Re: [perseus_SDR] Wellbrook loop
- Il giorno 03/mar/2012, alle ore 21:28, Fabrizio Magrone ha scritto:I agree with Fabrizio.I have used ALA-1530 from many years (in a long period I had two of them). It's one of the better antenna at all for restricted space, indeed.I've only few square meters of space on the roof and there are some antennas: three ham vertical antennas, a Mini Whip (very good also) and a Wellbrook ALA 1530 with its rotator.For listening purpose I use mostly the last and the Mini Whip (except in VLF, where I use more often MW) with Perseus.Time ago I had a problem with one of my two ALA: Andy Ikin solved it very soon, with a good replacement, as he's a very kind manifacturer (I thanked and thank him very much).If I had more space probably I'd try also also other antennas, but surely ALA 1530 would be always there, in its rotator :-)73 de salvo IT9CLU (swl IT9-4639)
- Hi Werner,Many others on this Yahoo Group are more qualified to discuss the theory, but I'll comment from a "hands-on" DXer point of view.The reception pattern of a small loop is similar to a dipole antenna, as can be seen on this instructional page:http://www.ycars.org/EFRA/Module%20C/AntLoop.htm There are a few other useful web sites linked from this page, which go into greater discussion on small loops.I'll appreciate corrections if I am wrong, but it's my understanding that only a theoretical, infinitely small "point" antenna (isotropic antenna) is perfectly omni-directional (i.e., no polarization). Any antenna that has any length whatsoever, in any X-Y-Z plane, has some amount of directionality or polarization. It depends greatly on the received frequency too (the Wellbrook and Pixel loops are essentially omni-directional at mid and higher HF frequencies).When you turn a small loop horizontal, all you a really doing is orienting skyward the direction of greatest nulling. For most DXers there is no benefit to this, but I suppose there are situations where you may want to favor a groundwave signal constantly, and seek to reject interfering skywaves on the same frequency. Perhaps a radio station wanting to do off-air monitoring of their own signal would use a horizontal small loop to reduce night time, skywave interference.You asked about the strength of the polarization. To my way of thinking, this is another way of asking how many dB of nulling can be expected for a small loop antenna that is broadside to a signal. There are a number of factors to consider such as symmetry of the loop and the steadiness of the offending signal's arrival angle. In actual use of these small loop antennas on a rotor I've measured from 30 dB (common) to 50 dB (infrequent) nulls (on medium wave) when measured with the Perseus SDR's highly linear signal meter. If the loop can be tilted in elevation, it can be possible to null the interfering signal even further. That's why good MW receiving loops like the Radio Plus Quantum Loop (ferrite core) and the Kiwa Loop (air core) antennas can be tilted as well as turned.Guy AtkinsPuyallup, WA USA--- In perseus_SDR@yahoogroups.com, Werner Karn <werner.karn@...> wrote:
> Hi Guy and others,
> what is the reason for this effect ? ( polarisation ? ) and how strong is
> it approximately in average ?