Sensitivity is not always important. Small loops in general receive less noise and the real exercise is balancing the internal noise floor against the actual signal received. In some cases a loss up to 20 db can be acceptable the numbers are easy enough to run.
On 6/16/12 8:17 PM, Brian Miller wrote: > Hi Tim > > I also agree with the previous comments on this thread about detuning the > transmit antenna (or any other wires/cables that are resonant on 160M) and > isolating the coax feed line from the RX loop. > > It is also important to identify the direction of the main source of the > noise and orientate the loop accordingly so that is being properly nulled. I > use a small portable tuned loop to identify the direction of the noise.. > > Of course, if the noise is coming from the same direction as the DX then you > are not going to see much (or any ) improvement in the signal-to-noise > ratio. Also, if the noise sources are in multiple directions then it will > also be difficult to null the noise properly. I have found that small tuned > loops (with their bidirectional nulls) are often more effective in such a > situation. > > One of the problems with small tuned loops made from wire is their low > sensitivity. Rather than using a pre-amp you can boost the output by making > the loop larger (e.g., a circumference of 0.1 wavelength or even larger). > The larger loop maintains a directional pattern similar to the smaller one > but also exhibits a higher radiation radiation resistance and hence lower > losses. > > Good luck with the experiments and let us know how you get on. > > 73, Brian VK3MI ZL1AZE > >> From: [email protected] >> To: [email protected] >> Date: Sat, 16 Jun 2012 13:28:38 +0000 >> Subject: Topband: Receiving loops >> >> I want to try a new receiving antenna for the summer Stew Perry. Last >> winter was my first foray onto 160M and I really felt like an alligator. I >> could work everyone I could hear, with just 100W. I think that means I >> need a better receive antenna. If you look at my score in the winter Stew >> Perry I think I did great QSO-number wise, but my average distance was >> very poor, I'm guessing typical alligator. >> >> I have tried pennants and K9AY's over the winter with little success. >> Compared to my transmitting antenna (A "T" with a poor radial system) most >> signals were still better, S/N wise, on my transmitting antenna. I feel >> like I must've been doing something wrong. Still the fact that a few >> signals came in on the loop with by ear much better S/N, maybe I was on >> the right track and just didn't try hard enough. >> >> I will be trying a small tuned magnetic loop tonight (e.g. the last one at >> http://www.w8ji.com/magnetic_receiving_loops.htm with the 9:1 transformer) >> . And maybe a terminated beverage but I'm limited to about 150'... well >> maybe I could run something longer down the driveway as long as I clean it >> up before the sun comes up and the neighbors see. >> >> I was fairly impressed with small tuned magnetic loops when I was doing >> some BCB DX'ing several years ago. I wasn't comparing with beverages or >> anything. >> >> Tim N3QE >> _______________________________________________ >> UR RST IS ... ... ..9 QSB QSB - hw? BK > > _______________________________________________ > UR RST IS ... ... ..9 QSB QSB - hw? BK > _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
