Electronics > RF, Microwave, Ham Radio

Impact of elevator on 14MHZ (and how to remove it)

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mehdi:
Hi
When 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):

--- End quote ---


Elevator starts to work:

--- End quote ---


Elevator stops:

--- End quote ---


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

Jeroen3:
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.

JimRemington:
Try grounding the cable shield.

uncle_bob:
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

cdev:
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.

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