey for the SWR option so I just use a $ 45 Mini Circuits 20dB RL Coupler and look on the chart for RL to VSWR.
Hi David and thank you very much for taking the time to watch my video & more importantly to comment. Great minds think alike on this matter hi-hi....I had considered that but realized that because of the heliax I use my losses are under 1 dB. The smallest I use is 7/8" some 1-5/8".... It is still an excellent point that you make & I should have mentioned it for completeness. I decided to finish things the way I did was because for me, many times I do not necessarily care what the exact SWR is at the antenna but what it will be down in the shack when I try to dump a kW using a SSPA into that load. Sometimes a little loss in the feedline can be a blessing as it helps lower the "apparent" SWR in the shack. Since I like using mast mounted LNA's & we don't worry abt the receive loss. But again, excellent points and TU for sharing them with us all ! 73
I thought your wife was amazing for the Siglint SA Christmas Present….
After getting a peek at your yard of antenna towers…
I’m now convinced I was correct.
I am quite familiar as my wife is amazingly patient with my love of the RF hobby.
Here’s to great spouses! 👍🏻
Thanks again for the great and informative videos!
Here Here ! A toast to our wonderful spouses.
Thank you again! Yes, I owned a 2-Way Radio Company here for some 29 years, my Son runs it now days. On what we termed "High Band" or 150 MHz., back in the day, always ran 7/8" Heliax up the tower, later on with 450 Mhz., Repeaters, 1-5/8" was used to minimize the losses. We had a very "Sharp" Steeplejack who would always measure the Forward/Reflected power at the base of normally a 10dB gain Vertical. Had it logged for checks usually every few years. That procedure came in handy one time. I retired just as 800 MHz Trunk was allowed above line "A". I believe he has 20 channels on that. 73's David. K8KEM
Great video my dear OM.
Have you ask yourself what is that you didn't do yet in RF?
There is something and that is *Zenneck Wave* in the interface Air /earth.
Dr. Corum and Viziv pays with it
I and my friend Dr Hans -we play with it too.
I do appreciate your work .
73 .
Thanks for sharing...'course in the middle of the video I had to shuffle off to eBay to get my very own HP Reflectometer Calculator so watching your video cost me about $12! I have a Rigol SA with their version of the 2GHz bridge and a MiniVNA; now you got me considering a real VNA (I just can't afford to watch your channel!). Glad I found your videos, off to subscribe and watch more. 73 - Dino KL0S
Hi Dino, you made me chuckle ! I am really glad you found the video useful and together we are helping out the economy . I will be putting out another video where I try out various directional couplers and some of the trouble you can get into when trying to measure complex loads. TU agn for watching & taking the time to comment.
Great video, tnx !!!!
You are not actually measuring the antenna performance but rather the antenna/coax combination. If you look up the coax loss at 145Mhz and factor that in you will find that the actual antenna return loss is not nearly as high as you may think. That will change your results quite a bit.
Hi Roger. Yes sloppy of me for not making that more clear. I tried not to say I was measuring the SWR of the antenna itself but I should have made an actual statement to that effect right up front. In the AIM portion I do refer to it as the "system" implying antenna and feedline but I really should have made that much more clear. While I was aware of this I did a poor job mentioning that to our viewers so thank you very much for pointing that out.
As a side note, the loss of this heliax and jumpers at 2m is just under 1 dB. This has a neat effect on the RL & SWR of the system down in the shack. The measured RL down in the dungeon will be 2X the attenuation of the feedline (in dB) + the RL of the load (in dB). Thus in reality the RL of the antenna by itself (up at the antenna feedpoint) is 2 dB less then shown.
How does this affect the SWR up at the antenna and down in the shack? A 1 dB coax loss means that if the SWR of the antenna up at the feedpoint was 1.5:1 then the SWR measured down in the shack would be a hair under 1.4:1
@@w8bya Well, it seems like you are well aware of the effect of the feedline loss so no need to preach to the converted. Anyway, only a young diehard ham is going to climb the tower to do a SOLT calibration at the end of the feedline!
Very informative. Thank you! 73, AA7US
I like your SOLT.
Thanks Roger !
with the sweep settings you are transmitting on frequencies you are not licensed for, all be it at very low power levels.
Hi John. What an excellent comment. Thank you. I too have wondered about this situation given that so many different antenna analyzers etc are floating around out there that generate sweeping RF signals. I could not find any mention or warnings in my MFJ analyzer for example about connecting it to a high-gain VHF or UHF antenna. I thought I would take a quick stab at seeing what kind of FS we were generating using the Siglent. Check my numbers for me pse.
The FCC has a document entitled "UNDERSTANDING THE FCC REGULATIONS FOR LOW-POWER, NON-LICENSED TRANSMITTERS", OET BULLETIN NO. 63. I assume this document is applicable here. Section 15.231 covers 140 MHz to 150 MHz with Intermittent Control Signals.
If I did my math right, one is allowed to generate a F.S. of ~2100 uV/m (@ 3m). My Siglent TG defaults to an RF level of -20 dBm and with the directional coupler attached actually outputs closer to a -25 dBm signal. Assuming a free-space antenna gain of ~16 dBi & 2 dB total coax loss (heliax + jumpers, rotor loops, etc) I calculated a radiated FS of ~0.015 V/m (15,000 uV/m (@ 3m) which puts us about 17 dB over limit. It appears when testing high-gain 2m VHF antennas the RF TG level should be reduced an additional 20 dB. I suspect lower gain, HF antennas would not have this issue but I have not run the numbers.
Thanks for the video! 73 DE NØJVW
Hello Joe. You are very welcome and hope it was useful for you. 73
Witam, bardzo ciekawa prezentacja oraz dużo przydatnych informacji, używam kilku różnych modeli BIRD-43 i zrobiłem wiele badań oraz porównań z innymi miernikami mocy, takimi jak HP-435B, HP-437B oraz kilka Marconi 6960B, używam też kilku innych mierników mocy, przeprowadziłem wiele porównań pomiędzy tymi miernikami. Czy znasz moją web site, sp5mxf.com ? Na tej witrynie opisałem bardzo dokładnie właściwości tych mierników a najciekawsze są porównania pomiędzy różnymi miernikami. Na badanie mierników mocy przeznaczyłem dużo czasu i opisane wyniki oraz porównania są efektem 2 lat pracy przy pomiarach mocy. Jestem bardzo zainteresowany pomiarami mocy mikrofal. A tu jest bezpośredni link do tego miernika:
sp5mxf.com/bird-43-thruline-rf-wattmeter/
sp5mxf.com/pomiary-mocy-w-cz/
Moja web site sp5mxf.com jest napisana w języku narodowym Polskim, co na pewno stanowi pewną trudność, lecz obecnie używając translatora google można czytać dość dokładnie teksty w różnych językach. Ja w ten sposób czytam w różnych językach, dziś są różne narzędzia i możliwości, jest łatwo. Ciekawi mnie twoja opinia na temat informacji które zamieściłem w opisach mierników mocy.
Napisałem ten komentarz po polsku, następnie użyłem translatora google żeby go przetłumaczyć na język angielski więc pewnie będą pewne problemy, lecz powinno to być w miarę zrozumiałe.
Pozdrawiam Tomasz
Hi Tomasz, I am very glad you found the video interesting & useful. I will have a look at your site. Thanks
@@w8bya Thank you for your answer and I apologize for the mistake, instead of putting the translated text translated original in Polish, I have already corrected.
I am interested in your review and evaluation of my work which I did on my web side, I am aware that the problem will be a language version, it is in Polish but you can use a Google translator and you can read it, this tool is getting better and at the current stage source texts in other the tongues become understandable. Write to me and rate my work.
I greet you warmly