Impact of elevator on 14MHZ (and how to remove it) - Page 1
Forum section: electronics / rf-microwave

author: mehdi
author_rank: Regular Contributor
timestamp: February 14, 2016, 03:23:24 pm
content: HiWhen our elevator is working, I can not receive anything on the 20m band. (I haven't checked other frequencies)At first, I thought my SDR is faulty, but this week I connected the antenna to a commercial rig and experienced the same problem.Here's the images:Normal condition (elevator not working):Elevator starts to work:Elevator stops:My antenna is a dipole (for 14MHZ). I live in a 5-storey apartment (in 3rd floor) and my cable (RG58) is passed through the elevator room and then besides the elevator cabinet to my room (inside a flexible plastic pipe)I haven't grounded the shield (is it important?)Any ideas how to remove this noise?Thanks in advance

author: Jeroen3
author_rank: Super Contributor
timestamp: February 14, 2016, 03:50:49 pm
content: Do you own the elevator?If so, get proper filtering, earthing and shielded cables for the VFD's used to operate the elevator.Which it seems it uses, can you get a span from dc to 100khz with your device to determine the switching speed of the vfd?If not, ask the authority that does telecommunications and executes the regulations regarding telecommunications in your country (which bands you are allowed to transmit, or how much you are allowed to interfere). But before you do, lookup your local regulations to determine if the elevator is actually exceeded them.

author: JimRemington
author_rank: Regular Contributor
timestamp: February 14, 2016, 04:24:22 pm
content: Try grounding the cable shield.

author: uncle_bob
author_rank: Unknown
timestamp: February 14, 2016, 06:18:29 pm
content: Hi(read the whole thing before dashing off to do stuff ...)Ok, one possibility is that the main elevator drive motor is DC and it's up next to your antenna. There is not a lot you are going to do in that case.Here's what to try:Put a balun on the dipole so it is not ground referenced. That will kill one common path for the RF.Make sure your cable is good quality. If you are unsure, try swapping it out with RG-6 quad shield TV coax. (it's dirt cheap).Next up, put a common mode choke on the feed line at the bottom end. First step is just a few coiled turns of cable. More aggressive is to use clamp on ferrite cores. You can also spend a fortune on inline chokes (probably not useful).So how to test things:1) Pull off the antenna up on the roof, short the top end of the coax. No noise? It's not the RG-58 shield. It's likely the antenna.2) Pull the antenna off the radio and short a 10' length of cable. Attach that to the radio. Got noise? It's coming in from the AC line or local to your shack. All the messing with the antenna was not needed.3) If the radio is portable, take it up to the roof and connect it to the antenna. No noise? It's cable related (or in the shack).4) Move the antenna (like 90 degrees). Noise changes? It is most likely local to the antenna.Yes I suppose there are other things you could check. The tests above are in no particular order. A lot depends on how much access you have to various parts of the system. The one thing I would very much avoid .... don't mess with the elevator yourself. There are regulations about that sort of thing.Best guess, you will be able to fix the problem. You will still have some noise, but it will be a lot less than you have now.Bob

author: cdev
author_rank: Super Contributor
timestamp: February 14, 2016, 07:55:03 pm
content: Are you using a 1:1 balun, a good one, at the antenna end? To decouple the antenna from the feed line.You can make a good 1:1 balun pretty easily with two binocular cores - just a few loops through them, use two stacked.Look at the elecraft switchable balun for the wiring. I would use that design. Its very efficient.

author: mehdi
author_rank: Regular Contributor
timestamp: February 14, 2016, 08:46:21 pm
content: Thank you for all the answers.Some more info:My antenna is using a 1:1 balun.Here are two pictures of both the antenna and the balun itself.Antenna:(The elevator is installed in the room in the right side)Balun:Elevator is not mine. The building is new (it's not finished yet). I should check with the guy who built it, to see whether he has grounded the elevator power. (I suspect it's not grounded). I will also check the rig on the roof.The RG-58 cable is made in Taiwan and the length from balun to my rig is about 50m (I don't know whether it's a high quality one or not; When the elevator is stopped, I don't have any issues at all)

author: German_EE
author_rank: Super Contributor
timestamp: February 14, 2016, 08:57:27 pm
content: As a former elevator service engineer and a radio amateur I may be able to help here.1) Routing your antenna cable through the elevator machine room is not really a good idea. It would be better if the route of the cable is as far as possible from electrical machinery and power lines.2) Your antenna cable should have the shield connected to the chassis of your receiver/transceiver at the shack end. At the antenna end a balun MIGHT help but this is not guaranteed. If you do fit a balun then try fitting some large ferrite beads or rings to the outside of the coax.3) If you are still receiving interference then contact the company responsible for elevator maintenance by mail, include screenshots of the interference, and explain your problem to them. Work with them, this will be one engineer talking to another here, and you will hopefully find that they are willing to help. For example, they may try ferrites on the elevator wiring BUT you supply the ferrites and the elevator engineers must fit them.4) Under no circumstances touch or attempt to modify the elevator equipment. This is a safety critical installation.

author: uncle_bob
author_rank: Unknown
timestamp: February 14, 2016, 09:02:33 pm
content: Quote from: mehdi on February 14, 2016, 08:46:21 pmHiGo out for lunch with the elevator install guy. Get to know him well enough that you are a friend and not just some bothersome tenant. Once he realizes that you know a bit about this, I'll bet he shows you a *lot* of how the elevator system works (plan on an hour or two). I certainly enjoyed my tour of a system like that ... errr ... 45 years ago. Once you see how things are setup and done, you will have a much better idea of what might or might not be the problem. Don't touch anything, don't try to tell the guy what to do. He has a major responsibility for safety. It is possible that *together* you might spot something.Bob

author: cdev
author_rank: Super Contributor
timestamp: February 14, 2016, 09:24:11 pm
content: Unless it was routed with the support and cooperation of the elevator engineers, you should- no must is a better word, route your coax through an air shaft or outside the building - some other way than the elevator shaft. Also, looking at your photo of the roof, I notice that nice metal roof, that is an ideal ground for a vertical, if you can get adequate lightning protection for it. With a metal roof so close underground, my gut feeling is telling me that your 20 meter dipole might lose the biggest benefit of its height, a low angle of radiation. Sending too much of the signal straight up into the air.Another antenna that you could consider, a remotely tuned *balanced* (to negate the noise) magnetic transmitting loop, a magnetic loop with two motors, a motor for tuning it (typically they use a stepper motor and a vacuum variable) and a rotator on it, that uses the metal roof as a counterpoise. I think its likely that would give you a far better signal and more noise immunity due to it being balanced. the noise from the elevator is likely common mode noise so it would be amenable to common mode rejection techniques. I also think that a lot of ferrites on your coax - around it, would reduce the noise problem. Even if you dont implement the loop idea, see if it is possible to ground the center tap on your balun. If not get one that lets you do that. Most baluns should - the schematic I was telling you about lets you ground the middle.is that an air core balun? if so it may not be doing its job correctly, in my experience air core baluns don't work as well as one made with a toroid or especially two binocular cores.In a pinch you can substitute a bunch of super cheap noise reduction clips (if they are made out of #43 iron powder material I think that would work best for 20m) and make a balun out of them, a fairly good one. Try four to make a two binocular core type. Use them open attached to one another. use a multiple of two- i.e. four or eight.Alternatively use a power appropriate core of #2 (red) material for broadband HF 3-30 MHz. You also might want to consider using an antenna tuner and a wire elsewhere. Or a magnetic loop in your apartment near a window.

author: mehdi
author_rank: Regular Contributor
timestamp: February 15, 2016, 12:44:18 pm
content: I went to the roof and connected the balun directly to a receiver. I have the same noise, so it has nothing to do with the cable. The elevator room transmits noise (I even tested with a portable radio too)It fills about 2MHZ of spectrum with strong noise:So it's not in my hands now. I should talk to elevator's manufacturer/engineer.Thanks for the help.

author: uncle_bob
author_rank: Unknown
timestamp: February 15, 2016, 02:03:51 pm
content: Quote from: mehdi on February 15, 2016, 12:44:18 pmHiYes, I should have mentioned the portable radio !! That is a great tool for tracking some of this down.I would still consider talking to the install guy in a friendly manner. You probably will learn some things. Just keep it friendly and don't do anything that would get the poor guy in trouble.Bob

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: February 15, 2016, 03:57:16 pm
content: Hi,Watch:Not recommending this approach, but they don't have interference from the elevator. May be you could find a building with a broken elevator ?Regards,Jay_Diddy_B VE3...

author: uncle_bob
author_rank: Unknown
timestamp: February 15, 2016, 05:13:44 pm
content: HiOne thing that has not (yet) been asked:What brand (manufacturer) is the elevator? I'd hope that would be fairly obvious. In some countries it's not. The information all points to the local maintainer rather than to the manufacturer. If we get into any sort of analysis, it might be a useful thing to know.Bob

author: mehdi
author_rank: Regular Contributor
timestamp: February 15, 2016, 05:27:18 pm
content: Quote from: uncle_bob on February 15, 2016, 05:13:44 pmHiThe controller unit is designed and built by a local company. The motor is not local (I will check its brand tomorrow. It's European)For now, I will make sure that everything is grounded properly and also clap some ferrite beads to the power cables between motor and controller (9 ferrites: 3x3)@Jay_Diddy_B: I prefer to brick it by a more "electrical" method. EMP maybe?

author: HAL-42b
author_rank: Frequent Contributor
timestamp: February 15, 2016, 08:09:22 pm
content: You may need a line reactor at the input of the motor inverter. It is like a common mode choke but for three phases.

author: cdev
author_rank: Super Contributor
timestamp: February 15, 2016, 09:14:03 pm
content: No no no, in a situation like this, don't touch their equipment.At least i wouldn't now.Even if its right there, its theirs.Make contact with them, tell them you are a ham, try to work with them and do everything in writing until its clear that they are going to work with you in more than a token way.Also, those images look SO empty of signal outside that range. Ive never seen noise so narrowly confined like that. Were you using a really really small (loop?) antenna or an attenuator to capture that image?My guess is the elevator likely has no filtering on it at all.What about harmonics? There must also be harmonics at 28 MHz and so on?

author: mehdi
author_rank: Regular Contributor
timestamp: February 16, 2016, 07:09:34 am
content: Quote from: cdev on February 15, 2016, 09:14:03 pmI'm using that 14MHZ dipole and no attenuator. The bandwidth of generated noise is about 2MHZ and yes I have harmonics.Here are some more images:7MHZ (with elevator):21MHZ (with elevator):21MHZ (without elevator):28MHZ (with elevator):I don't wanna go off-topic, but things are different in my country (First, there are only 29 registered/legal hams here, so people don't know what's ham radio. Even this simple dipole has raised lots of eyebrows. Second, the guys who install/support the elevators, are not professional engineers; They just install it according to their training and don't know anything about filtering, frequency noise, etc)Thanks

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: February 16, 2016, 08:22:37 am
content: Hi,I am very suspicious of the shape of the noise being 2 MHz wide. I think it is the bandwidth of your antenna or something else. I would expect broadband noise.Jay_Diddy_B

author: uncle_bob
author_rank: Unknown
timestamp: February 16, 2016, 06:01:02 pm
content: Quote from: mehdi on February 16, 2016, 07:09:34 amHiWhich is why I would go directly to the install guy and see if it's possible to make friends with him. He will have a pretty good idea of what can or can't be done. He likely also is the one that ultimately will put the missing bolt in the ground strap connection (or whatever it is).Bob

author: cdev
author_rank: Super Contributor
timestamp: February 16, 2016, 07:31:29 pm
content: Have you considered not using a roof antenna and instead using a loop in your apartment? For example, a large bicycle rim and a capacitor with wide enough spacing can be tuned to the 20 meter band and get out better than most dipoles, assuming you are up high. No grounding is required.You will have to re-tune it when you change frequencies.

author: uncle_bob
author_rank: Unknown
timestamp: February 16, 2016, 11:17:21 pm
content: Quote from: cdev on February 16, 2016, 07:31:29 pmHiIf you try a tuned loop, be very careful with RF fields. You can easily wipe out stuff in the next apartment. This is unlikely to make you popular with the neighbors. I do have practical experience with just how mad they getBob

author: cdev
author_rank: Super Contributor
timestamp: February 17, 2016, 03:28:40 pm
content: Bob, when you say "wipe out" do you mean temporarily, (interference) or permanently ?If permanently- Ouch!

author: uncle_bob
author_rank: Unknown
timestamp: February 17, 2016, 06:07:17 pm
content: Quote from: cdev on February 17, 2016, 03:28:40 pmHiMost often, it's "wipe out" as in off the air while you are operating. Occasionally it's "this broke and I'm sure it's your fault" ....Simple solution ... don't nuke the neighbors when you are transmitting.Bob

author: mehdi
author_rank: Regular Contributor
timestamp: February 18, 2016, 08:27:07 pm
content: Quote from: uncle_bob on February 15, 2016, 05:13:44 pmThe manufacturer of the motor is Gem (Italy)Here's a picture:http://i63.tinypic.com/23t0f4m.jpgThe controller unit is made by a local company (based on Atmel AT89C51)By the way, the earth connection is not connected. So the next step is: I will first fix the earth connection, then if it didn't solve the problem, I will go for the ferrite beads and decoupling capacitors.P.S: You were correct. I tried to become a friend with the support guy. At first he wasn't interested in my problem, but after showing my antenna and my test equipment and radios, he was fascinated and asking me all sorts of questions about Electronics and radios

author: mehdi
author_rank: Regular Contributor
timestamp: February 18, 2016, 08:34:17 pm
content: Quote from: cdev on February 16, 2016, 07:31:29 pmWill I be able to contact DX stations with a mag loop? Can it tolerate 100W?

author: cdev
author_rank: Super Contributor
timestamp: February 19, 2016, 01:18:04 am
content: You should read up on them. Google "magnetic loop"They have advantages and disadvantages. For receiving they sometimes can't be beat. They let you turn the loop and cancel out noise in their null.One thing I would worry about in an apartment or indoors generally, another user had an experience with a loop in that transmitting created a field so strong I think it damaged neighbors electronics, living in an apartment building you have to be careful because your neighbors are only a few feet away above and below you.If you put the loop outdoors - maybe on an arm extended out from a balcony it might look a bit strange but likely would be safer for nearby people and electronics. One person I know who uses a loop brings his loop antenna and his (battery operated) radio to a neighborhood park.Also, capacitors need to sized in relation to the voltage you may have flying around the loop. The kinds of capacitors in radios vary in terms of their suitability and sometimes melt or arc over unexpectedly, and if that happened your radio's final would likely be toast in a second.What I am saying is, do your research first and know what you are doing. Its not the kind of antenna you can just throw up and use without much thought as to what's happening there.You should know, I am not a ham yet. I dont drive, dont own a car and need to get it together to get licensed, (basically swallow my pride and ask somebody to drive me or go into the city some evening by bus). However, the info I am giving you here is accurate.(I've lived most of my adult life in cities with world class public transpo. but don't live in one now.)I am quite familiar with using mag loops to receive. "They rock"

author: uncle_bob
author_rank: Unknown
timestamp: February 20, 2016, 01:02:33 am
content: Quote from: mehdi on February 18, 2016, 08:27:07 pmHiGet the guy on your side and you will get this solved.Actually it's a pretty good "life lesson". Making friends generally gets better results than yelling ...Bob