I'll certainly second David's, G3UNA, comments about using a wire for transmitting.
Loops can be very effective for receiving though, as you noted. Any decent receiver (like the K2) has plenty of excess gain to make up for the losses in the loop itself, and they do tend to pick up less noise. With a receiving antenna, signal-to-noise ratio is everything while in a transmitting antenna efficiency becomes very important. You'll likely see more articles about small transmitting loops during the next sunspot peak when extreme low power will "work the world" and the very poor efficiency of a small loop is not so apparent. If you have access to the attic space in your building you might consider a single wire or doublet directly under the roofing material if it's not a metal roof. You can fabricate open wire line with some nominal sized wire and makeshift spacers. The spacing isn't important nor does it have to be entirely consistent. Such feeders can pass through tiny holes in most ceilings no larger than a small nail and which are easily patched when you leave. A bit of "spackle" or even the apartment dweller's friend (tooth paste) will plug the little holes when you're done. Depending upon the composition of those bricks (some clay has much more metal ore in it than others), you may not see as much attenuation as you expect if you're limited to a wire inside your unit. You wrote: "A big plus is being able to match the antenna directly bypassing the KAT2 for higher efficiency. My built-in K2 tuner is more efficient than my MFJ tuner even though the MFJ has some usefulness for use with balanced lines and built-in dummy load." I wouldn't assume that is true unless you are talking about transmission line losses between the loop and the K2. You don't mention how far apart they are, but indoors it's usually a very short distance. In either case you are resonating the system with lumped values of inductance or capacitance. Whether they are at the antenna or at the rig in the KAT2 should make no difference except, as you noted, it's much easier to tune a high-Q antenna at the rig. If your MFJ tuner is one of their most common 300 watt (or lower) units, it's a T-network. While they can be very good matching networks, a T-network is notoriously inefficient when matching to a very low impedance load like a small loop, so I wouldn't expect it to do as well as the L-network in your KAT2. Looking at some scenarios in an on-line T-network simulator (http://www.ve3sqb.com/hamaerials/w9cf/), an antenna presenting a non-reactive feed point impedance to the T-network of 100 ohms at 7 MHz will see 0.1 dB loss while an antenna presenting a non-reactive impedance to the tuner of 0.5 ohms (not unusual for a small loop) at 7 MHz will show a loss of over 5 dB. Like the small transmitting loop, those loses are resistive losses in the inductor in the tuner and go up as the inductance required goes up at lower frequencies. The losses just about double, for example, on 80 meters. The bottom line is to get as much wire out there as possible to raise the impedance at the feed point. That reduces circulating currents which are the greatest source of loss, whether they are in the antenna as in a small loop, in the a transmission line with high SWR, or in the matching network, either at the antenna or at the rig. Ron AC7AC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
