ridgescan
Member
Glad you are allowing it-I am very interested in seeing this.
Indoor Shortwave Antenna
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ka3jjz
Wiki Admin Emeritus
Yup, that will work too. Go for it...Mike
ka3jjz
Wiki Admin Emeritus
Since we're talking about loops, let's throw this article from our wiki out there and see what develops...
Loops - The RadioReference Wiki
Is your design already here, perhaps? Mike
Loops - The RadioReference Wiki
Is your design already here, perhaps? Mike
Mike and others:
There's nothing new about my loop design. My original post about them is merely stating that I believe that if one must resort to an indoor antenna, the loop is probably the best and least expensive solution.
It's late, so I'll post some pics and commentary on this subject tomorrow. Basically, I'm just going to provide some construction details and some tips demonstrating an inexpensive and easily constructed antenna.
later...
There's nothing new about my loop design. My original post about them is merely stating that I believe that if one must resort to an indoor antenna, the loop is probably the best and least expensive solution.
It's late, so I'll post some pics and commentary on this subject tomorrow. Basically, I'm just going to provide some construction details and some tips demonstrating an inexpensive and easily constructed antenna.
later...
13 to 30 Mhz receiving loop
First, lets get some disclaimers out of the way...
(1) No indoor antenna will work as well as one outdoors.
(2) An indoor loop antenna will not work miracles if there is a lot of "noise" in the home... digital or otherwise. It only makes it possible to have some sort of radio listening hobby... to do the best you can (inexpensively) with the loops ability to null noise.
(3) You possibly can do better with more elaborate and expensive schemes such as electronic phasing with utilizing multiple antennas. I'm just showing a low cost-low, low effort solution.
(4) Some apartments that are surrounded by other rooms, walls and tenants around them are nearly "rf proof" at hf. You're just about out of luck in some situations unless you have access to a balcony or such.
O.K., with that out of the way...
Pictures show my "13 mhz to 30mhz" receiving loop. You can't reasonably cover the entire SW spectrum with one loop efficiently, so for now , we'll just deal with this freq range. This loop is based on a childs' hula-hoop roughly 20 inches in diameter. I like to strip off all the plastic tape stuff that makes the hoop attractive to the kids. I usually use copper foil tape as the main conductor of the loop. I run the tape on the inside of the hoop to make attaching wires easier. A wide conductor is known to be more efficient at carrying rf than a small wire. You can use aluminum tape if you can't get copper, and you can solder to it.
The inner loop is made from #14 or #12 solid conductor house wiring. The diameter is about 7 inches. You can see that is self supported and attached to a two-terminal block mounted on the base plastic housing. It is not connected in any way to the main loop. The size of the inner loop will change a couple factors. A small loop will make for sharper tuning, a larger loop will make for broader tuning. You can make the tuning too sharp, and sigs will suffer, and also tuning on a sig will be too difficult. If you go too large on the inner loop, tuning will be too broad, sigs will suffer, and tuning range of the loop will decrease. Everything with loop antennas is a "balancing act", and you have to find the balance by some experimentation. If you find that my choice of a 7 inch loop doesn't suit you, feel free to experiment.
The only real expense of the loop will be the air-variable tuning capacitor. Fortunately, I had a nice 100pf tuner cap with steatite low-loss insulators. This makes for lower loss at the higher SW freqs. You can use a cap with phenolic insulators with only a slight loss in efficiency. Use what you can afford or have already. The capacitor simply is wired to the ends of the copper loop as can be seen in the pic. I used extension cord wire to connect between the cap and the coil.
The cap mounts on to the plastic base housing and I drilled a couple holes for the cap wiring to be brought out to the copper. You may notice that I made an extension of sorts for the tuning knob. It's very possible that you may experience the "hand-capacitance" effect. In other words, you will change the resonant frequency of the loop by placing your hand on the tuning knob. When that happens, you will change the "peak" of the sig you are tuning. You will hear the change in reciever signal as you do this. Sometimes I use the barrel of a plastic ink pen to slide on the shaft of the tuning cap so that I don't have to deal with the hand-effect.
If you look at the pic of the inner base housing, you can see the tuning cap, and also the method used to firmly attach the loop to the housing... ty-wraps.
Lastly, I'll direct your attention to the feedline from the loop to the radio. If you'll look close, I'm using "zip cord". This is a balanced feed system. I like to use the loops in a balanced configuation because they'll have a better null for noise. I have modified my Yaesu FRG-100 receiver to have a true balanced input as well as the traditional 50 ohm coaxial input. You can use coax for the loop output, but you should use some sort of balun to keep rf off the shield of the coax since that reduces loop performance. You could use a simple toroid to wind a few turns of the coax feedline through. Place the toroid close to the output of the pickup loop, and attach the other end of the coax to your receiver.
Using the loop is very simple. You just tune for maximum signal... the loop has a sharp peak, and you'll have to pay attention to receiver noise. You will have to re-tune the loop, of course, with even minor moves in frequency. This is the price to be paid for noise rejection and good signals from a very small antenna. I've been amazed at what I'm able to hear indoors with such a small antenna. Rotating the loop does a very good job in nulling noise while still providing a good signal for the receiver.
First, lets get some disclaimers out of the way...
(1) No indoor antenna will work as well as one outdoors.
(2) An indoor loop antenna will not work miracles if there is a lot of "noise" in the home... digital or otherwise. It only makes it possible to have some sort of radio listening hobby... to do the best you can (inexpensively) with the loops ability to null noise.
(3) You possibly can do better with more elaborate and expensive schemes such as electronic phasing with utilizing multiple antennas. I'm just showing a low cost-low, low effort solution.
(4) Some apartments that are surrounded by other rooms, walls and tenants around them are nearly "rf proof" at hf. You're just about out of luck in some situations unless you have access to a balcony or such.
O.K., with that out of the way...
Pictures show my "13 mhz to 30mhz" receiving loop. You can't reasonably cover the entire SW spectrum with one loop efficiently, so for now , we'll just deal with this freq range. This loop is based on a childs' hula-hoop roughly 20 inches in diameter. I like to strip off all the plastic tape stuff that makes the hoop attractive to the kids. I usually use copper foil tape as the main conductor of the loop. I run the tape on the inside of the hoop to make attaching wires easier. A wide conductor is known to be more efficient at carrying rf than a small wire. You can use aluminum tape if you can't get copper, and you can solder to it.
The inner loop is made from #14 or #12 solid conductor house wiring. The diameter is about 7 inches. You can see that is self supported and attached to a two-terminal block mounted on the base plastic housing. It is not connected in any way to the main loop. The size of the inner loop will change a couple factors. A small loop will make for sharper tuning, a larger loop will make for broader tuning. You can make the tuning too sharp, and sigs will suffer, and also tuning on a sig will be too difficult. If you go too large on the inner loop, tuning will be too broad, sigs will suffer, and tuning range of the loop will decrease. Everything with loop antennas is a "balancing act", and you have to find the balance by some experimentation. If you find that my choice of a 7 inch loop doesn't suit you, feel free to experiment.
The only real expense of the loop will be the air-variable tuning capacitor. Fortunately, I had a nice 100pf tuner cap with steatite low-loss insulators. This makes for lower loss at the higher SW freqs. You can use a cap with phenolic insulators with only a slight loss in efficiency. Use what you can afford or have already. The capacitor simply is wired to the ends of the copper loop as can be seen in the pic. I used extension cord wire to connect between the cap and the coil.
The cap mounts on to the plastic base housing and I drilled a couple holes for the cap wiring to be brought out to the copper. You may notice that I made an extension of sorts for the tuning knob. It's very possible that you may experience the "hand-capacitance" effect. In other words, you will change the resonant frequency of the loop by placing your hand on the tuning knob. When that happens, you will change the "peak" of the sig you are tuning. You will hear the change in reciever signal as you do this. Sometimes I use the barrel of a plastic ink pen to slide on the shaft of the tuning cap so that I don't have to deal with the hand-effect.
If you look at the pic of the inner base housing, you can see the tuning cap, and also the method used to firmly attach the loop to the housing... ty-wraps.
Lastly, I'll direct your attention to the feedline from the loop to the radio. If you'll look close, I'm using "zip cord". This is a balanced feed system. I like to use the loops in a balanced configuation because they'll have a better null for noise. I have modified my Yaesu FRG-100 receiver to have a true balanced input as well as the traditional 50 ohm coaxial input. You can use coax for the loop output, but you should use some sort of balun to keep rf off the shield of the coax since that reduces loop performance. You could use a simple toroid to wind a few turns of the coax feedline through. Place the toroid close to the output of the pickup loop, and attach the other end of the coax to your receiver.
Using the loop is very simple. You just tune for maximum signal... the loop has a sharp peak, and you'll have to pay attention to receiver noise. You will have to re-tune the loop, of course, with even minor moves in frequency. This is the price to be paid for noise rejection and good signals from a very small antenna. I've been amazed at what I'm able to hear indoors with such a small antenna. Rotating the loop does a very good job in nulling noise while still providing a good signal for the receiver.
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gpsblake
Member
My very unprofessional opinion for an apartment would be the loop antenna. While attic antennas can have an advantage, they can also have a huge disadvantage by picking up more electrical noise and interference. Some people think then they plug in a longwire and hear more gain, it's working, but it's just increasing the noise level. Location of the antenna is the most important part in an apartment, find the best spot in your apartment (probably by a window), then either build or buy a loop antenna.
But as others have said, experiment. If antennas were simple that one design works best on all of them in all environments, we would never hear discussion of different types of antenna.
But as others have said, experiment. If antennas were simple that one design works best on all of them in all environments, we would never hear discussion of different types of antenna.
True, use the advantage of the small size of the loop to locate in the place with least noise, then use the null to decrease the noise further.
It's all about the signal to noise ratio.
AC9BX
Member
Options I would look at:
Attic antenna, random wire, dipole, or loop
Loop antenna, tuned or not
and the "broomstick" antenna works surprisingly well.
Attic antenna, random wire, dipole, or loop
Loop antenna, tuned or not
and the "broomstick" antenna works surprisingly well.
Great little loop project!
You can make it even simpler by using a tuner at the rig instead of the antenna and tune the entire antenna "system" instead of at the loop feedpoint itself. The reason being is that indoors, you are typically running a very short length of feedline, and precise impedance matching is not absolutely necessary for rx-only.
You may even find that the inner loop is unnecessary and attachment to the major loop to your coax is all you need if you use a typical C-L-C T-type tuner at the radio. While a Palstar AT4K might be overkill, the less expensive mfj types work too.
The two-loop system is classic and works very well. However you may find that with such short lengths of feedline indoors, a simpler approach may provide *nearly* the same results with the convenience of loop tuning at the radio due to very short feedline lengths. Tuning may be very touchy, so one must go slowly especially with small loops like this. Vernier-type reduction-gear mechanisms on the tuners help.
You can make it even simpler by using a tuner at the rig instead of the antenna and tune the entire antenna "system" instead of at the loop feedpoint itself. The reason being is that indoors, you are typically running a very short length of feedline, and precise impedance matching is not absolutely necessary for rx-only.
You may even find that the inner loop is unnecessary and attachment to the major loop to your coax is all you need if you use a typical C-L-C T-type tuner at the radio. While a Palstar AT4K might be overkill, the less expensive mfj types work too.
The two-loop system is classic and works very well. However you may find that with such short lengths of feedline indoors, a simpler approach may provide *nearly* the same results with the convenience of loop tuning at the radio due to very short feedline lengths. Tuning may be very touchy, so one must go slowly especially with small loops like this. Vernier-type reduction-gear mechanisms on the tuners help.
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Good ideas hertzian... thanks for the tuner tip.
In my use of the loops, I like to be able to turn the loop by hand from the operating position to null noise without having to get out of my chair, (just laziness I guess), so I keep the loop close to me. I've noticed that when I move in frequency that the noise will "shift direction" and the loop has to be readjusted somewhat to compensate for it.
In my use of the loops, I like to be able to turn the loop by hand from the operating position to null noise without having to get out of my chair, (just laziness I guess), so I keep the loop close to me. I've noticed that when I move in frequency that the noise will "shift direction" and the loop has to be readjusted somewhat to compensate for it.
satellit5000
Member
This is a really cool project I plan to embark on. Never built a home brew antenna before.
I currently use a KA33 antenna and it really helps to bring in weak signals and in some instances, I would only have static. I am curious how this one will fair against it.
A few questions:
1. Would using a 1.5 inch width copper tape be overkill for this project? I was thinking the wider the better
2. Would using a 500pf be a bad idea?
3. Can you paint over the copper tape w/o affecting the performance?
Thanks!
I currently use a KA33 antenna and it really helps to bring in weak signals and in some instances, I would only have static. I am curious how this one will fair against it.
A few questions:
1. Would using a 1.5 inch width copper tape be overkill for this project? I was thinking the wider the better
2. Would using a 500pf be a bad idea?
3. Can you paint over the copper tape w/o affecting the performance?
Thanks!
satellit5000
Member
I did have a follow up question also:
How does this antenna compare to an indoor Pixel, Wellbrook, or MFJ loop antenna?
How does this antenna compare to an indoor Pixel, Wellbrook, or MFJ loop antenna?
Can you please give me details about this antenna, I want to make one. Thanks
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