Hello. I am new to SDR listening and just purchased one of these magnetic loop antennas. I was planning on mounting it on the roof along with a discone for wideband listening/decoding. I understand these can be rotated but how much difference does that make? Is that primarily to reduce the noise and is more of a set and forget? I really don't want to get a rotator unless really needed. Would a simple 25' wire antenna in the attic be better?
rotator?
- Thread starter cw937
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ka3jjz
Wiki Admin Emeritus
It would be very helpful to know which loop you are going to use.
Loops are better fairly close to the ground - no more than a few meters (say 15 foot or so). This takes advantage of any ground wave pattern you wish to remove, which brings me to the rotator...
The loop's advantages lie in nulling out a source of interference or another station that might be on the same frequency, (when you are dealing with LW and MW). The noise reduction will work on HF, too, but because propagation changes somewhat when you move up the band (skywave tends to be more dominant), the nulling ability is lost. This is physics - nothing you can easily do about that. The rotator will make it easy to turn the loop in the desired direction. Usually the plane of the loop should point in a given direction (not broadside, like a dipole). Keep it as far away from the home and metallic objects as possible.
These are things you simply can't easily do with 25 foot of wire. Now if you had 2 or more lengths of wire outside, there is another solution, but it gets somewhat pricey for what you want to do.
Mike
Loops are better fairly close to the ground - no more than a few meters (say 15 foot or so). This takes advantage of any ground wave pattern you wish to remove, which brings me to the rotator...
The loop's advantages lie in nulling out a source of interference or another station that might be on the same frequency, (when you are dealing with LW and MW). The noise reduction will work on HF, too, but because propagation changes somewhat when you move up the band (skywave tends to be more dominant), the nulling ability is lost. This is physics - nothing you can easily do about that. The rotator will make it easy to turn the loop in the desired direction. Usually the plane of the loop should point in a given direction (not broadside, like a dipole). Keep it as far away from the home and metallic objects as possible.
These are things you simply can't easily do with 25 foot of wire. Now if you had 2 or more lengths of wire outside, there is another solution, but it gets somewhat pricey for what you want to do.
Mike
Thanks for the info. It is a MLA-30+. MLA-30 Plus Loop Antenna I'm surprised to hear it would be better lower than on the chimney which was my plan. Would there be a lot of difference? If I had no rotator and had to choose a direction I would think point it N,NW for general coverage?
ka3jjz
Wiki Admin Emeritus
HF doesn't necessarily work that way. It greatly depends on from where the desired signal is arriving - they don't always follow a straight line, but rather tend to take a route known as a Great Circle path. This can be thought of very roughly if you were to put your location on the top of a globe, and pull a string to your target. Mind you that HF tends to 'disperse' the greater the distance they travel, so it's never just one very narrow width - it's likely several degrees wide.
And as for height - yes it makes a difference. Too high, and you might receive more skywave propagation on the lower (LW and AM) frequencies making it more difficult for the loop to discriminate them
Mike
And as for height - yes it makes a difference. Too high, and you might receive more skywave propagation on the lower (LW and AM) frequencies making it more difficult for the loop to discriminate them
Mike
ka3jjz
Wiki Admin Emeritus
Remember too that you might need to turn the loop to avoid a noise source. Even though a loop is basically omni above about 2-3 Mhz or so, this alone is an important characteristic, especially if you're in an urban area....Mike
So it sounds like I should maybe just put it on a tripod or something as apposed to mounting it. I'm glad I asked. very new to this. Does the same concept go for longwire antennas? Meaning if I sloped it from the chimney down to my fence, would that be better or worse?
ka3jjz
Wiki Admin Emeritus
Far and away worse in terms of noise pickup, and without a second antenna for phasing (yes there are such units, not infringing on Star Trek copyrights, heh) nowhere near as flexible in terms of tuning out one signal to get another. However there's absolutely nothing to say that having a second antenna is a bad thing; if it's not coming in well on the loop, you have another option to try.
Being a bit more scientific about your wire antenna will help - there are lots of places you can go to read up on HF antennas. The ARRL and the Radio Society of Great Britain both have superb publications on this very topic, and this will also help...
wiki.radioreference.com
Mike
Being a bit more scientific about your wire antenna will help - there are lots of places you can go to read up on HF antennas. The ARRL and the Radio Society of Great Britain both have superb publications on this very topic, and this will also help...
HF Antennas - The RadioReference Wiki
Mike
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markclark
Member
cw937:
I use a Pixel loop with an RCA VH1226 rotator. I believe the rotator is also sold under other brand names. You can find a budget rotator on Amazon. The wind load on a 3 ft. or so loop is relatively small. Rotating a loop will markedly improve or null signals (and noise) from a given direction. I recommend you install a rotator with your loop antenna for best listening results.
Good luck!
I use a Pixel loop with an RCA VH1226 rotator. I believe the rotator is also sold under other brand names. You can find a budget rotator on Amazon. The wind load on a 3 ft. or so loop is relatively small. Rotating a loop will markedly improve or null signals (and noise) from a given direction. I recommend you install a rotator with your loop antenna for best listening results.
Good luck!
highwayman1224
Member
I have my loop on a tripod and it's great.
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