SW Antenna + Noise - Page 1
Forum section: electronics / rf-microwave

author: Lord of nothing
author_rank: Super Contributor
timestamp: March 13, 2019, 05:00:12 pm
content: HiNow I will buy a HF Antenna. We have our own Garden who is not that long/ wide so a long wire will not my first option.I use an several meter long wire at the moment with my SDR. Sadly I pick up a lot of noise. The (Speaker) Wire is outside beside of a small peace and the SDR is Inside.I dont know where the Noise is comming from.Does it is possible to have an Wideband Antenna for Shortwave?Thanks

author: 9aplus
author_rank: Regular Contributor
timestamp: March 13, 2019, 05:26:54 pm
content: You can try with closed wire loop antenna, or magnetic-resonant loop.Source of noise can be your PC PS, LED lights, even my notebook glide point is producing noise on LW too

author: Lord of nothing
author_rank: Super Contributor
timestamp: March 13, 2019, 06:19:22 pm
content: How many M Wire do I need for 2Mhz?I dont know any good Calculator for that. Is the Polarisation important?

author: 9aplus
author_rank: Regular Contributor
timestamp: March 13, 2019, 07:02:55 pm
content: Well from my experience for that band,the best is to take RG58 cheap coax cable and use hula hoop toy with10-12 turns, ends short, fixed with zip tie + any variable C from old MW radio.One turn separate pick up and input to SDR...With that kind of antenna I am able to hear GleichenbergGBG NDB beacon near Graz from Adriatic sea side, almost 500 kmPS noise on the right is from notebook glidepoint, when like to hear that part must use external mice

author: Lord of nothing
author_rank: Super Contributor
timestamp: March 13, 2019, 08:16:46 pm
content: Here you see the Noise and in the Center a Radio Band.

author: radiolistener
author_rank: Super Contributor
timestamp: March 14, 2019, 03:28:12 am
content: Any non-symmetrical antenna will use feed line for it's balance.It means that your feed line will be a part of the antenna.And it means that it will suck in all noises from your home.So, it is very important to use RF chokes and baloon on the feed line for non-symmetrical antennas (such as long wire).RF-choke is needed to reduce parasitic RF currents on the outer side of coax cable braid.But long wire is very unbalanced antenna, so it will be hard to eliminate parasitic currents on feed line.That's why long wire is very sensitive to noises.If you're want to reduce noise, it is better to use balanced antennas, such as half wavelength dipole.And use RF-choke filters (from both side - near feed point and near receiver) and baloon on the feed line to avoid using feed line as a part of antenna.Here is example on how to make RF choke with ferrite core:Another important thing here is antenna near field region.You can calculate near field region radius with the following formula:D is the size of your antenna (in meters)λ is wavelength (in meters)Antenna is very-very sensitive to any noise source which falls into antenna near field region.The most sensitive part of near field region is reactive near field region.For 2 MHz (150 meters wavelength) and half-wave length dipole (75 meters length), reactive near field region can be calculated in the following way:R = 0.62 * sqrt( 75^3 / 150 ) = 33 metersIt means that you're need to place your antenna at least for 33 meters away from any noise sources, mains, wires, any metal things, ground or other things.The near field region (include radiating part) can be calculated in the following way:R = 2 * 75^2 / 150 = 75 metersIt means that ideally, you're need to place your antenna 75 meters away from any noise source or other things. Unfortunately it is hard to implement for low frequency antennas due to large dimensions of antenna and long near field distance.Sensitivity in the near field region falls by not linear law. It depends on r^2 and even r^3 at close distance to antenna. So, if you're not able to keep your antenna 33 meters away from any things, then try to keep that distance as big as possible. It will reduce noise and will improve your antenna efficiencyFor receiver antenna there is a nice trick. You can use small size antenna + RF amplifier (placed near antenna).Since antenna has a small size, it has small near field region. But also it has small efficiency.The amplifier will compensate small efficiency. Such kind of antenna is named active antenna.But there is a low limit of reactive near field region for very small antennas. For a very short dipole, or equivalent radiator, the outer boundary is commonly taken to exist at a distance R = λ / (2 * pi) from the antenna surface.In your case, for 2 MHz band, it means that you're need to place small active antenna at least R = 150 / (2*pi) = 24 meters away from any noise source or other things.Quote from: Lord of nothing on March 13, 2019, 05:00:12 pmBandwidth and noise level are related things.Wide bandwidth antenna will suck in a lot of noises, so it will have higher noise level.Narrow bandwidth antenna is sensitive to a narrow spectrum of frequencies and as result it has low noise level.

author: DaJMasta
author_rank: Super Contributor
timestamp: March 16, 2019, 05:08:37 am
content: Got most of what's needed above, but in your case you may be getting some added noise from overloading your SDR's frontend. Putting in some attenuation in or turning down your gain stage should solve some of the nonlinearities you're seeing from the frontend being overloaded - the solid red bands are a good indicator of overload, but a lot of times the noise associated with it manifests as those evenly spaced tones across much of the spectrum, the large spread of lines in your spectrogram.

author: Lord of nothing
author_rank: Super Contributor
timestamp: March 16, 2019, 04:05:54 pm
content: HiNow I put this:https://www.delock.de/produkte/S_89435/merkmale.htmlin the window and use an Adapter for both sides to get pro the crap connector who is connect with the "antenna" (aka Wire). Now I could reduce the noise.I also put the power down.EDIT: I forgott to tell I wrapped the Delock Cable in Alu Tape.

author: Lord of nothing
author_rank: Super Contributor
timestamp: March 18, 2019, 04:54:52 pm
content: @radiolistenerI am sourroundet by Metal thinks. Even the Fence are Made out of Metal Wire.So what can I do?

author: radiolistener
author_rank: Super Contributor
timestamp: March 18, 2019, 05:27:05 pm
content: Quote from: Lord of nothing on March 18, 2019, 04:54:52 pmtry to setup your antenna as far as possible from metal things.You can use tall trees in order to install antenna at high altitude and get it away from the ground and metal things.Use long coaxial cable in order to install antenna on long distance from home and metal fence.Use symmetrical antenna, such as half-wave dipole or inverted vee.It will helps to avoid use feed line as a part of antenna and reduce noises.Add RF choke on coax cable and balun at antenna feed point, it also helps to reduce noise.If it is not possible, then it is bad.But you can still use small active antenna with amplifier, just lift it as high as possible to get away from metal things.

author: Lord of nothing
author_rank: Super Contributor
timestamp: March 18, 2019, 07:49:33 pm
content: I cant mount anything hight how about an Cable next to the floor?

author: Lord of nothing
author_rank: Super Contributor
timestamp: March 27, 2019, 01:52:23 pm
content: So I wan built one of this nice and shiny Cable Antenna what do I need for?THX!

author: trevatxtal
author_rank: Contributor
timestamp: March 28, 2019, 06:52:44 am
content: I don't know where the Noise is coming from.A quick and cheap method to detect RF noise source is to use a battery powered Medium Wave radio receiver that has a fer-rite rod antenna.Tune the radio off station so only background noise is heard, then rotate the radio .It will be found that noise will be more in two directions, if very close to the source of interference then in all directions as the signal swamps the receiver.By moving about your property you should be able to track down the source.Happy Hunting.

author: Lord of nothing
author_rank: Super Contributor
timestamp: March 28, 2019, 10:14:10 am
content: I use my 2nd. Laptop for SDR Stuff in the Momment and cant Post another Picture yet but trust me the Noise is that wideband you will not hear anything or it sound like some hight frequency brbrbrbrbr...

author: radiolistener
author_rank: Super Contributor
timestamp: March 30, 2019, 04:30:39 pm
content: The noise coming from switching power supplies which is used in various home electronics, digital electronics also emits a lot of RF noise (computers, notebooks, etc). Also the noise comes from cheap Chinese LED lamps, or other cheap so called "energy saving" lamps. For example fluorescent lamps or magnetic induction lamps. Faulty mercury-vapor lamp can emit very strong noise in short wave band. Also high voltage power lines with a damaged insulator can produce very strong noise in short wave band.All these things emitting RF noise.Chinese guys save money mainly on components which is intended to limit noise leak.So, more cheap = more noise.Any modern home is full of these noise sources.

author: Lord of nothing
author_rank: Super Contributor
timestamp: March 31, 2019, 02:53:45 pm
content: So I will try to make an good Antenna and see what I could receive with.Are there any recommendation for?

author: radiolistener
author_rank: Super Contributor
timestamp: March 31, 2019, 06:32:45 pm
content: I already provided you with recommendations:1) use long coaxial cable to place your antenna far away from home, mains line and any kind of metal things, wires or ground.2) place good RF choke on both side of coaxial cable and connect coaxial cable to antenna through balunAlso you're need to make sure that coax cable is matched with antenna input impedance. It may require some matching circuit. Usually, if your antenna is tuned for resonance (X=0), then it can be done with properly chosen balun. Otherwise, you will need some tuner circuit at the antenna feed point.You can place tuner circuit near the receiver, but in such case you will have a lot of loss in the coaxial cable.Regarding the antenna, the most simple antenna is a Half-wavelength Dipole.Also you can use Inverted-V. Both are simple and very popular for short wave.In order to match your antenna with coaxial cable, you're needs antenna analyzer, which can measure impedance (R and X components) of the antenna at selected frequency. With help of antenna analyzer, you can calculate proper impedance matching circuit. Also you can use antenna analyzer in order to tune your antenna for desired impedance, in such way you can use some existing matching circuit or a balun with standard impedance transformation ratio.Also note, that a wire used for antenna should be low resistance at high frequency.Because any resistance will leads to loss (part of energy will be loss to heat wire).Copper wire is the best for antenna, because it has low resistance, but it is expensive.Aluminium wire has more loss due to higher resistance, but also can be used since it gets enough efficiency.But if you're planning to use high Q antenna, aluminium wire will be bad.For high Q antenna it's better to choose copper and even silver plated wire.Also note, that wire insulation affects wave propagation speed and may lead to higher loss in the dielectric.This influence is not so significant for short wave, but should be taken into account, because it leads to shorter wavelength.So, the size of your antenna should be properly corrected. Antenna analyzer will helps you.