Excellent! I’m a new ham and antennas are fascinating. I’m wanting to learn more about velocity factor as my insulated copper wire 40m inverted V dipole has the SWR dip at 7.034 with a much shorter antenna length than the calculations suggest. I suspect velocity factor is the primary reason. So, I’m wondering, is there a way to measure the VF of a wire (not coax) using a NanoVNA?? And, I’m curious, would the velocity factor of a wire or cable not change based on length? Great stuff and thanks for posting!!
This is running split frequencies, not crossband repeat. Still useful, though. You could do the exact opposite on a second radio to effectively have a cross band repeater… but this is not a crossband repeater. Also, when setting up crossband repeat on any radio, use PL tones.
Great video. Did you perform the VNA calibration at the end of the long patch cable? If you do the short/open/50 ohm calibration at the SMA jacks on the VNA, then plug in a long cable via some adapters and finally onto the antenna, what you're measuring is the combined cable-adapters-antenna system as a whole, whereas if you do the calibration at the far end of the cable where the antenna plus in (which might need different calibration standards to suite the connector at that end) you get accurate results.
Great video, one of the best explanations on what that "phase saw-tooth" is really describing. Sent here from NanoVNA io group posting. Thanks for making that video. I am anxious to try this out... Regards wb7ond...
If you use manual focus, and set the distance equal to distance from camera to NanoVNA you will get perfect focus every time, regardless of what you do with your hands.
Excellent! First video of many explaining it correct way. I am about to program frequencies for ISS and other AMSAT satellites. You made it easy. Just got today radio, and no programming interface, so I should to do it manually.
Hello! It's my question that how we can test an antenna for a bipolar monopulse uwb signal for example if that signal has a 5ns width and 100khz repetition..What is the frequency that I have to use as start and stop on nanovna to measure my antenna parameters?????
Regarding the USB to DB9 serial cable: are true RS232 levels used or are they TTL ? Are popular USB to TTL (3,3- 5V) FTDI based boards giving correct voltage levels to use this circuit ?
Are there radios that will function as a crossband repeater? Meaning that whatever they receive on their RX frequency, they will immediately TX on a different frequency
When doing stuff like this try to mount your antenna on a pole or in free space dangling on a fishing line etc. but note it will act differently in each situation. If mono-band you can add a coax transforming loop (balun /tuner / filter) at the feedpoint to minimize any effect of the coax shield acting as part of the antenna which can also help to minimise some unwanted swr results / changes due to coax lengths and some objects in proximity to coax runs. Adding such tuned transformers such as these coax loops or baluns as well as ferrite sleeves at the feedpoint can also change your radiation pattern as well as help to maximise efficiency and reduce unwanted noise both in and out of the system.
Could anyone help me with how i can do this for an open wire or balanced feedline. I would like to measure the velocity factor and impedance of the home made feedline or ladder line. I would also like to be able to then compensate / calibrate for the balanced feedline length on the vna so i can hoist it up 100ft to the antenna feedpoint and then read the parameters of the antenna back at the tuner end with the VNA. From what i understand i will have to make a 1:1 unbal and a 1:1 balun to be able to calibrate the vna with the open wire feedline attached and then be able to look at the antenna with the vna attached at the transceiver end of the balanced or open wire feedline. Problems could include a difference in velocity factor of any pigtails used to get to and from the 1:1 unbal and 1:1 balun. For example the pigtails could have a velocity factor of 66% and the open wire might have a velocity factor of 88%. The mission is to build a balanced HF antenna, probably inverted v or doublet, then measure it's parameters at height (100ft high feedpoint). After this, design and build a ladder line as best matched in impedance to the antenna as possible and then finally to be able to measure the impedance back at the tuner in order to choose the best ratio balun for the tuner in order to go back to 50 ohms. Just trying to get a vna to do all these things and in the correct manner and order does not seem easy to me. lol One solution i thought of was to hoist the vna up to the feedpoint to either connect back to me, either via powerful bluetooth, with a complicated array of usb extensions or by observing it with a camera such as a gopro. or to first use coax and calibrate the vna at the end of the coax, then use coax to observe the antennas parameters in order to find out what parameters my ladder line or balanced feedline should be to best match that antenna. finally to build the ladder line and then to measure it back at the tuner to help choose the correct balun. I have some 300 ohm ribbon feedline which i could initially run up to the feedpoint but it's all starting to sound complicated just so i can observe the antennas parameters at height and then build the ideal balanced feedline as every open wire feedline has it's own impedance depending on spacing and wire diameter. Ideally i want my feedline to have the same impedance as the antenna. So step one will be finding out the antennas parameters at height, step two decide on feedline impedance and try to build it in order to obtain an impedance matched to the antennas impedance once built. Step 3 will be to measure total impedance of the system at the tuner end and step 4 will be selecting the best ratio balun for the tuner to convert back to 50 ohm unbalanced. If anyone has any ideas on this i would much appreciate any input. Thanks.
In the beginning of the video you said that you want... "to see the performance of the antenna". Thank to a so low SWR, now we know that the losses in that antenna are almost 28%. After the coax losses, only a 72% of the remaining power will be radiated
Some clarification: The wording here implies that this Baofeng will operate as a cross-band repeater. It will not. What's done here is program a memory location to be able to transmit to and receive from a DIFFERENT radio that is configured as a cross-band repeater. Confusion aside, it's a good instructional video on how to configure a channel for a cross-band offset, as I think a lot of people may not realize that you can set a very large offset like this. I am configuring my Wouxun KG-UV980P (cross-band repeater capable) to receive on a VHF frequency and transmit that received signal (repeat) on a UHF frequency (cross-band). This is so that low-power handhelds can transmit on a frequency that propagates better and receive from a high-power high-altitude antenna. Cross-band repeater = good performance using the same antenna without buying two radios and a duplexer. Win-win.
Sir , great presentation on cross band operation but that's not crossband repeater if it was anyone transmitting on one band frequency will make the radio transmit on the other band .
This video is very good I had to watch it over and over to see what you were doing finally I got it but now you need to show a video on it actually working as a repeater
All good with swr but what about conductance or capacitance behaviour of this system, (coax cable & antenna)? I mean when i have an antenna with transmission line which give to me a good swr factor and z, (aprox 50Ωμ), but i have a small value of capacitance, (200pF for example), to smith graph. Is this value of capacitance affect the tramsmission signal or not?
As this is an education video wouldn't it have been nice to have described that the calculation was and included the units? Something like "wavelength = speed_of_light / the frequency" or 299792458 m/s / 61MHz here. And for common usage you can just divide 300 by the frequency in MHz.
Crossband repeat means the radio will automatically retransmit what it receives onto the transmit frequency (i.e. the radio functions as a repeater). This radio transmit when the PTT button is pushed... it has no crossband repeat function.
how about hart tools? do they require thermistors to work? know anything about bauer tools? i picked up a cheap driver i hoped to use for automotive but i can't get it to run. don't want to buy that overpriced battery.
