Field Day 2014

jack_cw_tentThis may be my last region two field day for a while, as plans are rapidly coming together for the move to Madagascar in August. I’m not writing off the possibility of field day next year as I know that I’ll be stateside in June for the American Society of Clinical Oncology meeting in early June, and there are some other meetings during the month that could reasonably keep me here. Also, I might throw in a bit of leave time since I’ll probably be wiped out after field day and want a day or two to cool off before heading back to Antananarivo.  In any event, this was a good chance to shake down some of the equipment that I will be bringing with me, particularly the hexbeam antenna from K4KIO.

As usual, field day planning started far in advance of the event. This year’s field day czar, Regis KF4PIY introduced a few innovations into this year’s FD, the most visible of which was tighter clustering of the stations. In the past, we spread over a large field near the entrance to Burke Lake Park, with some of the stations “down the hill” and some up. Having been “down the hill”, I can attest to the perception that it is better to be “up the hill” both from an antenna perspective and in terms of being nearer to the food and bulk of the social gathering. The obvious concern was that tighter clustering would lead to more interference. However, after a few antenna pow-wows, the band captains were happy the proposed layout and our RF gurus were reasonably confident that it would all work.

Equipment stacked up and awaiting transport.
Equipment stacked up and awaiting transport.

As for the last three years, I was band captain for the non-40m CW station. Most of the equipment that went to field day had gone the previous year. The main rig was the Elecraft K3 with 200 and 450 Hz filters, my main CW rig at home. I brought along the microphone just in case, and that turned out to have been fortuitous, as we had plenty of opportunity to jump on bands that other stations were not working, scoring the only voice contacts for six and ten meters. I gathered the equipment over the course of a few days and queued it up in the front hall. The day before field day, it all got loaded into the car and carted out to Burke Lake Park. I had considered staying out at the park that night and did pitch a tent, but so many others overnighted at the park that I decided a good night’s rest in my own bed would be the smarter decision.

Essentially all of the antennas were pitched on the afternoon before field day including the hex beam. Leon NT8B had purchased an AB577 mast system at one of the winter hamfests in the area and we decided to combine it and the hex beam. Despite being the first deployment of both pieces of equipment, it went smoothly. The AB577 is an intimidating piece of gear; it is repurposed military gear and looks it. It is painted some official shade of matte olive drab and the five foot sections come in a rack that looks like a portable rocket launcher.

Jacob KK4WJA cranks up the AB577
Jacob KK4WJA cranks up the AB577

The rack itself becomes the bottom portion of the antenna and sections are fed into it and cranked up into position, with a joining clamp added between each section. The diameter of these sections is about five or six inches, but the sections themselves are much lighter than they appear; they can be easily lifted by one person. An adapter piece goes on the top, and its outer diameter is about two and quarter inches.

We decided to set up the mast at 45 feet, which required three layers of guying, with guys in three directions at each level. Cables, stakes, and clamps to tighten the lines are all part of the AB577 kit. The lines are all attached at the start, but do not play a significant role until the mast is up fifteen or twenty feet.

When we got the first couple sections of the mast in place, it was time to add the antenna. The hexbeam comes in an unexpectedly small box, about five feet long corresponding to the length of the longest spreader section. Each spreader consists of three telescoping fiberglass segments. Loops to retain the wire elements are already in place on these segments.

In addition to the long box that contains the spreaders and central support column, a smaller box also showed up at my door. This box contained the base plate which anchors all of the spreaders and the central column and when installed sits on top of the supporting mast. I had ordered elements for all possible bands, so 6, 10, 12, 15, 17, and 20 meters. The wires for these bands were also in the box, as were support strings, ferrite rings, heat shrink and instructions. The ferrite rings must be ordered according to the intended feed line, in my case RG213. The rings go over the coax near the feed point and are held in place with the shrink wrap. These ferrites function as a choke and keep RF off the feed line.  Since 12 and 17 meters are not included in field day, I left them out of the set up this time.

hexbeam1
Items in the accessory box: wire elements, strings, and the central hub.

Spreader segments and the central column.
Spreader segments and the central column.

Many hands made quick work of putting the hex beam together. Once we had read the instructions, it took less than fifteen minutes from crate to full assembly. It really is a dead simple antenna to put together because all of the attachment points are already set and the wires are cut to exactly the right length. For someone who never had a store-bought antenna before, this seemed almost like cheating, but I reminded myself that the next time I’d be doing this, I would be far away from the club and likely wouldn’t have as many helping hands.

Bob connects a support string to the central hub while Thor stabilizes the antenna.
Bob connects a support string to the central hub while Thor stabilizes the antenna.

John holds the antenna during rigging of the band-specific wires.
John holds the antenna during rigging of the band-specific wires.

We did run into one snag: the outer diameter of the support mast was about an inch wider than the than the flange on the antenna base plate. The sun was already low on the horizon at this point, but we were eager to find a solution that evening. I made a quick trip to Home Depot and picked up a two foot piece of one-inch black pipe, which is actually about 1 and quarter inches outer diameter. I also grabbed a bunch of U-clamps. Putting the whole thing together additionally involved a bunch of duct tape and two tent stakes that were hammered into shape as adapters.

Members working on finding a mounting solution for the hex beam.
Members working on finding a mounting solution for the hex beam.

By the time the sun set, we were convinced that our adapter was rigid. We set the hex beam down on the grass for the evening rather than attempt to attach it to the mast and raise it in suboptimal lighting.

The next morning, we were able to hand the antenna up to members on a ladder. They tightened the hex bolts on the hex beam’s flange, and the antenna stayed level. Additional sections of the AB577 were then added, and the antenna climbed skyward in five foot increments. Around twenty feet up, the guy lines began to have more and more importance. We had minders on each of the guy lines as well as spotters to assure that the tower was staying vertical in all planes. When the antenna was finally in position, the clamps on the end of each guy line were tightened.

ant_in_place

Finally, the antenna reached 45 feet up, plus a bit for the extension.  A quick check at 5W verified that the antenna was working, with responses up and down the east coast.   An 80m dipole (the same one used in the Indiana QSO Party last year) was also erected to cover that band.

After the antennas were in place, the rest of the station was set up, based on the Elecraft K3 transceiver, N1MM running on a laptop, and trusty Bencher paddles.

the_setup

The station remained in continuous operation from the start until the end of Field Day 2014, concentrating on 20m during the day and 80m in the evening and early morning. However, since we did not have a dedicated VHF station this year, on the morning of day two, we quickly ran the band on both voice and CW, chalking up about 10 local contacts. We also ran 10  meters when it was open. We started on voice and had a good run, but conditions were fading by the time we got to CW, so ironically, we made more contacts on voice than CW. We also had a chance to work on 15 meters for a while on day one, when the other CW station was doing good business on 40m. Although 15m and 40m are harmonically related, simultaneous operation did not result in interference.

Band mode qsos
3.5 cw 278
3.5 ssb 240
7 cw 718
7 ssb 676
14 cw 542
14 ssb 467
21 cw 151
21 ssb 19
28 cw 19
28 ssb 50
50 cw 3
50 ssb 7

 

A major difference from last year is that all four stations remained on the air around the clock; this is strongly reflected in our score for this year, which broke 10,000.

John K3US concentrates on code in the wee hours of the morning.
John K3US concentrates on code in the wee hours of the morning.

A loading coil for 80m

inboxAs the days grow shorter with the approach of winter and activity shifts towards longer wavelengths, I took stock of my log and noticed that while I have racked up a reasonable number of contacts on 15, 20 and 40 meters, 80 meters lags far behind. I anticipate moving overseas in about six months, but before I go, I’d like to even up the score on 80 meters for this QTH.

My lack of contacts on 80m is a function of my antenna limitations — where I live, I can’t put a lot of metal in the sky. I have one outdoor antenna, a 43-foot vertical; the rest of my antennas are in my attic. My vertical antenna is, intentionally, not much to look at: a single, black wire that runs from the ground up into the top of a tree and is almost impossible to see from a few feet away. However, under the gravel of my backyard, there is a DX-Engineering radial plate. Eight radials spike out underground from that point under my property and into the adjoining forest.  The antenna is fed by a coax line that runs underground from the house to that plate, where the center conductor feeds right into the antenna. The antenna was never very well tuned on any specific band, but it managed pretty well on 30 and 40 meters with either built-in or external tuners in the shack. With difficulty, it could tune 15 and 17 meters, and my LDG tuner could force it to work on 80 meters, but the amount of energy actually going out the antenna was pitifully small.

Winding the coil with the help of a vice, some PVC and a couple wood sticks.
Winding the coil with the help of a vice, some PVC and a couple wood sticks.

So, I decided that for this winter, the vertical would become a dedicated 80m antenna. The attic antennas can handle the other bands. My first thought was to make an inverted L for 80m, but the far end would extend off my property and would increase visibility of the antenna, particularly in the winter when there are fewer leaves for cover. I decided to work with the vertical radiating wire that was already in position, but to interpose a loading coil at the base.

Pete, K6BFA, lent me his MFJ antenna analyzer, and I measured the impedance of the antenna at the point where I anticipated the matching coil would be located. I measured at 3.7 Mhz, a bit higher in frequency than where I intended to operate and the complex component of impedance measured 278j. Since the antenna is a shortened radiator, this would be capacitive reactance, so -278j.  I calculated the inductive reactance needed to null it out as xL = Xc/2*pi*freq, or 11.9 uH.

I had made a coil form from Schedule 40 PVC labeled “one and a half” inches, but measured its outer diameter as 1.9 inches. I wanted to wind a coil big enough for the about 12 uH needed above, plus extra so I would have some for shunt inductance (which I guessed would be around 2-5 uH).  I figured 18 uH would be enough to have room to spare. Using the formula of n-turns = sqrt(inductance((18 * coil diameter)(40 * coil length)))/coil diameter, all values in inches, I came up with a three inch long coil with about 28 turns. This fit nicely inside the box that I had, so I went with it.  Note that the coil shown in the box in the picture was my first attempt, and the coil turned out to be too small. There is a learning curve for this sort of thing, you know.

The coil was mounted on nylon screws and coils were made rigid with epoxy. The coil wire itself was some 18 gauge hook up wire that turned out to be too large for my protoboard, so I am glad it found a good home in the matching coil.  The top of the coil goes to the antenna. The coax comes in the side of the box, and initially, I probed the coil to find a good matching point tuning at 3.7Mhz, intentionally above the CW portion of the band, where I wanted to operate. I found the optimal spot to bring the complex portion of the impedance to zero, and then played with the ground lead, trying to find a point lower on the coil that would yield lowest SWR at 3.560 Mhz, the QRP CW watering hole frequency.  After playing with the placement of these two leads for a while, I was satisfied with the resulting SWR curve, which is shown below.

SWR RX

I could have shifted the curve higher in frequency, but I really don’t operate much voice, so I made the decision to optimize the antenna for CW and digital mode transmission at the lower frequency end of the band.

Back in the shack, I verified that I got the same measurements and switched the antenna through to my K3. The rig read the antenna as SWR near 1:1, so I made a couple test transmissions and worked stations in Hungary, Italy and Jamaica. I then turned power to 5W and worked a station in NY. It’s anecdotal, but the antenna seemed to be working fine. After calling CQ at 5W, I checked the reverse beacon network and noted that I was greater than 10 dB above noise as reported by stations in W1, W2, W3, W4, W5 and W7, which seems much better than previously.

IMG_20131021_180739

Some references:

Making a loading coil for 43-foot vertical antennas (de AD5X)

Winding your own coils (de W3JIP)

Coil inductance calculator (imperial and metric)