What’s so great about a J-pole?

Building a roll-up J-pole antenna with ladder line.

Building a roll-up J-pole antenna with ladder line.

Our club hosted a workshop this past weekend to teach folks how to build a “roll-up” style J-pole antenna for handheld radios.  Our workshops are typically sparsely attended affairs, but somehow we received more than 20 pre-registrations for this antenna workshop. I didn’t know quite a few of them, as they are either very new hams or not club members.

I was surprised at the level of enthusiasm for what I consider to be a handy, but ultimately boring antenna. I have one of the dual-band Arrow J-poles for 2m and 70cm. It’s a rugged antenna, can handle nearly legal-limit power and costs less than $40. Arrow even makes a club project pack for $300, than contains enough parts to build 10 of these suckers.

There’s not much that can be said about the J-pole. It’s an omnidirectional antenna — actually a variation of the dipole, with a single half-wave radiator and a quarter wave tuning stub. They are easy to build if you have a spare piece of ladder line and some coax. Any ham should be able to construct one without much fuss, particularly those Amateur Extras and Generals. Plans for the J-pole abound, and the antenna itself was even lampooned in the April issue of QST this year, in what ultimately became a functional design known as the “Q-Pole.”

As antennas go, the J-pole has no gain over a dipole. It’s functional for hitting the local repeaters and for some simplex work.

Anyway, I shot some images for the club website of these new hams having a good bit of fun on a beautiful Saturday morning out in the wilds of Calhoun County. They will be able to take their new antennas and do some public service work, or stash it in their go-bags.

A new antenna for 6 meters

The Par Electronics "Stressed Moxon" mounted at 20 feet.

The Par Electronics “Stressed Moxon” mounted at 20 feet.

I’ve been looking for a 6-meter solution for a while, and I finally decided to get the lightweight “stressed Moxon” antenna by Par Electronics out of North Carolina.

The antenna arrived this week and I set out to construct a mast for it. I looked at getting a push-up aluminum mast or a similar solution, but didn’t want to pay the premium price for it. I finally decided to make my own mast from PVC pipe, based on a design by N1RIK for the Moxon at his QTH.

I started with two 10-foot sections of PVC, one 2-inches and the other 1-1/2 inches. I inserted the smaller diameter pipe a bit more than a foot into the other and used some hefty bolts to join the pieces together at the overlap. If I want to lower the mast or take it apart, I just need to pull the bolts out.

I mounted the antenna itself on a smaller piece of PVC, and secured it to the top of the mast with some wood screws. The whole mast was then lashed up to the back deck of my house. Obviously, I’ll be rotating it by hand. It’s not pretty, and it may not be well-constructed, but it seems to work fine for the moment. Once the 6m season dries up, I intend to take it down anyway.

Total cost of the mast? Less than $20.

As for the Moxon itself, the verdict is still out. We had what looked to be a nice opening last night and all I could hear were some fading CW signals around 50.100. Saturday afternoon I received a DXmaps.com alert regarding an opening to the southwest. I aimed the beam and listened but only heard faint voices slightly above the SSB calling frequency.

I should note that I don’t have enough coax on-hand to run the antenna into my FT-847 yet. All my experimentation has involved me standing on the back deck with the FT-817.

When I first put the Moxon up I wanted to check my SWR, so I connected my wattmeter and keyed up some AM carriers across the band. SWR seemed to be flat. I started calling CQ at 5 watts on 50.125 and someone came back to me immediately with an AL7 prefix, easily S9. Wow! I had to have heard that call wrong.

Nope, it was an Alaska prefix alright, but the guy was literally right down the road, 1.5 miles from my QTH. Apparently he monitors 50.125 because he mentioned I broke his squelch. Not exactly a DX contact, but nice to meet another ham in the vicinity.

I did another test this afternoon and spoke with my pal Todd, KN4QD, about 20 miles away.  We both reported S1 signal reports.

The HVAC antenna?

HVAC Antenna (3)I was working some JT9 the other night, and typically at the end of a QSO, the other station will mention their power level or the type of antenna in use.

I was a little surprised when during a QSO with W0OHU, he reported “2W HVAC” … what the heck kind of antenna is that? So I checked his QRZ page and it turns out he’s literally using the HVAC ducts of his home as an antenna, at QRP levels no less.

I was amazed at his description of the arrangement (from QRZ.com):

My current HF antenna is the HVAC (furnace/AC) ducts in the ceiling of our home. I use a MFJ-969 tuner with a short piece of RG-6, with the center connected to the ceiling register cover screw (the shield is not connected to anything). The register is in the center of a 30 foot run of the HVAC (furnace/AC) duct. (It works GREAT on 30m thru 6m running 1-9 watts)

If it works it works.

New antenna project?

I missed out on all the 6-meter action this summer because my dipole is pretty deaf on that band. I managed to check into a 6-meter net hosted from Lexington one evening, but even that was barely copyable. Consequently, that’s the only time I’ve heard anything on the Magic Band.

I considered buying a cheap 6M yagi and mounting it on a push-up pole attached to the rear deck of the house. After exploring other options, I think I’ll try building a Moxon.  From what I can gather, it’s a simple directional antenna, with a driven element and reflector, and can be made of lightweight wire. I figure I could mount this on a lightweight pole and rotate it by hand as needed.

With any antenna, it’s all about measurements. Here’s the Moxon for 6 meters, centered on the SSB calling frequency of 50.125. The design software is available here.

Screen Shot 2013-02-18 at 4.08.55 PM

I may use another DX Engineering wire antenna kit for this. A few weeks back I used one of these kits to build my Field Day antenna. The kit was missing some hardware. I just bought what I needed from a local home improvement store.

Last week the folks at DX Engineering e-mailed me for feedback on their product. I gave it a glowing review, but mentioned some hardware was missing. To my surprise, they sent me another one. Good folks up there at DX Engineering!

QRP Saturday, Part 3

I haven’t actually written parts 1 and 2 in a “QRP Saturday” series, but I might point to this post and this post as evidence of my recent weekend exploits 🙂

I was up early this past Saturday and decided I would take down the Buckmaster OCF dipole and do several things: One, check the condition of the antenna, coax, fittings and ropes, as the antenna has been hanging for nearly a year now; two, get the dipole up another 10-12 feet; and three, while the Buckmaster was on the ground, string up the home-brew TV twin-lead antenna and see how it loaded up on bands beyond 20 and 40 meters.

I lowered the Buckmaster and everything appeared to be in good shape. The coax connecter had a little play so I snugged it back up. The RF choke was looking a bit sloppy, so I worked it back into a nice circular shape. Ropes all looked good.

I decided I would toss a line over the next big limb on the tree so I could hoist the OCF up another 10+ feet. Using a partially-filled water bottle as a weight on the end of a length of thin nylon cord, I tried several times to sling the cord up over the limb. My trajectory was good, but I didn’t have the height. I tried to conjure up all my masculine energy and explode with one giant heave that would enable the line to coast up and over the limb on a true course.

The unintended effects of this burly endeavor were two-fold: One, my weighted line shanked wildly to the left, as my clumsy release was way too late. Two, as I torqued my body counter-clockwise to generate the needed thrust, I managed to over-rotate and began losing my balance. My left foot remained planted and suddenly supinated, turning inward and immediately sending a hot, throbbing pain into my ankle. The momentum continued carrying me around until I landed with a heavy thump sideways into dead leaves, moist dirt and what was certainly dog poo.

I managed to pull myself back up to a vertical position and assess the damage. Mostly, my pride was wounded, but my ankle hurt like hell too. I wondered if the neighbors on either side of me had noticed the stunt. I was determined to get the line up in the tree though, so I persisted. An hour later, I hadn’t made any progress and gave up.

I did hoist up the home-brew antenna and connected it to the FT-817 for a fine hour and a half of sunny operating on the back deck. The twin-lead antenna tunes to a flat SWR from 40M to 10M. I wasn’t as lucky on 6M, as the 817 was showing 2-3 “bars” of SWR even after a successful tune cycle. I suspect it would work, albeit in a compromised fashion. I didn’t have my meter out there with me, so I don’t know exactly how bad the SWR really is on 6.

There were several nice QSO parties going on, so I plugged in the Heil Traveler and went to work, first making a SSB contact on 20 meters with PI4DX out of the Netherlands. Anytime I make a contact with this little radio, I’m impressed. But I’m ASTOUNDED when my signal makes it across the pond!

I tuned around 20 meters a bit and managed to grab three more stations, two from the Vermont QSO Party and one from Minnesota. I tried 15 meters and picked up another nice Minnesota station. The final “test” of the day remained on 10 meters. The 10-10 International Net was holding a contest and WA7NB was booming out of Arizona. It took me a few tries, but I finally made contact. He had a perfect copy on my convoluted call sign too.

I spent the rest of the evening with my swollen ankle on ice, wrapped in a compression bandage. Fortunately, by Sunday I was up and walking around normally and it looks like there was no serious damage.

A messy affair: First home-brew antenna

It's not pretty, and I don't even know if it works yet...

It’s not pretty, and I don’t even know if it works yet…

I’ve wanted to build a ladder-line dipole for a while now. Last summer during field day, my partner Steve constructed a brilliant one for operating on 15 meters and he gave me a spool of 450Ω ladder line to play with. I was browsing on DX Engineering the other day and saw a hardware kit for building dipoles. I remembered Steve’s ladder line, and decided to order the kit in hopes of cobbling together a nice antenna for SPAR Winter Field Day coming up this Saturday.

The kit arrived Monday, along with an LDG 4:1 voltage balun for connecting the ladder line to the antenna tuner. I noticed two problems: My roll of ladder line was too wide for the dipole “T” which was apparently designed for something much narrower. Not really a big deal, but annoying.

Problem two manifested itself later when I started assembling the centerpiece and realized the included nuts were the wrong gauge and they only supplied three of them, instead of the 8 listed on the parts sheet. Rather than send the kit back to DX Engineering, I just bought the parts I needed from a local home improvement store.

I sought narrower ladder line locally, and arrived at this stuff, sold at Radio Shack of all places: 300Ω TV twin lead. Not really ladder line, but it’s low-loss balanced line and many hams seem to like it, evidenced by the numerous reviews on eHam for it. I bought a 100-foot roll, and enough 18-gauge spooled wire to make a dipole for 40 meters and on up.

Once I arrived home I set out to strip back the covering and foam insulation to get at the twin wires. I found the process much more difficult than I expected. Fortunately I have a technique now: Split the strip down the middle 2-3 inches with a very sharp knife and spread the wires apart. Carefully cut some of the plastic around the wire, but don’t cut too deeply or else you’ll cut the copper wire itself. Just score it. You can then give the scored portion a twist and the plastic will break. Pull upwards and the foam and outer plastic will slip off the copper wire. I don’t know if that’s the right way to do it, but it worked for me.

Anyway, I assembled this thing and I’m looking forward to seeing if it works at all on field day this weekend. If it fails, I still have the vertical…