VNA 'S come in 50ohm or 75ohm impedance and antennas come in various impedance. then that implies the use of transmission line transformers to connect them (ref. your #73 video) . thanks for your video
Joe, A 75 ohm VNA can easily measure impedances (S11) without any external matching transformers. As this video showed if you are calibrating with a 50 ohm transmission line in the nominally 75 ohm circuit you might need to be a little more careful if you intend to calibrate at different frequencies than you are scanning at. However if you are using a 75 ohm VNA to make through transmission measurements in a 50 ohm circuit you will experience mismatch loss on both the generator and load side. The mismatch loss is .177dB on both ends and it is usually corrected for with resistive pads increasing the loss to 2 times 1.76dB. I didn't try to imply the need for transmission line transformers. Larry, W0QE
I'm wanting a VNA from 160M to at least 10M But i want to be able to attach it at the feedpoint 60ft up and then read what the antenna is saying in situ. I was looking for a vna with bluetooth so i could observe it from on the ground. I'm planning on using open wire 300 Ohm ribbon but can't find much info on using a vna with open wire. Wondering if the way to do it is to calculate a good coax length with the vna, then observe the antenna so it can be tuned with the tuned coax, then swap out the coax for open wire?
Several people have added bluetooth modules to do exactly what you want to do. I have such a module for my AIM 4170. Search for a USB to Bluetooth adapter. Larry, W0QE
@@w0qe Thanks for the reply Larry. I have been wondering how to use open wire feedline with the VNA. I am considering making a micro sma 1:1 balun adapter and a 1:1 unbal for each end. I found small commercially available sma antenna balun boards with a 9:1 balun but i also have seen the smd balun transformer available with a 1:1 winding. I was considering trying to make a 1:1 balun and a 1:1 unbal so i can add the length of the ladder line and it's velocity factor. I feel like i'm stepping into no man's land here. The other complicated factor is if making home made ladder line i would have to also calculate or measure the velocity factor and impedance. I might be stuck at this point or left to make some guesses. I'm guessing my line will be around 500 Ohms with a velocity factor between 85 and 90.
No. The true SWR at the antenna will be slightly higher than what you see at the transmitter end of the coax due to the loss in the coax but you can still tune for minimum SWR at the transmitter. However if you wanted to know the actual impedance of the antenna then you would need to calibrate you VNA to that point. Remember that for any SWR there are an infinite number of impedances except for an SWR of 1.0:1. Larry
@@w0qe So if I check SWR with say a 9ft, 18ft or 50 ft lead SWR goes down a little because of loss on longer coax? But all those lengths are fine to check SWR without calibrating at the end of the line first?
@@RC-Heli835 Yes, provided that if the initial 18' piece of coax is 50 ohm and the subsequent pieces of coax you use are all the same 50 ohm impedance. SimSmith can show this easily. Larry
@@w0qe I set the SWR on my friends Big Rig last night with the Nano VNA 4 with a 6ft coax. We finally cut enough of the antenna off to get a low SWR in the middle of the band ch 20 - 27.205 Mhz. 1.56:1 on each end of the band and 1.3 :1 ctr. I hooked his 18ft coax back with an analog SWR Meter w/6ft jumper and channel 40 was 3.5 :1 SWR so had to trim nearly another inch off to get it right for the 18ft coax. Also read perfect again on the Nano. We cut around 5 inches off this antenna because it was resonating in the 12 meter band. The antenna would have worked as 1st tuned on the 6ft lead but not the 18ft coax.
@@RC-Heli835 I can't explain exactly what you are seeing unless either the 18' or the 6' piece of coax are not the same impedance or the SWR meter in you friend's transmitter is in error. The SWR meters in many CB radios are not too accurate. I would try a different SWR meter or if you are happy now just continue to learn and use the NanaVNA. Larry
It's just dumb firmware. The VNA should have the ability to calibrate across a range of frequencies saving all the data during each step. Every time you fit a short an open or a load it should sample a range of frequencies, rather than it just taking one frequencies measurement at a time. With 3 calibrations it should be able to save the data for an entire range why don't they just update the VNA's to work this way?
there are tons of flaws in this video but one of them is that for your information when you work on smith chart (which is nonlinear in terms of impedance values) you have to take the average of two points in terms of their complex reflection coefficients NOT the impedance and if you do that it will end up right in the middle of that straight line between the two points and for your information this is how it is done by all VNAs including cheap nanovnas. Also who in the world calibrates VNA with 50 feet lines attached to the ports!!!!???
Anyone who wants to make a measurement of an object that is 50 feet away from the VNA would want to calibrate with 50 feet of of line. I have done this many times. Larry, W0QE
I plan to build an antenna with a feedpoint 100ft high. I will not know the characteristics of the antenna until it is hoisted into position. It might be a doublet or inverted v and angles are whatever is available depending on final height and surrounding fixture points such as the location of trees to fix the ends of the elements insulators to. If i am to know the characteristics of the antenna then i need to measure it at the feedpoint. I have 4 options. Use vna with powerful bluetooth, use vna with usb back to a computer with powered ports along the way to supply enough power for that length of usb cable, hook a gopro or similar camera to the vna or just input the compensation into the vna for the length / type of feedline being used and calibrate at the end of that length before attaching the antenna, to avoid further real word complications i would also check these results at the planned feedpoint when hoisted to full height. Only then could i be sure of the parameters of the antenna i have made and installed when at height. The simplest way to do this would be with some coax but this is only the first step for me as i will be using balanced feedline, as much as 170 ft of it. Once i know the parameters of the antenna i will then try to build an open wire balanced feedline that matches the impedance of the antenna. This way i can hope to avoid the feedline interfering with the antenna system and hopefull will only require 1 balun transformer back at the transceiver / tuner. The idea will be to keep the antenna impedance and feedline impedance the same all the way back to the transceiver and then be able to measure the total impedance in order to know what ratio balun is the ideal balun to add in the tuner as the standard 4:1 balun might not be the ideal match. If for example i find i need a 9:1 i will wind one and swap out the 4:1 that is currently fitted in the tuner. Problems include not knowing the velocity factor of home made open wire feedline or it's impedance until it is constructed. Also adapting the vna to balanced and back to unbal for the load / terminating calibration. I plan to use a 1:1 unbal and 1:1 balun for each end of the open wore feedline so that i may compensate for the balanced feeder when doing my final tests and adjustments. Ideally i would connect the open wire feeder to the antenna at height and use the vna to see the result back at the tuner but with all these baluns / unbals, home made feedline etc it all becomes to get complicated, especially for someone who has never studied smith or used VNA's. I literally can't find one video or document on this in a real world example. I have looked into DUT's to make this conversion but i am an amateur with no access to high end equipment or advice from people who carry out such operations in real world situations. Open wire is rarely used these days but it is more efficient and it is better suited to balanced systems in order to help with a better match at the feedpoint and to help reduce common mode issues and general noise on receive by keeping the system balanced all the ay back to the tuner. I find this especially appealing when running longer lengths of feedline.
VNA 'S come in 50ohm or 75ohm impedance and antennas come in various impedance. then that implies the use of transmission line transformers to connect them (ref. your #73 video) . thanks for your video
Joe,
A 75 ohm VNA can easily measure impedances (S11) without any external matching transformers. As this video showed if you are calibrating with a 50 ohm transmission line in the nominally 75 ohm circuit you might need to be a little more careful if you intend to calibrate at different frequencies than you are scanning at. However if you are using a 75 ohm VNA to make through transmission measurements in a 50 ohm circuit you will experience mismatch loss on both the generator and load side. The mismatch loss is .177dB on both ends and it is usually corrected for with resistive pads increasing the loss to 2 times 1.76dB. I didn't try to imply the need for transmission line transformers.
Larry, W0QE
@@w0qe Thanks
I'm wanting a VNA from 160M to at least 10M But i want to be able to attach it at the feedpoint 60ft up and then read what the antenna is saying in situ. I was looking for a vna with bluetooth so i could observe it from on the ground. I'm planning on using open wire 300 Ohm ribbon but can't find much info on using a vna with open wire. Wondering if the way to do it is to calculate a good coax length with the vna, then observe the antenna so it can be tuned with the tuned coax, then swap out the coax for open wire?
Several people have added bluetooth modules to do exactly what you want to do. I have such a module for my AIM 4170. Search for a USB to Bluetooth adapter.
Larry, W0QE
@@w0qe Thanks for the reply Larry. I have been wondering how to use open wire feedline with the VNA. I am considering making a micro sma 1:1 balun adapter and a 1:1 unbal for each end. I found small commercially available sma antenna balun boards with a 9:1 balun but i also have seen the smd balun transformer available with a 1:1 winding. I was considering trying to make a 1:1 balun and a 1:1 unbal so i can add the length of the ladder line and it's velocity factor. I feel like i'm stepping into no man's land here. The other complicated factor is if making home made ladder line i would have to also calculate or measure the velocity factor and impedance. I might be stuck at this point or left to make some guesses. I'm guessing my line will be around 500 Ohms with a velocity factor between 85 and 90.
My friend has 18 ft coax going to his truck antenna on 27 Mhz.
Would I need to calibrate the coax to tune the antenna for lowest SWR?
No. The true SWR at the antenna will be slightly higher than what you see at the transmitter end of the coax due to the loss in the coax but you can still tune for minimum SWR at the transmitter. However if you wanted to know the actual impedance of the antenna then you would need to calibrate you VNA to that point. Remember that for any SWR there are an infinite number of impedances except for an SWR of 1.0:1.
Larry
@@w0qe So if I check SWR with say a 9ft, 18ft or 50 ft lead SWR goes down a little because of loss on longer coax?
But all those lengths are fine to check SWR without calibrating at the end of the line first?
@@RC-Heli835 Yes, provided that if the initial 18' piece of coax is 50 ohm and the subsequent pieces of coax you use are all the same 50 ohm impedance. SimSmith can show this easily.
Larry
@@w0qe I set the SWR on my friends Big Rig last night with the Nano VNA 4 with a 6ft coax. We finally cut enough of the antenna off to get a low SWR in the middle of the band ch 20 - 27.205 Mhz.
1.56:1 on each end of the band and 1.3 :1 ctr.
I hooked his 18ft coax back with an analog SWR Meter w/6ft jumper and channel 40 was 3.5 :1 SWR so had to trim nearly another inch off to get it right for the 18ft coax. Also read perfect again on the Nano.
We cut around 5 inches off this antenna because it was resonating in the 12 meter band.
The antenna would have worked as 1st tuned on the 6ft lead but not the 18ft coax.
@@RC-Heli835 I can't explain exactly what you are seeing unless either the 18' or the 6' piece of coax are not the same impedance or the SWR meter in you friend's transmitter is in error. The SWR meters in many CB radios are not too accurate. I would try a different SWR meter or if you are happy now just continue to learn and use the NanaVNA.
Larry
It's just dumb firmware. The VNA should have the ability to calibrate across a range of frequencies saving all the data during each step. Every time you fit a short an open or a load it should sample a range of frequencies, rather than it just taking one frequencies measurement at a time. With 3 calibrations it should be able to save the data for an entire range why don't they just update the VNA's to work this way?
there are tons of flaws in this video but one of them is that for your information when you work on smith chart (which is nonlinear in terms of impedance values) you have to take the average of two points in terms of their complex reflection coefficients NOT the impedance and if you do that it will end up right in the middle of that straight line between the two points and for your information this is how it is done by all VNAs including cheap nanovnas. Also who in the world calibrates VNA with 50 feet lines attached to the ports!!!!???
Anyone who wants to make a measurement of an object that is 50 feet away from the VNA would want to calibrate with 50 feet of of line. I have done this many times.
Larry, W0QE
I plan to build an antenna with a feedpoint 100ft high. I will not know the characteristics of the antenna until it is hoisted into position. It might be a doublet or inverted v and angles are whatever is available depending on final height and surrounding fixture points such as the location of trees to fix the ends of the elements insulators to. If i am to know the characteristics of the antenna then i need to measure it at the feedpoint. I have 4 options. Use vna with powerful bluetooth, use vna with usb back to a computer with powered ports along the way to supply enough power for that length of usb cable, hook a gopro or similar camera to the vna or just input the compensation into the vna for the length / type of feedline being used and calibrate at the end of that length before attaching the antenna, to avoid further real word complications i would also check these results at the planned feedpoint when hoisted to full height. Only then could i be sure of the parameters of the antenna i have made and installed when at height. The simplest way to do this would be with some coax but this is only the first step for me as i will be using balanced feedline, as much as 170 ft of it. Once i know the parameters of the antenna i will then try to build an open wire balanced feedline that matches the impedance of the antenna. This way i can hope to avoid the feedline interfering with the antenna system and hopefull will only require 1 balun transformer back at the transceiver / tuner.
The idea will be to keep the antenna impedance and feedline impedance the same all the way back to the transceiver and then be able to measure the total impedance in order to know what ratio balun is the ideal balun to add in the tuner as the standard 4:1 balun might not be the ideal match. If for example i find i need a 9:1 i will wind one and swap out the 4:1 that is currently fitted in the tuner. Problems include not knowing the velocity factor of home made open wire feedline or it's impedance until it is constructed. Also adapting the vna to balanced and back to unbal for the load / terminating calibration. I plan to use a 1:1 unbal and 1:1 balun for each end of the open wore feedline so that i may compensate for the balanced feeder when doing my final tests and adjustments. Ideally i would connect the open wire feeder to the antenna at height and use the vna to see the result back at the tuner but with all these baluns / unbals, home made feedline etc it all becomes to get complicated, especially for someone who has never studied smith or used VNA's. I literally can't find one video or document on this in a real world example. I have looked into DUT's to make this conversion but i am an amateur with no access to high end equipment or advice from people who carry out such operations in real world situations. Open wire is rarely used these days but it is more efficient and it is better suited to balanced systems in order to help with a better match at the feedpoint and to help reduce common mode issues and general noise on receive by keeping the system balanced all the ay back to the tuner. I find this especially appealing when running longer lengths of feedline.