Sunday, August 31, 2014

The 2014 Colorado QSO Party

I started out set up on a county line sharing Jefferson and Boulder counties.

I took the MFJ Big Ear along thinking I could more easily straddle a fence or boundary. I setup at the JEF/BOU boundary about 1500Z but at only 13 feet high, I wasn't pleased with its performance. So I bailed on the Big Ear and set up my Park Portable Doublet at 30 feet. That was better but no outing is devoid of mishap and one of my Cabela's end support poles broke near the top under stress. Battle damages or breaking something while using it aren't a concern for me. Stepping on it in my basement, that's when I would have gotten upset. I ran 27 QSOs on 20m there and decided to change location. 

I went over to a spot inside Weld county east of Erie and operated from a park. Conditions had changed a bit so I checked 15m and put out some calls on 40m. I heard some weaky squeaky signals from CO on 7.050 but was unable to QSO. I went back to 14.050 and ran 26 more before everybody left. So I tore down and headed over to Adams county. I found a spot near McKay Lake that may have worked out but it started to rain, so I came home.

That's it. 53 QSOs and now I have to figure out how to report all of this on the summary sheet! It seems overly complicated.



Here is the stats for the RBN spots.

JEF/BOU: 44 spots with an average of 13.36dB and a standard deviation of 7.42dB from 1635-1730Z with antenna radiating North/South.

WEL: 50 spots with an average of 9.96dB and a standard deviation of 8.00dB from 2015-2120Z with the antenna radiating East/West.


Sunday, August 10, 2014

2014 NJQRP Skeeter Hunt

I operated the test just east of my QTH at Country Vista Park. I walked over at about 10:30 (1630Z) and got setup and CQing by the opener at 1700Z. I started out on 20 and switched to 15 but it was deader than a door nail. I went back down to 20 and my QSO rate was 7 QSOs per hour, yikes. Oh well, I had lunch in that time as well.

My total station weight carrying over to the park was 16 pounds. That's the rig, battery, WVØH Park Portable Doublet, solar panel, Crazy Creek stadium seat, tarp, umbrella, iPad, notebook, 3 fishing pole masts, anchors and guy lines. The whole shootin' match.


So I was set up on on the air by 1655Z. Whew, five minutes to go. I spun around the dial on 15 a bit, nothing, then back down to 20 and that's where I started.



This is what my final log looked like. (In reverse order).


Thanks to all who made this a great outdoor adventure and thanks Larry, W2LJ for putting this on.

Myron 
WVØH





Wednesday, July 30, 2014

So How Do You Carry It All?


So how do you fit 10 pounds of field expedient HF gear into one Lowepro Edit 140 bag and chair?
You go to great lengths optimizing the gear!

So that when you are done packing it all looks like this. No extra stuff and just enough needed to get the job done.

Happy packing,
WVØH Myron



Sunday, July 20, 2014

Why 65.5 feet?

I've had a question or two about why I chose 65.5 feet for my PPD length. (For that version anyway)

Well, quite truthfully, it was coincidence. I ordered two 100 foot rolls of #26 wire. One measured 101.5 feet and the other about a foot longer. I cut the longer one to match the other, so they both equalled 101.5 feet. A bakers dozen I figured.

This length formed the basis of the MiniBAC antenna I wanted to build. Along the way I wanted to build a 130 foot or so quad loop for Field Day so I had to cut down the two wires to somewhere around 65 feet a piece and join them in the middle at the top. As I was about to cut the wires I realized that my pole being 36.5 feet extended would allow my rig to be about a half a foot off the ground to keep the jewelry clasps from binding up in the S-Biners at the apex in doublet mode. This was back before I realized the importance of stressing the pole.


So, as I cut only 36 feet off the ends, what was left was 65.5 feet per leg.

Now these jewelry clasps are kinda neat. I can use male/female pairs to join sections of wire together mechanically as well as electrically. They are made of Sterling Silver and can be found at Hobby Lobby.


So there you go a full-sized 101.5' per leg MiniBAC or a shortened version, a 65.5' per leg version. When the shortened version is deployed on my stressed 36.5' mast, the apex clips end up at midpoint making for a 32.75' radiator and equal riser Tx line. Hmm, a 40m doublet.


The 101.5' version up 30 feet under a stressed pole yields a 143 foot doublet. Not stressing the pole much, say 35 feet of riser line, you could get a 133 foot doublet. But with the 700-800Ω riser line, it matters not. The feedpoint impedance will be transformed to something else anyway. The BLT will take care of the match.

72 WVØH

Saturday, July 19, 2014

Just Another Day in the Park


Today I walked over to what my family calls the "Purple Park". It is just east of my home QTH and is easily accessible on foot.
I decided to take along the 23 foot cheapie end support poles too. All that I had is shown here. 
I setup the 65 foot per leg wires in the WVØH PPD fashion and proceeded to call CQ. I started out on 20m and raised several stations and a Tuna Tin 250mW station out in California. 
Then I QSY'd up and then down the bands. 15 was dead, so was 17 meters. By the way, I forgot my 3G iPad so my plan to post live updates was dashed.
Then along came a sparrow and he had friends. They all decided to gather on the aerial. "Shoo". I said but they decided that I wasn't that threatening.
The wire is pretty close to half and half, I have a red mark where mid-point is and I could see that the apex clips were right at those points. 32.75 feet in the riser and 32.75 feet for the radiator, per leg.
But all in all 20 was the best and actually worked an XE2 on 30m. Cool.
There are tuning solutions that don't require the parallel capacitor, this is one of those times.

Forecast high temp was to be in the 90s but it feel that hot sitting next to the stream and having a breeze blow over the stream to me. For about 4 hours of op time it was super fun. I didn't feel hot until I got home and looked at the thermometer, 94°F! But this is Colorado. 


73 everybody.


Wednesday, July 16, 2014

Attaching a spike to the MFJ-1910 pole


The MFJ-1910 pole is a good support for wire antennas but can be difficult to secure at the base. I obtained a 3'x3/4" mason spike and two rubber plumbers union joints (boots) from the local hardware store. The union joints are positioned 2 feet apart on the base of the pole.
I used the hose clamps that secure the union joints to the pole in such a way as to create a cradle for a 3/4" x 3' spike to nest. 
Once those rubber boots have been adjusted the spike can be secured to the boots by attaching another SS hose clamp over the entire assembly.
To put up the pole you start by extending one section (the tip top) of the pole first, the drive the spike in the ground 12 inches deep with a 4-lb sledge hammer, then slip the assembly over the spike. Tighten the two clamps securing the pole to the spike leaving the four around the boot alone. When done, loosen the two clamps, slip off the pole, remove the spike from the ground and slide it back into the cradle for storage.



Saturday, May 31, 2014

WVØH Park Portable Doublet Analysis

Since putting together this antenna system I have noticed a fairly good match with the 4:1 balun on 20 meters. I ran the numbers and here are results providing that good match.

I took readings with my uncalibrated AA-600 and 4:1 balun across the HF band and see that the input to the line is 139-j384Ω on 20m. Now this is with the 4:1 balun causing the readings to be normalized to 200Ω. So for practical reasons, I will stay in that 200Ω system for calculating convenience.

The first thing I would like to point out is that 90° transmission lines tranform impedances by the following formula set. The antenna Z I have here is just an example.


Knowing the input impedance of the antenna and line we can insert them into the second formula and arrive at an answer. But like all things in this world exact values are rarely achieved because of the antenna impedances are location dependant because of varying soil conductivity, etc. causing shifts in the readings. What we can see from this experiment is a general range or location of solutions that lie in certain quadrants of the Smith chart. To get close enough to the center is enough to gain an understanding of the sensitivity and direction we would like to go.

The transmission line is approximately 800Ω and the line input Z = 139 - j384Ω (at 200Ω system impedance). My earlier back yard measurements revealed that an 8 inch spacing yields a characteristic impedance of 725Ω, so when it is greater than that, ~10-12 inches, 800Ω is close enough for the math.

Zantenna = 533 +j1474Ω (AA-600 with 4:1 balun behind our line)

Now, the line is approximately 20 feet long and we need to remove it mathematically to see what the antenna input impedance is as well. I generated a spreadsheet table showing the length of various fractions of wavelengths for a line slowed down by 6% due to imperfect effects of the wire and insulation on that wire. My arrival at 94% velocity factor is from an actual measurement.


So a 20m quarter wavelength piece of that line is physically 16.5 feet long. Since we are at about 20 feet I would like to know how electrically long 20 feet will be. So in the last two columns I took that 20 foot piece and calculated the how long (in wavelengths) that piece of feedline is for each band. At 20m it is approximately 0.3 wavelength and I converted to electrical degrees (with each 90° wrap removed for simplicity on the Smith chart) in the last column.

This yields 109° for 20 feet at 14MHz given a velocity of propagation of 0.94.

Adding the antenna impedance, line impedance, and length into the Smith chart one can see that the resulting input impedance is approximately centered. 


Since the load can vary a certain amount out in the right quadrant by a somewhat large numerical amount, the amount of area travelled on the Smith chart is relatively small. This means that the other end of the line back at the input varies in the vicinity of the blue VSWR circle. That is why, when the wind blows on the antenna or the open wire line dances around a bit, the actual VSWR doesn't change that much and is close enough to the center to provide a good match. Again, all of these values are at the 4:1 or 200 ohm level through the balun.

The blue circle represents VSWR values of 2.2:1, any value inside that circle is under 2.2:1.

Next, I will run the EZNEC model and see if the input Z matches what I have measured.

-WVØH
Printed on Recycled Data