RadCom April 2024, Vol. 100, No. 4

Technical I do a fair amount of HF portable operation from campsites, spanning from one to three nights per location over a one- to three-week road trip. Generally, I select an antenna not only for given bands, but also for the space available to me, the number of trees, the terrain around my site, and how long I expect to be at the location. Also, I keep playing with different antenna designs, which means I carry them all, making the minivan a bit more cramped. “But, I might need one of them”, I say as I dust off one of the V/UHF Yagi antennas. For some sites and lengths of stay, I may put up a 30ft (9.1m) telescopic fibreglass mast with a 40m off-centre-fed dipole. At other times, it maybe a ham-stick-like antenna that I put on top of my minivan, or throw a line to a tree. I might use a ground-mounted phased vertical antenna, a fan dipole, an off-centre-fed dipole, a linked dipole, a random wire, a V/UHF Yagi, a roll-up J-pole, in fact enough stuff to fill a couple of tote boxes and a kind of a golf bag just for antennas. And I sleep in the van too... Simplifying the problem A year ago, I began to think about simplifying what I carry with respect to providing me with reasonable adaptability. I started with a review of the items I rarely, or almost never, use; that is, things I could leave at home. Then I looked at what the antennas I use have in common. Pretty quickly, I saw the feed point as the item reproduced for almost every antenna I carry. I began sketching out what eventually became the ‘Porcupine’ antenna platform. I wanted something that could support as many dipole variations as possible, was waterproof, and was able to handle at least 100W. It must also be quick to change over to support different types of antennas, to work with wire, ham-stick type, and telescopic tube antennas, and which I could build using the few tools I have at home. Off to the hardware store I went, and the prototype was born (see Figure 1 ). Simple and easy to use, it worked well at the campsite, but it didn’t support all the different antennas I could use. Every antenna I use includes some type of balun or unun and/or an RF choke. These items tend to make a bit of a train hanging from a feed point. I decided I wanted to have space in the box for a removable T-240-43- sized toroid to reduce the length of the train. I wanted enough space to accommodate either a homemade unit, or one of my commercial units. I decided, as part of this project, to wind my own balun. This isn’t hard to do, although it helps to have three hands. Also, I found some of the commercial ones I have are not all they promise to be when tested with a vector network analyzer. Porcupine antenna accessory Waterproofing Since I live in the Pacific northwest of the United States on the western (rainy) side of the Cascade Mountains, the box had to be waterproof. I purchased a ready-made plastic box with an O-ring seal, and every fitting, screw, connector, etc used in construction is sealed on the inside with clear silicone sealant. The exposed UHF connectors on the outside are wrapped in ‘cling film’ when the coaxial cable is attached. Remember, this is a temporary installation. Connections The two important features of the box are the Porcupine’s ‘spines’ and ‘nose’ (see Figure 2 and Figure 3 ). The spines are sixteen stainless-steel M4 FIGURE 1: The prototype version of the Porcupine accessory, using an outdoor electrical enclosure and caulk. FIGURE 2: The Mk2 version. This lacked additional support for heavier telescopic tubes. FIGURE 3: The Mk4 version, now with additional support for heavier telescopic tubes using a PVC flange and bush. 74 April 2024