Interference

[JCR]

Sources of Radio Frequency Interference (RFI)

Anything "wireless"

• Wireless (turn wireless off on your computer and phone so they do not transmit)
• Bluetooth
• Cordless telephones
• Remote mice and slide advancers
• Mobile phones: Edge, 3G, 4G, LTE...

At home

• Microwave ovens (keep your radio observatory petryon-free)
• Flourescent lightbulbs (compact flourescents as well)
• Hairdryers with DC motors (AC okay)
• Electric shavers or trimmers?

Anything with a switching load above 2 amps

• transmitters
• toaster ovens
• electric blankets
• electric bug zappers
• touch controlled lamps
• CRT monitors
• anything with a de-gaussing coil (we flatscreens)
• DC motors (food processors)
• air conditioners
• anything with a circuit board
• electronics in general (rather than electrical things)

Audio and visual

• electronics camera shutters
• video cameras

 

 

 

this pretty much covers everything i have and do.......how much is this relevant?

do i need to build a room with lead walls?

[tweiss3]

@JCRAre you experiencing a significant amount of interference? While yes, almost all of the above utilize RF or can cause RF interference, there is no point in tracking down RFI around you if you are not experiencing any issues. Based on your list above, I have specific comments:

 

Anything "wireless"

• Wireless (turn wireless off on your computer and phone so they do not transmit) - This is extremely broad spectrum
• Bluetooth - This is less than 7mW in the 2.4 GHz spectrum (2.402-2.48 GHz)
• Cordless telephones - These are typically low power in the 1.9 GHz range
• Remote mice and slide advancers - These use bluetooth or other 2.5 GHz in the ballpark of 3mW
• Mobile phones: Edge, 3G, 4G, LTE... - These technologies have their own protected spectrum that cell companies pay a ton of money for. Their spectrum does not affect LMR.

At home

• Microwave ovens (keep your radio observatory petryon-free) - Don't put anything next to a large transformer or microwave
• Flourescent lightbulbs (compact flourescents as well)  - This can cause issues, but usually dont. Make sure you use the correct transformer/bulb match to avoid RFI.
• Hairdryers with DC motors (AC okay) - Why would you leave a hair drier on long enough to cause lasting RFI?
• Electric shavers or trimmers? - Same as above. Significantly short term RFI you shouldn't worry about.

Anything with a switching load above 2 amps

• transmitters - obviously another radio can cause interference
• toaster ovens - large transformer inside
• electric blankets - transformers inside
• electric bug zappers - transformer inside
• touch controlled lamps - transformer inside
• CRT monitors - transformer inside. also, HDMI and video cards often use 433 MHz as a clock speed, and can cause RFI.
• anything with a de-gaussing coil (we  flatscreens) an obsolete comment
• DC motors (food processors) Short term
• air conditioners not so much anymore
• anything with a circuit board yes, but likely hood of all circuit boards causing any noticeable RFI is zero
• electronics in general (rather than electrical things) yes, but likely hood of all circuit boards causing any noticeable RFI is zero

Audio and visual

• electronics camera shutters - Maybe, but very minor
• video cameras - Maybe, but very minor

 

In other words, unless you are having issues, don't worry about it. If you are having issues, track them down. You are not going to get RF free home. You can shut off your phones and wifi, but your neighbors wifi will still be in your house, and cell phone RF from the towers will still be all around you.

[JCR]

THANKS

[DownEastNC]

I live in an RV, which is essentially a Faraday cage with all the aluminum framing. I got WiFi going, two mobile phones, a notebook on WiFi, streaming tv and I can't say that I'm suffering from interference except for reception of some FM commercial broadcast which I have remedied by putting an antenna outdoors.

[PACNWComms]

+1 on only worrying and reacting if you experience problems. The only situation I experience in a stick built house, with lots of cell phone towers, HF equipment, and electronics, is when I key up a TDMA digital radio too close to a CB (27 Mhz "Rubber Duck" style CB, not Europe/Australia UHF CB) radio. You can here the TDMA flutter between time slots on the AM radio when keying up the DMR radio. 

In some cases, choke coils, physical separation of power and signal wires, buying better radio equipment, and even Faraday cages and aluminum foil have been used to mitigate interference. One other note, was one of my Trbo radio sites said they experienced "interferance" which was other users on their: channel, frequency, and TalkGroup (Trbo trunked network). Well the problem with that was they were hearing voice and speech on an encrypted licensed channel, and then admitted they had lost some radios. The local construction company was later found to be using them, as their voices were heard on my companies radios. This was resolved pretty quick with law enforcement assistance, and the fact that these missing/stolen radios still had company engraving on them....and it was not "interference" but actual communications taking place.

[WRFP399]

My Epson Workforce printer throws out RFI in the 462 range. It will open the squelch on my radios if I am within 10 feet on channels 2 and 19.

 

 

[wayoverthere]

My "shack" shares desk space with a work laptop and a personal laptop, a couple LCD monitors, a network switch and mesh access point, a Google speaker, a wireless charging pad, and a few radio chargers that may or may not be plugged in at any given time.  The power source for the radios is also a switching power supply, though it's one designed for radios (alinco).

The only RFI I've run into is the work issued monitor (few year old Samsung) hits the lower end handhelds (wouxun and Midland) on ch 3 and ch 6. The vertex stuff isn't bothered unless it's literally right next to the screen; the BTech mobile doesn't notice it either , with the antenna sitting roughly 6 ft away.

[mbrun]

There is always RF noise around us. I agree that you only need to worry about the RF noise to the degree that is is adversely affecting you and to the degree you are generating noise that might adversely affect others. You take the actions necessary to solve the problem, whatever it may be.


Michael
WRHS965
KE8PLM

[dhardin53]

While at the loacl hospital sitting in parking lot wating to go in I noted i believe on channel 17. A constant  high gain RF disturbance.  When i drove away it lasted 8 to 10 blocks. That channel was completely unusable within that range. 

 

[WRKC935]

Lead walls are really not that good. 

IF you really what a space that has ZERO RF in it you need a Faraday Cage.

You can look this up but i will give a brief explanation.  You need to DOUBLE line the space with wire mesh.  They make copper mesh for doing this, but aluminum window screen does a pretty good job.  This needs to FULLY enclose the space. Ceiling, walls floor. 

If you are looking to build such a room, start with creating a floor frame for the room to set on or have access to install the screen on the outside of the studs all the way around the room.  This would be done on the outside of the studs of the room.  THe outside of the room at minimum gets grounded on all four corners, and the four ground rods get bonded together.  Then on the inside of the room put up another layer of screen and then you can drywall it if you desire to do so.  Offset the screws or nails from the inside to the outside to that there is NO connection between the two.

The door for the room need to have BOTH layers of screen and they need to connect independently to the two layers as well.  The inner layer can use a wire and the outer layer can use  brass or copper weather stripping or finger stock if you really want to go the distance.

 

ELECTRICAL

For electrical there are a couple things that need done here to keep the RF OUT of the enclosure. 

First is the power feeds need to be transformer isolated.  The second is the isolated side needs capacitors to ground That are of a value that they will shunt RF to ground but allow 110 volts at 60 Hz go.  There is a manual online that the military created on grounding and RF shielding.  That manual has the values of the capacitors needed. 

 

The effectiveness of a properly build Faraday Cage is simple.  There is a 130 plus dB isolation from the inside to the outside.  Or in layman's terms.   If you are 50 feet from a radio station and you take a radio tuned to that station frequency, when you close the door you will no longer hear that station. 

[AdmiralCochrane]

I worked on a demo job at a three letter agency building once, it was isolated as described above. The laborers carried literal tons of copper screen to the recyclers. One floor, maybe 20,000 sq ft and 10,000 - 15,000 fully wired telephone connections.  Desks with headsets and typewriters - old school telephone intercept building.