Experience with mag loops?
Wondering what the experience is with mag loops in the PRA?
I'm always looking into making improvements in my stealth antenna. I've tried all kind of long wire installations, flat top dipoles, and inverted vees.
I've always been suspect of any HF antenna as compact as a mag loop. I also have heard that the matching tuner on a mag loop is the expensive part of a mag loop designed to handle any appreciable amount of power (beyond QRP) because of High Voltage tunable capacitors. What is the experience of PRA members who may have employed a mag loop capable of 100W? I would hate to invest in an antenna that does not surpass the performance of my sloping inverted vee. But a mag loop might open up 80M operation..question is..how much performance? An incandescent light bulb might equal the performance for a lot less money!
I have used the MFJ magnetic loop that can handle 100 Watts and it works fine RF-wise, but it doesn't cover 80 meters.
I have had issues with the remote tuning of the capacitor on the MFJ unit, but once tuned it does quite well.
They actually do work despite their relatively small size, but my experience is the MFJ unit doesn't do any better than a half-wave dipole as far as RF performance goes. So, if you are looking for something that performs better than your wire antennas, then I would be hesitant to say that a mag loop will do any better for you. But, I have only used the MFJ for 100 Watt mag loop operation. MFJ uses aluminum for the loop, and a copper loop may perform better, so there might be other brands out there that would do better.
Some general observations of the mag loop:
They can pick up less noise than a traditional dipole or vertical antenna, so they will seem quiet, but don't mistake that for it being a dud antenna.
They have a very narrow tuning range, so if you move up and down in frequency on a band (or change bands), then you will always be re-tuning the antenna. This is what most people find to be an operational disadvantage.
As I mentioned above, they are typically quieter than other antennas, so if you have a high HF noise level at your QTH (like most of us in a typical neighborhood) then a magnetic loop can help reduce that noise level. Plus, the loop is somewhat directional, so you can reduce a specific noise source to some degree by turning the antenna until the noise is at a minimum.
They are small, relatively speaking, so for space restricted lots, they can be a decent alternative. An 80 meter loop does start to get pretty big, but it still doesn't require nearly the space that a half-wave dipole requires. And, since it doesn't necessarily look like an antenna that people recognize, you can tell your neighbors it is a piece of art that you are putting in the backyard, hi.
A vertically mounted loop can be just a few feet off the ground and perform well, so no climbing on roofs or up trees required.
There are plenty of online articles for building your own mag loop, so you could possibly save some $$ by rolling your own. You are correct, the capacitor is often the biggest expense. If you want to be able to remotely tune the antenna from inside the shack, then a vacuum capacitor is commonly employed, but those can often cost hundreds of dollars and then requires a motor with reduction gearing to drive the capacitor shaft, so it can get somewhat involved construction-wise and end up being pricey.
As a side note, for QRP use away from the shack, mag loops can be very nice. I can put up an AlexLoop quickly and easily, and it doesn't take me trying to find trees or other supports for a wire antenna. My whole setup is contained within a small area, and the loop works well on 40 through 10 meters. And, the AlexLoop (and other models like it) break down into a small bag that can be easily transported.
Hope that helps a little,
73 - Gary, WB5PJB