Transmitting near a computer monitor

[JamesO]

While the cheaper radios could be a bit dirty on the output, at the end of the day you are dealing with RF energy which can couple on to both analog and digital circuits. Near field RF energy tends to be the most problematic. Usually once you are 10+ feet away from items with reasonable power, under 25 Watts this is not usually going to be a problem.

A few instances of RF that I have had over the years are:

400 MHz Motorola hand held keyed up around a computer keyboard and watched at the characters fly across the screen.

Testing some 220 MHz gear in a commercial office building and the smoke detector(s) in the area were triggered.

Way back in the day had many experiments with lighting both florescent and neon bulbs near or one antennas.

And back in the CB days I recall all sorts of fun things: TVI, audio systems receiving near field CB transmissions and I have even seen a mobile CB radio that are turned off but near another car with a CB transmitting do strange things. Was sitting in a friends car with the CB radio off and a few others were parked nearby that had CB radios. One person keyed up his radio and we could hear the entire transmission through the radio and even saw the S meter increase while the transmission was in progress. All with the radio turned off!

Just keep in mind poorly shield equipment and/or unfiltered or poorly filtered circuits can allow RF energy to couple on to analog and/or digital circuits. With digital circuits the RF energy can cause all sorts of unusual behavior.

I do not think to date I have caused any failures due to the near field RF energy.

 

[DrLoomis1978]

KK4JUG

Actually, it wasn't the radio, good quality or otherwise. It was the RF. That's why they don't recommend using radios around any suspected explosive device, especially IEDs.

Now that you mention it, I remember a scene in Die Hard 3 where the police are told by the terrorist not to use their radios because they could trigger the bomb, and the NYPD uses Motorola, so now I understand what you're saying about the quality not being the issue. Thank you.

 

[DrLoomis1978]

JamesO

While the cheaper radios could be a bit dirty on the output, at the end of the day you are dealing with RF energy which can couple on to both analog and digital circuits. Near field RF energy tends to be the most problematic. Usually once you are 10+ feet away from items with reasonable power, under 25 Watts this is not usually going to be a problem.

A few instances of RF that I have had over the years are:

400 MHz Motorola hand held keyed up around a computer keyboard and watched at the characters fly across the screen.

Testing some 220 MHz gear in a commercial office building and the smoke detector(s) in the area were triggered.

Way back in the day had many experiments with lighting both florescent and neon bulbs near or one antennas.

And back in the CB days I recall all sorts of fun things: TVI, audio systems receiving near field CB transmissions and I have even seen a mobile CB radio that are turned off but near another car with a CB transmitting do strange things. Was sitting in a friends car with the CB radio off and a few others were parked nearby that had CB radios. One person keyed up his radio and we could hear the entire transmission through the radio and even saw the S meter increase while the transmission was in progress. All with the radio turned off!

Just keep in mind poorly shield equipment and/or unfiltered or poorly filtered circuits can allow RF energy to couple on to analog and/or digital circuits. With digital circuits the RF energy can cause all sorts of unusual behavior.

I do not think to date I have caused any failures due to the near field RF energy.

Funny, almost everyone who has replied mentions those florescent bulbs. Amazing what RF can do. I too remember those CB days where they could cause all kinds of problems. Growing up, I lived in Brooklyn, NY right next to the expressway and as my grandmother would play her organ through the amp, the truckers would come right through. But now I'm understanding what's going on thanks to all of you guys. I appreciate all the feedback.

 

[DrLoomis1978]

wtp

what is the name of those nearly indestructible laptops the the cops have in their cars ?

Good point...I'd like to find out how that works without interference.

 

[DrLoomis1978]

zz0468

Your success with the LCD monitor is hit and miss. I've seen LCD monitors act up in the presence of trying from an HR. The typical failure mode is the monitor will shut down and require cycling power to restore to normal.

Consumer grade electronics are not designed to operate in the presence of strong rf fields, and newer designs are no better than older ones in that regard.

Your advice was really the easiest and safest way. I'm just going to transmit away from electrical equipment like monitors, TV's...etc. That's my best bet.

 

[DrLoomis1978]

SteveC0625

Panasonic ToughBooks. I have a CF-29 and love it.

Thanks, I'm definitely going to check that out.

 

[DrLoomis1978]

wtp

what is the name of those nearly indestructible laptops the the cops have in their cars ?

I looked further down the page and was given these names of those police laptops...Panasonic ToughBooks CF-29, General Dynamics/Itronix.

 

[fyrfyter33]

Prepare thyself for sticker shock. A new Panasonic Toughbook is about $3500-$4k, depending upon the specs.

You will have to find a used one to save money. The GD/Itronix and many of the others are similarly priced.

I am replacing tough books at work with Microsoft Surface Pros in Ruggedized cases to keep in our fire trucks and ambulances.

 

[elwood_blues]

Funny, almost everyone who has replied mentions those florescent bulbs. Amazing what RF can do. I too remember those CB days where they could cause all kinds of problems. Growing up, I lived in Brooklyn, NY right next to the expressway and as my grandmother would play her organ through the amp, the truckers would come right through. But now I'm understanding what's going on thanks to all of you guys. I appreciate all the feedback.

For years I lived @ a 3/4 mile from an FM radio station transmitter tower. I kept getting spurious music while recording on an old 8 recorder. I found when I cranked up the recording inputs, I was getting the radio station on it!

Early 90's, when I was in the FD, we kept having problems with the CO monitor on our new Rescue Truck's breathing air compressor. The manufacturers were baffled. I just happened to be in the compressor compartment one night when someone keyed the mic for a radio test. The CO monitor immediately pinned the meter and went into alarm!. I reset it and said "key the mic again". BOOM. Right off the scale and into alarm.

Live and learn.

 

[KK4JUG]

Prepare thyself for sticker shock. A new Panasonic Toughbook is about $3500-$4k, depending upon the specs.

You will have to find a used one to save money. The GD/Itronix and many of the others are similarly priced.

I am replacing tough books at work with Microsoft Surface Pros in Ruggedized cases to keep in our fire trucks and ambulances.

For what it's worth, Consumer Reports has withdrawn its endorsement of the Surface units because of their poor predicted reliability. Apparently, when they worked, they worked well, however. The operative phrase there is "when they worked."

Of 9 brands listed, the Microsoft Surface has a 25% breakage rate versus Apple's 10% rating and Samsung's 16%.

 

[JamesO]

In high RF rich areas, smoke detectors and CO detectors may need to be covered with a screen cage that is well grounded. Basically a Faraday cage that the detector is mounted inside of. The wiring may also need some Ferrite beads or a toroidal doughnut that the wiring is wrapped around.

The smoke/CO should be able to be inside the mesh cage and hopefully RF will be reduced or eliminated with a cage and/or Ferrite/Toroidal doughnut for the signal and power wiring.

 

[fyrfyter33]

In high RF rich areas, smoke detectors and CO detectors may need to be covered with a screen cage that is well grounded. Basically a Faraday cage that the detector is mounted inside of. The wiring may also need some Ferrite beads or a toroidal doughnut that the wiring is wrapped around.



The smoke/CO should be able to be inside the mesh cage and hopefully RF will be reduced or eliminated with a cage and/or Ferrite/Toroidal doughnut for the signal and power wiring.

Define “High RF rich areas” ? Doesn’t WiFi make something RF rich? I’m not sure this methodology still applies to smoke detectors as they don’t put cages on them in commercial buildings along with numerous WiFi networks.

 

[JamesO]

Define “High RF rich areas” ? Doesn’t WiFi make something RF rich? I’m not sure this methodology still applies to smoke detectors as they don’t put cages on them in commercial buildings along with numerous WiFi networks.

Wifi is not a problem. An RF rich area by my definition is where high levels of "Near Field" RF transmission is active. For example locations where handheld radios may be used within a few feet of the detectors either by design or accident. Unless the power level is pretty high over say 4-5 Watts, once you are 10-15 feet from a detector, then this should not be such a problem.

I would assume this is more of a problem with "networked" or "monitored" detectors that are connected to an alarm or annunciator panel either in a home or commercial environment. Stand along smoke detectors may be a bit more tolerant to high RF transmission levels?? Have not tried my home detectors with a handheld within a few feet.

I have personally triggered a smoke alarm in a commercial building where we were specifically running tests on RF transmitter equipment. Turned out there was a smoke detector almost directly overhead where we were testing and it triggered almost immediately when the transmitter was activated. As I recall we then decided it was not a wise idea to do this type of testing in this location and we relocated to an area were we were more isolated from these detectors. In this case the problem was solved by relocating along with reducing the power output of the transmitter.

 

[jonwienke]

Define “High RF rich areas” ? Doesn’t WiFi make something RF rich?

No. Wi-Fi power is measured in milliwatts, and isn't normally powerful enough to cause the kind of interference being discussed here.

 

[fyrfyter33]

Thanks for an explanation. It’s a term of actual power output, not how much RF is roaming around.

 

[bharvey2]

Actually, it wasn't the radio, good quality or otherwise. It was the RF. That's why they don't recommend using radios around any suspected explosive device, especially IEDs.

When I saw your comment, this was the first thing that came to mind though I suppose IED's aren't labeled accordingly:

This device complies with part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation.

On a more serious note, Whenever I key up my HT around my work computer monitor, the screen freezes, I noticed that I can't scroll the mouse and key up at the same time.

 

[DrLoomis1978]

fyrfyter33

Prepare thyself for sticker shock. A new Panasonic Toughbook is about $3500-$4k, depending upon the specs.

You will have to find a used one to save money. The GD/Itronix and many of the others are similarly priced.

I am replacing tough books at work with Microsoft Surface Pros in Ruggedized cases to keep in our fire trucks and ambulances.

Yep, I did some research on those and they're just a bit out of my price range LOL. It's not even worth finding a used one, I'll just stick with an ipad or something like it.

 

[DrLoomis1978]

elwood_blues

For years I lived @ a 3/4 mile from an FM radio station transmitter tower. I kept getting spurious music while recording on an old 8 recorder. I found when I cranked up the recording inputs, I was getting the radio station on it!

Early 90's, when I was in the FD, we kept having problems with the CO monitor on our new Rescue Truck's breathing air compressor. The manufacturers were baffled. I just happened to be in the compressor compartment one night when someone keyed the mic for a radio test. The CO monitor immediately pinned the meter and went into alarm!. I reset it and said "key the mic again". BOOM. Right off the scale and into alarm.

Live and learn.

I'm learning more and more everyday how much RF can do to interfere with so many different devices. This is why I come to these forums. You guys always offer tons of info. Thanks elwood_blues.

 

[fyrfyter33]

For what it's worth, Consumer Reports has withdrawn its endorsement of the Surface units because of their poor predicted reliability. Apparently, when they worked, they worked well, however. The operative phrase there is "when they worked."



Of 9 brands listed, the Microsoft Surface has a 25% breakage rate versus Apple's 10% rating and Samsung's 16%.

I need Windows devices, so I’m kind of stuck. So far, so good and we got extended warranties so no worry on my end.

It was much easier to sell a $22k upgrade, with the thought we may have to replace a surface or two along the way, than to sell a $45k upgrade, specc’ing more Toughbooks.

 

[lmrtek]

Regardless of who made the radio, ANY hand held radio can cause damage to monitors so its important that you don't transmit at higher power levels near them

I've had to repair many monitors because some rent a cop keyed up in front of the monitor

They are usually shielded very well but a 5 watt radio from a few inches away can still cause problems