How to Calculate how long a Wire must be for HF? - Page 1
Forum section: electronics / rf-microwave

author: Lord of nothing
author_rank: Super Contributor
timestamp: August 18, 2019, 02:18:09 pm
content: HiI am still an SDR and CB Radio User.I will make much more on HF since the work here well.But how to use an Stell Wire for? A "local" Shop sell them like this:https://www.obi.at/stahldraht/lux-drahtseil-verzinkt-4-mm-x-20-m/p/32674654mm thick 20m. Sure longer are available. For the different Freq what kind of length Should I use?Are there any way to combine multiple Bands for the Wide Band SDRs like Hack RF?Thanks

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: August 18, 2019, 03:16:38 pm
content: What are your intentions , receive / listening ?If transmitting , then look into becoming a ham radio [ licensed in you country ] operator .You mention HF - those bands are for licensed use only [ for transmitting ] but it is a great idea to listen for some time , to help to learn how to operate and see if that is in your interest .Part of getting a ham license is learning about RF - Radio Frequency , antenna theory etc.It gets deep very quickly , if you really want to get into ham radio as a hobby , many these days are called appliance operators - buy a station & transmit vs. the good old day, where most people had technical interests that lead them into building there own gear .Now days one of the issues is , there are almost now real kits for full-blown radios , amplifiers ect.As far as antennas go , this is probably the single most important part of radio - knowing how to build & setup and then propagation [ how RF works in real life / environment ] .A few general rules frequency is a wave length , so to build an antenna you generally start withhttp://www.radioqth.net/dipole#targetText=Dipole%20Antenna%20Length,each%20leg%20of%20the%20antenna.

author: Kalvin
author_rank: Super Contributor
timestamp: August 18, 2019, 03:32:58 pm
content: Here are some articles for different kind of antennas at ARRL site:http://www.arrl.org/your-first-antennaUsing Google will give you plenty of more good references.

author: fourfathom
author_rank: Super Contributor
timestamp: August 18, 2019, 03:46:36 pm
content: Quote from: Lord of nothing on August 18, 2019, 02:18:09 pmThat looks like galvanized steel wire. This is useful for guy wires (keeping antenna towers from falling down), but not the best choice for an antenna wire. For a receiver operating below 30 MHz, the antenna is often not that critical, since the atmospheric noise will generally limit your sensitivity. A "better" antenna will not significantly improve your ability to receive a signal.So you can probably use a "random" length wire, say about 5-to-10 meters long. Copper wire is best, and I often use the solid wire as used in house wiring: #14AWG in the USA. You can keep the insulation on the wire. You will need a coax cable from the receiver to the antenna wire, and a ground connection of some sort. You may prefer a dipole antenna, which needs no ground connection.Look up "dipole antennas", "end-fed" and "long wire" antennas on Google. the ARRL has a bunch of antenna info available.

author: Lord of nothing
author_rank: Super Contributor
timestamp: August 18, 2019, 04:21:59 pm
content: QuoteI dont want or need listen to Amateur Radio stuff when I hear the talk about on your Multiple Local Repeater.QuoteWell I dont find that much Information beside some weird conpericies theories.QuoteJust receiving.Sorry i dont be willing to pay the Monthly Fee for Amateur Radio stuff.QuoteWell the Theory isnt the Problem its more like the practical usage of that knowledge.Quoteno not realy. The do there stuff I do mine...QuoteIt sound more like the want to chat round and talk about there nasty deceases.QuoteWell a SDR is wideband and use Multiple so I cant type in just one.Can I use a half wavelength on SW to?QuoteI would like use the long Side of your Garden between the to Buildings. Its not a good idea to run a long Coax truth our Garden when I run a long (single) Wire.A normal Wire like this:https://www.obi.at/kunststoffschlauchleitungen/aderleitung-h07v-u-2-5-mm-violett-100-m/p/2236495?

author: MarkF
author_rank: Super Contributor
timestamp: August 18, 2019, 05:00:36 pm
content: Your question is too general to answer.For example:- What type of antenna are you trying to build?- Which HF band are you interested in?https://www.electronics-notes.com/articles/ham_radio/ham-bands/hf-amateur-frequencies.phpI have found Kevin Loughin's YouTube videos interesting and informative.He shows building several antenna types and baluns that may help narrow your questions.https://www.youtube.com/user/loughkb/videos

author: fourfathom
author_rank: Super Contributor
timestamp: August 18, 2019, 05:25:25 pm
content: Quote from: Lord of nothing on August 18, 2019, 04:21:59 pmYes, that wire is 2.5mm2solid copper, and will be fine. Your SDR has a coaxial connector that is designed to connect to 50-Ohm impedance coaxial cable. Interfacing this to a single wire can be done, but to "do it right" takes a little work with grounding and impedance matching. Fortunately in your receive-only over a wide frequency range application, you can take some shortcuts. A perfect solution doesn't exist, and a less-than perfect installation should work for you. Do take a look at ham wire antennas designed for (say) 20 meters (14 MHz). This is the middle of the HF range, and something close to these dimensions will get you an adequate receiving antenna.After you have experimented a bit you may want to learn more about antennas. The resources others have mentioned are a great way to start. If you want to optimize performance for a particular frequency or direction there's a lot you can do. You may also find that you are receiving interference from your computer, LED or fluorescent lights, or other local electronics. There are things you can do to help. But first put up a wire and see what you can hear.

author: radiolistener
author_rank: Super Contributor
timestamp: August 18, 2019, 06:09:21 pm
content: you're needs two wires. It's named half-wavelength dipole antenna.The total length of half wavelength dipole is half wavelengthwavelength = vf / frequency,where vf is phase velocity of the wave propagation.For usual air it is very close (a little smaller) to the speed of light in the vaccum - 299'792'458 m/s.But if you're using insulated wire this speed will be a little smaller due to insulation.You can just use 299'792'458 m/s for calculations and then just tune your dipole by cutting length with a small pieces.For example, if you're needs half wavelength dipole for 27'000 kHz, then:wavelength = 299'792'458 / 27'000'000 = 11.1034 metershalf wavelength = 11.1034 / 2 = 5.552 metersso, the length of wires should be = 5.552 / 2 = 2.776 meters.It means that you're needs two wires, each 2.776 meters length.Then you're needs to use vector antenna analyzer to measure it's impedance. And you can trim your dipole to desired frequency by cutting length of wires with a small pieces and check how X value is changed by vector analyzer. X value (reactance) should be zero.You can buy vector analyzer here:https://www.aliexpress.com/item/33016805196.htmlThen you're needs to connect your antenna with receiver with coax cable. Usually input impedance of half wavelength dipole is 73 Ohms. But if it's close to the ground it has less efficiency due to loss and its impedance will be a little less. You can check it with vector analyzer after tuning your antenna length - this is R value.So, it's better to use 75 Ohm coax cable. You can also install ferrite RF choke on coax cable near the point where you connected coax cable to antenna (at the center of dipole). It will reduce noises.

author: fourfathom
author_rank: Super Contributor
timestamp: August 18, 2019, 07:28:21 pm
content: Quote from: radiolistener on August 18, 2019, 06:09:21 pmThis is all good advice for a single-frequency antenna, but it sounds like the OP wants to receive all over the HF range. If so there's no reason to fine-tune the antenna for a specific frequency. Also, at HF the practical difference between 75-Ohm coax and 50-Ohm is minor -- especially if the intent is to use the antenna over a broad range of frequencies. If we were proposing a broadband log-periodic beam then these things might matter.One other approach the OP may want to try is the "active antenna", which is usually a short whip followed by a high-impedance preamp. I've never used one of these but apparently they do work. Here's an example (which I have not tried, and there are no doubt others):https://www.mfjenterprises.com/Product.php?productid=MFJ-1022

author: radiolistener
author_rank: Super Contributor
timestamp: August 19, 2019, 09:06:59 am
content: untuned half-wavelength dipole has up to 20 dB worse efficiency.75 to 50 Ohm mismatch also add loss which will depends on cable length.If you're hunting on a weak signal, such loss will be unacceptable.

author: bd139
author_rank: Super Contributor
timestamp: August 19, 2019, 10:23:09 am
content: If it's receive only just chuck any one bit of wire 20m+ in length out the window and get it as high as possible. You can have debates all day about which antennas are best and stuff but there's a whole load of good enough on the table with that solution. Perfection is not required for a functioning radio system.Best stuff is 16/0.2 but 7/0.2 will do the job. I use this stuff as it's ridiculously strong, small and coloured so the neighbours can't see it:https://www.sotabeams.co.uk/antenna-wire-lightweight-100m/I actually tend to throw an unmeasured chunk of that up in a tree in a built up area in the middle of London, lay out a few radials and connect it to my K2 and use it as a transmit antenna too with the internal tuner. This will no doubt piss off all the people running 20m high 40m beams and stuff and weird ass antennas but I can get contacts half way across Europe on bugger all power out of that on CW at the arse end of the solar cycle. On WSPR I can get spots on the other side of the planet running less than a watt out.To note I do have two proper dipoles, RigExpert and stuff but it's not really needed up front and definitely not for RX only.Edit: to give you an idea of minimal requirements, this is a bit of wire around the living room whacked in the back of a deaf NE602/LM386 receiver

author: fourfathom
author_rank: Super Contributor
timestamp: August 19, 2019, 04:20:02 pm
content: Quote from: radiolistener on August 19, 2019, 09:06:59 amSometimes this matters, often it doesn't.QuoteBut not much. In context not enough to make a difference.QuoteSo he won't hear the weak ones. What is he supposed to do when he wants a simple wire antenna to receive across multiple random HF frequencies? It's not like he is asking how to design an antenna for 20-meter SSB DX...If you are transmitting, or require good directionality, then a well-matched antenna can be important. If you are only receiving then as long as you hear the atmospheric noise when you connect the antenna you are probably OK. The goal is signal-to-noise ratio, and usually the atmospheric noise sets the noise floor, not the antenna.

author: radiolistener
author_rank: Super Contributor
timestamp: August 20, 2019, 04:12:14 pm
content: Quote from: fourfathom on August 19, 2019, 04:20:02 pmif 20+ dB difference doesn't matter, you can place just a random piece of wire near switching power supply of your PC and use it as antenna, isn't it? At least it will works pretty good for nearby powerful FM stations...But if you want to get best RX antenna, you're needs to calculate it's length for specific frequency. In such way your antenna will works as preselector and will have gain at specific frequency. The best amplifier is a proper antenna. This works for both directions - for receive and for transmit

author: fourfathom
author_rank: Super Contributor
timestamp: August 20, 2019, 06:41:06 pm
content: Quote from: radiolistener on August 20, 2019, 04:12:14 pmNice strawman.QuotePerfect is the enemy of the good. The OP doesn't need the best RX antenna. Are you suggesting that every time the OP wants to listen on a different frequency that he change the length of his wire antenna?Look, I like good antennas. At home I generally cut a dipole for a specific band, and then trim it as needed for low SWR. But that doesn't stop me from using it on other frequencies. I even transmit on other frequencies, using a matching network (antenna tuner) to keep my transmitter happy. It usually works pretty well. Not perfect, but good enough, especially for receiving.

author: radiolistener
author_rank: Super Contributor
timestamp: August 21, 2019, 05:32:55 am
content: Quote from: fourfathom on August 20, 2019, 06:41:06 pmhe can calculate antenna for most interest frequency and then can use it also for other frequencies. It's better than just random piece of wire, isn't it?

author: fourfathom
author_rank: Super Contributor
timestamp: August 21, 2019, 07:07:39 am
content: Quote from: radiolistener on August 21, 2019, 05:32:55 amYes it is. I even suggested that he try making his antenna for the 20m ham band as a likely compromise. I suppose we should get more info from the OP, so see if there is a specific frequency he is interested in. I read the original post as asking about reception across many frequencies, but perhaps that isn't right. My main point was that a random piece of wire will often be more than adequate for reception on the HF bands, since atmospheric noise will be setting the noise floor anyway.

author: tkamiya
author_rank: Super Contributor
timestamp: August 22, 2019, 04:21:31 am
content: I am a licensed Amateur Radio operator but I don't transmit anymore. Just listen and often not the ham band.My antenna is 25 meters of copper clad steal going from my roof to a tree. That is directly connected to the center of a coax and the braid side is grounded to a good ground system. All that is fed to an RG8X coax of about 5 meters into my room.It is all "wrong", I know, but it works well for my purpose. Just listen. I used similar setup in Japan for transmit via an antenna coupler but performance wasn't great.I've used steel guy wire for antenna as well. I made a dipole out of it for 28MHz band: very close to CB band in frequencies. It actually worked very well for transmit and receive. If you look around the Internet, you'll see argument over use of steel for antennas. It really isn't matter in practical sense.Since your use is very general, I wouldn't worry at all about details. One important factor in my antenna is a good ground system.By the way, what you hear on your local repeater is not a representative of Hams in general.

author: Lord of nothing
author_rank: Super Contributor
timestamp: September 11, 2019, 11:16:57 pm
content: QuoteI dont know what the best is.QuoteSince there is so much stuff on such a narrow space I want to receive all.QuoteI have it done and it work ok but I need to build some Stationary Setup to order Parts for it.QuoteCan the be in a right angle?I want use this: AntennaJet ASM300http://www.bonito.net/manuals/antennajet/QuoteIf the work I will put 3 Antenna with the different Ranges in the Garden and connect them together.QuoteWell I cant mount anything on the Roof and my Parents are not happy when something Wire is next to the Wall even the dont see it just when the come back.QuoteSure for example Radio and some Number Station. The problem the are across the Band.QuoteWell there are 2 Fregs on the Radio Band who are for National Transmission there.Who it could use I dont kow. The are definitely not for Mil.Quotesry Amateur Radio is the last interesting stuff since I cant replay and I dont care when the Italians call."The problem" is I use a CB Radio on the Roof for some Transmission across the Day and Night so the Antenna must be away from the CB Radio Antenna to not damage the RX Stuff.The Upper Freq I want receive is ~25Mhz and the lowest ~2,5Mhz where the normal HF Radio start.So the total Bandwith must be 22,5Mhz.QuoteTrust me the mentality of retired People here (at lest who worked where some kind of electronic is involved) is every new think is Bad.DRM is bad because it make weird Noise on NFM Radios.Or its hard to Program the Caller ID List into a Radio.When you see how much Repeater here are:https://www.google.com/maps/d/viewer?hl=de&mid=1lwESpY7bEi3ebHYCF_SKsRDX46A&ll=48.20905395703353%2C16.358630882767102&z=11it feel like the have more than the Authority use.Every single hill have there own Repeater from the one and only Amateur Radio Club. (Sure the did it to prevent other People, Clubs,... to put there competitive System on Air! Now the Authorities argue the could not permit any more because there are enough.) The same think when the refuse to use normal Words and Phrases insted of the correct therms. Why? The use them since the Austrian - Hungarian Empire so the must be right.....