RadCom April 2024, Vol. 100, No. 4

April 2024 75 Technical x 70mm screws to support radials or counterpoises. The screws are long enough to allow for doubling up the wires, but I only use sixteen in the field. I used hex nuts to secure the wires, but some may want to use wing nuts instead. How long do I make my ground radials? I decided to make each of them a little over 2m long to form, roughly, a circle of diameter 4m. This seems to work adequately for 7MHz and higher, and fits in the space I generally have available at a typical state campsite (see Figure 4 ). I often sleep in my minivan, and use the tent space for my radial area when going with a ground-level vertical antenna. If elevating the vertical antenna, you will need a set counterpoises that are cut and tuned to each band. I have a linked counterpoise set to make this easier for me. The Porcupine’s ‘nose’ is an M10 x 70mm nut that you would normally use with whips. The nose accommodates my telescopic anten-nas, HF loading coil, and ham sticks. There is a large washer under the nose (see Figure 2) to help spread out the stress from mild antenna wobble. Additionally, I use ring terminals at the end of any random wire, end-fed half-wave antenna, or wire vertical antenna, with an M10 short bolt to affix the antenna to the platform. Wind Surrounding the nose is a PVC flange and bushing (see Figure 3). I use the Porcupine with my homemade 5.23m vertical aluminium telescopic antenna. When I mount this antenna, I screw it in to the platform, and then slide a 1m section of PVC pipe over the antenna and push it into the bushing. This helps support the antenna, and reduces ‘wobble stress’ on the box. I have a guy ring near the top of the antenna to add ropes for additional stability. I find that a length of less than 4.3m doesn’t require guy lines when the wind is light. To increase the stability of the platform for ground-level vertical antennas, I secure the Porcupine to the ground using thick tent stakes or weights, depending on the situation. In Figure 4 and Figure 5 , the Porcupine is mounted on an aluminium plate with key rings to hold the tent stakes. I have also mounted the Porcupine on an old plastic cutting board, and I have a 61cm-square piece of wood that accepts the unit. The wood base has holes for the tent stakes, and four tie-down points for the antenna. The larger surface of the wood board is handy, using weights when stakes can’t be used. In use Can you use the Porcupine for a raised horizontal dipole? Yes! I can release J1 and J2 from Bar B and D and attach J1 to J5 ( Figure 6 ) and the spines become the tie points for the left and right legs of the dipole (it can support a fan dipole too). An eyelet on the box makes it easy to hoist the Porcupine to the desired height. Can the Porcupine be mounted on a mast? Yes! You just need to add a mounting plate to the back; there are screw holes already available. How about an elevated vertical wire dipole? It can handle this, but the box will need to be mounted on a mast, and remember that the coaxial cable has to run perpendicular to the antenna for a short length. For a ground-mounted quarter-wave vertical fan dipole, you could place the box at the bottom of a mast, remove J1 and J2 from Bar B and D (Figure 6), attach J1 to J5, and use the Bar B-D spines for radials. At the top of the mast, you can mount a 2m to 5m PVC pipe to serve as the attachment points for each of the four vertical elements that connect to the spines on Bar A. The Porcupine could also support an elevated quarter-wave vertical antenna with a counterpoise, if you build a mounting plate for it to sit on a tripod, which isn’t hard. However, I haven’t done this yet. I have used the Porcupine antenna platform for over a year now, and I am pleased with it. For example, having a pair of Porcupines enables me to create a phased vertical array, which is a treat when camping. I have also made a third Porcupine to test out new modifications and additions. However, I have not yet reached the state of ‘one Porcupine fits all’, but I am getting there. David A. Okrent, W7DAO dokrent@usa.net FIGURE 4: The radial field without a vertical element fitted. FIGURE 5: A Porcupine with a 40m home-made telescopic whip, showing the extra piece of PVC pipe for additional support. FIGURE 6: Inside of the Mk4 version. The 1:1 balun can be replaced as needed.