VHF PLUS: A VHFer’s Holiday Gift List… An Antenna Project for 1296 MHz

vhf plus

BY TRENT FLEMING, * N4DTF

AVHFer ’ s Holiday GiftList Plus … An Antenna Projectfor 1296MHz

The year draws to a close, and I would like to wish all of you a very Merry Christmas, Happy Hanukkah, Happy New Year’s, and any other holidays you observe. My best to you for the coming year as well. It continues to be my pleasure to curate this column. Please continue to participate through sending activity reports, project updates, comments, or critiques on my columns, and suggestions for future columns.

This month is one of my favorite issues, the Technology Special issue. So, I thought I’d offer some comments (and maybe some Christmas wishlist suggestions for you) about handy tools or components that I have found useful. After a particularly helpful presentation at the Huntsville Hamfest in 2021, I resolved to focus on learning to use my NanoVNA in as many situations as possible. This includes standing wave ratio (SWR) measurements, calculations involving failures in cabling, and testing antennas that you are designing and modeling. I also found that the Pelican 1040 Microcase is a good fit for my NanoVNA and accessories.

My Fluke 17B+ digital multimeter is never far from my hand when I’m working on a project. The ability to measure a wide range of voltages, plus capacitance, resistance, and even diode quality means I can get a lot done with a single device. At the same time, my old Radio Shack analog VOM remains handy, as a swinging needle sometimes provides a better indication of activity than digits on a screen. Just a couple of things to remind you that the right tool can go a long way in making a project or repair job easier.

In August 2022, I wrote about the bands above 1 GHz, particularly mentioning that many newer rigs, including the very popular IC-9700, include 1.2 GHz as a standard feature. The 1.2GHz band (or 23-centimeter band if you prefer) is a great starting point to learn about the microwave portion of the spectrum. One major advantage is that antenna size goes down as frequency goes up ... so antenna construction and placement are easier than ever. I reached out to “Mr. Gigahertz” himself, Paul Wade, W1GHZ, for permission to reprint his article on building a simple 1296-MHz antenna to get you started (see sidebar).

Paul cautions that, “you should warn them that it will take a better antenna and good coax to work DX. ” However, this will certainly get you started. As with any of the higher bands, you should also find a buddy to work with, because you don’t want to get a new band on the air and then have no one to contact. Please let me know if you try this project, and how it worked for you. My thanks to W1GHZ for his willingness to share his ideas and expertise with us.

Photo A. A tropospheric duct opened over the Gulf states in early October, producing excellentpropagation on 2 meters.

On the Air

This month, we do have some activity reports for 6 meters and higher bands, including trans-equatorial propagation (TEP) openings, and some Gulf Coast tropospheric ducting. 2 2-Meter Tropo

On Saturday morning, October 15th , our friend David Thier, WA3GWK, was operating in EM60 and made the fol-

lowing contacts (PhotoA): KB5WB (EM02), KC5AD (EM40), K5LLL (EM10), WD5DJT (EM12), K5HCS (EM20), W5FLY (EL49), WB5HIL (EM43), W5EME (EM32), K5CNU (EM30).

From EM82, Greg, N3BYR, reports the following activity that same morning: Bands and path were great to the south this morning from EM82. ManagedseveraldailycontactsintoFloridawithgreat enhancement(mostwere20overthataretypicallyat5x3ish on 432 and 222 MHz). Also managed 303 miles on SSB on 1296.100MHzthismorning, alsoonasmall14-elementlooper Yagi running on 15 watts. Finally, beginning Monday, October 10th , we saw several days of TEP activity from the GulfCoast and the Caribbean into South America. A few stations across the mid-South, including Steve, W4DTA, linked to the TEP via tropo or Sporadic-E (Es) and also worked South American stations, including HC5VF on 50.115-MHz single-sideband(SSB).

As always, I welcome your reports of operating activity That’s it for this month. See you next year!

Quick and Cheap Omni Antenna for 1296 MHz

BY PAUL WADE,

* W1GHZ

Recently, I was browsing through the latest IEEE Antennas and Propagation magazine, in which they publish papers without enough divergences, curls, or triple integrals for the regular Transactions. In one article on crossed dipole antennas1 , I came across a sketch of an antenna simple enough that it could be easily built. Details were limited, since it was taken from another paper2 in a journal to which I don’t have access, but I could build one and try it. I left the magazine on my bench, open to that page, and it occasionally re-emerged as a reminder until I finally decided to build one.

The antenna, shown in the sketch in Figure 1, has two crossed dipoles of unequal length. The longer one, shown in blue, is specified as ~0.527-wavelength long, while the shorter one, shown in red, is ~0.42-wavelength long. They are fed by coax, with a 1⁄4-wavelength balun shown in green. The idea is that the longer dipole has an inductive reactance, while the shorter one has a capacitive reactance to compensate. The antenna is claimed to radiate circular polarization in the boresight direction.

The sketch in the article has dimensions for 1.7 GHz and uses 0.086-inch semirigid coax. I scaled the dimensions to 1296 MHz and found a piece of 0.141inch semi-rigid coax with an SMA connector on one end. The wire size was the first spool I found on the workbench, and the whole thing was soldered together in a few minutes, resulting in the precision assembly shown in Figure 2.

I then plugged the SMA connector into my miniVNA Tiny <miniradiosolutions. com> to sweep the return loss. With the initial dimensions, best return loss was at 1.14 GHz, so I pruned the dipoles proportionally to move it up to 1296 MHz. As can be seen in Figure 3, I trimmed a bit too much, so it ended up tuned to 1340 MHz, but the return loss is still a very good 22 dB at 1296 MHz. I couldn’t find my tool for putting stuff back on, so I figured this Figure 1. Crossed Dipole Antenna

is good enough. The dimensions for 1296MHz are 55 millimeters for each side of the long dipole, 45 millimeters for each side of the short dipole, and 57.5 millimeters for the length of the balun — but leave a little extra on the dipoles for trimming. So how does it work? A quick test with both dipoles horizontal shows that the radiation favors the longer dipole, and the polarization is mostly linear and horizontal. However, radiation in the boresight direction, along the coax axis, has less variation with polarization, and may be Figure 2. 1296 MHz by W1GHZ

more circular. Better evaluation will require an antenna range better than my shack.

But whether this is a great antenna or not, it is really simple to build, costs nothing, and is handy for a test source for local beacon or whatever you fancy. And it can be scaled to whatever frequency you might need.

References: 1. Son Xuat Ta, Imko Park, and Richard W. Ziolkowski, “Crossed Dipole Antennas, A Review, ” IEEE Antennas & Propagation magazine, October 2015, pp. 107-122 (Fig. 9). 2. B. Y. Toh, R. Cahill, and V.F. Fusco, “Understanding and Measuring Circular Polarization, ” IEEETrans. Educ., Aug. 2003, pp. 313-318.