Continuing to catch up on past due blog posts, today we arrive at the Super Antenna MP1. Many operators want the convenience of an end fed half wave antenna, in a rapid deployment package like the MP1 . Unfortunately, the MP1 is a quarter wave vertical, without transformer, requiring quarter wave radials. You’ve seen on the channel how we have made the MP1 into a balanced antenna. We used two of them on the hot and cold sides at the antenna feed point. This allowed us to deploy configurations like horizontal dipole, or lazy L. Neither of those configurations require radials or counterpoise wires.
Now what if you could just stick the mp1 in the ground, connect your coax to your radio without needing any radials? Seems like it would be incredibly interesting!
Actually it’s incredibly simple to do, but not without losing a bit of efficiency. If you’re not trying to dominate the contest, limiting your Communications to regional or intermediate range, the setup can actually be quite effective.
All we need is a single length of coax cable the length of the lowest band we plan to operate on. Generally I’m using RG-316 but any coax cable can be used. I use rg316 because it’s lightweight and relatively lossless on HF, when using short lengths.
I didn’t have a long enough coax cable for 60 m, so I used a 10 meter length of coax cable, which basically gives us a quarter wavelength on 40 meters. A bit of efficiency is given up with the shorter “counterpoise”, but we’re just doing this for the sake of the experiment. In practice a longer length of coax cable would be used, one matching a quarter wavelength on 60 m.
Next we’re going to need a 1:1 choke balun. The crazy thing about the balun is, we’re not going to put it at the feed point of the antenna. The choke balun will be placed at the end of the coax cable, just before our radio. Placing the choke balun at the “wrong end” of our coax, makes the coax part of the antenna. This effectively uses the coax shield, as the cold side of the antenna. Next we place a small jumper between the radio and the choke balun, to finish up this installation.
The final step is adjusting the slider on the Super Antenna MP1 to dial in the SWR, for our chosen frequency.
This “trick” will work with any unbalanced antenna, but it isn’t as effective is having quarter wavelength or half wavelength counterpoise or radial wires on the cold side of your antenna. One interesting project for the channel might be converting the MP1 into a half wave end fed, or even building a quarter wave compatible transformer to test.
So why do we do this at all? Well, while in Lapland earlier this week, my travel partner tripped and stumbled over my counterpoise wires, bringing the entire antenna system down. A quarter wavelength on 20, 17, 10m isn’t that bad. When we’re talking about 40 meters, 60 m, 80 meters … it becomes relatively easy to get all tangled up in all those wires. To alleviate this problem we sacrifice a bit of efficiency replacing the counterpoints wires with a single quarter wavelength coax and balun.
If you’re interested in this antenna, make sure to check out the videos I’ve done on it previously.