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Author Topic: Time for a Faraday cage for my rig?  (Read 496 times)

XW0LP

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Time for a Faraday cage for my rig?
« on: April 14, 2021, 04:05:20 AM »

In my quest to reduce the S7-S9 band-wide QRN at my QTH, I just made an important discovery!

My house on the outskirts of Luang Prabang has a garden where I erected my quarter-wave fan wire verticals for each band, (top band has a loading coil), and I use either 32 ground radials or 2 tuned elevated radials for each band.  I've been trying all sorts of ground/antenna systems to reduce the noise level on receive. Magnetic loop, pennant antenna, MFJ noise canceller etc - nothing reduced the back ground noise level at all.

There is a 3 phase transformer 50 metres away and 220 volt 3 phase cables on 2 sides of my property.  My transmit signal gets out well!  But especially on the low bands, the stations that hear me (and call me), are lost under the S7-S9 noise...

I tried powering my rig from a car battery = no reduction in noise level.
With the rig powered from the battery, I switched off the 220 volt mains supply to the house and everything in it, and powered off my UPS that I use for my wifi routers.  The noise level stayed the same!

I've used a 'sniffer' to look for noise sources, but it's wideband, presumably coming from the power lines on 2 sides of the house.

Today, I took my rig down to my antennas, (about 25 metres away from the house and perhaps 15 metres away from the nearest power line), and powered the rig from the car battery, and connected it to my antenna feed point.

WOW!!  The background noise level has dropped on all bands to about S1 - S2!!  Signals are booming in :)

So why is the noise level so high in my house, with everything powered off, common mode choke on both ends of my coax feedline?  How is the noise getting into my rig, even when it's powered from a battery?  I'm stumped!!

..... stumped, but also very happy that the noise level all but disappears when I use my rig next to my antennas.

So.... since I don't really want to play DX in a tent camped by my antennas in the garden, what's the best way to eliminate the noise that gets into my rig when it's in my house?

The only solution that I can think off is to place the receiver inside a faraday cage, with just the antenna cable and power lines/battery line coming into the cage.

I would appreciate your suggestions!

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W9IQ

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Re: Time for a Faraday cage for my rig?
« Reply #1 on: April 14, 2021, 04:56:51 AM »

You probably have common mode current on your coax. The noise from your shack area is being coupled into the antenna system. Several proper ferrite chokes with > 5 k of real resistance will probably help.

Also check the integrity of your coax connectors. A fraction of an ohm of resistance can allow the induction of noise.

Don't overlook the possibilty that your UPS is a source of RFI - they often are.

Best wishes in solving the issue.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

WA9AFM

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Re: Time for a Faraday cage for my rig?
« Reply #2 on: April 14, 2021, 06:25:52 AM »

Ditto!!  Look for loose or corroded connectors at both ends.  You didn't mention the age of the coax.  If it has been in service for a while, it might be a good time to install fresh feedline.
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XW0LP

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Re: Time for a Faraday cage for my rig?
« Reply #3 on: April 14, 2021, 06:40:31 AM »

You probably have common mode current on your coax. The noise from your shack area is being coupled into the antenna system. Several proper ferrite chokes with > 5 k of real resistance will probably help.

Also check the integrity of your coax connectors. A fraction of an ohm of resistance can allow the induction of noise.

Don't overlook the possibilty that your UPS is a source of RFI - they often are.

Best wishes in solving the issue.

- Glenn W9IQ

Thanks for your comment.  I have a very good ferrite choke at both ends of my coax line.  I'm running the rig from a motorcycle battery for my RFI tests, not using the UPS :)

The coax is new (I had the same noise problem with old coax).

The coaxial connectors and all pigtail coax and connectors to/from my ATU have been checked or resoldered or are new.
« Last Edit: April 14, 2021, 06:43:53 AM by XW0LP »
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XW0LP

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Re: Time for a Faraday cage for my rig?
« Reply #4 on: April 14, 2021, 07:32:26 AM »

Quote
...The noise from your shack area

I forgot to re-state in my last post that my noise floor is S7-S9 when ALL my shack equipment AND the electrical supply to ALL of my house is switched off.  So the noise is coming from outside my house and I guess because it's wideband that it's the mains transformer and power lines that border 2 sides of my property.

Anyway, I've built the frame for a faraday cage.  I'll buy some fine metal mesh to complete the cage and then do tests with my rig inside it!
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W9IQ

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Re: Time for a Faraday cage for my rig?
« Reply #5 on: April 14, 2021, 07:33:53 AM »

Would you mind describing your ferrite chokes in some detail?

To have that much of a noise difference points to bad coax, bad connections or common mode current - especially when operating off of a battery.

Are there any other devices on the coax such as ground connections, lightning arrestors, antenna switches, SWR meters, etc. that are not there when connecting to the antenna while away from the house?

Have you used the TDR feature in your VNA to check for any impedance bumps?

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

K6AER

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Re: Time for a Faraday cage for my rig?
« Reply #6 on: April 14, 2021, 09:26:40 AM »

When you disconnect the radio from the antenna is your noise still there? If not, a faraday cage will do nothing. Then the noise is commong in via the coax.

Is the noise random static?

Is it constant in level?

Does your radio have a spectrum scope? If so what are you seeing on the water fall?

Is there a 50-60 Hz component to the noise? If not, then the power lines are most likely not the source of your noise.

What bands does the noise appear on?

How close are your neighbors?

Does the noise ever go away? If so, when?

Good luck.


Mike - K6AER
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XW0LP

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Re: Time for a Faraday cage for my rig?
« Reply #7 on: April 14, 2021, 03:41:38 PM »

When you disconnect the radio from the antenna is your noise still there? If not, a faraday cage will do nothing. Then the noise is commong in via the coax.

Is the noise random static?

Is it constant in level?

Does your radio have a spectrum scope? If so what are you seeing on the water fall?

Is there a 50-60 Hz component to the noise? If not, then the power lines are most likely not the source of your noise.

What bands does the noise appear on?

How close are your neighbors?

Does the noise ever go away? If so, when?

Good luck.


Mike - K6AER

Mike, to answer  some of your questions:

When my rig is in my shack operating position, the noise is still present at S7-S9 levels when the antenna feedline is disconnected!  The noise falls to S1-S2 if I do the same test with the rig next to my antenna feed-point, (and is still S1-S2 when I connect the antenna as well).

The noise is wideband and relatively constant all the time.  I'm pretty sure that it's the power lines next to my house.

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AC7CW

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Re: Time for a Faraday cage for my rig?
« Reply #8 on: April 14, 2021, 05:07:57 PM »

The ARRL published some tests of equipment in faraday cages and got some funny results. One rig was shielded better when the door was open to the cage. You might want to experiment a bit with your cage once it's built.
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KC9NVP

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Re: Time for a Faraday cage for my rig?
« Reply #9 on: April 15, 2021, 05:07:50 AM »

Am I missing something?  With the radio connected to the coax cable and antenna you have S7-S9 noise.  At the antenna feed point its S1-S2, with no coax cable.  All the while you have 220 volt power lines along two sides of your property.   Between the two test you get a lower S noise closer to the power lines.  If the power lines are the issue, how can that be when the noise is lower closer to the lines than when the radio is in your shack?

You also indicate that with the radio in the shack and no coax connected, the noise is S7-S9.  To me this indicates something in your house is the source of your noise.
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KH6AQ

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Re: Time for a Faraday cage for my rig?
« Reply #10 on: April 15, 2021, 08:49:25 AM »

What is the receive antenna?
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K0UA

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Re: Time for a Faraday cage for my rig?
« Reply #11 on: April 15, 2021, 12:56:47 PM »

to the original poster:  Are you saying with your rig sitting on a wooden desk and running off of a battery and NO ground wire connected to it and everything in your house turned off, AND no antenna coax connected to it, you have an S7 noise level on the receiver?  Is that what you are saying?  Just to be clear.
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73  James K0UA

XW0LP

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Re: Time for a Faraday cage for my rig?
« Reply #12 on: April 15, 2021, 08:27:14 PM »

Am I missing something?  With the radio connected to the coax cable and antenna you have S7-S9 noise.  At the antenna feed point its S1-S2, with no coax cable.  All the while you have 220 volt power lines along two sides of your property.   Between the two test you get a lower S noise closer to the power lines.  If the power lines are the issue, how can that be when the noise is lower closer to the lines than when the radio is in your shack?

You also indicate that with the radio in the shack and no coax connected, the noise is S7-S9.  To me this indicates something in your house is the source of your noise.

"Between the two test you get a lower S noise closer to the power lines."

I don't recall saying that.  My shack is close to the power lines, and the S level is about S7-S9, with or without my antenna connected.  At the feed-point of my antenna, which is further away from the power lines, the S level is about S1 without the antenna connected, and about S2 with it connected and receiving signals.

Since the S level in my shack is the same high level, with or without antenna connected, and also the same high level when I cut the mains supply to my house completely and power the rig off a battery, - I have to conclude that the high noise level is not due to currents on my coax feedline (I use hefty chokes anyway), does not come from within my house (the noise level is still there with everything powered off), and therefore is likely to come from outside the house.  The wideband buzzing nature of this RFI leads me to think that it is from the nearby power lines.  My test with a faraday cage around my rig should provide more data to reach a better conclusion :)
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XW0LP

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Re: Time for a Faraday cage for my rig?
« Reply #13 on: April 15, 2021, 08:29:27 PM »

to the original poster:  Are you saying with your rig sitting on a wooden desk and running off of a battery and NO ground wire connected to it and everything in your house turned off, AND no antenna coax connected to it, you have an S7 noise level on the receiver?  Is that what you are saying?  Just to be clear.

Yes!!  It's very frustrating...

Also, I have a different rig (Icom 706) sitting next to my main rig (Icom 735).  That 706 rig exhibits exactly the same problem with S7-S9 noise , WITH NO antenna connected.

Do you think someone is aiming high power RFI at me from outside ? :)
« Last Edit: April 15, 2021, 08:32:07 PM by XW0LP »
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K0UA

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Re: Time for a Faraday cage for my rig?
« Reply #14 on: April 17, 2021, 07:33:32 AM »

to the original poster:  Are you saying with your rig sitting on a wooden desk and running off of a battery and NO ground wire connected to it and everything in your house turned off, AND no antenna coax connected to it, you have an S7 noise level on the receiver?  Is that what you are saying?  Just to be clear.

Yes!!  It's very frustrating...

Also, I have a different rig (Icom 706) sitting next to my main rig (Icom 735).  That 706 rig exhibits exactly the same problem with S7-S9 noise , WITH NO antenna connected.

Do you think someone is aiming high power RFI at me from outside ? :)

Well, it is certainly something I have never seen. No answer readily comes to mind.
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73  James K0UA
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