RFI

Status
Not open for further replies.
Maybe Dereck knows differently, but I don't think a POCO generated interference would wipe out cell phones, satellite radio, etc.

Are you sure that the reason the devices don't work is because of RFI, or could it be that the location just is in a bad area and the signal strength is very low?
 
I looked for receivers that covered up to 2 gigs and no luck. I did find this hand held field strength meter for a couple grand.

http://www.testequipmentdepot.com/b...paign=BK Precision&utm_term=bk precision 2640

bk2640.jpg
 
shoot! lost my post! here is a condensed version rewritten...

try googling: wideband receiver scanner

It will show various ham receivers for well under $ 1000 that cover above your 1.5ghz...

like icom ic-r20 for <$500 upto 3.9ghz

like alinco dj-x10 for a few hundred....

Come to Dayton, OH for world's largest Hamvention in May and see dozens of models to choose from new and used!

73,

AC8V
 
hurk27 said:
I would have a hard time expecting that a problem from the power lines or a transformer is affecting the front end of a GPS receiver at 1.5ghz??? but anything is possible???
Click to expand...
Hold the bus here. I just caught that we are talking microwave radio frequencies. Power lines are not likely to affect any high frequency communications. Possible but highly unlikely. If it is power line interference you can still find it with a AM radio, but I have doubts it is power lines.

I have a hunch I might know what this is, and it has been happening a lot as of lately. Look around for a nearby Cell Tower, and if there is one nearby find out who the operator is. If it is LightSqaured, you likely found your source of interference. LightSquared operates on a band very close in frequency to GPS L1 band of 1525-1559 MHz. GPS L band operates at 1575.42 MHz. That is only a 160 Khz difference and if the GPS receiver front end is loose, the cell tower is over driving the front end of the GPS RX.

Another source could very well be associated with an airport, golf course, or other area needing precision GPS. In which case there maybe what is called Differential Correction GPS which is a land based transmitter. If near an ocean there is another correction system called SBAS and for FAA operations WAAS.

With Microwave to locate the esource will take a directional antenna, Spectrum Analyzer, and a trained operator to find it. .
 
Last edited:
Interesting Never knew about LightSquared and the problem before, a quick Google of LightSquared turned up quite a bit of information on the issue:

GPS.gov

Of course this doesn't explain the problem with the other services (cell phone and satellite radio) unless they are also close to this frequency, but maybe it is the problem?

Thank's Dereck
 
dereckbc said:
I have a hunch I might know what this is, and it has been happening a lot as of lately. Look around for a nearby Cell Tower, and if there is one nearby find out who the operator is. If it is LightSqaured, you likely found your source of interference. LightSquared operates on a band very close in frequency to GPS L1 band of 1525-1559 MHz. GPS L band operates at 1575.42 MHz. That is only a 160 Khz difference and if the GPS receiver front end is loose, the cell tower is over driving the front end of the GPS RX.

With Microwave to locate the esource will take a directional antenna, Spectrum Analyzer, and a trained operator to find it. .
Click to expand...

Math error?: That is a large >16.0 mhz difference

16mhz SHOULD be far enough away for all but the cheapest 1.5ghz receiver; but perhaps the OP receiver is suspect after all? How about posting a schematic of the rf istages of your device? Some of us hams and others may be able to spot a design issue? I suspect you are using a single chip receiver? What are the specs on the receiver? sensitivity and selectivity?

Also, although I would LOVE to have a $ 4000 spectrum analyzer to trace this problem, I would be almost as happy with a $ 400 sensitive wideband scanner and handheld $ 10 yagi.... plus I would end up with a cool scanner when done with the project.
 
Last edited:
mike_kilroy said:
Math error?: That is a large >16.0 mhz difference

16mhz SHOULD be far enough away for all but the cheapest 1.5ghz receiver; but perhaps the OP receiver is suspect after all? How about posting a schematic of the rf istages of your device? Some of us hams and others may be able to spot a design issue? I suspect you are using a single chip receiver? What are the specs on the receiver? sensitivity and selectivity?

Also, although I would LOVE to have a $ 4000 spectrum analyzer to trace this problem, I would be almost as happy with a $ 400 sensitive wideband scanner and handheld $ 10 yagi.... plus I would end up with a cool scanner when done with the project.
Click to expand...

Actually The spectrum allocated for the GPS "L1" signal by the FCC is 1559 to 1610 MHz which butts right up to LightSquared controlled block of the United States spectrum (1525-1559 MHz) in the L-Band,if you go to the Google link in my post above it has a lot about it and the problems it has caused for GPS users including the military, LightSquared has opted to not operate the upper part of their block of frequency at this time to help with the problem but many that are involved with GFS systems are worried that if the FCC does not rescind the licenses to operate in that band area LightSquared may opt to use it anyway as their demand for frequency increases at a later date and the FCC would not have much power to do anything then, the problem is that GPS receivers have to be very sensitive to receive the very weak low power sat signals, but these land based high power transmitters are a 100 to a 1000 times stronger for those who are close by one of these towers. take a look at the two links in my above post.
 
Since a location like FL would be hard to obscure satellite coverage, that doesn't seem likely cause.

So pretty much only thing left IS interference, and that would have to come from many hundreds of KW transmitter (not possible on Ghz freqs) nearby, or on IF freqs of YOUR receiver (possible). I would still vote for the scanner/receiver over the spectrum analyzer.

Most spectrum analyzers I have used since my 1rst Class FCC license repair days were pretty low input sensitivity (maybe 10 uv/20db quieting for the $ 20,000.00 ones we used) whereas the scanners are likely more like 0.5uv full quieting input - so they may be 20x more sensitive (means hear farther) and it probably will take same time to scan 1.3-1.7ghz as it would to setup the spectrum to show the same on screen....

OP wants a solution: If it is found to be interference from the sources already listed or others, they probably will not get a solution by forcing those folks to cease and desist, but may by redesigning their rf input to be more selective. I vote for posting the front end circuitry for comment here since there are a lot of rf savy folks here: it may be simple solution to tighten up the OP receiver selectivity.....
 
Last edited:
If the interference is on a single fixed frequency, putting in a trap for that frequency may be more practical for equipment in that area than making the RF input stage more selective but still covering the needed input band.
A local Amateur Radio operator may even be familiar with the problem already, if you can make that connection somehow.

Tapatalk!
 
GoldDigger said:
If the interference is on a single fixed frequency, putting in a trap for that frequency may be more practical for equipment in that area than making the RF input stage more selective but still covering the needed input band.
A local Amateur Radio operator may even be familiar with the problem already, if you can make that connection somehow.

Tapatalk!
Click to expand...

Traps have not been found to be effective enough to ward off signals that are strong enough to overload the front ends of radios.

Nonetheless, you are putting the cure in front of the ailment. I think that if RFI is suspected, it should be tested for and verified before attempts to correct it are being planned.

Also, how would one put traps on cell phones?
 
Last edited:
Cell towers TX @ +43 to +46 dbm per carrier and can have up to 6 carriers. FWIW +43dbm is 20 watts and +46 dbm is 40 watts so a single cell site can have up to 240 watts per sector x 3 sectors or roughly 750 watts. A fully loaded site operating LTE (700 Mhz) Cellular band (800 Mhz). PC band (1900 Mhz), AWS band LTE (2200 Mhz) can have up to 3 Kw of TX power. Only places you will find that is in large cities, but possible and they are out there.
 
mike_kilroy said:
Math error?: That is a large >16.0 mhz difference
Click to expand...
Yes a math error, but still a narrow difference when talking 1.5 Ghz. A strong +46 dbm (40 watts) transmitter can easily bleed over into a RX operating nearby with poor selectivity. I work for Verizon Wireless and it is causing problems with our adjacent cell sites GPS receivers. We have had to add notch cavities to the cell site GPS receivers.

Cell towers cannot operate without GPS timing. To take it one step further no telephone office can operate without GPS receivers. Little known fact the DOD can shut down all communications in the USA and abroad with a simple key click. All they have to do is shut down the civilian GPS and all communications will grind to a halt within 24 hours.
 
dereckbc said:
All they have to do is shut down the civilian GPS and all communications will grind to a halt within 24 hours.
Click to expand...
Are you talking about shutting down civilian access completely or just turning on the standard mechanism for crippling the time resolution (and therefore spatial resolution) by using military encryption for the least significant digits of the time code?
 
GoldDigger said:
Are you talking about shutting down civilian access completely or just turning on the standard mechanism for crippling the time resolution (and therefore spatial resolution) by using military encryption for the least significant digits of the time code?
Click to expand...
No the Military can completely shut down all communications with a few simple key clicks.

All cell towers, telephone switching offices, and internet all use synchronous transmission and that timing is from GPS receivers. Look closely at any cell tower and you will see the GPS antennas just above the roof line of the shelter.It looks like a dunce cap about 6 inches in height. They are backed up by cesium clocks that can keep the site going for up to 24 hours if the clock fails to give technicians time to replace them, but after 18 to 24 hours they will get out of sync and shut down. In the ole days of digital asynchronous TDM Ma Bell had a stratum clock in Kansas City that all communications were synced up down stream but that is long gone and now GPS BITS CLOCKS are used universally and required. In addition Every cell phone made has a GPS RX in them that can be turned on/off without your knowledge to locate you.

DOD can even control the accuracy or I should say inaccuracy at any given moment time to make it useless. May sound strange but that is the way it is designed in the event of an cyber or guided weapons attack. That is why Russia, China, and the UK are developing and deploying their own navigation and timing systems. Right now they Freeload off the DOD GPS.
 
I just ordered some stuff on Amazon. I'm doing the $20 setup to start and this is what I'll be running; it's a Spectrum Analyzer from MIT open source.
http://sdrsharp.com/

Using this: http://www.amazon.com/gp/product/B0...veASIN=B009U7WZCA&linkCode=as2&tag=kiloohm-20

Based on recommendation from this: http://kiloohm.com/rtl-spectrum-anylyzer-sofware-defined-radio-ads-b/

I have not ordered an antenna yet because I'm not sure if I need usb or coax. This might sound nuts, but I want an antenna that I can affix to a hard hat so I can walk, turn, etc. and I'd like to have a vehicle mount antenna as well so I can drive through a community.

I already have a quite elaborate satellite locator so between the two, if nothing else, I can really impress my customers! :happyyes:
 
mgookin said:
I just ordered some stuff on Amazon. I'm doing the $20 setup to start and this is what I'll be running; it's a Spectrum Analyzer from MIT open source.
http://sdrsharp.com/

Using this: http://www.amazon.com/gp/product/B0...veASIN=B009U7WZCA&linkCode=as2&tag=kiloohm-20

Based on recommendation from this: http://kiloohm.com/rtl-spectrum-anylyzer-sofware-defined-radio-ads-b/

I have not ordered an antenna yet because I'm not sure if I need usb or coax. This might sound nuts, but I want an antenna that I can affix to a hard hat so I can walk, turn, etc. and I'd like to have a vehicle mount antenna as well so I can drive through a community.

I already have a quite elaborate satellite locator so between the two, if nothing else, I can really impress my customers! :happyyes:
Click to expand...

Have you ever thought about getting a ham radio license? By the sounds of things, you would fit right in.

Right Dereck??

:lol:

th
 
K8MHZ said:
Have you ever thought about getting a ham radio license? By the sounds of things, you would fit right in.

Right Dereck??

:lol:

th
Click to expand...

When I was a younger man I had a cb for running up and down I-95 along the US east coast. I had a fuzz buster mounted right on top of it on the dash. In probably 30+ trips I got pulled over once (cop in the median turned on radar only after he saw me) and I paid $50 cash and no points/ record. Not sure where the $50 went and didn't care.

I've known some radio operators but just don't have time to commit to the hobby. Enlighten me though, other than civil emergency, what are some constructive uses for two way radio?

Now that we have tv, cell phones, texting, antisocial networking, etc. is amateur radio waning? A cell phone really is a two way radio.
 
I count NINE antennas on that Ford Escort. What are all of them for ? Is each one a different wave length or band ?

mgookin: Ham radios are just from Ham to Ham AFAIK. They could operate from remote islands in the Pacific ie: Bikini Atoll to New York with a portable generator.
 
Status
Not open for further replies.
Top