TTT325 VNA with non 50 ohm Systems

How to use a nanoVNA with systems that do not have 50 ohm nominal impedance. A nanoVNA is used on several devices used in 75 ohm TV applications, including necessary calibration of the nanoVNA at 75 ohms.

[@wayneparris3439]

I have no idea what a smith chart or a VNA is but it makes pretty pictures. I will take your word for it that your conclusions were accurate. I guess I need to learn about this stuff. SOOO much to learn and so little time to do it!

[@clytle374]

Thanks for the education. BTW, this video will not display in my watched later list. Please consider moving your videos to alternative site for prosperity sake

[@DavidLopez-bz4rj]

Hi, good videos. I use 75ohm cable and antenna for my VHF 5 watt ham radio walkie talkie. Do you think I could use one of those TV splitters to phase 2 similar antennas? Will it handle 5 watts of power? I have some spare 4 ports and 2 ports splitters for free. Thank you!

[@bobflyer4346]

Thanks for the video, I am interested in using my H4 with 75ohm systems. However, my question is, since the hardware/software is designed for 50ohm systems. How do you convert the measurements to 75 ohms, I know the software in H4 is designed for 50ohms, but does the smith chart show accurate results for a 75ohm when calibrated with a 75 ohm (SOL on channel 0), or does it just become relative. I see you mentioned mini circuits pads, 50-75ohm devices. Seems the mismatch without is 1.5 to one on SWR to start with 75ohms? So just a relative relationship when outside of the 50 ohm design? This is strictly for hobby purposes by me and for looking at the UHF/VHF home brew tv antenna's, such as hoverman, 4 bay, 2 bay, yagi's and others. Bandpass,SWR,Return loss as a relative measurement. Thanks again..enjoyed your presentations.

[@RapperBC]

The answer to your question lies within: kzbin.info/www/bejne/naiUhYyNrMupfc0

[@mavamQ]

Would you do a 75 ohm calibration, then measure a 50 ohm resistor, and 100 ohm resistor? I have tried that and it is not close, I seem to recall I got about 70 ohms with the 100 ohm and the 50 ohm measured low also.

[@N2Stooges]

Is there a reason why you didn't calibrate the VNA at the end of the short 75 ohm coaxial cable rather than at the VNA port itself? That would effectively eliminate the effects of the coaxial cable thus moving the calibrated reference plane to the end of the cable.

[@tomtektest8042]

There is no reason not to do as you suggest and, in fact, that would provide a better measurement. Since I have discussed this in earlier videos, I tend not to go back but perhaps it would be good to emphasize that no video is complete in itself, and each builds on the earlier ones.

[@__--JY-Moe--__]

🍟👍🤖

[@kingsman428]

Pretty sure you can't just calibrate the NanoVNA with a 75 ohm load, you need 2 x *50 to 75 ohm* impedance matching pads otherwise you will be causing your own reflections.

[@aduedc]

Hi you need transformer from 50 to 75 ohm. you can not just connect 50 to 75 Ohm and calibrate. Your VNA has a 50 ohm receiver and transmitter. Many things will be distorted. Here is why, the transmitter send a signal over 50 Ohm it reaches 50/75 interface, and some of the power gets reflected, then travels the 75 Ohm line to your load and based on load you may get reflected then travels back through 75 Ohm line to the 75/50 interface and some of it gets reflected again. By calibrating with 75 on at the interface you just account for one of the reflections. Open and short calibration just give the VNA the length of the line up to that point. That is an ideal zero length short should have 180 phase difference, but because of the length of your line it rotates to say some other value. VNA uses this information and adds the correct phase to your return phase measured. But when you connect 75 Ohm line part of the phase is result of line length and the other is because of transition from 50 to 75 and 75 to 50. Plus you get two reflections one at the load and the other from 75/50 interface, delayed by length of your line, which add up at the receiver.