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"His and Her"
Manpacks
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Featuring W2IK's New 2 Piece "Jiffy-Pole Antenna"
by Bob Hejl - W2IK all rights reserved
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This is an interesting package which incorporates all the radio equipment you'd need for an extended search and rescue mission. It's an updated version, for ham radio, of the military "man pack" which is used for field communications. The only difference is that it is very inexpensive to build. With my newly designed two-piece "Jiffy Pole" antenna you'll have extended range over any other walking whip antenna system. The battery pack, which acts as a counter weight to keep the pack in place, powers the HT radio in the pack for extended periods of comfortable operating. This is for serious search and rescue communications.
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Man Pack with "W2IK's Jiffy Pole" taken apart
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MAKING "W2IK's 2 PIECE JIFFY POLE"
with the "Super Flex" whip
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The first part in building the man pack system is to construct the two piece antenna system. First, obtain a 1/8 inch X 36 inch length of brass rod from a place such as "Lowes" or "Home Depot". This is a standard length that they sell. Take the rod and measure exactly 16 inches from one end and carefully bend it 90 degrees. Then bend it again at a point slightly LESS than 1/2 inch from the first bend. This will make the rod a "U" or hairpin shape with one side longer with the spacing between the rods LESS than 1/2 inch. The bottom of the "U" is the very bottom of the antenna. At a point about 9 inches from this bend, epoxy a non-conductive spacer between the rod lengths to hold them securely yet spaced evenly from each other. At the very top of the longer section, bend 1/4 inch of the tip back towards the other rod in a 90 degree angle. At the top pf this bend, straightly solder a 1 1/2 inch 1/4x20 brass screw with the threads pointing up. The slot on the screw head should nest with the bend in the brass rod. Make sure that this is a nice, snug, clean solder joint. Use plenty of solder to do this. Now take a 4 inch piece of thin wall (PVC 1120/SDR-13.5 PR.315 PSI) 1/2 inch PVC tubing. Placing a snug-fitting washer on the brass screw, insert and keep it in the pvc until the end of the threads just starts to stick out the end. Epoxy the screw and rod section so it makes a nice seal with the pvc WITHOUT getting any expoy in the threads and making sure the screw is vertical and centered in the pvc. After the expoy has set, turn the assembly up-side-down and heavily epoxy the underside of the rod/screw. (See picture below of finished screw top)
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After the epoxy has completely set, measure 1 1/2 inches from the bottom of the rod (where the "U" bend is) and solder a 4 foot length of either RG-8X or RG-58 cable with the shield soldered to the SHORTEST length of rod and the center conductor soldered to the longest run (the run with the brass screw assembly). See above pix
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Above: Hairpin rod assembly with cable, spacer and top pvc/threaded screw assembly
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"Super Flex" Whip Assembly
Putting the lower hairpin section aside for a while, now obtain a short telescoping fishing pole from a sporting goods store such as "Academy". The one I purchased was a 10 ft. Fiberglass Crappie Pole by "Tomahawk" item number APP-10, 0040704 from Academy for $ 7.99. It has no guides on it except the single one at the tip. Unscrew the bottom of the rod and remove the two top sections. These are the thinner sections that you will use to make your whip. Cut the top 3 inches from the thinnest section, as the wire you will be installing will not snake up this far. Expoy the hole (at the tip) that you've made by making this trim. Now cut off, from the bottom of the second (lower) section so that this section, when extended with the thinnest (top) section, is 38 inches. Remove the top section from the lower section by retracting it and add a thin film of epoxy to the lower, outer area of the top section and reinsert it and extend the section. After the epoxy has set, this will now hold the two sections firmly together. Now cut a 36 inch piece of 22 ga, stranded, insulated wire and insert it into the whip assembly leaving 1/2 inch exposed at the end At the end, strip the insulation off 1/8 inch and solder it to the rim of a brass 1/4-20 nut. snake the remaining wire completely into the whip so the nut rests flush at the edge of the fiberglass section. At the bottom of the whip, lightly sand about 2 inches so the epoxy you will be applying will adhere. Now get a 3 inch piece of 1/2 inch CPVC 4120 100psi - Tubing from the hardware store. This is much narrower than the 1/2 inch thin wall pvc tubing and will easily slip into it. Force the nut/whip assembly into this tubing until the nut is flush with one edge. (see picture) With the rod as straight as possible, and as firmly pressing on the nut, drip quick set epoxy into the void at the top of this piece until it fills. (see picture) Fill any small voids around the nut edge as it seats with the cpvc, keeping the epoxy away from the threads.This finishes the top "Super Flex" whip.
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LEFT: The whip section(cream and black) should screw deep into the lower "hairpin" pvc/screw assembly(white)
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After all expoyed pieces have completely set, slowly screw the "super flex whip" into the lower hairpin assembly. Make it snug, but do not over tighten. The depth of the mating makes for stronger support. You will probably have to screw/unscrew it a few times so the threads will "relax" and assembly each time will be easier. Slide the coax cable through a pvc coupler with a 22 inch piece of the thin wall pvc so it covers the hairpin assembly and fits into the short pvc that you installed around the screw assembly. DO NOT GLUE IT. Now attach a connector to the other end of your coax. In a clear area , position the antenna on a non-conductor such as a wooden chair and measure the SWR on 147 mhz. You will see that you need to make some adjustments. Because this design uses a brass rod and the space between the hairpin is unique, the construction measurements are NOT the same as if you made a "J Pole" using twin lead. (I've found that twin lead in this case is too fragile for rugged hiking and backpacking with the antenna hitting tree limbs, etc) Using an antenna analyzer slowly slide up/down the placement of the coax connections to the hairpin, you'll soon get an adeaquate match. Do not try to be too precise as "body coupling" when the antenna is near you will throw off the swr a bit. When you are happy with the swr, then you can cement the pvc hairpin cover together. Cut a small 1/4 inch wide slot at the bottom of the pvc and dress the coax through it before cementing on a bottom cap. (Above and Right: picture of the finished hairpin assembly mounted on pack) The two piece "W2IK JIFFY POLE" antenna is now complete.
Assembly Of The "Man Pack"
The gear I chose to create the "Man Pack" was based upon it's shape. I purchased a "Thermo Bak 3 L" (Made by "Camel Bak" in various colors such as green # 20131) which is in reality a back-pack style water storage pack that contains a bladder for storing water while in the field. When you remove the bladder you are left with a deep pocketed pack that nicely fits a 3x6x2.5 inch, 12volt, 7ah GEL battery in the bottom. Fusing the line, I added a short power cable with a mating plug that allows me to use it with my ICOM T2H (Sport) two-meter HT. The cost of this HT about $ 100. It has simple operating features and high power output making it ideal for this type of service. To make this HT work with an external power source, since it has no external power jack, I mounted a jack, regulator and diode in an empty AA battery case. This means that all I have to do is snap the modified battery case in place of the AA pack and plug in the power cable from the gel battery.
Since most in the field communications will take place on one frequency, whether it be to go to a repeater or simplex, I chose to have the HT stored in the pack right above the gel battery and locked on frequency. This keeps it off my belt and out of harm's way. The lower section of the "Jiffy Pole" is secured to several rings on the pack with plastic wire ties (As seen in the picture at the top of the webpage). The coax cable slips into a pre-made hole at the base of the pack and plugs into the HT with the excess coax coiled up in the pack. I use a speaker mic which clips on a front strap. This allows me full use of both hands. The weight distribution is such that it has little stress on the body when you wear the pack for extended periods of time. I am sure that there are other backpacks that could be used, however, this pack seems made-like-a-glove for this use and it is well constructed. All you need to do is turn on the HT, screw in the "Super Flex" antenna top and you are set to go for several days of search and rescue. I have even incorporated a small "wall-wart" charger so when I'm not using the man pack I can easily charge the gel battery without removing it from the pack. There is also some small additional room in the pack for pens/pad/and even power bars. When not in use, you can unscrew the "Super Flex" whip and slide it into the pack. I am quite happy with the outcome of my creation and I hope you will be able to copy it's design, especially my unique antenna system which is low cost yet durable.
Bob Hejl - W2IK
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