Gerald, I measured the choke resonant frequency using a 2-port VNA S21 measurement. I then calculated what the choke series-equivalent resistance and inductance would be at that resonant frequency us
I agree that simple S11 impedance measurements tend to produce false (low) resonant frequencies. And the higher the Q of the choke the bigger the error. But I can wind a high-Q air-cored choke, measu
Just to develop this a little further .... I referred earlier to a spreadsheet I had produced that allows me to specify the number of turns, the number of stacked cores and the stray C of a choke usi
Hi Ray, Here's a sketch of the test set-up I use with my VNA2180: http://www.karinya.net/g3txq/temp/s21/vna.png The choke under test fits between terminals A and B. If you compare it with Fig 40a (Pa
I was just asked by PM what Rt is in my sketch here: http://www.karinya.net/g3txq/temp/s21/vna.png For others who may be wondering it is part of the representation of the choke. In other words the im
I mentioned earlier the importance of the phase information provided by the VNA - it not only allows the choke R and X to be identified, but it also eliminates a measurement error in |Z| inherent at
A number of folk have expressed interest via PMs in the spreadsheet I use to perform the calculation of choke R and X from the VNA data. In case there is wider interest it's available here: http://ww
Yes, I've measured my feedline loss using the Open and Short circuit method; results were in line with calculated values. I wonder if the UK is unique in specifying power limits _at the antenna_? In
Jim, I did exactly that when I was developing the hexbeam. I had a reference dipole at the same height on a different mast, "pointing" in the same direction. I A/B switched at 1 sec intervals while l
Peter, The method is not "wrong" - it's just "difficult"! The results will *not* always be the same, because the two antennas were spatially separated and the incoming sky-wave signal had time-varyin
I don't know who made it, but that comment demonstrates a fundamental misunderstanding about coax feedline! When we connect coax feedline to a beam we are also (unwittingly perhaps) connecting a cond
On 26/11/2014 21:50, Wilson wrote: 3. As for balance, theres a good bit of impedance in a wavelength or two of coax shield, so I doubt if the shield end at the top is actually very near ground. Lengt
http://www.w8ji.com/steel_wool_balun.htm Steve G3TXQ On a related balun question...many years ago before beads were easily obtained some hams claimed that their solution was to run there coax though
Jim, I'm not sure why you would say that. Are you assuming that particular bonding point has a low impedance to ground? If so, I wonder why? Steve G3TXQ ______________________________________________
The level of CM current on a transmission line is *not* directly related to how well it is matched. You can have a badly mismatched line with no CM current, and you can have a perfectly-matched line
Interesting! I presume that if it's being compared to the Array Solutions VNA2180 it will do 2-port measurements? Steve G3TXQ On 10/12/2014 19:23, K7LXC-- via TowerTalk wrote: Howdy, TowerTalkians --
The problem with using dBd is that a Yagi's advantage over a half-wave dipole (at the same height) can vary with height! So a dBd figure is only valid at one particular height, over one particular se
I agree that Free Space figures are probably the least ambiguous; but I'm not convinced that "averages" are very helpful! What do we mean by "average"? What's the average of two F/B ratios, one of 10
Stan, I agree with what you say, but I'm challenging your idea of quoting an average. Let's say the F/R at 175 of the frequencies is 10db, and for the other 175 frequencies it is 20dB - what are you
Stan, I agree with what you say, but I'm challenging your idea of quoting an average. Let's say the F/R at 175 of the frequencies is 10db, and for the other 175 frequencies it is 20dB - what are you