Pop-Up Vertical 2.0
Craig LaBarge, WB3GCK
I like to do some QRP operating while out on camping trips in my 1999 Coleman Sante Fe pop-up camper. The original "Pop-up Vertical" antenna that I built back in 1999 served me reliably through 10 seasons of camping. The main drawback with the original antenna was the lack of coverage for 20 meters and the fact that I had to exit the camper on cold nights to change coil taps when I needed to change bands. However, it did what I designed it to do and it did that well.
A few years ago, though, I decided I wanted to try a different approach. Some of the design goals were the same as that for the original antenna:
I also had some additional goals for the new antenna:
After doing some research, I stumbled across a webpage by Rick McKee KC8AON describing his "Untenna." Basically, this antenna is a 23-foot wire fed through a 4:1 un-un transformer. Rick reported encouraging results from 40-10 meters with this configuration. KC8AON also had good results using a 50-foot radiator. I also found numerous references to a similar arrangement using a 43-foot radiator for coverage on bands below 40 meters. The un-un configuration was definitely worth a try.
The 23-foot length that Rick used was nearly identical to the 24-foot radiator I had been using with my old Pop-up Vertical. So I figured it would be pretty simple to swap out the loading coil from my old antenna with a homebrewed un-un (and it was). Since the camper was stowed away for the winter, I simulated this configuration on my pickup truck during the November 2009 Polar Bear Moolight Madness Event. For this test, I used a 26-foot radiator and an LDG 4:1 balun. I fed it with 18-feet of RG-8x coax and tuned it up with an LDG Z-817 autotuner. It loaded up from 40-10 meters and performance on 40, 30 and 20 meters was encouraging. The next step was to build one for the camper.
I followed KC8AON's instructions for the un-un, except that I used a larger T200-2 toroid with 19 bifilar turns of #20 solid hook-up wire. (My un-un is very similar to the one described by IW7EHC on his website, so you can look there for details.) The un-un was mounted in a 4" x 3" x 1.6" plastic enclosure. I use a small bungee cord to help secure it during operation. From the un-un, I ran a 10-foot length of RG-8x coax to the tuner located inside the camper. I re-used the 24-foot radiator and the ground clamp from the old antenna. For the ground connection, I just clamp onto the frame of the camper. No other counterpoise wires are used.
Initially, I just re-used the supporting structure from the old antenna. It's basically two 4-foot sections of 1-inch PVC pipe, a small stand on the bottom and a support for the 20-foot Black Widow fishing pole. I attached it to the camper with nylon cable ties and use a couple of wood blocks cut from a 2x4 to space it away from the camper a bit. My current configuration is much simpler. I simply use a 31-foot Jackite pole instead. I secure it to the camper with 3 or 4 large velcro straps, as shown in the pictures. My set up time is now well under 5 minutes and I don't have as much stuff to take along on camping trips. Also, now that I'm using the Jackite pole, I'm able to use a slightly longer radiator. The vertical wire is now approximately 27 feet in length. This length isn't much of a compromise on 40 meters.
Now, I have to be honest here. This type of antenna where coax is basically "force-fed" by a tuner has never really appealed to me. However, this thing really does work. During my first camping trip of 2010, I confirmed that I was able to load it up with the Z-817 on all bands from 40-10 meters. I was easily able to make QRP contacts with it. In fact, during a late afternoon, a station in the Netherlands responded to my CQs on 30 meters. So, this thing must be making some noise. It also works great when using my little YouKits HB-1B transceiver with an Elecraft T1 tuner. I doubt that this antenna is as efficient as its predecessor, however, the convenience of covering 40-10 meters without having to change coil taps is a worthwhile trade-off for me.
I'm already working on plans to press the Un-Un into service in a couple of additional configurations. One being a ground-mounted vertical and the other being a "stationary mobile" set up on my truck. More on those later...
So, as before... If you hear WB3GCK/P sometime, give me a call. I'll probably be working you with the Pop-up Vertical 2.0.-----
Un-Un Winding on T200-2 core
Inside the Un-Un
WB3GCK/P in Operation