Shortwave radio noise & the level of SWL Interference - Page 1
Forum section: electronics / rf-microwave

author: jonovid
author_rank: Super Contributor
timestamp: April 14, 2021, 02:43:56 am
content: recently I decided to hook up the trusty Tecsun 660 Shortwave radio to the outside 21 meter long wire urban wire antenna for some SWLin metropolitan Adelaide. as this was a working system in 2017but got only noise & Interference from 1MHz up to 18MHz thinking it was a loss of the impedance transformer grounding by a earth wire failure.I did re-test the external antenna and its indoor impedance transformer circuit, transformer grounding and the coax . however no fault found in the antennaso I decided to build a passive 0.5 to 30MHz tapped coil antenna tuner box with attenuator for receiving shortwave in the hope that this may help?however I decided post to the forum. before wasting any more time and money on SWLI have not used the shortwave radio for a year or two and new LED street lighting may have something to do with it?see image here is the outside 21 meter long wire urban wire antenna setup I use. its a copy of theTechnical and historicalsite SWL antenna design.this was ok back in 2015 when I did first got the Tecsun 660 and needed a good SWL antenna.I will also note that a891KHz AM signalis so strong it will drive the multimeter continuity test piezo buzzer as a speakerI get ABC Adelaide radio station 891 kHz AM on my multimeter piezo buzzer. even though the station is on the other side of the city .

author: coppercone2
author_rank: Super Contributor
timestamp: April 14, 2021, 03:08:03 am
content: I do know that with my tecsun some stations come in alot better on my shielded loop then on the normal antenna, it makes a huge difference, depending on where I am sitting. Keep in mind the ext antenna input there is not 50 ohms, the impedance is changed based on setting. Did you try different settings to see what happens?i.e. local, dx and the other one

author: ocw
author_rank: Regular Contributor
timestamp: April 14, 2021, 03:40:56 am
content: QuoteIf they have a significant length of wire between a noisy switching power supply and your street lights you have a nice antenna to radiate that noise. Some stop lights are worse here with their long "antennas."The 891 kHz AM signal could be overloading your radio, however it did not sound like that was the case before.

author: A.Z.
author_rank: Super Contributor
timestamp: April 14, 2021, 07:13:47 am
content: Quote from: jonovid on April 14, 2021, 02:43:56 amHello jonovid, here are some thoughtsFirst of all, LED street lights may generate noise, but then those lights should be off in the morning, so if they're the source of noise, you should notice some difference in the morning, also, if the very strong signal from ABC Adelaide was already there in the past and didn't cause issues, then you may exclude it from being the cause, otherwise for sure, such a signal may overload the frontend of your receiver making it deafAnyhow, you may run a quick test by disconnecting the PL660 from the external antenna and checking if, using the internal one, you're able to pick up something; you may also drive to some "quiet spot" and test reception there, those tests will at least tell you that the 660 is working and isn't causing issuesGiven that the 660 is working, the next step would be checking the antenna, you wrote that till 2017 it worked, but you hadn't used it for some time, so the antenna may have some issues; start by checking if the various connections at both ends (receiver, coax, antenna, grounds) present oxidization or problems, in case use some deoxit to clean them, also open the unun and the transformer boxes and ensure everything inside is ok; if that doesn't solve the issue, then it may be due to either the antenna wire being damaged (e.g. if using an insulated wire, the wire may be broken at some point and the insulation layer may be keeping the antenna up) or the buried coax being damaged; to run a quick check, try connecting the 660 directly to the antenna transformer (using your adapter box), if the reception works this way, then the issue may be due to a damaged coax otherwise you may want to lower the antenna and inspect it (as a note, I'd add a second pulley at the feedpoint side too, that would help lowering the antenna and checking it)

author: Emo
author_rank: Regular Contributor
timestamp: April 14, 2021, 09:14:30 am
content: Hi,Do you have (V)DSL services in the area. Depending on underground or overhead connections they tend to generate a lot of "noise" up to 17 or 35 MhzEric

author: A.Z.
author_rank: Super Contributor
timestamp: April 14, 2021, 09:19:15 am
content: Quote from: Emo on April 14, 2021, 09:14:30 amGood point, Eric ! If that's the case, then it may be possible to (partially) solve it by using a simple vertical loop likethis one, placed outside

author: nali
author_rank: Frequent Contributor
timestamp: April 14, 2021, 09:23:04 am
content: And powerline network adapters, they generate a ton of RF crap.Coincidentally I did the same, dug out my HF receiver a couple of days ago in order to sell it, I have S7+ of noise across most of the HF bands from Powerline. DSL, PCs printers, lighting and whatever else. OK, that was with a random wire out the back of the rig but still not good

author: vinlove
author_rank: Frequent Contributor
timestamp: April 14, 2021, 10:42:35 am
content: Please try switching on and tuning around it at different times of a day.RF noise and Noise Floor of receivers and antennas can vary considerably from morning, afternoon and nights.I noticed from my SDR over night recordings of MW band, the NF figure drops drastically to between -110 and -120 dBm making the receptionvery quiet and pleasure to listen to.During the day and early evenings, they go up to -90 to even to -80dBm, it is painful if not impossible to listen to any weak signals under this level of noise.And then, there are millions of factors which can affect the MW and HF reception noise, of course including your radio and antennas too.

author: A.Z.
author_rank: Super Contributor
timestamp: April 14, 2021, 01:59:15 pm
content: Quote from: nali on April 14, 2021, 09:23:04 amand then some more; switching power supplies used inside home, plasma TV sets, solar panels... and more, all those generate a dense "cloud" of interference, then add the interference coming from neighbourhood and the one coming from public stuff like street lights, AC power transformers and so on, and it's easy to understand the kind of "RF polluted" environment we live in; I must say that from that point of view I'm lucky, I live in a very small town, uphills, and my usual noise level is around -120 to -130 dB so I can't complain about that, but I've friends "suffering" the RFI issueQuoteYou're not alone, a randomwire (or an "inverted L" as the one used by the OP) aren't exactly the quietest antennas, sure, many years ago, when the RFI was much lower, they were ok, but nowadays if one isn't living in a pretty quiet (from RF standpoint) place, a randomwire won't exactly be the best choice. I'm NOT saying it won't work, mind me, an endfed wire antenna is the simplest to setup, is almost stealth and offers decent performances in TX, but when it comes to reception, in my humble opinion, it would be a better idea considering a loop antenna, it's simple too, but it offers better S/N ratio and, if it's a vertical loop, the NULLs it offers will be useful to attenuate some strong noise source

author: HB9EVI
author_rank: Frequent Contributor
timestamp: April 14, 2021, 02:28:17 pm
content: I'm running an Inverted L but in a suprisingly quiet environment; I prefer it for sending, while I use Whips or active loops for receiving.Certainly the noise level increased over the years, so no surprise that it can be shocking to listen on the frequencies after longer abstinence.but many problems with antennas are home made; most common of course will be, that not only the antenna receives but the feedline too due to common mode currents. Many believe it's a TX only problem, but it's a rather nasty issue on the RX side too.Also drowned feedline, corroded connectors and all the sort of things can cause rx problems.after such a long idle time, it's absolutely needed to verify the antenna system first; afterward you can start searching for external qrm sources.also if you have a strong local station, you have to count with any kind of intermodulation, if the receivers frontend is not really well designed. under such conditions you're going to see design flaws very easily and in very nasty manner.

author: A.Z.
author_rank: Super Contributor
timestamp: April 14, 2021, 02:53:23 pm
content: Quote from: HB9EVI on April 14, 2021, 02:28:17 pmHi Pascal, don't get me wrong, I'm not saying that the inverted L is a bad antenna, just that isn't as "quiet" as (say) a skyloopQuoteSure, but the OP (jonovid) wrote he used that antenna from at least 2015 to 2017, and while the RFI may probably be higher today, I doubt it may be so high to totally obliterate any signal between 1 and 18 MHz ... then ok, anything is possible, by the wayQuoteAgreed, and while the OP antenna schematic (see image) shows a buried coax (which should help with CMC), I think that going for a belt and suspenders approach and adding a pair of chokes (at the antenna and shack ends of the coax) won't be a bad ideaQuoteAnd that's why I suggested to perform some checks and tests on the antenna system, if you check my post you'll see that one of the checks I suggested is directly connecting the receiver at the output of the UnUn, that would exclude the coax, so if it's damaged it will be easy to spot it that way ! (edit: also, the screw connection may be oxidized and act as "diodes" and in such a case the whole "RF hell" will go down the coax, to the receiver)QuoteTotally agreed !

author: jonovid
author_rank: Super Contributor
timestamp: April 14, 2021, 07:21:18 pm
content: thank you all for your commentsI need more time to evaluate the problem and hopefully find the source of the noise.obviously something has changed in the last two years. if its from inside the house or the neighbors. its solvable IMO.back in 2015 the antenna setup I had the Tecsun 660 getting good reception of SSB on 40 and 80 meter bands also with good Interstate MW AM broadcast band performance at night.however in 2021if the source of the noise is compound or blanket in nature, even the best loop antenna may fail to null out the noise source.walking or cycling with the Tecsun 660 around the neighborhood is an idea for a night and also a daytime test of the levels.I hope to post if I have any interesting text results. however my location maybe different for you elsewhere making it somewhat irrelevant.-thank you all

author: A.Z.
author_rank: Super Contributor
timestamp: April 14, 2021, 08:19:39 pm
content: Hey ... NO c'mon, you can't come here with a problem and just disappear !

author: coppercone2
author_rank: Super Contributor
timestamp: April 14, 2021, 10:08:22 pm
content: Can you tell us what happens when you flip the switch on the side that says DX, Local and Normal, with the internal antenna and then with your external antenna? Try to do it on something thats somewhat audible but noisy.and maybe walk around the house with the internal antenna and see what it does in different rooms?this should be quick to do

author: cdev
author_rank: Super Contributor
timestamp: April 15, 2021, 12:18:01 am
content: Plasma TV's are bad news.. often cause RFI.Ive spent at least $100 on ferrite bead RFI suppressrs, and i feel its made for enormous improvements over no ferrites.Look for a popular packet of 40 ferrite beads in multiple sizes on ebay. Ihave found they work well and are fairly big, some of them.Its around $16 here in the US.Quote from: A.Z. on April 14, 2021, 01:59:15 pm

author: jonovid
author_rank: Super Contributor
timestamp: April 15, 2021, 07:07:10 am
content: Quotefound the source of the noise!it was the lab computer. so no internet when SWLingthe shortwave bands have returned to normal,computers are noisyQuoteferrite bead RFI suppressrs do work and they are free with most used electronics. old TV's & PC's have them.

author: A.Z.
author_rank: Super Contributor
timestamp: April 15, 2021, 09:30:21 am
content: Quote from: jonovid on April 15, 2021, 07:07:10 amIs the computer a laptop one with external PSU ? If so, try disconnecting the PSU (from AC and computer) and running the computer on batteries, if (as I suspect) the noise disappears, the culprit is the power supply (battery charger), in such a case you may either replace it or add ferrite chokes to both the AC line and the line going to the laptopQuoteWhile ferrite chokes don't perform miracles, they help lowering the noise generated by various appliances/stuff, if possible buy some quantity of snap-on chokes and place them on the AC cords of TVs, computers, LED lights and so on;here are some, just an example, you could find them from other sourcesAnyhow, happy to hear you found the noise source, now it would be a good idea finding a way to tame it so that you'll be able to use your computer even while SWLing

author: jonovid
author_rank: Super Contributor
timestamp: April 15, 2021, 09:51:05 am
content: Quoteyes true its a Lenovo desktop pc with a custom VGA DVR unit on the video it is a one year project that finally works.brings me finally this conundrum, software defined radio on shortwave defined on what hardware?non of my 3 SDR USB units worked with window's anyway.microsoft and China don't really get along'

author: A.Z.
author_rank: Super Contributor
timestamp: April 15, 2021, 10:06:06 am
content: Quote from: jonovid on April 15, 2021, 09:51:05 am

author: jonovid
author_rank: Super Contributor
timestamp: April 16, 2021, 10:30:22 am
content: sadly the noise has returned, radiating from the AC mains. centered around 6MHz from neighbors.making any long wire antenna over the house useless. so taking to the backyard with the Tecsun 660 in handon SSB 40 meters a 200W uk? amateur radio station was reporting that a VK station had heavy QRMso we SWL-ers are not the only one's with this.I may need to relocate any long wire antenna away from anything. going portable to the local park and throwing a wire up a tree for better DX-as excuse to get out of the house.

author: A.Z.
author_rank: Super Contributor
timestamp: April 16, 2021, 04:12:39 pm
content: Quote from: jonovid on April 16, 2021, 10:30:22 amIf you want, givethis antennaa try, to build a quick prototype you may use a pair of PVC pipes or wood sticks and build a cross to support the loop wire, the transformer may be wound using a toroid or a pair of ferrite sleeves, performances won't be like the original, but it will suffice for a quick test; alternatively, if you have a piece of yard/garden, you may trythis other antenna, both antennas offer good S/N ratio and may help you improving your reception

author: cdev
author_rank: Super Contributor
timestamp: April 16, 2021, 11:55:27 pm
content: Once I attempted to match my mini whip (has jfet preamp) to a tall tree in my backyard to get more signal over my local (wicked) QRM.It seemed to kind of work. Tree is a conifer and around 50 feet tall.Quote from: jonovid on April 16, 2021, 10:30:22 am

author: cdev
author_rank: Super Contributor
timestamp: April 17, 2021, 12:00:31 am
content: [I found that puting as many as I could ferrite beads around all wires entering or leaving my PC, especially Ethernet has helped a lot.Quote from: jonovid on April 15, 2021, 07:07:10 amBut not enough of them. The suppression per ferrite is not that high so must use a lot of them. Running wires through them several times (as many times as you can) also is super helpful.