7187Re: shielded loop
- Feb 5, 2010Danny It seems you are determined to have a shielded loop. I would suggest you look at a magnetic loop. Do some googling, the available materials, your ability to fabricate come into the picture. I am sure gold might be best but not practical. Silver may be better than copper and so on. Better than what? Litz wire was mentioned. That is what I have in a hula hoop of PVC for a magnetic loop. I could have used copper pipe but this is lighter and works as well. Some make Shielded Loops from coaxial cable!
I think you got some good answers. The answer is best found in antenna books (ARRL books are good) and looking at other successful designs. The topic of antennas I maintain is a science mixed with a little art. Antenna design can go very far into theoretical and mathematics and very fancy spectrum analysis gear to test. At our level and the HF band we are interested it..... there is not much new. Not to say someone might no strike upon a new configuration or design or material no one ever tried before. So research the subject in some good ARRL books and steal.... look at other antennas.
I tend want to assure the results before putting huge effort into an antenna project. I have no desire to invent something new in the antenna World. Clearly there is some creativity in how you make it, which I enjoy. The real joy is making an antenna that works and gives you more gain but best of all is better SNR - Signal to Noise Ratio. It took me a long time to realize that is really the name of the game, SNR. Every antenna has limitations. I still say (sorry know this is a loop group but) the a random wire or variations of it of sufficient length is the "standard" I use. Clearly loops can do better in many areas because it is usually a tuned and directional device, which is also it's drawback.
I don't know what you have tried before but a well installed random wire usually gives good results. The problem is few people install a random wire properly (grounds, baluns). If you have the best random wire installation and it's noisy, than you need to look into getting rid of the noise.
Noise is a big problem for everyone: atmospheric conditions, sun spots and so on, area interference from other stations or bad power transformer and the last area, usually the worst is your home. It is a RFI factory. That is why an outdoor antenna (a reasonable distance from the home) is best (but not always possible). It does not do a lot of good to have the best antenna ever made inside or bolted to your house. Antennas are not magic but amplified magnetic loops (like the welbrook) is the way to go in my opinion for SWL.
Any loop in general has good noise rejection off the sides. I started off with simple unamplified passive resonate loops. They do wonders. You can make two and have one to pick up a signal and another to block interference in an direction, like a phased array antennas. I do this "phased array" with my two MW passive loops. Two loops are better than one.
AM and HF stations use phased arrays to transmit very spacific directional signals in one or more directions while being NULL in other directions. So good luck. George
--- In email@example.com, "dannibou" <dannibou@...> wrote:
> --- In firstname.lastname@example.org, "dannibou" <dannibou@> wrote:
> > Hi! On the topic of shielded loop, can anyone tell me if the metal for build a loop is important electrically speaking.
> Hi again. Thanks to those who replied to my question. But I did a mistake in that question. Replace "electrically" by RF. In fact, I want to build a shielded loop because the electric noise level here is strong. My question should have been: if the metal I use for a loop is the kind that attract a magnet, will it lower the RF signal or is it unimportant? I'll upload a photo of the loop in the evening.
> The good side of my wrong question is that I learned a lot of things from your answer that I didn't know. Thanks for your help.
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