Saturday, June 13, 2015

Field 2015 Day Dry Run with the PPD-EXT-FD

"Wow"! That's the first thing I said after setting up my Field Day 2015 Park Portable Doublet and getting the first impedance reading from my AA-600 attached to the feedpoint, just wow.

I calibrated the AA-600 the night before with the Micro-Balun set, at first, to 4:1 and using a 200Ω carbon composition resistor but had some reservations about the extra capacitance found in these "Lil Devils". It was significant enough to warrant loosing the high Z accuracy and going back down to a balun setting of 1:1 and suffer the measurement inaccuracies using the well behaved HP 50Ω load resistor. That way all of the impedance measurements are displayed directly with no need to multiply by four.

My friend Gary, KØIMJ and I went off to what my kids call "The Purple Park" because some of the playground equipment is purple, set up the 28' Jackite in the center and the 2-20' Jackites as end supports, using the Park Portable Doublet construction method described in earlier blog posts. BTW, the lawn at the park was so lush because of the recent rains and very squishy and sloppy with flip-flops on. :(

I drove an Army tent stake down and Velcro'd the 28' Jackite base to the stake, while stringing 95# paracord guys. (Obtained from Hobby Lobby).

I took readings with the calibrated AA-600 center frequency at 14.1 and span of 28.0MHz making it sweep from 0.1-28.1MHz, with 80 data points (the native data point number for the AA-600 not tethered to a computer). The measured results (cloumns E and F) were very close to EZNEC predicted values as shown in columns A through D. 

Column G is the settings on the BLT where the clips are attached to the coil turn number from the center tap. I made a nemonic of the reporting of tap position with C-A-P representing where the tap points are with the (C) of the air variable capacitor tap point, (A) meaning Antenna tap point, and (P) being the switch position on the Elecraft BL2. The (+HC) is the addition of the Helper Cap in parallel with the air variable to help it out when it ran out of capacitance. The HC is an ARCO 427 set to about 75pF yielding roughly 175pF of capacitance needed to resonate the tuner on 80 and 60 meters at their respective tap points. The air variable was about 3/4 meshed.

In days prior to field deployment, I created discrete loads representative of the antenna's input impedance for each band, I used an air variable cap, a pot and some ferrite cores to create these discrete loads. I measured each load and attached it to the tuner achieving a match for each band, noting the C-A-P positions. These were my presets I used to get the tuner close when I set up out at the park. I reported only the final settings in the spreadsheet. The 'wow' factor came when the lowest SWR reading was dead on or only one turn different from the preset.

The RX graph above shows the periodic nature of the impedance (displayed in resistive and reactive componenets) as a function of frequency. Column E in the spreadsheet is color coded to show that the R or X (or both) can change quickly by varying the frequncy slighly over areas where the slope is the greatest. This accounts for the error between the calculated and measured impedances shown in the spreadsheet because the reading taken didn't line up exactly with the calculated value.

Results from modeling a Park Portable Doublet set up for Field Day 2015 are shown and align well with measured results taken with realatively inexpensive test equipment.

Carefully constructed EZNEC models can show a high degree of fidelity with the physical antenna characteristics. The model is validated by actual measurements that are in good agreement with predicted values.

Myron WVØH
Printed on Recycled Data

Friday, May 29, 2015

Back to Back BLT Test (Again)

Because I couldn't leave well enough alone, I had to retest the Elecraft BL2 BLT back to back with the Mini-Balun BLT. Same results. Low. How low? Read on.

I am planning for 2015 Field Day and there is a chance that it may rain. So I decided to enclose the remaining BLT in a Lexan weatherproof case. It was waterproof, but since I drill holes, it now "weatherproof". Now I will take two along for redundancy. My main antenna is the Park Portable Doublet, and it provides a high impedance at 20m, so I will tune the matchers for 14.050MHz. Here is when it is matching a 15-Ω load. An input impedance seen on 80m with the Park Portable Doublet. That's an ARCO 427 helper parallel capacitor in there to aid the air variable in achieving a match at these lower frequencies, set to 125pF here.

My back to back setup involves calibrating a through path to establish a reference power level with the Kenwood TS-2000 to a Bird 4311 (the older peak reading 43), and a 100W dummy load. 98-Watts, fine enough.

The procedure for getting the tuners aligned is as before, adjust each one separately with a 4.7kΩ load and then attach them back to back. After doing so, it is necessary to tweak the tuners just a little to dial-in the SWR. 

Once that is completed, we are now ready to attach the 100-W rig and play arcy-sparky! Let's hope not.

Good, it's not arcing anywhere. What's the power coming out the other end? Um, 83 Watts. Okay, what's the loss through the entire contraption? 

IL = 10*Log (98/83) = 0.721dB.

Well now, that's not bad. But that means that's for two BLTs. Yes, it is and it would be unfair to say that is an equal split because of the larger balun core and air-dux coil of the Elecraft BL2 BLT versus the MiniBalun BLT and T106-6 core. So what should the ratio be? 60/40? 70/30? 

So looking at the Smith chart S11 response of the matchers when open circuited at the output, one can see how well the response "hugs" the outer circle, indicating high Q and low loss. The BL2-BLT edges out the MB-BLT by a neck, 70/30...okay, so it's not that precise, but it's not a bad guess.

Okay so 70/30 passes the sniff test. So that yields an insertion loss of 0.5dB for the MB-BLT and 0.22dB for the Elecraft BL2-BLT. Neat!


Tuesday, May 26, 2015

Poor Man's Antenna Dipper

So. I have a love hate relationship with dragging extra gear out into the park for a typical HF portable operation. Antenna, rig, battery, seat, poles(s), tarp, iPad, and water. Maybe an umbrella if the WX looks less than fair and I certainly don't want to drag along my AA-600 just to tune the WVØH BLT on the Park Portable Doublet when deployed at the end of a 20 foot piece of coax, not co-located next to the rig. This scenario is likely when sitting at a sheltered picnic table and taking the rig down to the feed point to retune after QSY, just isn't the easiest thing to do.

I then proceeded to look for an inexpensive analyzer that wouldn't cost a lot and was ready to pull the trigger on an FG-01A when it hit me. Why not use my old Palomar Engineers Noise Bridge! Sure. You can tune by listening to the receive noise while tuning for a dip. All I needed to do was to calibrate, if you will, the noise bridge to a 50-Ω load and then attached it to the antenna at the other end of the coax next to the tuner.

The next "problem" is the noise bridge came in a aluminum housing that was too big for my tastes, and an Altoids tin would be more like it. What amazes me is the high quality air variable cap that is in there! That's going into another project for sure.

Since I am not interested in finding other complex impedances with it anymore, I use my AA-600 for that, I thought maybe I could hard wire in the values of R and C that will equate to 50-Ω at the "unknown" port. 

I found that the bridge was balanced at 50-Ω when the R was 73-Ω and the C was 63pF or so. I dug up a 52pF silver mica and a 20pf trimmer and a 100-Ω Bournes 10-turn pot. I installed those components in place of the Palomar ones, and it worked out well. I nulled the noise for 50-j0Ω on the antenna port while connected to my KX3.

The other problem that plagued me when using the Palomar version was always leaving the power switch on so it killed the battery. Phooey! Not anymore, enter a spring return, center off momentary switch that shuts off when you let go. There is no warm up period to be had, it's noise after all, and so this will keep the battery in fine shape. It should last a long time operating this way.

How does it work? Splendidly. Way beyond how I imagined this would work. Tuning for a dip in noise is instantaneous and very subtle nulls just leap out at you as you acquire a match. Very nice.

Printed on Recycled Data

Optima YellowTop Battery Anomaly Update

So the anomaly that caused the voltage fluctuations was a result of the Windows operating system. When I rebooted, the problem disappeared! Who knew?

Wednesday, April 22, 2015

Optima YellowTop Battery Anomaly

I recently purchased a West Mountain Radio Computerized Battery Analyzer and was hammering away (think: 'Give a Kid a Hammer') and noticed a peculiar discharge pattern when testing an Optima Yellowtop, D31T.

While in the early stage of discharge I noticed an abrupt drop from 12.4 to 12.2V with a noisy response in between.

This is curious, as I noticed this same anomaly when approaching full charge as well. My first attempt at discharging ended in a less then 75Ah capacity, roughly 50Ah.

Stay tuned for updates as I progress through this interesting feature.


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

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.