Innovative Thinking from W4ED

ABSTRACT: This entry is a common sense approach to an operating lap-top surface for use on the trail. It is useful for operators sitting on a chair, camp stool, sitting on the ground, or sprawled out prone on a blanket. It assembles in the field and requires very little metal work with a hacksaw and file. One side benefit is having two C-clamps on the trail -- you never know. Another benefit: the portfolio is a natural place to store log sheets and a pencil.

The parts list includes: one inexpensive 9" X 12" plastic covered folding portfolio (these are often promotional giveaways at seminars); one 1/2" aluminum angle approximately 18" long spar (which needs some metal work), and two 1" C-clamps.

I use 1" C-clamps but smaller would suffice. The 1/2" aluminum I purchased was much longer than needed, so it was cut to 18." Even if it is purchased to length, the ends should be rounded and deburred to minimize any snagging or sharp corners.

Field assembly is a simple matter of opening the portfolio then placing the aluminum spar just under the far edge. The aluminum spar is oriented so that one surface is flat against the bottom of the portfolio and the other surface is snug to the far edge and pointing upward. This spar gives lateral strength to the open portfolio. Then the first C-clamp is tightened, clamping the spar to the portfolio, and is positioned a few inches in from the left side. This assumes the rig is on the left and key is on the right. Then the second C-clamp is tightened on the right side near the edge. It clamps onto the back lip of a TFR key, as well as the portfolio and spar. This means a lightweight TFR key can be held in place, at a location of your choice on the far edge. This arrangement is shown in the accompanying figure. It's also in the photo, where I operated just off the Appalachian Trail, Georgia. The first C-clamp could secure a TFR rig as well.

TFR DUAL BAND WIRE VERTICAL

ABSTRACT: This entry is a lightweight dual band wire vertical antenna for 20 and 40 meters designed to be carried in a backpack with quick setup and take down by one person. One halyard lofted over a tall tree limb is the main support. It is field tuned by adjusting the height above ground, and doesn't require a tuner. The height above ground, ie., tuning, is adjusted by manipulating the halyard.

The vertical radiator is strung from the halyard downwards to the feedpoint. There it is soldered to 6-inches of flexible stranded insulated No. 18 wire. The No. 18 wire goes into one position of the 2-wire male Molex connector. The other wire in the Molex connector goes to the slanting horizontal radial.

The slanted horizontal radial is the only counterpoise and goes down from the feedpoint to an approximate 10-foot length of braided builders twine. The far end of the twine is either tied to another tree or staked into the ground with a "U" pin. Likewise, the opposite side of the feedpoint is secured by builders twine and is either tied off to another tree at the far end or staked with a second "U" pin.

If operating on 40 meters, then the 50 ohm coax is connected directly to the feedpoint. One end of the coax has the mating connector to the Molex already mentioned. If operating on 20 meters, then insert the 300 ohm twin lead Q-section between the feedpoint and the 50 ohm coax Molex connector. The Q-section has corresponding mating Molex connectors for this insertion. The opposite end of the coax needs a connector that matches your rig.

PERFORMANCE: I have used this antenna four times so far, it does work. The initial use was for design confirmation and involved setup, wire trimming, making a few contacts, then rolling it back up for storage. The second outing was to the Appalachian Trail (AT), where the accompanying photos were taken, approximately 3,300 feet. On that trip, I quickly made two 40 meter contacts on one watt (WV/599; IL/559).

The third use was for the NEQRP Field Day, in my back yard. With a power of 950 milliwatts, I made 8 contacts ranging from Alabama to New York during a few good hours, and worked around one nasty thunderstorm. The last time was the recent setup and test prior to the QRP ARCI Fall QSO Party.

The attached elevation plot shows performance (gain) in dBi on a slice along the azimuth having greatest gain, for both bands. The 20 meter gain was 6.9 dBi while the 40 meter gain was 4.6 dBi. SWR was 1.38:1 on 40 meters and 1.06:1 on 20 meters. The azimuth patterns are nearly circular. The 20 meter azimuth pattern had a 2.2 dB front to back ratio in the direction away from the radial. This simulation included a rocky soil ground, 300 ohm Q-section on 20 meters, and No. 22 copper wires. I made several iterations on both 20 and 40 meters, back and forth until the readings were achieved.

APPROACH: This antenna was modeled on a Windows-based NEC-2 PC program for low SWR at 50 ohms on both bands and maximum low angle radiation on 20 meters. The antenna was modeled with a 1/4 wave 300 ohm Q-section in line on 20 meters and without it on 40 meters. It was then built and tested in my back yard.

For the NEQRP Afield operation and QRP ARCI Fall QSO Party setup I left the 20 meter Q-section in line while on 40 meters, and SWR was below 1.6:1. However, NEC-2 modeling does not support this, so best to allow for its removal while on 40 meters. My guess is the nearby trees were having their way with the antenna feedpoint reactance.

One way to describe this vertical is as an off center fed dipole. That is an accurate statement for 40 meters. A more accurate description for 20 meters operation is as a 5/8 wave vertical, hence some low angle gain.

PARTS LIST:

(1) 38.5 ft., No. 22 copper wire (vertical radiator)

(1) 29.3 ft., No. 22 copper wire (horizontal radial)

(1) ~13.8 ft., 300 ohm twin lead (trim to 1/4 wave at 14.06 MHz)

(1) 20 ft., or more RG-58U (goes from feedpoint to your rig)

(2) 6 inch, insulated No. 18 stranded copper wire

(2) 2 pin male/female pair Molex connectors (RS No. 274-222)

(2) 9 inch aluminum "U" pins (like tent stakes) available from REI

(1) approximately 50 feet of braided builders twin (ala Walmart)

(1) small roll freezer tape

(1) small bright fence flag tape (see last paragraph)

(1) Cuban hand reel available from Brass-Pro Shop

CONSTRUCTION: The most challenging mechanical portion of this design is at the feedpoint. The current construction at the feedpoint is an improvement over the original. The male Molex shroud has a tab on each side. These tabs have a hole. On the ground radial wire side, feed the No. 18 wire through the tab hole. On the other side, tie the support twine into the tab hole. The accompanying figure shows this arrangement. Also, take care to seat the Molex connector pin going to No. 18 and vertical radiator. It holds up the bottom half.

I have found that crimping the inner Molex connector tab around the bare stranded No. 18 wire, then crimping the outer tab to the insulation, then soldering in such a way as to press the Molex connector into the hot/soft insulation results in a physically stronger linear member. It won't compress much, maybe 1/16 inch, but just enough to see insulation molding itself around the outer tab.

Keep in mind the twin lead Q-section length is a function of the twin lead propagation factor. Best to start long then cut to frequency, rather than take my length. There are several sources on methods of how to do this. Most deal with a half wave transmission line. You can use one of these methods then cut the 1/2 wave twin lead in half, "and then there were two." Or just trim a 1/4 wave section as if it were a 1/2 wave at 28.12 MHz.

The rest of the construction is straight forward and left to the reader.

SET-UP: To make for a quick set-up, the wires were rolled into a Cuban hand reel at the last take-down. The hand reel is available from Bass-Pro Shops at less than $2. An empty 6" diameter spool will work in place of the hand reel, but not as well. The secret is to keep the copper wires rolled as one long line. If the twine is left on the Molex feedpoint side tab, it can be rolled up with the wire but it begs to tangle with the wire.

First, the halyard (fishing line and golf ball) is lofted or cast over the desired limb and back down to earth. Detach the golf ball and stow it. Tie the fishing line to the top end of the vertical radiator, which was the last thing to be rolled onto the Cuban reel, then crank the halyard in via the fishing rod, thereby unrolling and raising the vertical radiator. Once the feedpoint Molex connector comes off the hand reel and is about four feet high, tie twine into the non-radial side Molex tab, if it's not already there. Walk this twine to its full extension and U-pin it to the ground. Lay out the 50 ohm coax from the feedpoint back to the rig. Lay the coax (and/or Q-section) perpendicular to the horizontal radial, as best as possible. Very carefully connect the female coax Molex to the male feedpoint Molex. Raise the feedpoint to about 8 feet via the fishing rod, then start 40 meter tuning. Doubt there would be any metal objects around, but if so, keep the Q-section away from them. At this point, on my last three set-ups, the vertical did not require further tuning

TAKE DOWN: Disconnect the feedline from the feedpoint. Release the far end of the horizontal radial twine. Tape the twine end to the Cuban reel. Roll up the twine and wire all the way to the feedpoint. Tape the male Molex connector against the Cuban reel so it won't flop around. Either untie the twine from the Molex tab or roll the twine up with the vertical radiator in the next step. If the twine was left on the Molex, then release its far end. Adjust the drag to minimum on the fishing reel or open its bail, then roll up the vertical radiator (and twine if so chosen) onto the Cuban reel. When the fishing line reaches the Cuban reel, tape the wire end to the Cuban reel and disconnect the fishing line. This wire is the starting point for a future set-up.

This leaves the antenna wound onto the Cuban reel so it comes off easily for set-up. If your backpack is cramped for space, then the coax and twin lead can be rolled on top of the wire antenna. The rest is left to the reader. This takes less time to do, less than to read, and a lot less time than to write about. Of course, getting the golf ball over the right limb, and down again can test one's resolve.

DISADVANTAGES: This antenna needs a tall tree to act as a sky hook. There are lots of tall pines here in Georgia, especially on the AT. This also means there needs to be a way to get the halyard up there in the first place. I use a collapsible fishing rod and reel with a golf ball as the "lure." The cast I make is half toss, half cast. It has worked well for me, but then I've done a lot of fishing, too. Been into more trees than fish, when fish'n, as I recall. Also the horizontal members can be low enough to present problems for people and critters. I tie on bright fence flag tape in case the horizontal wire becomes a people hazard. Critters beware.