30 meter full wavelength loop, diamond configuration,
This antenna is an easy one day construction project. It was made out of common number 12 stranded electrical wire. The side and top attachment points are made by removing two inches of insulation and wrapping and soldiering in short lengths of wire to create small loops. UV resistant non-electrical dacron rope should be used for the support line and side pullout lines. The bottom insulator was made from a peice of scrap Corion counter top about 3 by 5 inches in size. Two U-bolts fasten it to the tower leg and two 3/4″ stainless bolts are mounted on the corners to attach the antenna and feed line. Trimming the antenna to resonance was done at the bottom.
Start with the ARRL Antenna Handbook formula of 1032/Mhz to determine the total length. I ended up pruning about a foot off of each side to achieve resonance at 10.125Mhz. Since the 10Mhz band is limited to 100 watts, I used 72 ohm RG59 for the matching section. Make sure you take into account the velocity factor of the coax when cutting it to length. One method is to place a 100 ohm resistor at the end and use an antenna analyzer designed for 50 ohms to measure for zero reactance (and SWR) while trimming the section to the correct length.
The results are shown above. The numbers at the right represent where the cursor was when I shot the picture. At 10.125Mhz, the SWR is 1.08 to 1, R is 49 ohms and the return loss is better than -20DB over the entire band. The purple line represents reactance.
Placing a current balun at the the feed point would be a good idea. Number 77 material cores would make an effective and simple balun. When I got these results, I decided not to even bother with a balun.
Within a couple of hours of putting up the antenna I had made five DX QSO’s. It has performed well ever since. The antenna is not overly directional probably due to the wire sections all being 45 degrees with respect to ground.
These are the EZ-Nec plots calculated over earth as I have the antenna mounted.