Paul, A full sized 160 loop is not easy to set up since it needs to be around 500+ feet in circumference (1005 / 1.9 = 528 feet). This would make a square about 130 feet on a side.
After comparing a nearly full size, low height (30 foot apex) 160 meter inverted vee to a very low (10 to 30 foot) "L," the "L" was good enough that it worked for NVIS operation. It is directly connected to a multiband 80-6 meter ground mounted vertical but has quite a few radials up to 100 feet long and in the clear. If you use a dipole that is much smaller than 75% or so from full size, even with open wire line you can expect some substantial losses in the tuner. For example, using smaller than 180 feet for a 160 meter dipole can be lossy. It might be better to use linear loading or lumped inductances in the antenna. There are some hams giving out misinformation on low dipoles for NVIS operation, particularly on the NVIS yahoogroup. They believe that low dipoles only a few feet above the ground will give you a better S/N ratio and will actually work better for NVIS. I have done experiments with 80 meter inverted vee dipoles at 12 feet apex and 35 feet apex and the higher dipole is consistently superior than the lower dipole with just about any measurement you want to use, received signal strength, S/N ratio, and for sure, transmitted signal strength. The higher your horizontal antenna can be and still be below 1/4 wavelength, the stronger your NVIS signal. This means that you would have to exceed 60+ feet to be "too high" on 80 meters. Double that for 160 meters and half it for 40 meters. Needless to say, many of us have NVIS dipoles on the low bands without even trying:) 73, Rick, KV9U Paul L Schmidt, K9PS wrote: >Follow-up -- forgot 160m antennas. While a full-sized dipole or inverted >vee is nice for NVIS, there are options for smaller lots. > >A full-size dipole is in the ballpark of 250 feet total length, but a >full-size full-wave loop is only 60 feet or so on a side. Feed it >either in the middle of one side or at a corner. It's fairly close >to 50 ohm impedance, and you might even be able to get by without an >antenna tuner if you restrict your frequency coverage (1.8 to 2.0 MHz >is a 10% change in frequency!) and tune the antenna carefully. > >A shorter inverted vee will also work well on 160 -- the trick here is >to *NOT* try to use coax cable for the feedline. With an antenna that's >only half-size, the feedpoint impedance will have a low resistive >component but will have a lot of reactance -- meaning the VSWR on the >line will be terrible. Feeding with coax will result in all your >power being consumed in feedline losses. To get around that, the >two common tricks are to use the feedline as part of the radiator >(short the inner and outer conductors together at the antenna tuner, >and connect them to the antenna tuner long-wire output, feeding it >against ground). The other (and, in my book, preferred) solution is >to put up whatever size of dipole or inverted vee you can, and feed >it with ladder line. Either trick requires a tuner that will handle >160 meters, though. > > > >
