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Short Takes #10: Antennas, Antennas, Antennas!

By Dave Jensen, W7DGJ

Some old friends have asked me, those who are still at work, if I am enjoying retirement? I try not to rub it in, but sometimes I allude to the fact that it's like heaven. It's a place where I get to play with antennas all day long, and where I can be with my lovely wife, but still enjoy the most fun you can have in any one hobby! Living in Scottsdale, Arizona is wonderful. But having fun with ham gear anytime I want, now that is something I worked hard to achieve.

Antennas are almost a hobby niche in themselves, aren't they? Sometimes, I spend so much time fooling around with antennas that I don't get on the radio. The closest I've come to serious 'radio time' this week (the week before Hamvention) is putting an SWR meter up on a few new installations and then throwing out CQ's just to get signal reports.

I'm sure that there are others like me who enjoy thinking about what might resonate if you put RF to it. That was going through my mind recently when my wife's CPAP machine needed a new hose. For some reason, my wife refuses to throw anything out, so despite the fact that she's had a dozen new hoses provided to her by the doctor over the last few years, she's kept the old ones languishing in a drawer. I happened to look closely at one of them and thought to myself, "Wow, this thing could resonate if I put a signal to it." That's because the hose on these fancy CPAP machines isn't for air alone . . . it also brings humidity and warmth. In order to get that warmth, it has what looks like pure copper wire wrapped around the inside like a slinky.

I began playing with it to see just how long that wire might be inside, but there's no way to separate that copper wire from the flexible plastic tube that encloses it. But I began to think that if I used one of these CPAP hoses on each side of a center point, I might have something approximating a 10 meter dipole. The classic, cut-to-resonate dipole for 10 meters is about 16 and 1/2 ft; one of these hoses is about 6'6" long. So, I'd have a 10M dipole in only 13 feet, for a nice, "tight accommodations" antenna. While it's not a huge difference, there are lots of people with apartment patios or small yards who want such a thing!

I dug around in the ham junk boxes lying in my garage and came up with a 1:1 current balun that would make the ideal center point. I found some large Mueller 100% copper alligator clips, and attached them to the ends of the CPAP wire, put one hose on each side of the balun and went outside to see where I might install it to give it a test. There was a willing 25 ft. saguaro cactus outside of my wall and I began the (always fun, sarcasm intended) job of getting something up to the top of a very prickly and dangerous plant. As I've mentioned here before, this "Arizona Method" requires an old wrench and a parachute cord. Your job is to catch the top of the cactus -- a target zone of about 8-10 inches -- and to then get the wrench back on the other side (that's the tough part . . . my yard has a few tennis balls and a hammer around the top of other cacti, the result of situations where the prickers won and got to keep their prize.)

I had a couple of CamJam's with me (see photo at bottom of article) that made the job of tying off the dipole ends SO much easier. These are supplied by KF7P Metalwerks to the amateur radio community, and I've got to tell you, the usefulness of these gadgets can't be rated with anything other than an A+ in spades. I've got other antennas where I am always dealing with guy ropes flopping around. Since I've put a few CamJams in there are no issues remaining; one slight tug and the rope will not budge. They are time and hassle savers!

After installation, it turned out that I was off just a bit in my calculations and the antenna resonated with a 1.2 to 1 at 30 MHz. Well, that's not a hot frequency in my world. So now I have some fine tuning I can do. It was close enough that my Mercury AT immediately tuned it to 1.0 to 1 and I spent some time playing with the antenna, knowing that I made this wacky looking thing and that it would be nice to take to a park someday. Maybe for Field Day! (Side Notes: Thanks for the help Dave N4KZ in correcting a typo here. Also, I had some flack about using PVC coated wire, as evidentally some people believe it hurts radiation. I think that would be hard to measure, but it didn't appear to dampen my results! PVC does change the resonant frequency a tad however, according to what I've read.)

 

 

"Don't Buy Antennas, Build Them"

Each time I review a plug-n-play antenna of some kind, I get the usual comments and emails from people who say things like, "You paid how much for that antenna? I could build you the same thing for $5.00." Maybe that's an exaggeration, but the posts are still there for your reading enjoyment in the forums attached to my reviews. You'll find that these posters believe ready-made dipole antennas should not cost as much as they do. For example, I have the (well-received on eHam) Buckmaster 7-band OCF Dipole installed in my yard. I love that antenna, but the review was ripped to shreds by a few naysayers who felt they could build one for $20.  Of course, that's not fair to Buckmaster and it certainly isn't true.

As you now know from reading this issue of Short Takes, I build my own as well. But despite this (or maybe because of it) I'm the first one who recognizes a quality product when I see a dipole that is well made. And there are three of these that I've been playing with this week that I want to bring to your attention. Two of these wire antennas are for the QRP enthusiast and anyone who enjoys field operations and portable gear; the other is for the ham who has major QRO power behind his or her signal. Let's start with the QRP antennas.

Two Great Dipoles from N9SAB

Tim Ortiz (N9SAB) builds a really nice, inexpensive antenna for use by lower power rigs. i have two of them here, and I've operated on both. One of them is an end-fed longwire, with a removeable extension so that you can operate up to 80 meters. It matches well with rigs up to 25W on SSB (tested here on 10W CW). The other is an OCF Dipole, with a higher power handling capability. TIm makes both a 50W and a 100W version of the OCF.

Both antennas are designed for portable use, but I see them as perfectly workable, low power base station antennas. After all, what you want for a base station antenna is something well made, right? When you get these out of their provided drawstring bags, you'll see what I am saying. They are handsome and extremely well made. The matching unit for the longwire is a 9:1 (450 ohm) T106-2 Powdered Iron Toroid, with trifilar winding and schematics are provided. It is set into a PETG Carbon Fiber blend enclosure. Tim uses 22 AWG UL 1007 stranded wire which makes his antennas very light, flexible and easy to setup.

The longwire has an integrated element of 35.5 feet long, slightly longer than a quarter wave on 40M which allows operation on that band utilizing the tuner in your radio. In my case, the Xiegu G90 had it quickly down to a 1.5 to 1. The provided 80M extension is easy to attach and increases the overall length of the antenna to 71 feet, allowing operation on 80M as well as all other bands down to 6 (with your tuner). I found it nice to quickly drop the length back for operation 40M to 6M in a sloper configuration. Tim has a small grounding adaptor included with the antenna, and a bag to hold it all.

It's his OCF that I'd take with me on most trips (the 100W version would be left up at all times at my base station -- I'm reviewing the 50W version here). As I mentioned early in this article, I love the OCF design. This antenna is a 40M half-wave dipole fed 1/3 of the distance from the end. This raises the feedpoint impedance to approximately 200 ohms. To compensate, the antenna is then equipped with a 4:1 current balun embedded between the BNC female connector and the 22 AWG. The transformer uses two ferrite toroids (one for each element), with the result being a highly functional OCF dipole for use on 40 through 6M. If your tuner is anything like my G-90, you'll be able to effectively transmit on 40, 30, 20, 17, 15, 12, 10 and 6 meters. Of course, it's a "compromise antenna," but the compromise is minimal in comparison to the resulting ability to operate on many bands with something that fits into the palm of your hand. This antenna would be perfect for the guy hiking up for a SOTA activation, as long as that radio in the bag has a built-in tuner.

Both N9SAB antennas sell for $79.95 in his eBay storefront, linked above.

Pull out the Big Guns

With all the comments I had after my earlier review of the Buckmaster 7-Band OCF, I was delighted when I found a possible competitor to that antenna, at substantially less cost. I knew that Palomar Engineers produces very high quality antenna components, but I didn't realize that they were in the business of complete antenna systems until I started investigating other OCF antennas after my Buckmaster review. I am still working with this antenna, and will publish more about it in the future, but the initial impressions I have (from a quick test at sub-optimal positioning and height) are very positive. The Model # PAL-OCF 4010-5000 is a 5000W rated (PEP) antenna 64 feet long, operating from 40M to 6M. You'll find three power level selections for the Palomar Engineers OCF antennas at this link. This one reviewed costs about $220.00 from their website.

I have never seen a center impedance matching device with this build quality. If there's such a thing as an "overbuilt" qualification, this one earns it. This is a good and bad thing. It's very good when you consider the stress that an antenna is under in an environment like Arizona's desert. It's 115 degrees in the summer, and the black plastic junk that some baluns are made from is not appropriate. I don't know what the technical term is for the material used to produce this case, but I'd say it could take a bullet hit and survive.

It must weigh over 7 or 8 pounds, which is the only negative. Getting this big guy up into a tree (or my cactus) is a real bear. It's going to require a very specific kind of mounting scenario, where the support is something more than the branch of a tree. I've ordered an MFJ mast from DXE for this project and when I get it up about 32 feet or so, I'll let you know what kind of performance we get.

The Palomar Engineer OCF antennas appear to be at or better than the quality and performance of that Buckmaster I wrote about earlier. In fact, I would say that the build quality on this is superior to anything I've ever seen in a wire antenna. It's something beautiful to behold, that's for sure. Now, I'll finish a head-to-head test with this guy vs. the Buckmaster and come back to you with the details in a future column. 

73 for now, Dave

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Dave Jensen, W7DGJ

Dave Jensen, W7DGJ, was first licensed in 1966. Originally WN7VDY (and later WA7VDY), Dave operated on 40 and 80 meter CW with a shack that consisted primarily of Heathkit equipment. Dave loved radio so much he went off to college to study broadcasting and came out with a BS in Communications from Ohio University (Athens, OH). He worked his way through a number of audio electronics companies after graduation, including the professional microphone business for Audio-Technica.  He was later licensed as W7DGJ out of Scottsdale, Arizona, where he ran an executive recruitment practice (CareerTrax Inc.) for several decades. Jensen has published articles in magazines dealing with science and engineering. His column “Tooling Up” ran for 20 years in the website of the leading science journal, SCIENCE, and his column called “Managing Your Career” continues to be a popular read each month for the Pharmaceutical and Household Products industries in two journals published by Rodman Publishing.


Articles Written by Dave Jensen, W7DGJ

This page was last updated May 22, 2023 23:56