Thanks to the California QSO Party, I made more than 30 QSOs this weekend running < 5 Watts with Project TouCans: a Rockmite into a Tuna Topper, both mounted inside a pineapple can with a tuna can as a covering housing and antenna mount; the entire rig resides suspended at the feed point of a half wave dipole.
That’s a beautiful view with Mt. Diablo to the east. Also, a great QRP result in the CQP.
ReplyDeleteIt must be hard to really get the feed point high I would think, what with the weight of the radio/amp and the interface cable.
I think the feed point at the house is about 15 feet off the ground. Then, we've got this going for us:
ReplyDelete"For simplicity, first consider an antenna on the top of a hill with a constant slope downward. The general effect is to lower the effective elevation angle by an amount equal to the downslope of the hill. For example, if the downslope is −3° for a long distance away from the tower and the flat-ground peak elevation angle is 10° (due to the height of the antenna), then the net result will be 10° − 3° = 7° peak angle."
--from https://www.arrl.org/files/file/antplnr.pdf
The radio is also very, very light. The Rockmite itself weighs maybe two ounces. The tuna topper board is in the same boat weight-wise. The cans are also light. At one point, the Flying Rockmite was going up with 8 AA batteries attached. (See https://copaseticflow.blogspot.com/2023/09/the-month-rockmite-ran-around-naked-in.html )
Then, there's the beauty of butcher's twine, which is pretty cheap on Amazon, surprisingly strong—except when it isn't; pine sap is its chief nemesis—and hefty enough in a spool that it's easy to throw over a tree limb on POTAs—A stick placed in the spool's cardboard tube provides launching leverage.
The final piece of the equation which hasn't been an issue strength-wise—that I ever noticed—is using 12 gauge wire in the antenna. I've seen a lot of inferences that thicker wire is less desirable, but reading through the antenna lit, the wider the conductor the more forgiving the resonant bandwidth of the antenna. I personally noticed an increase in output power when I moved to the heavier gauge from 20 gauge. Whether that increase is a property of the reduced impedance on the real axis, or just that the Rockmite was particularly—and randomly—to benefit from the small change in feed point impedance, I don't know.
Finally, getting back to the angle of the hill thing, two more anecdote-ish notes. Dipoles on hills like to be lined up with the steepest gradient of the hill. Being cross-wise to the hill—especially on abrupt ridges—just confuses them. (I think it's because with respect to ground, being cross-wise to a ridge makes a V dipole.) More on that here: https://copaseticflow.blogspot.com/2023/02/rockmite-log-20230205-flyying-rockmite.html and more slope-of-the-hill-leaning-over-the-antenna-angle here https://copaseticflow.blogspot.com/2023/02/update-on-radio-mapping-baylor-peak.html
And then! What if the hill is a straight 20 meter-or-so drop within 20 meters of a 20 meter rig? Again, this was repeatable that evening, but who knows what other factors were involved. From the edge of a mesa in New Mexico, the 'flying' RockMite hit Costa Rica with the feed point eight inches off the ground. https://copaseticflow.blogspot.com/2023/04/playing-radios-at-night-twenties-and.html