Receiving antennas are about directivity, not sensitivity. That is the best way to reduce "noise" although a very small antenna can change the signal to noise ratio without being directional.
Sent from my iPad On Jun 17, 2012, at 11:16, W2XJ <[email protected]> wrote: > 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 _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
