Simple shortwave wire antenna in a room - best method to string it up? - Page 1
Forum section: electronics / rf-microwave

author: Mpegger
author_rank: Contributor
timestamp: March 21, 2024, 01:00:08 am
content: 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.

author: jfet
author_rank: Contributor
timestamp: March 21, 2024, 02:20:50 am
content: Since its just receive, I would make a single loop around the room and put it up as high as you can get it.

author: fourfathom
author_rank: Super Contributor
timestamp: March 21, 2024, 03:16:12 am
content: 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.

author: Mpegger
author_rank: Contributor
timestamp: March 21, 2024, 03:51:21 am
content: 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.

author: A.Z.
author_rank: Super Contributor
timestamp: March 21, 2024, 06:16:52 am
content: 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

author: radiolistener
author_rank: Super Contributor
timestamp: March 21, 2024, 06:33:56 am
content: 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.

author: radiolistener
author_rank: Super Contributor
timestamp: March 21, 2024, 06:48:20 am
content: Quote from: Mpegger on March 21, 2024, 03:51:21 amThere 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.Quote from: Mpegger on March 21, 2024, 03:51:21 amThe 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.Quote from: Mpegger on March 21, 2024, 03:51:21 amNo. Keep your antenna as far as you can from your computer. Otherwise it will flood your antenna with a bunch of digital noise.

author: Mpegger
author_rank: Contributor
timestamp: March 21, 2024, 07:27:06 am
content: Quote from: A.Z. on March 21, 2024, 06:16:52 amNone 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).Quote from: radiolistener on March 21, 2024, 06:33:56 amNo 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.

author: jonovid
author_rank: Super Contributor
timestamp: March 21, 2024, 07:30:49 am
content: if you must have a shortwave receiveing antenna indoors? use a rotating loop tunable or tuned circuit on a stand. if its under 10MHz IMOso 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.

author: radiolistener
author_rank: Super Contributor
timestamp: March 21, 2024, 07:36:30 am
content: Quote from: Mpegger on March 21, 2024, 07:27:06 amThat 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.

author: A.Z.
author_rank: Super Contributor
timestamp: March 21, 2024, 09:24:05 am
content: Quote from: Mpegger on March 21, 2024, 07:27:06 amThe 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 coaxAs for the 9:1 you may either use a commercial one, likethe one from NooElecor you may build it yourself, as explainedhere(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 tapeNote: 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

author: jonpaul
author_rank: Super Contributor
timestamp: March 21, 2024, 10:40:20 am
content: SDR will see mostly noise from local like LED/CFL lamps, SMPS.Needs shielded cable to outdoor antenna tuned for bands of interest.j

author: A.Z.
author_rank: Super Contributor
timestamp: March 21, 2024, 10:42:29 am
content: the RG6 is coax cableit's the one commonly used for TV/Sat antennas and is easily available, cheap and offers good performance for RX applicationsAn examplehttps://www.amazon.com/Coaxial-Antenna-Extension-Connector-Equipment/dp/B09ZPDCQ5Z... but it can be sourced almost anywhere

author: jonpaul
author_rank: Super Contributor
timestamp: March 21, 2024, 02:28:34 pm
content: use RG58/U for 50 Ohm much cheaper and thinner than RG6/Uj

author: A.Z.
author_rank: Super Contributor
timestamp: March 21, 2024, 02:34:09 pm
content: Quote from: jonpaul on March 21, 2024, 02:28:34 pmStayawayfrom RG58, costs more than RG6 and hasMUCH HIGHERlosses !

author: radiolistener
author_rank: Super Contributor
timestamp: March 21, 2024, 03:02:49 pm
content: yes, most of Chinese RG-58 fake cables has very bad quality and very thin braid, sometimes the braid even missing...

author: A.Z.
author_rank: Super Contributor
timestamp: March 21, 2024, 03:13:56 pm
content: Quote from: radiolistener on March 21, 2024, 03:02:49 pmIt'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 twojust to show one table amongst many othershttps://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

author: Mpegger
author_rank: Contributor
timestamp: March 21, 2024, 08:06:25 pm
content: 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.

author: A.Z.
author_rank: Super Contributor
timestamp: March 21, 2024, 08:09:04 pm
content: 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 setupI tried to offer you a decent setup, but again, try whatever and have fun.

author: audiotubes
author_rank: Regular Contributor
timestamp: March 21, 2024, 09:46:28 pm
content: 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.

author: A.Z.
author_rank: Super Contributor
timestamp: March 22, 2024, 07:48:35 am
content: Quote from: Mpegger on March 21, 2024, 08:06:25 pmJust to be even more clear, the idea is to setup an antenna like the ones shown herehttp://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

author: radiohomebrewer2000
author_rank: Contributor
timestamp: March 22, 2024, 06:16:09 pm
content: 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.

author: A.Z.
author_rank: Super Contributor
timestamp: March 22, 2024, 07:39:39 pm
content: 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...

author: Mpegger
author_rank: Contributor
timestamp: March 22, 2024, 10:28:08 pm
content: 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.

author: mike449
author_rank: Contributor
timestamp: March 23, 2024, 04:13:34 am
content: 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.

author: A.Z.
author_rank: Super Contributor
timestamp: March 23, 2024, 03:48:56 pm
content: well, willing to use the simplest antenna, one may build an aperiodic one, just pick a lenght of coax, the longer and fatter, the better; short the center and braid at one end using a resistor with a value near the characteristic impedance of the coax (e.g. 50 Ohm), next place a coax connector to the other end, but wire it "reversed", that is; the coax braid to the center and the coax center conductor to the connector "gnd", lay out the wire as possible and give it a trypossibly using a run of regularly wired coax to feed it (through a choke) and connect it to the receiver

author: A.Z.
author_rank: Super Contributor
timestamp: July 03, 2024, 07:03:07 am
content: Quote from: Mpegger on March 22, 2024, 10:28:08 pmrevamping this just due to curiositywhat did you end with ?

author: Mpegger
author_rank: Contributor
timestamp: July 07, 2024, 05:48:57 pm
content: The one mentioned, except I dont have a 16:1 balun on it, just a typical 1:9. Since it's only for receiving, I'm not worried about the mismatch. Picks up alot more then when I just had the wire in the home.

author: A.Z.
author_rank: Super Contributor
timestamp: July 07, 2024, 06:46:36 pm
content: ok, could you give me the size of the rectangle sides ? I may then calculate a resistor value to improve the match (and the signal to noise)

author: Mpegger
author_rank: Contributor
timestamp: July 07, 2024, 09:44:41 pm
content: Does it need to be as close to an exact wire length? Or just "close" enough? Took me a could of days just to get the wire strung up because of the stuff I had to move around as I moved the ladder around the garage, so "exact" length aint happening anytime soon. But if I can just get rough measurements of the garage interior, then I could probably have some numbers by the end of the week.

author: A.Z.
author_rank: Super Contributor
timestamp: July 08, 2024, 05:36:11 am
content: approx sizes will be ok

author: A.Z.
author_rank: Super Contributor
timestamp: July 08, 2024, 10:24:51 am
content: Here's a first coarse test, the attached image shows the antenna and the SWR curve, in the model I've set the long side of the rectangle to 7m and the short side to 5m, the low side of the roof is at 3m from ground, while the high point is at 4m, running the model in NEC and optimizing it for best match at 450 Ohm (9:1) resulted in a resistor value of 878 Ohm which gives the SWR plot you can see in the image below and which should be acceptable, not just that, but with such a setup, if you feel it may be needed, you may add whatever LNA you want, since the antenna will give it a good match at 50 Ohms, also, it would be a good idea adding a preselector at the receiver input to further improve things, as for the LNA if you don't want to build it yourself, consider this onehttps://www.nooelec.com/store/lana-hf.htmlpowered using a decent BIAS-T (or through USB) and a "clean" power supply it will allow to boost a bit the signals from the BBTD, then, if you are affected by strong AM band signals, you may also consider the idea of adding a bandstop filter like this onehttps://www.nooelec.com/store/flamingo-am.htmlbetween the antenna and the LNA (or if not using the LNA, between the antenna and the receiver); as a note, the antenna radiation/reception lobe will be oriented toward the feedpoint at frequencies up to around 10MHz, going up in frequency the lobe will become omnidirectional and then will be reversed, that is, it will be aimed at the resistor side, not a huge directionality, but something to keep in mind, also, the antenna will show "negative gain" going down in frequency, not an issue for an RX only antenna whose main task is "setting the SNR" but adding a preamp/LNA with around 20dB gain will bring back signals in case the receiver isn't all that sensitive

author: Co6aka
author_rank: Unknown
timestamp: July 09, 2024, 04:28:32 am
content: FWIW... If you're restricted to indoors, build a simple tuned loop. Lots of design ideas on the 'net. One of my designs used a camera tripod with a mount I fabricated to accept different size loops. The mount held the varicap and a few switched-in "additional" capacitors. The varicap had three 450pF sections with mini toggle switches between them. I used two-pin twinlead connectors to attach the loop conductors to the base unit. You can then build loops out wire and whatever support materials are available. Single turn, multiple turn for LF/VLF, etc. You can also interface ferrite rod style elements. Because it's bidirectional you'll only need to rotate 180 degrees. The drawback is of course it's not a broadband antenna, but the selectivity it provides is helpful, and the ability to null is even more helpful.Or, build/buy an active broadband loop.

author: radiolistener
author_rank: Super Contributor
timestamp: July 09, 2024, 07:27:35 am
content: Quote from: Mpegger on March 22, 2024, 10:28:08 pmif you understand it, then you understand why attempt to receive on antenna inside room is a bad idea. But since you're still want to use it inside room, the better antennas in your case are these which use magnetic coupling in near field zone. These are different kind of loop antennas. It includes ferrite rod antenna.

author: A.Z.
author_rank: Super Contributor
timestamp: July 09, 2024, 07:52:32 am
content: Quote from: Co6aka on July 09, 2024, 04:28:32 amHi Co6aka ! Nice to read you again!!Getting back on topic, the antenna he's using at the moment is something like thishttp://hflink.com/antenna/#BBTDROOFthat is a wire loop placed around a wooden roof, the termination resistor "flattens" the impedance so allowing to achieve a good match over a pretty wide range, as for the tuning, you're right but he doesn't seem to be willing to fiddle with DIY circuits, otherwise a nice addition to the above antenna (used for RX only BTW) would be this simple yet nice tuned preamplifierhttp://www.arrl.org/files/file/QEX_Next_Issue/Jan-Feb2018/Steber.pdfbuilding it so that the preamp unit sits at the antenna feedpoint (right after the balun/transformer) and the tuning unit sits on the desk would allow to improve the antenna performance, the idea in such a case would be using a (say) run of CAT5 cable to bring the power, the tuning voltage and some additional stuff, that is power for a couple of microrelays used to switch L1/L2 so changing the tuning range, no rocket science but then, as I wrote, if I understood it correctly the OP doesn't want to "build stuff" aside from simple one (like the antenna)

author: Co6aka
author_rank: Unknown
timestamp: July 09, 2024, 01:14:17 pm
content: Hiya! Yeah, I've missed y'all too, but during my absence once in a while I'd "read the mail" to cure my separation anxiety.I've experimented with the OP's type of antenna, and T2FD, etc. Many moons ago I helped a guy build a "stealth" under-crown-molding one room miniature version of such for mainly AM-BCB. His landlord approved and his wife liked it, but functionally it was a QRM magnet. After investing way too much time into QRM magnets over the years I realized the nulling ability of a loop makes it my preference for indoors. And, the loop can help in locating the QRM source. (Indoor loops also freak out non-radio people; I'd tell 'em they're for communicating with space aliens.)Fortunately I have the perfect antenna-roof and have active loops on rotors, but while experimenting with tuned loops in my basement lab I discovered how well overall they work indoors. One evening I had such a great signal from Radio Mauritania on the 60m band that I had to record it. It wasn't much better on the rooftop loop. And FWIW, I also discovered that indoor loops "work better" than indoor E-field probe types of antennas. If one can bring themself to do a little tinkering, play with loops.

author: A.Z.
author_rank: Super Contributor
timestamp: July 09, 2024, 01:33:09 pm
content: Quote from: Co6aka on July 09, 2024, 01:14:17 pmLOL !! Anyhow, welcome back !Quote from: Co6aka on July 09, 2024, 01:14:17 pmStrange, in my own experience, terminated loops (like the BBTD) can be much quieter than most other antennas, yet allowing to pull out signals; in general the "trick" which people often forgets (or doesn't know about) is using a "galvanic transformer" to feed the loop, that is a classic primary/secondary transformer with separated windings, that will allow the loop to "float" with respect to coax/ground and will make both the loop and the coax feeder short circuited at DC, and that alone will help quite a lotthen just add some choke along the feedline and the difference will be relevantQuote from: Co6aka on July 09, 2024, 01:14:17 pmUh.. the "perfect antenna" ? I thought it was something legendary like the "Graal"Seriously, small loops, and in particular tuned ones, have good performances, but then ... at least here in EU, where buildings are made with bricks and reinforced concrete, a loop will have some hard times, not only it will be "immersed" into the "electrosmog cloud" generated and radiated/conducted by domestic appliances/devices, but it will face a bunch of signal reflections/rotations, so the "nice 8 pattern" won't work as expected, so it's generally a better idea trying to put the antenna "outside", even if the "outside" just mean placing it on a balcony

author: radiolistener
author_rank: Super Contributor
timestamp: July 09, 2024, 04:56:38 pm
content: Quote from: Co6aka on July 09, 2024, 01:14:17 pmYeah, loop antenna has higher H coupling and lower E coupling in near field zone, while most of home noise sources have higher E coupling and lower H coupling. So, using loop antenna allows to reduce noise floor from nearby electronic equipment. Also H field is more hard to shield and it's better penetrate inside building which also increase signal strength.But when you use indoor antenna, you're needs to use very narrow bandwidth antenna with high Q in order to cut-off as much unwanted noise power as possible. On the other hand the con of narrow bandwidth antenna is that it requires it to tune it even for a small RX frequency change.The best implementation of such kind of antenna is ferrite rod antenna. Usually it is designed to have bandwidth about 10-20 kHz, just to pass AM station. But as result it needs to be tuned even if you change RX frequency for 3-5 kHz.Quote from: Co6aka on July 09, 2024, 01:14:17 pm

author: A.Z.
author_rank: Super Contributor
timestamp: August 18, 2024, 09:49:15 pm
content: any update about the antenna ?