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Simple shortwave wire antenna in a room - best method to string it up?
Posted by
Mpegger
on 21 Mar, 2024 01:00
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I haven't been able to find a good answer for this, but in a room/garage if one uses a long 150' wire antenna for shortwave receiveing only (no transmitting at all), how would one string up the wire for best overall reception? Obviously a 150' wire can wrap around a small room/single car garage a couple of times, but would that hurt reception? Is it better to hang the wire like loose christmas light strings without any overlap? Is it better/ok to just wrap it around the room in as straight a line as possible, even if there is overlap? Wrap it around with the wire spaced apart to prevent overlap? Hang it perpendicular to each major compass direction? I ask cause I plan on setting up some antennas in my garage for remote SDR listening, so once I setup the server, SDR dongles and antennas, I'm not going to be swithing components out and moving them around. Much like a TV antenna, I just want to set it and forget it. I have no room outdoors to setup a wire antenna for shortwave band reception, so it's going to have to be indoors.
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#1 Reply
Posted by
jfet
on 21 Mar, 2024 02:20
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Since its just receive, I would make a single loop around the room and put it up as high as you can get it.
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#2 Reply
Posted by
fourfathom
on 21 Mar, 2024 03:16
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And if you can't fit all 150 ft then cut it shorter. For receive there's nothing magic about the length, especially when it's randomly routed. In other words, don't worry about it.
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#3 Reply
Posted by
Mpegger
on 21 Mar, 2024 03:51
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So one loop around, no overlap. I think that'll put it around 40' or so. And I forgot to ask, what about the "ground" lead of the "antenna". Does the length of that matter or can I just run a couple of feet to a point of ground? Is a grounded computer case enough or proper? Or must it be to a ground rod in the dirt? The garage is all cinderblock and concrete, cept for the roof which is just wood. The only points of ground are the electrical outlet and the ground rods I've placed for the TV antenna mounted on the roof of said garage.
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#4 Reply
Posted by
A.Z.
on 21 Mar, 2024 06:16
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are you allowed to place the antenna above the roof ? If so, you could use 4 supports made with non conductive material (pvc, fiberglass, wood...) to hold the antenna wire at (say) 1ft above the roof and hang the wire, forming an horizontal "square" loop; add a termination resistor at one corner and a 9:1 at the opppsite one and use a run of RG6 coax from the 9:1 to the receiver
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Put shortwave antenna inside building is a bad idea, because building has mains wires and a bunch of electronics, both will give you a lot of noise. And building walls will reduce signal due to shielding and losses effect.
If you don't needs transmitting, you can install a short wire (1-2 meters) with LNA and a bunch of RF chokes on coax cable outside building. It don't take a lot of space. But try to place it as far as you can from any wires, metal things and building, it will help you reduce the noise. In such way you can listen for weak shortwave stations. And it will be much better than antenna inside building.
Another way is to use ferrite rod antenna with LNA, the principle is the same - put it outside building as far as you can and use a bunch of RF chokes on coax cable.
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So one loop around, no overlap. I think that'll put it around 40' or so.
There is no magic, the antenna efficiency depends on its size, so you cannot improve it with geometry change. The wire geometry just change antenna impedance, but you can match it with matching circuit or antenna tuner.
And I forgot to ask, what about the "ground" lead of the "antenna". Does the length of that matter or can I just run a couple of feet to a point of ground?
The length matters, but for antenna which size is much smaller than wavelength it doesn't matters much. There is a sense to use smaller wire if you have some nearby electronics. More shorten wire allows to reduce coupling with your nearby electronics. But at the same time it reduces reception efficiency which can be fixed with low noise amplifier, but gain ability is limited with noise floor.
Is a grounded computer case enough or proper?
No. Keep your antenna as far as you can from your computer. Otherwise it will flood your antenna with a bunch of digital noise.
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#7 Reply
Posted by
Mpegger
on 21 Mar, 2024 07:27
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are you allowed to place the antenna above the roof ? If so, you could use 4 supports made with non conductive material (pvc, fiberglass, wood...) to hold the antenna wire at (say) 1ft above the roof and hang the wire, forming an horizontal "square" loop; add a termination resistor at one corner and a 9:1 at the opppsite one and use a run of RG6 coax from the 9:1 to the receiver
None of the components I have for my SDR setup (including the wire I'm going to use for shortwave reception), are rated for outdoors except the feed wires and discone antenna that will also be used in this setup. I do have a 9:1 balun that I plan on using with the wire, but you lost me at adding a termination resistor. Are you saying that the wire should complete the loop and be connected straight to the balun at both ends, with a resistor on one of those ends? What about ground? From most of the posts and videos I've come across, having a ground source seems to be very important to help lower the noise floor and increase signal strength. Does the loop negate the need for ground? If so, any kind of resistor can be used, or you talking about some specific value/type of resistor? My pool of resistors is just a bunch of 1/2 watt carbon, and whatever I pull off old scrap components (mainly SMD).
Put shortwave antenna inside building is a bad idea, because building has mains wires and a bunch of electronics, both will give you a lot of noise. And building walls will reduce signal due to shielding and losses effect.
No mains in the garage other then 1 single outlet in the detached garage. And the only electrical stuff that will be running (once everything is setup) is a single computer and a single RPi inside the garage, plus a camera/motion detector outside the garage, and lights inside the garage which of course won't be on 24/7.
Also, as I said, the walls and floor are brick/concrete, but the roof (about 30 degree sloping inverted V) is all wood, mainly 2x4 for supports, and plywood exterior with shingles. No insulation what-so-ever so for the most part, it's just a single layer of 1/2" plywood and a single layer of shingles for signals contend with. Better then inside the home with the IR blocking windows, metal support frames, and 3 inch thick foam + aluminum barrier and stucco on the exterior walls. Indoor antennas just don't cut it.
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#8 Reply
Posted by
jonovid
on 21 Mar, 2024 07:30
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if you must have a shortwave receiveing antenna indoors? use a rotating loop tunable or tuned circuit on a stand. if its under 10MHz IMO
so its movable for the best reception in the room your in.
here is the outdoors antenna system I use . the 21 meters long wire is in a zigzag pattern from the roof to the backyard and back.
https://www.ciphermachinesandcryptology.com/en/swl.htmthis 21 meter long wire works best under 10MHz and the grounded antenna ferrite balun keeps the noise levels low.
with 5 meters of TV coaxial cable run to the shortwave receiver indoors with a 2nd ferrite isolator at its end.
see the antenna system in this link.
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No mains in the garage other then 1 single outlet in the detached garage. And the only electrical stuff that will be running (once everything is setup) is a single computer and a single RPi inside the garage, plus a camera/motion detector outside the garage, and lights inside the garage which of course won't be on 24/7.
That is enough to flood antenna with noise if you put it near such computers and mains wires. When I talking "near" I mean distance smaller than wavelength. But since shortwave band starts with about 100 meter wavelength, it means closer than 100 meters.
Using a small external antenna with LNA will be much better than antenna placed inside such building.
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#10 Reply
Posted by
A.Z.
on 21 Mar, 2024 09:24
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None of the components I have for my SDR setup (including the wire I'm going to use for shortwave reception), are rated for outdoors except the feed wires and discone antenna that will also be used in this setup. I do have a 9:1 balun that I plan on using with the wire, but you lost me at adding a termination resistor. Are you saying that the wire should complete the loop and be connected straight to the balun at both ends, with a resistor on one of those ends? What about ground? From most of the posts and videos I've come across, having a ground source seems to be very important to help lower the noise floor and increase signal strength. Does the loop negate the need for ground? If so, any kind of resistor can be used, or you talking about some specific value/type of resistor? My pool of resistors is just a bunch of 1/2 watt carbon, and whatever I pull off old scrap components (mainly SMD).
The idea is to pick a spool of insulated wire (single conductor) and connect it as for the attached image, both the loading resistor and the 9:1 will be hosted inside two small weatherproof boxes, the antenna will be suspended, using some non conductive support (PVC pipes, fiberglass rods, broomsticks...), at 1ft (or more) above the garage roof, a run of RG6 coaxial cable will run from the 9:1 (inside the box) down to inside the garage where you'll have your SDR; the termination resistor placed at the opposite point of the 9:1 allows to obtain a decent match to the 9:1 (and then to coax) over a very wide bandwidth, the resulting antenna will be almost omnidirectional with a slight better reception in the direction of the feedpoint (the 9:1), being a loop it is a "self contained" antenna so doesn't need a ground connection, but willing to add grounding, you may do so at the SDR end of the coax
As for the 9:1 you may either use a commercial one, like
the one from NooElec or you may build it yourself, as explained
here (scroll down to see the BalUn infos and pics), in either case it must be a transformer offering galvanic isolation (as in the two examples) so that the loop antenna and the coax feedline will be insulated (at DC); optionally you may add a choke on the coax, it may be as simple as 10 or more snap-on ferrites placed on the coax tightly grouped together and covered with duct tape
Note: i modeled the antenna as a 40ft loop and calculated the resistor value for such a length, if the antenna will have a different size you'll need to adjust the resistor value
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#11 Reply
Posted by
jonpaul
on 21 Mar, 2024 10:40
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SDR will see mostly noise from local like LED/CFL lamps, SMPS.
Needs shielded cable to outdoor antenna tuned for bands of interest.
j
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#12 Reply
Posted by
A.Z.
on 21 Mar, 2024 10:42
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#13 Reply
Posted by
jonpaul
on 21 Mar, 2024 14:28
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use RG58/U for 50 Ohm much cheaper and thinner than RG6/U
j
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#14 Reply
Posted by
A.Z.
on 21 Mar, 2024 14:34
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use RG58/U for 50 Ohm much cheaper and thinner than RG6/U
Stay
away from RG58, costs more than RG6 and has
MUCH HIGHER losses !
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yes, most of Chinese RG-58 fake cables has very bad quality and very thin braid, sometimes the braid even missing...
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#16 Reply
Posted by
A.Z.
on 21 Mar, 2024 15:13
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yes, most of Chinese RG-58 fake cables has very bad quality and very thin braid, sometimes the braid even missing...
It's not just the low-quality cables, have a look at the specs of the RG-58 and then check the ones of the RG-6, it's easy to compare the two
just to show one table amongst many others
https://www.w4rp.com/ref/coax.htmland, just to put it straight, check the marked columns, and remember that we're talking about RX, not TRX so power rating is meaningless here
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#17 Reply
Posted by
Mpegger
on 21 Mar, 2024 20:06
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I have RG8/u mini from back in my CB days that I'm going to use in my setup. The cable run from the mast mounted antennas to inside the garage should be around 15' or so, while the antennas inside the garage should only be a couple of feet as I plan on using USB extensions for the SDR dongles where possible.
Anything that requires having to manually flip switches, or turn a dial is out of the question, so no "tunable", or rotating antennas. This is again going to be a SDR server sitting in the garage, not me.
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#18 Reply
Posted by
A.Z.
on 21 Mar, 2024 20:09
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and... where did you see any switching thing in the loop I suggested ?
Anthow, as for the coax, up to you; yours the receiver, yours the setup
I tried to offer you a decent setup, but again, try whatever and have fun.
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#19 Reply
Posted by
audiotubes
on 21 Mar, 2024 21:46
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You can buy a commercial loop antenna. Sadly, Welbrook has closed but there are others. You will still have to rotate it but it nulls quite well and is effective even indoors.
Alternatives could include short whips with preamps like LF Engineering and possibly MFJ have to offer.
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#20 Reply
Posted by
A.Z.
on 22 Mar, 2024 07:48
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I have RG8/u mini from back in my CB days that I'm going to use in my setup. The cable run from the mast mounted antennas to inside the garage should be around 15' or so, while the antennas inside the garage should only be a couple of feet as I plan on using USB extensions for the SDR dongles where possible.
Just to be even more clear, the idea is to setup an antenna like the ones shown here
http://hflink.com/antenna/#BBTDhttp://hflink.com/antenna/#BBTDROOFin your case, since you're going to use a 9:1, the resistor value should be adjusted to offer a good match, and there's no need for the resistor to dissipate power since the antenna will be only used for RX, as you can see, such an antenna will have a good impedance match over a very wide frequency range and won't require switching, aiming or retuning, but to get better performances, I'll refrain my suggestion to put the antenna outside, that is above the garage roof, then the coax coming from the 9:1 will enter the garage and reach the receiver
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I do agree with radiolistener and others that the length (or really the electrical length) of an antenna does matter even for receiving. I noticed when the SWR was low on an antenna, I heard stations much better. I learned this in my early days in ham radio using a manual antenna tuner. As soon as the SWR got low, I heard more stations. And of course, the noise level went up.
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#22 Reply
Posted by
A.Z.
on 22 Mar, 2024 19:39
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let him go on and "break his teeth" the lesson will be useful, I suppose (and hope)
there's no "free lunch" and when it comes to RX, one must learn the difference between gain and S/N ratio, let him go on and build some experience...
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#23 Reply
Posted by
Mpegger
on 22 Mar, 2024 22:28
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I appreciate the help, but the question was about a simple wire antenna in a room for best reception, not what other gear could I purchase to replace a simple wire antenna in a room. It's what I have to work with, nothing more. I cannot/will not spend more money on gear that I cannot use because I cannot install it where it would be best to use said gear.
I've "cut my teeth" long ago in the 80's and 90's playing around with CB, scanners, SW radios and DX'ing FM stations (still have the 12 foot FM Yagi sitting in the garage) as a kid looking to get a ham operators license, but eventually moved away from that hobby. Here in my old age, I've been getting back into radios and antennas, having multiple SDRs, making multiple antennas not just for the SDRs running ADS-B feeds, but also GPS as I run a NTP server (and possibly a NTRip in the future) as well. I understand Gain, and SNR, I know that a simple wire inside a structure is not an ideal setup, but it's what I have to work with. I'm asking about how best to make of "Setup A", and you'r answering with get "Setup B" instead.
That being said, the Broadband Butterfly Terminated Dipole Antenna in the link you provided is the best answer for my setup I've seen so far. Even if I can't have the wire outdoors, I can set it up pretty much exactly as shown in the example image.
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#24 Reply
Posted by
mike449
on 23 Mar, 2024 04:13
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From my experience, a simple loop made of coax works best indoors. Let's say you have 3m of coax. One end is connected to the receiver input, shield and central wire (assuming that it has a coax input). On the other end, leave the shield dangling, and connect the central wire to the ground of the receiver at the input connector (i.e. loop to the shield where it connects to the receiver).
The downside is low sensitivity. The upside is that you can tune out the local interference by moving the loop around, so you still get better SNR than a linear (or bent) wire. Also, no ground required.
The best position will be frequency dependent. Sometimes people use the room door to "rotate" the loop.
Most modern receivers are sensitive enough to work ok with such antenna.
You really need to experiment to find what works best in your environment.