Tropical Cyclone Enawo

This storm is already intense and predicted to hit the north-east side of the island tomorrow morning with hurricane force. For the last three years, we have been lucky with storms tracking to one side or the other of the QTH, but the track for this one cuts straight down the center of the island and should pass near the capital city, Antananarivo. The prediction has been consistent and is now close enough to be sure that we will experience some rough weather in the next few days.

To that end, for the first time, I have lowered the hex beam antenna. I collapsed down the telescoping sections of the heavy duty 10m spiderbeam mast and threw some additional guy lines over the central plate to which the arms attach. The wooden support beam goes two meters into the ground and is surrounded by buried concrete, so I am not worried about the base, but I do expect the fiberglass arms to be battered about. I considered dismounting the whole antenna, but that would have required more manpower than I have readily available, so it will have to ride out the storm.

Continue reading “Tropical Cyclone Enawo”

SOTA: ZS/WC-043 Maclear’s Beacon

Over the last two weeks, I have traveled in South Africa and Botswana, primarily on business, but with a little time set aside for radio fun. Unfortunately, I didn’t receive regulatory clearance to operate in Botswana in time for the trip, so I left the radio in my suitcase there (despite the bilateral agreement on amateur radio between the US and Botswana, to operate, US hams need to file with BOCRA, which takes some time). However, in South Africa, I operated from Pretoria and Cape Town, visited a local ham club, and activated a SOTA peak.

While I would prefer to activate less common SOTA peaks, when traveling I often need to consider what is in range of public transportation. Table Mountain is a 50 Rand ride on Uber from downtown Cape Town and is also a stop on some hop-on/hop-off bus tours. Two hanging cable cars run from the base of the mountain to its top. There is a long path up as well, but as I was lugging more equipment than usual, I decided to take the cable car, which was something like 250 Rand round trip (about $20; pricey, but it is, after all, a tourist attraction).

Continue reading “SOTA: ZS/WC-043 Maclear’s Beacon”

40m Delta Loop

590px-Pythagoras_similar_triangles.svgThe rainy season runs from about November and sometime up to March, with peak cyclone activity at the height of summer, January and February. As a preventative measure, my next door neighbor trimmed one of the trees along our property line. I had some ropes in that tree to support a G5RV and when he gave me the heads up that crews would be whacking away at limbs, I thought it best to bring down the antenna. The G5RV never really hung high enough to work well and it stretched over the house, which may have added to noise, so I didn’t mind taking it down. Last week, I put up a new full wavelength 40m delta loop as a replacement.

I went with the delta loop because there is one large pine tree at the edge of the property and I was able to shoot a line over it with a wrist rocket. The lower corners are supported with guy lines from a telephone pole and another tree to each side of my house. The antenna is fed at the middle of the base, which is just at the edge of my roof, which makes it convenient to access. I had brought back a 50m roll of heavy duty green wire from Sotabeams in the UK. I have to remark that working with this very compliant wire was a pleasure after having made wire from household wire that loves to coil in the past.

By virtue of the position of supports, the antenna slopes from bottom to top towards the south, a bit more vertical than horizontal. Since I am feeding it from the bottom, the antenna polarization should be horizontal, but I believe that the sloping should add some directivity towards the North. I had considered feeding it up one side and using a quarter-wave of 75 ohm coax to transform the expected 100-ohm feed point impedance, but it would have been awkward to support a feedpoint at that position given what I had to work with.

I initially cut the antenna to a literal full wavelength, 299.8/7.1 * 1.05, where 1.05 was the fudge factor supplied in the ARRL antenna handbook. Initially, the resonant point was 6.9 Mhz, so I shortened the antenna in a few iterations, arriving at the intended 7.1 Mhz, where there was no reactive component and the resistive component was about 65 ohms — close enough to 50 for me to be happy to feed directly with 9913F7 coax and not worry about vSWR.

From the shack, the antenna works great with no tuner across 40m, but I don’t have a lot of experience at this point with regard to how the antenna performs. It is much louder on 40m than the hex beam, but most of the time that loudness is merely more noise thanks to the environment around the station.

Wifi for the Garage

A look inside the Linksys WRT54GS router used in this project.
A look inside the Linksys WRT54GS router used in this project.

Propagation has been abysmal, so it’s time to hang out in garage and work on projects. One catch: the garage PC gave up the ghost about a month ago. The Windows 7 computer had been functioning for a few months as a wifi repeater that let me use other wireless devices in the garage. Unfortunately, it looks like a power spike may have taken out the motherboard. I have retired that PC, and came up with a replacement: a linksys wrt54gs router reflashed with DD-WRT firmware and hardware modifications to add a cantenna.

Last week I made a video about putting up the hex beam, and now that I have the video editing software, I made one about the wifi repeater bridge project. Making video is somewhat addictive, so I think there are more on the way. I have a ways to go in terms of production quality – maybe Christmas will bring a better video-capable camera.

On the subject of videos, my home club, the Vienna Wireless Society, is now posting videos of presentations made at the club.

5R8SV: The Hexbeam is Up

hexbeam_finally_upTL;DR? See the video on youtube.

My greatest limitation up to this point has been my antenna. For a few months, I worked QRP with the end-fed LNR 40/20/10, and it did a great job, although it wasn’t up very high. Putting up a G5RV allowed me to run 100W when my main shipment arrived, but the antenna was not ideal for my location – in particular, the twin-lead feed line, which is a radiating part of the antenna, came down low over the metal roof of my house and I had to tie it off to the side to keep it from detuning. Now, however, I have a “real” antenna up: the K4KIO hexbeam is mounted on heavy duty spiderbeam 10m mast, which sits atop a Yaesu G450 rotor.

It is effectively a two-element antenna on each band (6, 10, 12, 15, 17 and 20 meters), but each band is resonant and I do benefit from directivity, particularly in terms of noise reduction. I am hearing better from every direction, but particularly Asia. I’d write more in praise of the antenna, but I’m too eager to actually get on the air and use it…

I have been posting small interim updates on the station’s  QRZ site, and as they get stale, I’m moving them over to the blog for the record. Here are updates from last October through the beginning of this month:

June 21 2015: You know the drill — I had much more travel in April and May than I would have thought possible. The hexbeam? No, still not up. I’ve done a lot of metal work for the supports for the rotor and thrust bearing, but I won’t mount them until later this year. I’ll back back in the US from later this week (just in time for Field Day) through the beginning of August. I’ve updated all my online logs and sent an update to Phil, my QSL manager.

9 April 2015: I am in Madagascar for April except for the third week, when I’ll be in South Africa (so maybe you will hear a call from ZS/AI4SV at some point). I am trying to take advantage of the existing propagation while I can. I’ve had some contacts with VK/ZL in the last few days on 10m, including a few on voice. The highlight of my week, though, was tossing out a call on six meters and having a train of replies from around the Mediterranean: Italy, Malta, Jordan, Israel and several others. The K3 limits to about 70w using my G5RV antenna, which is certainly not ideal for 6m operation anyhow. I’ve been talking about putting up the hex beam for quite a while, hopefully I’ll get it done this month.

9 March 2015: I got back to Madagascar in time to spend a few hours on ARRL DX SSB and worked about thirty stations, including the Washington, BC, and the Northwest Territories, but with a predominance in New England. Alaska continues to elude me. I’ll be in Madagascar until the 14th and then away for the rest of the month. I did manage to get the post for the hexbeam anchored two meters deep in the backyard, so when I get back, that will be the first project.

24 February 2015: Thanks to everyone who worked me this past weekend during the ARRL DX CW contest. I hadn’t really planned to participate in it, but suddenly it was Saturday, I was home, and I had a working antenna, so there you go. I was very pleased to get 496 contacts including some states and provinces that I hadn’t previously reached. Work on the hexbeam continues in the background — I just slapped another coat of paint on the support post.

10 February 2015: The G5RV has worked out well, and I have contacts on 10, 12, 17, 20, 30, and 40 meters on it. Again, my limiting factor is local electrical noise, which is very variable. At some point I may try noise cancelation with a local sense antenna.

1 February 2015: I hung the G5RV today and discovered that it barely fits on the property. The matching section comes down over the house, so rather than let it hang straight down, I pulled it to the side and suspended it from a tree branch to keep it away from the metal roof. I can only imagine what this does to the radiation pattern. I swept the antenna with an analyzer, and get < 3:1 on 80, 40, 20, 17, and 10 meters. I get high SWR on 30m, so I don’t expect to run that band, and I’ll have to see how the built-in tuner in the K3 does on the other bands. I hopped on 17m earlier this evening running 100W for the first time for this station. I ran 100+ contacts, so at least I know it is not a dummy load. I am hoping to try out the other bands after work in the coming week.

From my trip to the US last week, I did bring back the hex beam mast, so that longer term project can now move ahead as well. I also picked up a powergate, which provides battery backup. We have intermittent power losses and even if backup power comes on line, I found it awkward to be mid-QSO and lose power. If I was operating split, the K3 would forget the set up and I’d need to reprogram. Now, the radio switches seamlessly to battery until main power is restored. Finally, the TS-450SAT is now set up for digital operation. I had a couple PSK31 contacts last night and will try some more digimodes as time permits.

18 January 2014: In the US for a week of meetings: a couple days in Seattle and a couple in Washington, DC. I should be back in Madagascar at the very end of January. Barring any complications getting the spiderbeam mast through as luggage (Air France says it’s okay in terms of dimensions as a “second bag”), I’ll get to work on raising the hex beam, but this will entail digging a big hole, finding a suitable post, anchoring in concrete, etc. – I’ll get it up as soon as I can if weather cooperates. Meanwhile, I’ll try to put the G5RV in place. I’m also hoping to get a digimode radio on the air in February, so maybe you’ll soon hear strange sounds eminating from the Red Island.

29 December 2014:  It has been a little more difficult to get things set up than anticipated for two reasons: 1) worked related travel; and 2) rainy season. It only rains a couple hours on certain days, but when it rains, it comes down hard. I had anticipated making a workshop in the garage, but the floor floods briefly when the rain pounds down. Consequently, project #1 has become raised flooring and shelving in the garage. While that will be an ongoing project for the next month, I’ve started setting up the shack indoors and have created an access route to bring feedlines into the shack. I have brought the coax from the LNR end-fed antenna into the shack and it is now hooked up to the K3. The antenna only handles 25W, but that’s 5x more than what I had before, so at least I am heading in the right direction.

26 November 2014: The station gear finally arrived last week. Due to work, I’ve just started unpacking it all. Now that I have tools and materials, I can start wiring up the house as needed. This is probably going to take a while since I’ll be away on business (and vacation) for much of December. When possible, I’ll continue to operate from the porch, perhaps with a bit more power using the K3. However, now that rainy season is upon us, it’s trickier to operate from that location. I’m hoping to upload everything to date to LOTW this week.

19 Oct 2014: A bit less activity in the last week or so due to business and travel, but still accruing the new DXCC entities as time permits. Some highlights include working my QSL manager G3SWH, Phil, a mobile station in Germany, DF4TD/M and a few stations in the Oceania DX contest. No change in equpment: the main station gear is still on the way, probably delayed a couple weeks by the Air France strike at the end of September. I’ve had some discussions with a local engineering company about putting up a “pylône de télécommunications” to support the hexbeam and G450A rotor, so that project is also cooking in the background.


Field Day 2015. The 40m CW tent and its plastic cocoon. In the background: a ground-hugging hexbeam awaiting better weather for extension.

I’m back in the US for about a month, part vacation, part work. Stop one was field day with the Vienna Wireless Society at Burke Lake Park in Virginia. After that, I joined the family first in New Jersey and now in Montauk, New York. I’ll be in Montauk through around July 12th and then back and forth a bit to Washington, DC. I have a week of work, from July 20 to July 27 in Bethesda, and then the last few days in Indianapolis to attend GenCon.

Field Day was as always enjoyable, but this year particularly wet. I arrived less than 48 hours before the event, so I was still on Madagascar time, which helped with the late night operating. On the Thursday before field day, I was driving all over the place to catch up on shopping, including a visit to Ham Radio Outlet in Woodbridge, VA. On the way back, I passed the field day site and noted that a huge tree had been chopped down. This tree is right in the middle of the field day site and was traditionally used for antennas in the past. It had a number of dead branches last year (I’m not blaming RF) and the park authorities decided that it represented a hazard. Consequently, the antenna plan needed some rearrangement.

On the Friday of field day weekend, I showed up around noon to Lee’s (KD4RE) house to see if I could help with antennas. He was in charge of both food and antennas, but had simulated some designs in the previous week, so I followed his drawings and put together wire and PVC spreaders for a 20 meter and 40 meter vertically polarized delta loop. In the past, we’ve had some issues with interstation interference, so the idea was to cross polarize the various antennas where possible. The 40m was used by the 40m SSB station and the 20m by the GOTA.

Oh noes. That was the antenna tree.

Antenna deployment was slowed by heavy rains on Friday. In areas near the park, roads flooded, rivers overflowed, and our simulated deployment came nearer and nearer to being an actual deployment. We got most of the antennas in place including a huge 40m moxon, but left the hex beam and spider beams just above ground level because we were worried about wind. Additionally, we were liberal in the use of plastic sheeting to supplement the weatherproofing of our tents, particularly the network operations tent, which already had equipment in it on Friday.

A LeeCAD rendering of the 20m delta loop.

The next morning was sunnier, but the fields (and our shoes) were saturated with water. The antennas went up, with extra care to secure ground guys to either very large stakes or other fixed objects that would hold in the muddy soil. By the start of the event, 14.00h, the four HF stations were ready to go. In addition, we had the GOTA, a VHF/UHF and a satellite station in the field. GOTA attendance was somewhat down due to weather, which cut down on foot traffic through the park. We did not succeed in the satellite contact; we heard the ISS APRS beacon, but no one was operating from the station. Otherwise, the timing of the couple of operational FM birds was not favorable. Almost all of the contacts made were HF, although we did get in a little 6m activity at the end.

Field Day was successful in a number of ways: as always, a large club turn out despite the weather. There were many new (to me) faces at this year’s event, so that bodes well for the general health of the club. At least one CW and one SSB station stayed on the air around the clock. Finally, the club maintained its tradition of gourmet food — amazing steak, pulled pork, chicken, beans, potato salad, hamburgers, hot dogs, eggs, sausages. No one went hungry and the calorie/QSO ratio remained strongly positive.

The girls on vacation. AI4SV/MM.

After FD, I drove up to Montauk, threw a rope in the trees and set up shop on an elevated porch with my FT817. I tested the set up in the Canada Day event on July 1st. In an about three hour period, I logged 51 QSOs, mostly CW, but seven were SSB. For provinces, I got ON, QC, MB, BC, SK, NL, NB, and NS. Since everyone can work everyone in the event, I also picked up a few stations from even further over the pole: Belarus, Ukraine, Czech Republic and Slovenia. A 5Ah battery lasted the whole operating period, as I was mostly S&P, although I did get a handful of replies to CQs.

Since then, I’ve operated sporadically, both CW and voice. I had forgotten how useful 40m is, since that band is next to useless at my QTH in Madagascar due both to noise and lack of close-in stations. In the last few nights, though, I’ve had very clear contacts to the west coast on 40m.



Two additional bands: 6m and 15m

The Madagascar equivalent of the FCC or OFCOM -- this is where radio licenses are issued. The office is about a km from my house.
The Madagascar equivalent of the FCC or OFCOM — this is where radio licenses are issued. The office is about a km from my house.

I am still operating when I can from my porch, using the FT817 and wire antennas; it is a modest operation, but I’ve managed over 200 contacts. By my reckoning, I’ve worked 45 DXCC entities, almost all on 10 and 20 meters. My prime times for operation are in the early morning before I go to work  and in the evening around dinner time. In the morning, 20m is usually open to North America, whereas the evening favors Europe on 10m. I’ve had only a few contacts to the East including Japan and New Zealand, so I have yet to find the optimal times and band to work those areas. Continue reading “Two additional bands: 6m and 15m”

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.

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.


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 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.


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.


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)