Exactly! I show how to measure the Velocity Factor of a feedline using this exact method in this video: ruclips.net/video/RRb_iJYjh5k/видео.html I am planning on resurrecting the same method for measuring the impedance of a transmission line, soon. Square wave generator, a few junk box components and a scope and you have yourself a fine TDR.
@@MidlifeRenaissanceMan A "slab" of beer? Oh, I get it! A quantity of beer that weighs as much as a concrete slab. Of course, if you already have a scope & pulse or square-wave generator, you can do it for free.
@@Pootycat8359 sorry. A colloquial term we use here in the antipodes to describe a box of two dozen beers, traditionally arranged in a 4 x 6 x 1 configuration. Typically would sell for a pineapple, being a common term for. $50 note on account of its colour being close to that of said fruit. About the same as a cheaper version of the NanoVNA As the owner of an old Tektronix 485, but lacking a square wave generator….save for some 555 timers in a drawer….I will say that the NanoVNA I picked up for the cost of the slab of something better than the usual domestic swill, paid for itself in an afternoon in saved time with a magnetic loop and my dual band 2m / 70cm whip on my car. The smith chart is one of the most underrated features of that device. It prompted me to invest in a used NanoVNA F with the larger screen for people like me who’s eyes are F’ed
@@MidlifeRenaissanceMan Well...this depends on the particular incarnation of the nanoVNA you buy. The cheapest options are ... well...OK, but compromises were made to produce them more cheaply and these compromises can make a big difference in measurement accuracy. Nonetheless, the cheapest of them is still *WAY* better than the MFJ 259!
I need to watch this series so I'll comment more later. If it's anything like your others I'm sure it will be awesome. Did you know that you can modify the MFJ 259B to go below 1 mhz? I've tried to find out how, but there doesn't seem to be any info on it. I was wondering if you had any? If not, I can post info on here if you're interested. Thanks and can''t wait to watch this.
Thank you for the compliment. 🙂 I have to admit that I did not know that the 259B could be modified in that way. Me? I am not a huge fan of the MFJ-259. It's great for *quick* measurements of SWR and the like; very, very handy! But for impedance measurements ... ugh! I don't know if you can make new posts on the community page. If not, let me know and I can place a post you can add a comment to with the information.🤓
I have been still researching on modifying this analyzer and have found some info on the internet. It involves changing an inductor. I would like to do some experimenting with this analyzer and will keep you posted with the results. I want to also experiment with the tuning capacitor, perhaps with a varactor diode or something more stable than the factory tuning capacitor. Thanks for answering me and you run a wonderful channel here. I appreciate all that you do!@@eie_for_you
thanks Ralph. Really informative and topical for me. I have a section of coax on my EME array exhibiting 1.5:1 with a 50ohm DL and only six meters long run of LMR400. I suspect water ingress. My other three sections (4x Yagi's) read fine however i will apply as many tests you have recommended as i can to all four. It did make me ask myself when tuning an antenna and one is connected via a section of coax similar or larger in wavelength to the antenna designed wavelength, are there re any traps for young player or can i expect to get to be able to tune the antenna via an analyzer whilst connected via coax that maybe 1.5 x wavelength of the desired frequency without issue please?
i should say that the VSWR of 1.5:1 on the 50 ohm terminated coax piece shown that when above approx 2MHz. closer to 1:1 when below. The yagi shows about 1.2:1 when connected to the analyzer by a known good section of coax. When connected to the suspect piece it reads 1.108:1. That may falsely make one think its all great when its probably not (when tested at 144.2Mhz) .
If we consider the lossless feedline that the Smith Chart assumes, you will see the same SWR along the entire length, but the impedance will change composition along the way. But we do not HAVE lossless feedline. The signal from the analyzer/transmitter is attenuated along the way to the antenna because of feedline loss. Some percentage of the power that arrives at the antenna gets reflected back as the analyzer/transmitter due to impedance mismatch at the antenna. This reflected power returns to the analyzer/transmitter and is also attenuated along the way due to feedline loss. As a result, the measured SWR at the analyzer end of the feedline is going to appear to be better than it truly is at the antenna. This isn't too much of an issue at HF frequencies, but once we arrive into the higher VHF and higher frequencies, this becomes more apparent because feedline loss increases with frequency. At any 1/2 wavelength length (electrically speaking, including the velocity factor and all), the impedance seen at the analyzer's end of the coax will match the impedance of the antenna. This is only true if the coax is *exactly* a multiple of 1/2 wavelength long. Knowing exactly how long the coax is (electrically speaking), measuring the impedance at the end of that coax and then using a Smith Chart, you can get a pretty good estimate of the antenna's actual impedance. ruclips.net/video/bPmtIVmlJok/видео.html There is so very much *MAGIC* and weirdness associated with R.F. that it just breaks the mind.
![ARGENTINA vs. CHILE [3-0] | RESUMEN | ELIMINATORIAS SUDAMERICANAS | FECHA 7](http://i.ytimg.com/vi/De3AWmXzhuA/mqdefault.jpg)
For those of us who are economically compromised, note that you can MAKE an improvised TDR, with a scope & pulse generator.
Exactly! I show how to measure the Velocity Factor of a feedline using this exact method in this video: ruclips.net/video/RRb_iJYjh5k/видео.html
I am planning on resurrecting the same method for measuring the impedance of a transmission line, soon. Square wave generator, a few junk box components and a scope and you have yourself a fine TDR.
While being economically compromised, a NanoVNA can be had for cheaper than a slab of beer….at least they used to be.
@@MidlifeRenaissanceMan A "slab" of beer? Oh, I get it! A quantity of beer that weighs as much as a concrete slab. Of course, if you already have a scope & pulse or square-wave generator, you can do it for free.
@@Pootycat8359 sorry. A colloquial term we use here in the antipodes to describe a box of two dozen beers, traditionally arranged in a 4 x 6 x 1 configuration. Typically would sell for a pineapple, being a common term for. $50 note on account of its colour being close to that of said fruit. About the same as a cheaper version of the NanoVNA
As the owner of an old Tektronix 485, but lacking a square wave generator….save for some 555 timers in a drawer….I will say that the NanoVNA I picked up for the cost of the slab of something better than the usual domestic swill, paid for itself in an afternoon in saved time with a magnetic loop and my dual band 2m / 70cm whip on my car. The smith chart is one of the most underrated features of that device.
It prompted me to invest in a used NanoVNA F with the larger screen for people like me who’s eyes are F’ed
@@MidlifeRenaissanceMan Well...this depends on the particular incarnation of the nanoVNA you buy. The cheapest options are ... well...OK, but compromises were made to produce them more cheaply and these compromises can make a big difference in measurement accuracy. Nonetheless, the cheapest of them is still *WAY* better than the MFJ 259!
I need to watch this series so I'll comment more later. If it's anything like your others I'm sure it will be awesome. Did you know that you can modify the MFJ 259B to go below 1 mhz? I've tried to find out how, but there doesn't seem to be any info on it. I was wondering if you had any? If not, I can post info on here if you're interested. Thanks and can''t wait to watch this.
Thank you for the compliment. 🙂
I have to admit that I did not know that the 259B could be modified in that way. Me? I am not a huge fan of the MFJ-259. It's great for *quick* measurements of SWR and the like; very, very handy! But for impedance measurements ... ugh!
I don't know if you can make new posts on the community page. If not, let me know and I can place a post you can add a comment to with the information.🤓
@@W1RMD Thanks for looking into it. 🙂
I have been still researching on modifying this analyzer and have found some info on the internet. It involves changing an inductor. I would like to do some experimenting with this analyzer and will keep you posted with the results. I want to also experiment with the tuning capacitor, perhaps with a varactor diode or something more stable than the factory tuning capacitor. Thanks for answering me and you run a wonderful channel here. I appreciate all that you do!@@eie_for_you
thanks Ralph. Really informative and topical for me. I have a section of coax on my EME array exhibiting 1.5:1 with a 50ohm DL and only six meters long run of LMR400. I suspect water ingress. My other three sections (4x Yagi's) read fine however i will apply as many tests you have recommended as i can to all four.
It did make me ask myself when tuning an antenna and one is connected via a section of coax similar or larger in wavelength to the antenna designed wavelength, are there re any traps for young player or can i expect to get to be able to tune the antenna via an analyzer whilst connected via coax that maybe 1.5 x wavelength of the desired frequency without issue please?
i should say that the VSWR of 1.5:1 on the 50 ohm terminated coax piece shown that when above approx 2MHz. closer to 1:1 when below. The yagi shows about 1.2:1 when connected to the analyzer by a known good section of coax. When connected to the suspect piece it reads 1.108:1. That may falsely make one think its all great when its probably not (when tested at 144.2Mhz) .
If we consider the lossless feedline that the Smith Chart assumes, you will see the same SWR along the entire length, but the impedance will change composition along the way.
But we do not HAVE lossless feedline. The signal from the analyzer/transmitter is attenuated along the way to the antenna because of feedline loss. Some percentage of the power that arrives at the antenna gets reflected back as the analyzer/transmitter due to impedance mismatch at the antenna. This reflected power returns to the analyzer/transmitter and is also attenuated along the way due to feedline loss. As a result, the measured SWR at the analyzer end of the feedline is going to appear to be better than it truly is at the antenna.
This isn't too much of an issue at HF frequencies, but once we arrive into the higher VHF and higher frequencies, this becomes more apparent because feedline loss increases with frequency.
At any 1/2 wavelength length (electrically speaking, including the velocity factor and all), the impedance seen at the analyzer's end of the coax will match the impedance of the antenna. This is only true if the coax is *exactly* a multiple of 1/2 wavelength long. Knowing exactly how long the coax is (electrically speaking), measuring the impedance at the end of that coax and then using a Smith Chart, you can get a pretty good estimate of the antenna's actual impedance.
ruclips.net/video/bPmtIVmlJok/видео.html
There is so very much *MAGIC* and weirdness associated with R.F. that it just breaks the mind.
@@eie_for_you thankyou again