Hi IMSAI Guy, great video. There is a shortcut you can take when calibrating the NanoVNA for coax loss measurements which you might have already stumbled upon since you made this video. You can skip the open, short, load and isolation part of the calibration and just do a thru calibration if just doing loss measurements (or phase shift measurements) using the S21 port. Just select the frequency range you want to use, connect your jumper cables together just as you did, select calibrate, select reset, select calibrate, select thru, and select done. You don't need to save this calibration, and the calibration will be valid as long as you don't turn the NanoVNA off or recall a previously stored calibration. This shortcut procedure is nice in that you don't need to use your open, short, and load calibration standards, and you don't need to save the calibration in an already stored calibration that you might have wanted to keep. Just FYI, Don
As an old RF guy using the high end HP, Agilent and Rohde Schwarz VNA's and Spec An's spanning a 40 year career I wanted to thank you for these tutorials to get me converted to using my Nano VNA and Tiny SA. One thing I learned from a HP sales rep, when I got started, was connector care. It's not a good idea to turn the basket (female) of an SMA connector when connecting to a male connector. Rather it is much better to turn the nut (male) of an SMA connector to keep the center contact from rotating. Reverse Polarity of course reverses this.
True, but... Try to hold the SMA 'Short' body from turning while turning it on. Impossible. Even the 'Load' lacks much of a hand-hold, so it inevitably turns the pin. So every calibration cycle means that everyone needs to violate this otherwise good advice. One can purchase SMA-male to SMA-female "adapters" that are also known as "Connector Savers". Or, we can realize that the NanoVNA is so incredibly cheap that it's not worth worrying about. Some of them are $50, while even the Connectors Savers are $6+, so I'm not even sure using connectors savers are good value.
Nice. Now I know how to check my cables the easy way. All I need now is a big pot of "Cable Stop Leak" to paint my RG58 coax with. It might even turn it into LMR400
TNX 4 another great video! Acualy you would be surprised on how lossy cheap Chinese adaptors can be! Even the small SMA barrel connectors. You should make video using known good quality vs the el-cheapo, like they say "you get what u pay for" ! 73 N8AUM
Thanks for sharing your knowledge. I just bought a NanoVNA from China and will be arriving next week. It's a good start to be armed with knowledge you just taught so that I could design and cinstruct s good antenna system for my HF, VHF and UHF radios.
You can also use the elect-delay function to compensate for small bumps from connectors etc. Without disturbing your calibration. W2AEW has a good video on this..
Awesome video!!! You've done a huge service to our hobby by producing these videos. You've singlehandedly turned this confusing little device into a truly useful and necessary piece of equipment. Thanks so much! 73rds from 992, Mr. "Zip Tie" Maysville GA.
Thank you so much for that informative, yet concise, video. I've been using my NanoVNA as a glorified SWR meter, so you just made this nifty little tool even niftier. I'm going to check out the rest of your videos now. 73
Thanks! I built a common mode choke for HF last week and tried to measure both the common mode attenuation and the through loss, and got the same numbers for both. (Losing 25 dB of my transmitter power was going to pinch.) I didn't realize I had to use Trace 1 to view the Port 1 magnitude. I just tested again and the common mode attenuation is 25 dB or more, and the through loss is less than a half dB. Not too bad for something cobbled together on a whim.
To put this loss into perspective, every 3dB loss cuts your power in half. So that 5 dB at 440 means this cable eats most of your power. 50W at the radio will give only 16W at the antenna. This is why cable quality and cable length are both critical. I'm using 35ft of LMR 400 to get to the antenna on my roof which gives me 0.6dB measured loss at 144MHz and 0.95dB loss at 440MHz. So 20W at the radio gives me 17.4W on 144 and 16W on 440 to the antenna. Also, you really should calibrate out those adapters. The do have loss, and stacking them like that can cause more loss than you think.
If your radio is putting out 20w, and you believe that an adapter has even just 1dB of loss, then you should expect that the adapter would therefore be dissipating about 4w of power as heat, and being so small it would be soon glowing red hot (or at least a burn hazard). If it's not glowing red hot (nor a burn hazard), then perhaps your assumption that the adapter is significantly "lossy" needs to be reevaluated.
I have several antenna analyzers. But, since getting my Nano VNA SSA2, I have not touched them since the SAA2 does so much more and weights so much less! Great video on loss measurements! Thanks!
I am amazed at the lack of understanding of coaxial loss at VHF and UHF. I had a couple of my repeater users that run 100' of RG-8X at 444.x and can't understand why they would be weak into the repeater. I explain that for every 3dB of loss you're essentially cutting your power in half. 100' RG-8X has loss very close to 9dB at 444 MHz. 30W/2 = 15W/2= 7.5W/2 = 3.75W. That's a lot of power to be throwing away
Thank you IMSAI Guy and Frank Sweeney. I have been searching for that exact number for days. I read it somewhere but couldn't remember the numbers. I seem to remember reading that 1dB loss is about an S3 loss at the receiving end. I recently used this (IMSAI Guys') video to see the loss in my coax cables as they are quite old. I compared them to manufacture's loss sheets to see how close my cables were to new ones. Some were 2 to 3 dB lower than specs. I though, looking at 2 and 3 dB differences were not bad at all. Well, if 3 dB is equal to loosing half your power, it might be time for me to get new cables. Thank you both.
Thanks for the info. I've had my VNA a few months now and was wondering how to do this. I'm thinking of using a dummy load on the end too and see how much r.f. is arriving at the dummy load on h.f. only because my oscilloscope is not much use above 25 MHz. G4GHB
For the 45 years I've been a ham I've always heard that there is "some" loss at every connector so if you use 2 or 3 adapters on each end of the cable are you sure that you didn't introduce "some" loss? Or were you implying that it was negligible as far as the measurement. I would have thought that half of the 2 meter band loss was in the plethora of adapters. Please understand that I'm not disputing you. I just want be sure I understand what is factual. Thanks for one of THE MOST INSTRUCTIVE videos I've seen on using the VNA devices. I am building 2 meter base antennas out of junk parts for new hams on tight budgets and the VNA will be helpful in adapting the pieces and parts to 2 meters. I just subscribed to your channel.
I hope that by they time I buy a NanoVNA, they put a time-domain representation in it. At higher frequencies, it's good for separating the connector-launch from the cable.
Thanks for the excellent videos. To compensate for the coax adapter loss shouldn't one attach the adapters and perform the calibration at the adapters? Not an issue at HF but it may make a difference at UHF.
Yes it would be better but it might not be measurable at low frequencies. watch my video: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-GOCD5DvOj5c.html
@@IMSAIGuy Thanks. The NanaVNA is so inexpensive that I bought a couple of them and permanently mounted BNC, N and UHF adapters on each and made corresponding OSL&Thru cal kits.
Now I'm thinking that for less than the price of CoAx, I could get a SDR Dongle and a USB over CAT5 repeater, and just mount the SDR directly to the antenna with as short of cable as possible...
many times you will want to measure a device that can not be connected directly to the VNA. if you cal at the vna then do the measurement. the measurement will be the device and the cable both. if you calibrate at the end of the cable then all of the properties of the cable will be ignored
if there is an open cable, then you assume 100% of the energy is reflected back. An S11 measurement would show loss on a two way journey so that loss divided by two will be the one way loss. This is not as accurate as the method I showed.
if you have an antenna at the other end of the cable you just measure SWR using Channel 1 only. The adapters are two to do a "thru" test. This is how I'm measuring filters.
well the problem will be with impedances. The device is set for 50ohms out 50ohms in. The balun takes the 50ohms to 450ohms. so trying to measure with a 50ohm input will not work. you will not need phase information so a simple setup with an RF generator and oscilloscope measuring across a 450ohm resistor would be fine
@@IMSAIGuy this is how you call it? Buddy system? Kind of doing that when I buy components, just to make sure I have a large sample to pick good tolerance parts from.
The most correct way to do an isolation calibration on a VNA is to have channel 0 and channel 1 both with 50ohm loads. They only supply one 50ohm load so the next best thing (if you don't want to buy a second load) is to use the load on channel 0 and leave channel 1 with nothing on it. The internal attenuator on channel 1 will be sufficient.
@@IMSAIGuy I went ahead and bought another calibration set from eBay for about $12 so that I could calibrate both channels. Thing is, the loads don't seem to match. I if I SOL calibrate with the set that came with my NanoVNA and then attach the new load from ebay, I get 51.5 Ohm. ...seems like that's too much variation for a calibration tool. Interestingly, when I attach my MFJ 100W dummy load, I get 50.1 Ohm. Do you think I got a lemon of a load? Or, is this within acceptable tolerance for $12 calibration hardware from eBay to be used on a $50 device? ;-)
@@IMSAIGuy I missed that obvious step! Thank you for the nudge. The load that came with the NanoVNA measures 50.4 on my Fluke 117. The eBay load measures 52.7. The MFJ dummy is 50.2. ...I think I'll use my MFJ as the #2 load to do an isolation calibration. (good idea?)
@@TroyCraft you are worrying way to much about the isolation calibration. any of those would be fine. it does not need an exact 50 ohms or mechanical reference plane like the S11 calibration. on the nanovna having nothing on that port still gives a fine isolation calibration.
@@IMSAIGuy no I mean I get that much loss with my VNA calibrated and the cables connected with through. I am not even measuring. Something must be wrong with the calibration.
Wouldn't the coax being coiled up cause inaccuracies, I'm saying one wouldn't actually install it coiled up, maybe a test with one long continuous loop would be best and not coiled. just a thought
@@PascalCASTRATARO I think one of the techniques shown is using an S11 measurement. the cable needs to be disconnected from the antenna so it is an open. then the return signal is measured in an S11 measurement on the VNA. The loss will be twice since it is a return path. It is not very accurate but would show gross problems.
In the total scheme of your system for this test, with all its connectors, adding the little OPEN terminal to calibrate is a waste of time - you may as well calibrate with nothing on the end.
Where is Episode #564b? And another Episode #564b? It is OK to delete an offensive comment if you want to take your part in The Cancel Culture, so enjoy now.
the 'b' series were due to the TinySA coming out too early. I had a bunch of videos already shot but the TinySA arrived too early and instead of pushing things around I just posted two videos per day. Now things are getting back to more normal.
@@IMSAIGuy Hi, thanks for explanation. I probably have some mental disorder because I simply can not stand such irregularities and those two videos both numbered #563b was simply too much for my nerves... Sorry for being somewhat rude to you. Keep up the great work here! Best regards, Tom
I think everybody by now knows how to calibrate a nanovna. Why don't you just do the measurement and you will have a 2 minute video which is all the useful content here.
You would be amazed to find out how many guys do NOT know how to calibrate a nano VNA .. why one needs to calibrate it with the pigtails when used, and how many forget to press RESET when they start a calibration, or not save it after it's completed.
