homebrew magnetic loop antennas for 13-29.6MHz and 50MHz

20 - 10m
Since august 1998 I use a magnetic loop antenne in the AMA-3 style. The antenna is under the roof and mounted in horizontal polarisation. So you have an omnidirectional radiation pattern.  In a short resume I can say that such an antenna is more than a compromise. 144 DXCC on 10m (1999-2001) shows how it works. Its the only antenna witch covers 5 bands with a acceptable performance and TVI and BCI are nearly absent!!

The loop is made with 18mm copper tube with a diameter of 78cm. The capasitor is comercial by Annecke (11-110pF, 8,4KVss, here tuned at 28.5MHz) and allows tuning from 12MHz to 29,6MHz. The power rating is about 250-500W. To cover the complete 10m band, the antenna must be outside the attic. It is a bit of the frequency because of the very close surrounding. The tuning is made by a small 6VDC gear-motor (abt. 2000:1) and a small eletronic motor control.

6m
The loop is made with 18mm copper tube with a diameter of 45cm. The capasitor is homebrew, in a wide range tuneable and allows at minimum 100W. The SWR is <1,5 in a range of 200khz, so no remote tuning has to be done. The feeding system is very simple: just a SO-239 plug and a bit 1,5qmm copper wire.

Both antennas has a wave trap (1:1 balun) on the feed point.
For detailed picures, see the magnetic loop gallery.

Conclusion:

I made a lot of tests in our attic and there is everything different, i.e. a 40m wire-loop must be 37m... my VHF-UHF antennas gives me also very often some mysterys. So after several tests with indoor wires , the magnetic loop was the only antenna which covers some requirements. I have 5 bands, lower QRM than a wire, and it needs not much place. Of course this antenna is a compromise but it is doing his job! During better sunspot days i worked all around the world, even on 20m. In these days (late spring 2009) in hear lots of north and south America on all bands! Working these stations is much more difficult, because all others are stronger ;-) but last year I worked USA, Puerto Rico and Brasil on 10m!!
An other good example from today (6.6.2009) is my 6m QSO with CU3, sporadicE dobble hopp !!
If you are able to mount a magnetic loop in free surrounding, it will perform even better!!
I also tested a 1,4m square-style loop for 40m and 80m and there it is very noticable that the QRM is very low. I heard VK6 on 80m with RST419 these days (may 2009).