Brainstorming session: what broadcasts at 300MHz?

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Brainstorming session: what broadcasts at 300MHz?

Postposted on Wed Nov 30, 2011 1:46 am

Besides being the transition point between the VHF and UHF radio frequency bands, what uses 300MHz?

Reason for the question is that the remote fob for my car alarm runs around 302MHz according to the FCC ID code on the back. Recently, it just about won't work when I'm parked in my carport. Either nothing happens in multiple attempts, or it unlocks without chirping the horn as though I held the button for the extra half second, even if I didn't, that sort of thing. This just started a month ago and the interference is not continuous, but has been found at all hours of the day, and is there more often than not. I know it's not the fob battery or the master unit within the car, because first, I double-checked both and they're fine; second, the unit works normally everywhere else; and third, it worked normally in the carport until just about a month ago. There are major TV transmitter towers a couple miles northwest of me, but those have always been there and AFAIK nothing has changed recently.

So, my best guess is that one of the neighbors must be playing with something on or near 300MHz band, and I'd like to try and figure out what and where. Any suggestions? If this continues I'll report suspicious interference to the sheriff's department, but it would be helpful if I could point to the probable origin, first.
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Wed Nov 30, 2011 10:26 am

It's potentially a frequency used by the military for voice communications. I googled a PDF mentioned in a dead link at the bottom of the UHF article, and found this:

http://tsc-60.cellmail.com/tsc-60/TSC-1 ... 64_pdf.pdf

Note the operating frequency mentioned on the last page.
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Wed Nov 30, 2011 12:08 pm

Very interesting, and 10W of broadcast power could definitely swamp other nearby signals operating in the mW range, although there are no military operations or training facilities within broadcast range of my neighborhood, nor any nearby transportation routes (military aircraft will fly over the area once or twice a month at most, typically). Closest that I know of would be the USAF Academy in Colorado Springs, and a couple small USAF R&D bases in the same area, all 80+ miles south and southeast.
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Wed Nov 30, 2011 1:18 pm

What about Warren AFB in Cheyenne? Or if if you are into tinfoil hats, Warden Valley West. Allegedly has a tunnel to Montana! :D
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Wed Nov 30, 2011 1:44 pm

Well, I was hoping to discover something more like a malfunctioning baby monitor, but (a) those usually operate in the 900MHz range AFAIK and (b) I like where this thread is going :lol:

What about remote control toys? Last I knew those were all either 27MHz or 49MHz but I've been out of the loop a good long while...
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Wed Nov 30, 2011 4:14 pm

If he was into tinfoil hats, he wouldn't have this problem. Well, not if his car was wearing the hat. And he was inside it along with his car. Tinfoil carport? Hmmm, 300mhz works out to exactly 1m wavelength, yes? That's conveniently human-scale. Wonder what the drones at Home Depot would say if you went down and asked them about the best wire for building a Faraday cage? (Clearly as part of the apocalypse coming in 2012 the New World Order is going to prevent us from being able to unlock our cars to run away, since Americans no longer remember how to use actual keys, and they're testing this in Colorado. )

To return to reality, the FAA uses various frequencies in the UHF-VHF range for beacons and communications (and so does the military, as TwistedKestrel noted). It's possible there's some new repeater or facility in your area. You could always try filing a complaint with the FCC, but obviously you need more information (and good luck with that in any event).
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Wed Nov 30, 2011 4:29 pm

UberGerbil wrote:If he was into tinfoil hats, he wouldn't have this problem. Well, not if his car was wearing the hat. And he was inside it along with his car. Tinfoil carport? Hmmm, 300mhz works out to exactly 1m wavelength, yes? That's conveniently human-scale. Wonder what the drones at Home Depot would say if you went down and asked them about the best wire for building a Faraday cage? (Clearly as part of the apocalypse coming in 2012 the New World Order is going to prevent us from being able to unlock our cars to run away, since Americans no longer remember how to use actual keys, and they're testing this in Colorado. )

To return to reality, the FAA uses various frequencies in the UHF-VHF range for beacons and communications (and so does the military, as TwistedKestrel noted). It's possible there's some new repeater or facility in your area. You could always try filing a complaint with the FCC, but obviously you need more information (and good luck with that in any event).

I hear brass screen or sheeting works great, but neither are cheap. As for accessing the car...the keys work fine, but unfortunately, this is a lower-end aftermarket system which doesn't have lock cylinder switches in the doors, so neighbor annoyance is guaranteed -- especially if this is one of those times when I happen to be out and about during very odd hours of the day. So far the three of us who share this townhouse have a good relationship with the neighbors, particularly the family on one side with four young kids, and the older widow on the other side with the excitable terrier and lots of free time to spend at the HOA meetings.

I think what I really need is an affordable handheld device that can detect incoming RF in a given band, and then point in the direction of the source. I can't say as I've seen a device with VHF/UHF detection capability that could be described as affordable.
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Thu Dec 01, 2011 8:34 am

How about trying to find your local Ham Radio club and posing it as a puzzle to them? I'm sure they'll either know about the transmitter already or have the equipment to get to the bottom of it.
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Thu Dec 01, 2011 9:01 am

Hams enjoy the fox hunt. You'll definitely find an enthusiast willing to hunt down the signal if you ask.
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Thu Dec 01, 2011 10:20 am

Have *you* acquired/moved/reconfigured any electronics in your house around the time when the trouble started? Just because something isn't a radio-frequency device doesn't mean it isn't radiating EMI. For example, it could be a PC with sub-standard EMI shielding that got moved closer to the carport or had its BIOS settings changed (tweaking clock settings or disabling "spread spectrum" can shift the frequencies of the emitted EMI).

Easiest way to rule this in/out would be to temporarily shut off all electronics in the house, and see if the problem persists.
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Thu Dec 01, 2011 10:43 am

Don't some mobo primary frequency standards run in the 300MHz area?
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Thu Dec 01, 2011 10:50 am

Captain Ned wrote:Don't some mobo primary frequency standards run in the 300MHz area?

Not sure how close to 300MHz the master clock is, but there's *all* sorts of stuff inside a PC that switches in the 10s and 100s of MHz. Furthermore, since they are digital pulses (squarewaves), you're radiating at all the odd harmonics (3x, 5x, 7x, etc.) of the actual switching frequencies as well.
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Thu Dec 01, 2011 11:25 am

Remote controlled toys run typically at 2.4gHz or 72 Mhz. i.e. they won't be the problem.

I can't believe they still install car alarm systems in that band. It has been a known issue that ~300-500MHz gets TONNES of interference from police/radio/etc.

Only thing you can do is the top gear trick of sticking the key to your head when you try to unlock it.

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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Thu Dec 01, 2011 12:12 pm

yep sticking the remote to your chin then hitting the buttons doubles its effective distance,somehow our domes act like a amplifier antenna.
I have 1st hand results from work looking for cars getting serviced.Toyotas but seems to work with most every transmitter.
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Thu Dec 01, 2011 1:25 pm

just brew it! wrote:Have *you* acquired/moved/reconfigured any electronics in your house around the time when the trouble started? Just because something isn't a radio-frequency device doesn't mean it isn't radiating EMI. For example, it could be a PC with sub-standard EMI shielding that got moved closer to the carport or had its BIOS settings changed (tweaking clock settings or disabling "spread spectrum" can shift the frequencies of the emitted EMI).

The one possibility that I know of is that I rebuilt my main PC back in October, and then moved 80% of the old hardware into the media PC in the basement. However the media PC is normally shut down, and the new build upstairs -- which would be physically closest to the carport -- is in sleep mode whenever I'm not using it. From an RF perspective it is rather tightly sealed up inside an Antec Sonata (even have all of the spare slot bracket blanks installed). No funky acrylic windows or anything.

yogibbear wrote:I can't believe they still install car alarm systems in that band. It has been a known issue that ~300-500MHz gets TONNES of interference from police/radio/etc.

Only thing you can do is the top gear trick of sticking the key to your head when you try to unlock it.

That one I did try but without much effect. Regarding the operating frequency, this alarm was probably installed by the original owner or the dealer when the car was new, back in 2002, so the technology may be old, or there may be FCC restrictions, who knows. Some garage door openers are also 300MHz, and in any case, the signal only has to transmit very briefly so interference is usually less of a concern than if the signal had to broadcast continuously (e.g. WiFi).
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Thu Dec 01, 2011 1:31 pm

yogibbear wrote:Remote controlled toys run typically at 2.4gHz or 72 Mhz. i.e. they won't be the problem.

75MHz is apparently allowed for ground-based toys (i.e. RC cars/boats but not aircraft). There could be a 75MHz toy with a sloppy RF transmitter that is radiating significant 4th harmonic...
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Thu Dec 01, 2011 1:43 pm

ludi wrote:
just brew it! wrote:Have *you* acquired/moved/reconfigured any electronics in your house around the time when the trouble started? Just because something isn't a radio-frequency device doesn't mean it isn't radiating EMI. For example, it could be a PC with sub-standard EMI shielding that got moved closer to the carport or had its BIOS settings changed (tweaking clock settings or disabling "spread spectrum" can shift the frequencies of the emitted EMI).

The one possibility that I know of is that I rebuilt my main PC back in October, and then moved 80% of the old hardware into the media PC in the basement. However the media PC is normally shut down, and the new build upstairs -- which would be physically closest to the carport -- is in sleep mode whenever I'm not using it. From an RF perspective it is rather tightly sealed up inside an Antec Sonata (even have all of the spare slot bracket blanks installed). No funky acrylic windows or anything.

OK, so that's *probably* not it. But there are still clock signals in sleep mode, since the system needs to continue refreshing the DRAM. Couldn't hurt to try turning that PC off completely once, just to see if there's any effect.

For the test, I would unplug everything from the wall (monitors, printers, etc. typically still have some active circuitry in them even when they are "off"), and make sure any wireless peripherals (e.g. cordless mouse) are switched off or have their batteries removed. If you ran Ethernet to the upstairs room from a switch located elsewhere in the house, unplug the network cable at the switch end too.

If you do these things and the interference continues, I think you've conclusively eliminated that PC as a potential culprit.
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Thu Dec 01, 2011 1:49 pm

Have you simply tried replacing the battery in the key fob? Perhaps you have a place with marginal reception for whatever reason and a partially discharged battery is giving you less power out than you had a month ago.

Is the carport metal or has significant amounts of metal in its construction? Other things stored in and around the carport that may have moved between the working and non-working time periods. Radio wave can get reflected or obstructed by many objects. In the case of a reflection your reciever might be seeing the same signal but twice over two different paths causing interference....you could see this look visually as ghosting back in the days of analog TV reception.

If you go chasing an interference problem, also keep in mind that it could be intermod. So, not necessarily a 300 MHz emission causing you problems but two seperate frequencies that combine to cause you grief in your frequency.
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Thu Dec 01, 2011 2:18 pm

videobits wrote:If you go chasing an interference problem, also keep in mind that it could be intermod.

For anyone who is wondering what "intermod" means: http://en.wikipedia.org/wiki/Intermodulation
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Wed Oct 31, 2012 10:42 pm

An epilogue, of sorts:

Over the past ten months I've concluded that the problem is broader in my local area than I originally thought, as I have identified other locations around town where it will have trouble picking up. The carport just happens to be uniquely bad, I assume the steel roof and adjacent townhouse act as a "trap" to concentrate the interfering signals. At some point I spread out the base unit's antenna wire in a different orientation within the dash console for better pickup, and although I sometimes have to be standing next to the car to activate the remote, it will always lock/unlock now.

I still wouldn't be surprised to learn that some sort of tower was activated or increased in power about the time I first started having problems, but I never did find out what it might be.
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Fri Nov 02, 2012 2:32 am

According to this PDF the only things in the 300Mhz range are Aeronautical Radio-Navigation and Maritime Radio-Navigation Beacons.

http://www.ntia.doc.gov/files/ntia/publ ... lochrt.pdf

If you're by an an AFB that might be is after all.
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Fri Nov 02, 2012 10:46 am

tfp wrote:According to this PDF the only things in the 300Mhz range are Aeronautical Radio-Navigation and Maritime Radio-Navigation Beacons.

http://www.ntia.doc.gov/files/ntia/publ ... lochrt.pdf

If you're by an an AFB that might be is after all.

Nearest AFB is Buckley, which is over 20 miles east, and that's an R&D facility. At this point the more likely scenario is that high-power RF on a different bandwidth is simply swamping other signals.
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Fri Nov 02, 2012 2:11 pm

Yeah, when I mentioned navaids up-thread I went and looked at the sectional for Denver and didn't see anything new or unusual; if you're 20 miles west of Buckley there shouldn't be anything powerful around you at all, at least from an aviation standpoint. (There are some unusual flight restrictions on the chart for the next couple of days apparently because of an Air Force Two visit, but that has nothing to do with this)
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Re: Brainstorming session: what broadcasts at 300MHz?

Postposted on Fri Nov 02, 2012 2:11 pm

20 Miles isn't very far, that's still line of site for a tower (or airplane). Assuming a digital signal getting 20 miles shouldn't be an issue even with pretty low wattage.

If it is an harmonics issue that is causing the problem; someone's HW is messed up.
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