February 1, 2018
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I have started to do some testing of the miniVNA I bought from RA0SMS. The software that Anton points to downloaded and installed without issue. I also downloaded jVNA and installed after installing the Java JRE. The first software worked pretty much out of the box. The jVNA software was giving completely bogus results until I realized I had to adjust the DDS factor so that the frequency output is calibrated. Anton recommends a value of 34,354,689 for this which I verified using an oscilliscope.
Once this was setup, the two programs gave largely the same results. I tested a 50 Ohm load, the 40m vertical and the 20m vertical through the miniVNA, RigExpert AA-230 Zoom and the mini60 analyzers. The first thing that showed up was that the SWR & Xs curves have generally the same shape and indicate the location of minimum SWR correctly. The magnitude of the SWR at minimum is not matching up. When I look at the 50 Ohm load data, the RigExpert and mini609 are dead on but the miniVNA is reading several Ohms lower.I am going to have to dig around a bit as I suspect this is a calibration issue.
Update: Google translate does not work to well on Russian…there are some tips on calibration and accuracy on RA4NAL’s website but her’s a sample of the translation “There can be no personal podebarking, because we do not reference and lyubitelsky device for setting the actual antenna instead for pseudo-scientific research. What is the difference when work on the air, if the SWR = 1.1 or 1.05?”
Arrrgh my head hurts!
December 10, 2017
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There were some things bothering me about the EFHW matchbox. I would run a scan using the RigExpert with a 3.9K Ohm resistor from the antenna line across to the ground and sometimes get a good reading and sometimes not. I suspected a poor solder connection or the el cheapo binding posts I was using. Well I am done with the el cheapo binding posts! From now on I am using stainless steel machine screw hardware. I replaced the binding posts with these and the readings settled out.
I made a few other changes for round 2 with this antenna today. First up, I wrapped the end of the RG-58 cable eights times around an FT240-43 core to act as a choke at the feedpoint. I added about six feet of counterpoise. I went back to setting this up a a low inverted V of sorts. The feedpoint is over a tree branch on one end about 6 feet off the ground. The other end is supported by a fishing pole. Unfortunately, this configuration had a huge amount of sag in the middle. I placed another pole in the middle so the apex is up about 16 feet. Not happy with this configuration. I will use a sturdier pole and set this up as a true inverted v next time around. meanwhile, I am running some test in this configuration. SWR was good on 40m and 20m but a bit high on 15m:
Initial WSPR results on 20m look promising. 1/2W signal is showing a good ratio to received spots. I tried a few SSB contacts but none were closed. I’ll run WSPR on this over night on 40m and 20m and see what the data shows. I’ll then switch to a 10m pole to support the middle of the wire into an inverted V.
One more thought is that I’ll add a 110uH coil to the end of the wire then about 2m more of wire, the idea that it can trap 40m and then act as a loading coil on 80m. I have worked out the coil dims for this using a 1-1/4″ PVC pipe coupler as a coil form. 110uH works out to 52 turns of #20 magnet wire.
October 8, 2017
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Rudy Severns, N6LF, published a paper entitled “Measurement of Soil Electrical Parameters at HF” where he shows several methods of measuring the electrical properties of soil. I built an OWL probe using his directions made from two parallel 1/2″ aluminum rods spaced 4″ apart and 11″ long.
Once assembled I measured the capacitance of the probe with the L/C capacitance meter which measured it to be 6.16 pF. I inserted the probe in the ground around my vertical antenna then connected the RigExpert AA-230 Zoom and measured impedance at several frequency points in the HF bands. The Resistance and Reactance are used to calculate the soil conductivity and Er values. Here is a graph of the results:
The data collected at this one point confirms that the soil in South Texas is quite good in terms of conductivity and Er. I will use these values when modeling antennas with EZNEC. This was the initial test and I will likely try some other areas of the backyard and see how much it varies and whether the data is consistent
June 13, 2017
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I was going to try and adjust the loading coils on the homebrew Buddipole but after reviewing the SWR plots in more detail I have decided against this. The resonance point is on the high end of the band but I’ll be operating mainly voice. The SWR is below 1.6 across the band and the reactance is within ±3 Ohms of the resonance point. Better to leave it alone at this point.
I did add a couple of cable ties to the arm to allow me to better control the antenna swinging in the wind. I am working to build another 1:1 current balun which I will replace the BNC to binding post adapter I am runing now. It will be interesting to see if adding this balun will change the SWR curve. Here are the current curves:
Hopefully I can retest the deployment of this antenna this weekend perhaps at 20 ft and with luck maybe at 30 feet on the military mast.
May 27, 2017
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Sometime ago I built a homebrew version of a Buddipole horizontal dipole antenna. I only deployed it once to test and have not really used it much since. I am considering using this antenna for Field Day this year on the 20m band and wanted to test it out. Happy I did for several reasons. Here is the antenna deployed at 16ft with a painters pole:
The antenna is guyed at two levels. The painters pole is inserted into a speaker stand tripod. Here is the SWR plot:
Most of SWR is below 2 however the resonance point is outside the band on the high side. So I have to lengthen the antenna slightly. The whips are already at their max so I will have to adjust the loading coils. One more turn on each should give me room to adjust with the whip lengths if necessary.
Something else that needs to be addressed is that the antenna swings around in the wind. I need to add an attachment point for a separate line to secure it from swinging. The old “Armstrong” method of swinging the antenna around. Finally, I need to put a true 1:1 current balun at the feed-point. I have the kit to build one and will do so this week.
The antenna has performed well. I called CQ this afternoon and made 5 contacts from South Dakota to Florida and North Carolina. Band Conditions have been fairly bad with considerable QSB. Europe will open up in a couple of hours and will try it again then.
April 28, 2017
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My posts on the Mini60 antenna analyzer remain the most popular views on this blog. I have not been using it much since I acquired a RigExpert AA-230 zoom. The RigExpert is so easy to use and provides a wealth of information when tuning antennas. That being said, I have not given up on the Mini60 as I intend to use it on Field Day.
I am going to be retro-fitting a bluetooth module to the Mini60 over the next few days. I need a USB to TTL adapter to program the bluetooth before installation and then wire it into the PCB. Worst case I end up trashing the mini60…best case I’ll have a wireless Android interface for this over bluetooth. Stay tuned as I’ll post some detail on how this proceeds.
December 28, 2016
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One page that folks following my blog seem to gravitate to is my review of the Mini60 antenna analyzer.It is the Sark 100 copy sold on Ebay and produced in China. I personally have found this analyzer to work quite well and I have used it exclusively to test out my antennas. Your mileage may vary.
Now that I am doing some additional antenna work I have purchased a RigExpert AA-230 Zoom. This unit is a bit pricey compared to MFJ units and certainly to the Mini60 but from what I have done with it thus far it is well worth it. I’ll publish a comprehensive review later but for now I am sold on it. It is light, provides accurate and quick scans, has an impressive array of features including cable TDR testing and a great USB interface. The software works great with a PC and can save files in a format that Zplots can read.I used it for the first time in the field on the 40m loop and it made short work of tuning it. The interface takes a little getting used to but overall is very smooth to handle.
I will not be getting rid of the Mini60 as for quick and dirty measurements it still can’t be beat for the money. The RigExpert will be for more advanced testing and data collection and will of course help me with 2m antenna work.