Sunday, March 29, 2015

AA-600 Reference Plane Calibration

While the Rigexpert antenna analyzers are factory calibrated, the reference plane of that calibration is inside the Type N female connector on the unit. So one will need to "bring" that plane out to your device under test (DUT). 

The reason you would want to bring that plane out to your DUT is to know the phase information of that device, otherwise just leave it alone and use the factory cal. Here is how to calibrate the RigExpert AA-600 series antenna analyzers.

First turn on your analyzer and let it warm up for 30 minutes. This helps to satisfy the RF test engineer in you. Next, simultaneously push the F and 8 keys to enter into the CAL mode. Then attach the open cal standard and press the 2 button.


Continue to enter in to the calibration mode to measure the short and load standards. You'll have to go back into the cal mode each time a sweep is run, F + 8.

While it doesn't matter what order you perform the cal, it makes it easier if you establish an order so that your brain is always progressing through in the same order, 2, 3, 4; open, short, load.


You can do either female calibration or male calibration depending on the DUT connector. I made mine out of regular connectors, the same connectors that many of my Baluns and Ununs have.


You'll need to push the run button one more time to show that the unit is calibrated. When that sweep is complete you will see a CAL symbol in RED in the lower right hand corner of the display.

Using any balanced load requires the use of a balun or at least a binding post adapter.


 Calibrate it the same way using discrete cal components. For the open, just leave the binding posts screwed down without anything in there. For a short, I flattened out a round copper shield from some 0.141" semi rigid coax. You can just use some flat strip or copper. I glued a "handle" on mine.

The 50-ohm cal resistor I got from a hamfest directional coupler that was broken or so they said.


If the resistor is undamaged, it is guaranteed to have better than 42dB return loss by HP cal standard protocol. Good enough for me.


Once the calibration is complete you can then proceed to some measurements. One drawback of the AA-600 is the lack of being able to save cal sets into memory. There are 90 sweep and 10 TDR memories. It would be nice to be able to save cal sets as well.

72 Myron
WVØH





Saturday, March 28, 2015

PPD Junior and Variations

So this winter I was dreaming of being outside with my KX3 and Park Portable Doublet but often considered it to be a bit large for quick deployable operations. Having the remaining 36 or so feet of the 19/38 (#26) stranded wire from my two original 100 foot spools, I decided to investigate what configuration I could use it in the same manner as my Park Portable Doublet. 


The Park Portable Doublet consists of two 66 foot wires supported at 33 feet and stretched out to form a 40m doublet (or a 17m EDZ as I like to call it). I could support the Park Portable Doublet Junior at 20 feet instead of 33 feet to allow a full-sized 20m doublet to form. Granted, it would only be up 20 feet and the ends would be around 10 feet but then ran the numbers in EZNEC and it was an acceptable trade. Only giving up a couple of dB gain coming in at about 6.5 dBi on 20m and getting better the higher in frequency you go. 


So all that was left was to build it. Having now three 20 foot poles, I planted the apparatus next to the fence in the back yard last night.

Anxious to try out my "new" Johnson Matchbox 275, I got acceptable matches from 10-40m, although the 40m SWR was about 4:1.

Then today, I decided to try a different approach. Mount all poles bases in one central location and extend the two arms if you will out in a crisis-cross fashion.


So, I got out some 3/4" PVC a scraps and fashioned an "X" type base, with two nail type tent spikes and the "Two Fister" regular screwdriver for the main vertical support.


Driving the two nail spikes half way in the ground at 45° angles, I placed one shorter section over the spike and then drove the other kind of guessing where it should go in relation to the other. Both at 45s toward each other but allowing the whole PVC cross to hold the two 20' Shakesphere Wonderpoles nicely.


After putting this contraption up, I was left with a pretty small footprint if you didn't want to have any place to tie down the ends. They could be left floating in the air if you were on a narrow jetty of land.


So then I used my Elecraft BL2 with B&W coil attachment forming an autotransformer called my BL2-BLT.


I ran through the bands tuning and logging tune points/taps, etc.


I was pleasantly surprised to obtain a good match on 40m and heard considerable band noise. It might actually work on 40. I checked a few RBN spots and sure enough, I was heard.


When I was up on 15 calling CQ, Gary, KF7NWS came back to me! And fairly loud too considering he was off the end of the wire! We chatted a bit and the signals were pretty steady considering a single hop out to Ory-Gun.

Removing the antenna was pretty straight forward, just reverse the process. 


And you're done.



72,
Myron
WVØH









Saturday, March 14, 2015

Ununs. How Not to Wind Them.

Awhile ago I posted some results winding many different configurations of ununs, both 9:1 and 16:1 varieties. Most performed with a very narrow bandwidth and I didn't investigate the reason why they were poor performers.



Then this week, my friend John, KN5L and I were debating the use of ununs and he whipped up a perfectly flat 9:1 unun. This made me more curious than ever of course wanting to get to the bottom of  this differing SWR led me down the road of once again getting out the magnet wire and ferrite cores.

The first observation from his photos (below) was the loosly wound winding that was employed. Mine had always been tight, flat and, a bit more aligned.


Then it was beginning to become more clear. Sevick had always been a proponent of keeping the windings on his baluns the geometric mean of the two impedances. For example, if you had a 4:1 balun, the windings should be spaced such that the characteristic impedance is 100-Ω. When I read his books, he didn't say what the impedance should be for ununs and the photos were no help, they all showed them nicely bundled in a flat strip of windings.

Enter, the loosey goosey winding approach.

John's, toroids were FT140 sized cores which allowed for some extra real estate to spread out the windings. I used 114 sized cores with a need to be careful about wire diameter. I wound three ununs. One with #22 wire, one with #19, and one with #16 wire. All wrapped with no tape.




When I was able to spread out the windings and separate them from each other, the change was dramatic.


I did run some sweeps with a calibrated fixture but it didn't seem to matter for the rectangular VSWR graphs at HF.


This last photo here is the FT-114-43 with 6 tri-filar turns of #16, loosely wound and spread out. The geometric mean of 50Ω and 450Ω is 150Ω, about as far as you can separate these wires on the core.


The load resistors are metal film Radio Shack jobbies, 470 Ω || 15kΩ.

I went back and reread some of Sevick's literature and he does mention the inter-winding spacing sensitivity when building ununs on rod cores but doesn't mention the toroidal cores specifically. In my experimentation, not only does the inter-winding separation matter but, as well, the inter-filar spacing matters and makes a significant difference in bandwidth when everything is spread out. 

Thanks to John, KN5L, for his photo and in his parallel verification efforts today. You can see his work at his website, http://www.kn5l.net/unun-test/.

Myron - WVØH






Saturday, February 7, 2015

2015 FYBO Test

Short and sweet. Operated for 2 hours. Worked 14 stations. Some MN QSO Party on 40. Used the MFJ-2289 Big Ear antenna up 13 feet at apex, KX3 running 5 Watts and temp was 58 degrees F. So much for freezing. In fact last nights low was 57°.

Here is the 14 QSOs I logged.

Score = 14 x 6 x 2 x 4 x 2 = 1344 points





So pretty fun except it wasn't very cold, which was a good thing because I didn't feel too well coming off a cold.

72, WVØH Myron


Monday, January 26, 2015

Zplots by AC6LA is Cool

A post on the Internet said that AC6LA's Zplots can automatically generate vf, |Zo|, insertion loss for you!

So the thing I was missing from my 26 AWG transmission line graph was the velocity factor and |Zo|. Well, since I calibrated to 725 Ω with a conventional transformer that resulting plot of a 50 Ω graph was pretty boring so I just plotted the loss and velocity factor on one graph.



As you can see the velocity factor is pretty constant over the HF band and the loss was as I reported before, maybe a smidge lower because my line length was actually 101 feet long and Zplots can normalize to 100 feet automatically.

72, WVØH 

Sunday, January 25, 2015

Revisiting Park Portable Doublet Transmission Line Loss

Ever since posting loss curves about using my #26 (19/38) stranded wire I use for my Park Portable Doublet, I've wondered about selecting another verification method to cross check my work. My friend John, KN5L has been evaluating some transmission lines, investigating loss, and coming up with loss verification methods that are useful for this purpose. While his investigation has been with balanced 300-Ω window line Universal Radio sells, mine is over 800-Ω. 

Higher impedance line will exhibit lower loss using smaller conductors than equivalent conductors at lower impedances because of the I^2*R property in Ohms law and I use that property to maintain portable status for this gram weenie. I compiled the data into a chart that looks like this from a previous post. Plotted the data a did a curve fit. It is supposed to be a straight line on log/log paper but there may be some errors in my measurement system that may account for this non-linear response but the general principle is there.


So I've always wondered about how I could use a second opinion to verify what I measured is close enough. Well, today John writes that I can get an approximation using RF resistance numbers from a website compiled by VE3EFC, located here.


In his tables, the RF loss can be made into a ratio of characteristic impedance to RF loss resistance. The characteristic impedance can be found by, (#26 wire). 

Zo = 276 x log(2S/d), where S (S = 8.25, d = 0.016) is the spacing and d is the diameter of the wire,

Zo = 276 x log(16.5/0.016) =832Ω 


Since the total resistance of the wire is comprised of DC and AC (RF) resistance we will add them together. 

DC resistance = 34.43 ohm per 1000 feet for #26 (19/38), so for 200 feet we get 6.9 Ω.

Now, the 15 MHz RF resistance for #26 stranded is similar to one gauge size smaller because of the stranding and surface irregularities so #28 at 15 MHz yields R = 34.83 Ω per 100', or 69.66 Ω per 200', the up and back distance. Plugging all of that into a loss ratio and "dB-ing it", we get,

Loss at 15 MHz = 10 log((832 + (7+70) / 832) = 0.38 dB 
The chart shows just over 0.4dB loss at 15 MHz, and that is close enough for me.

Since I use only a third of that line in my deployment of the Park Portable Doublet, the loss is 0.128dB. Couple that to a MiniBalun/BLT with less than 0.3 dB loss at 15-MHz and we have acceptance in the last dB club, finally weighing in at 0.43dB loss of the tuner and TL up to the antenna feedpoint. With an antenna that has around 6-dB broadside gain on 20m and with 5 Watts (+37dBm) applied to this antenna system, the receiving station would say that I am running around (36.9897+6-0.43=42.56dBm) 18 Watts.

72 from a charter member of "The Last dB Club",
WVØH Myron


Saturday, January 24, 2015

I'll Take a BLT in a Box, To Go, Please.

I was wondering about when I wanted to operate my Park Portable Doublet when it rains. My MiniBalun BLT isn't exactly waterproof let alone weather proof. Field Day certainly can be rainy, even here in Colorado.

I decided that a waterproof enclosure would be just the ticket. So here it is, one clear plastic box with a nice seal to keep the rain out.





Now I'm ready for a rainy day.
72,
Myron
WVØH