Are there any HAMs or RF savvy EE's here who can recommend a reasonably accurate method of determining the output signal strength of a local cellular tower array?
I don't know the exact frequencies involved so I assume I'd need something capable of sensing the entire licensed bandwidth and would like to do it for a good deal less than a $MultiK spiffy R&S rig.
Any suggestions would be really appreciated.
Thanks
I don't know the exact frequencies involved so I assume I'd need something capable of sensing the entire licensed bandwidth and would like to do it for a good deal less than a $MultiK spiffy R&S rig.
Any suggestions would be really appreciated.
Thanks
All modern cell phone systems require the phone to adjust its power output to the minimum required to reach the tower. This is usually done by measuring the signal level that the phone receives from the tower.
Therefore the phone has the ability to measure the signal received from the tower. Many phones have a method of reporting this signal level to the user.
On my Samsung Galaxy Note II it can be reached by entering the settings menu, then pressing "about device", then press "Status." The signal strength is shown along with a few other things. This menu is usually found in most Android phones, but may be buried somewhere else depending on the Android version.
The phone will only report the signal level from the cell site that it is currently registered on, and connected to. It has no way of knowing about any other signals coming out of the same tower.
AT&T recently stuck a LTE tower about 250 feet outside my front door. I have examined the signals emitted from it with a spectrum analyzer. There are four 5 MHZ wide carriers in the 870 to 890 MHz region. LTE will have 50 "resource blocks" embedded in each 5 MHz carrier. Each resource block represents the aggregate energy of one 100 KHz carrier, and this is what the phone is reporting, the strength of one of these blocks. There are 200 of these blocks streaming from the tower in my front yard.
The tower near my house is not typical. Many towers lease space to multiple cellular carriers, microwave links, and commercial two way radio systems. There could be hundreds of signals of widely different power levels coming out of a cell tower. The cellular signals are carefully adjusted to a relatively low level in heavily populated areas so that they don't interfere with neighboring towers. They are cranked to the maximum in rural areas to increase the coverage. Two way radio signals are on dedicated frequencies, so they can be very strong if needed to be.
For several years I took specialized equipment out to cell sites to investigate interference issues. Short of borrowing a spectrum analyzer there is no way of telling just what signals come from a given tower, and how strong they are. These transmitters must all be licensed, and it should be possible to look up the tower at a given set of GPS coordinates, but finding the info on the FCC's or DOC's web site is impossible.
Therefore the phone has the ability to measure the signal received from the tower. Many phones have a method of reporting this signal level to the user.
On my Samsung Galaxy Note II it can be reached by entering the settings menu, then pressing "about device", then press "Status." The signal strength is shown along with a few other things. This menu is usually found in most Android phones, but may be buried somewhere else depending on the Android version.
The phone will only report the signal level from the cell site that it is currently registered on, and connected to. It has no way of knowing about any other signals coming out of the same tower.
AT&T recently stuck a LTE tower about 250 feet outside my front door. I have examined the signals emitted from it with a spectrum analyzer. There are four 5 MHZ wide carriers in the 870 to 890 MHz region. LTE will have 50 "resource blocks" embedded in each 5 MHz carrier. Each resource block represents the aggregate energy of one 100 KHz carrier, and this is what the phone is reporting, the strength of one of these blocks. There are 200 of these blocks streaming from the tower in my front yard.
The tower near my house is not typical. Many towers lease space to multiple cellular carriers, microwave links, and commercial two way radio systems. There could be hundreds of signals of widely different power levels coming out of a cell tower. The cellular signals are carefully adjusted to a relatively low level in heavily populated areas so that they don't interfere with neighboring towers. They are cranked to the maximum in rural areas to increase the coverage. Two way radio signals are on dedicated frequencies, so they can be very strong if needed to be.
For several years I took specialized equipment out to cell sites to investigate interference issues. Short of borrowing a spectrum analyzer there is no way of telling just what signals come from a given tower, and how strong they are. These transmitters must all be licensed, and it should be possible to look up the tower at a given set of GPS coordinates, but finding the info on the FCC's or DOC's web site is impossible.
Thanks for the comprehensive reply ! I thought that was probably the case. I can get the info on the company that owns the tower and the frequencies they transmit in but it's the power output that I really want to know about.
I'm a denizen of a city center ant farm and a few years ago an array started to appear about 200 feet from and level with my kitchen and living room windows - pointed straight at them. I never thought much about it until they added several more panels and then covered the whole thing up with a cap that blends in with the rest of the building so well you wouldn't know it was there if you hadn't seen them do it.
Last year something got to the nerves in my shoulders and arms and gave me a skin rash and a lot of pain. I figured it was shingles and waited it out, and then a few months later my neighbor on that side of the building broke out in a bad rash on his face. I never had the thought that there could be any connection until my wife started to break out in a rash a few weeks ago and while looking for possible causes I started finding reports that linked cell tower signals to various health conditions, including skin disorders. I'd seen stuff like that before and they always seemed to be directed at the sorts of people who like to get emf sensing meters and go looking for ghosts but this time, having more vested interest in the outcome , I looked more seriously and started finding posted papers by university profs and reasonable sounding national news media reports talking about harmful effects of prolonged exposure.
So, I'm not on a witch hunt but I'd like to know. I have a spectrum analyzer window on my usb scope (100MHz). Do you think there would be a feasible way (ie - not consuming all my free time for the next few months) for me to capture the signal and covert it to a lower frequency my scope can see?
The waves are far too long to affect only the skin like a sunburn.
Photons of far too low energy for one by itself to damage anything.
Many photons together could damage by cooking. If it was cooking
you on the inside, your eyes would be full of cataracts by now. If
you are able to read this, your rash is something else...
Photons of far too low energy for one by itself to damage anything.
Many photons together could damage by cooking. If it was cooking
you on the inside, your eyes would be full of cataracts by now. If
you are able to read this, your rash is something else...
Last edited:
too much info to explain
http://www.airmet.com.au/admin/Products/DownloadProductFile.aspx?FileTitle=RF%20Fields%20on%20Human%20Body&uniquename=radiation_human_body1.pdf
this should give you an outline on the effects of non ionising radiation.
http://www.airmet.com.au/admin/Products/DownloadProductFile.aspx?FileTitle=RF%20Fields%20on%20Human%20Body&uniquename=radiation_human_body1.pdf
this should give you an outline on the effects of non ionising radiation.
I didn't realize your reasons for interest from your first post. Many people here know that (for 2 more months) I work for a major electronics company that manufactures cell phones and two way radios. They have funded and performed a lot of the research on the effects of RF exposure on humans and animals. There were two PHD researchers that did most of the work in the facility where I work. I knew both of them. One left the company, the other was murdered (unrelated to his work). I believe that they did state of the art work and attempted to cover all the angles. I remember one experiment where high powered equipment (equal to 100 cell phones) was strapped to the heads of a heard of pigs for their entire lifetime, and they the pigs heads were cut open. Their conclusions were that there were no observable effect.
I also had a relative develop brain cancer. It was a fast growing tumor that took her life rather quickly. She used a cell phone quite a bit in her job, and the cell coverage is not so good in her area, so the phone was probably at max power. She was examined by the cancer research group at the University of Pittsburgh Medical Center. I talked with one of their PHD guys. He said that the incidence of brain cancer is rising, and the tumors tend to appear on the side that the user prefers to hold their phone to. He also stated that there MAY be a causal link, but the data is not conclusive. Who do you believe?
I believe there is still a lot we don't know about the effects of RF, so I try to minimize my exposure. A cell phone 1 inch from your head is far stronger than a thousand phones a few meters away. The tower outside your window is transmitting 24 hours a day, even if nobody is talking. It's power level at your window is probably pretty low (especially in high density areas), but the human effects are related the power level AND the exposure time. I think RF exposure can cause some weird symptoms, but I don't think it is related to a skin rash. I would expect some type of allergen in the buildings air....but I am no expert by any means.
If you can do the RF level test with a phone, it will give you a relative reading on how much RF energy is making it into your residence. You can also find out where the hot spots are.
All cellular transmitters in North America fall into a few frequency bands. 700 to 780 MHz, 820 to 890 MHz, 1.8 to 2.2 Ghz, and 2.4 to 2.7 Ghz. These are all relatively high RF frequencies that are fairly easy to block. If your building is concrete, it is a good absorber for all cellular frequencies. It is more effective above 1 GHz (1000 MHz). This is why the major cell carriers use both 700 to 900 MHz for inside building coverage, and 1.8 GHz and up for high data rates.
Metal reflects all RF waves. The lower the frequency, the thicker the metal needed to block the signal. All cellular waves can be severely attenuated by ordinary aluminum window screening. If your windows have the typical plastic/fiberglass screens on them, replacing the screen with aluminum can dramatically lower the RF level inside a concrete building. Even the aluminized window tinting film made to reflect sunlight reflects a significant amount of RF energy (the shiny silver stuff, not the black stuff).
You can perform tests on the effectiveness of these types of shields with nothing more than a cell phone that has the ability to display the signal strength of the incoming signal. Record the signal strength over several days, nights and weekends with the phone in the same place every time, say the window facing the tower. It can vary from day to day. You can test any shielding experiments....hold a sheet (about 1 foot square) of ordinary aluminum foil between the phone and the window. The signal numbers will drop.
The number displayed will be in dbm, decibels below 1 milliwatt. 0 dbm is 1 milliwatt of received power. Each 10 dbm is a factor of 10 lower. +10 dbm is 10 milliwatts, and -10 dbm is 100 microwatts.
I have seen levels from -20 dbm (strong, but still only 10 MICROWATTS) to -100 (femtowatts) on public roads near cell towers. A cell phone puts out 200 to 600 milliwatts about 1 inch from your head (50,000 times stronger than the strongest -20 dbm signal). A police walkie talkie can put out 6 watts of RF power (500,000 times stronger), it is typically held a few inches from the users head.
The average SINGLE cell transmitter can put out anywhere from 1 to 50 watts. Typically about 10 watts. There can be 10 to 50 transmitters running on a single tower. This puts the total combined power from a cell tower from 10 to 2500 watts. The power is split up between 3 sets of antennas facing in 3 different directions (cells), so the most in any given direction is less than 1000 watts. A commercial radio broadcast station may crank out 50,000 watts and a US digital TV station is permitted 1 MILLION watts!
I see -80 dbm inside my living room (large window facing the tower), -90 dbm in my lab, -60 dbm in the front yard facing the tower, and -40 dbm on the roof closer to antenna level. There are rather weak signals.
I see more power here in my lab from the TV towers that are 7 miles away than the cell tower outside my front door. There are 9 TV channels operating from 3 towers with a combined power of about 7 million watts.
When I was an RF tech apprentice my boss requested I complete a site antenna survey, the tower had two GSM services, a plethora of commercial two way comm antennas (uhf and vhf) and at the top a panel antenna with 5 x 50W (analog service)TV transmitters combined into it. I spent 6 hours up the tower, 1 hour in close proximity to the TV panel antenna. Had a dizzy spell (I couldn't drive) for the rest of the day, never had anything like it since.
I had read an article years ago regarding UHF and its affects on the blood brain barrier, I can't find it but this comes close.
Effects of radiofrequency radiation exp... [Electromagn Biol Med. 2011] - PubMed - NCBI
Since then I've worked in aviation (RF equipment from 199Khz to 9.375Ghz, passive RF and now back to RF site work. currently our work policy is to carry a Radman at all TV and radio broadcast sites due to the high power density involved.
At one TV site I talked to one of the TV techs regarding the changeover from tube to solid state transmitters. one of the new 2KW transmitters he was working on was generating a VSWR condition, and found the coax tail connector at the transmitter wasn't terminated properly from the manufacturer. He spent 30min at the transmitter where it was radiating at UHF, and received a headache and a serious nosebleed for it.
I had read an article years ago regarding UHF and its affects on the blood brain barrier, I can't find it but this comes close.
Effects of radiofrequency radiation exp... [Electromagn Biol Med. 2011] - PubMed - NCBI
Since then I've worked in aviation (RF equipment from 199Khz to 9.375Ghz, passive RF and now back to RF site work. currently our work policy is to carry a Radman at all TV and radio broadcast sites due to the high power density involved.
At one TV site I talked to one of the TV techs regarding the changeover from tube to solid state transmitters. one of the new 2KW transmitters he was working on was generating a VSWR condition, and found the coax tail connector at the transmitter wasn't terminated properly from the manufacturer. He spent 30min at the transmitter where it was radiating at UHF, and received a headache and a serious nosebleed for it.
One of my friends took the elevator to the top of one of the three 1000 foot TV towers I mentioned previously. He went out on the observation deck to take RF measurements using specialized equipment. The tower he was on was about 1000 feet from each of the other two towers and directly in front of the TV transmitting antennas, which were still running NTSC analog TV at the time.
Since this was his one and only trip to the top of the tower, he took a Sony camcorder and a Nikon pocket camera. Neither would work at the top of the tower, but both returned to normal once back on the ground. My friend said he didn't feel quite right while up there, and acquired a monster headache that lasted for two days about an hour after the trip. The tower worker who accompanied him said that is common. It stops happening after a few trips. Wonder is he will live a long and happy life?
Since this was his one and only trip to the top of the tower, he took a Sony camcorder and a Nikon pocket camera. Neither would work at the top of the tower, but both returned to normal once back on the ground. My friend said he didn't feel quite right while up there, and acquired a monster headache that lasted for two days about an hour after the trip. The tower worker who accompanied him said that is common. It stops happening after a few trips. Wonder is he will live a long and happy life?
Well, that puts it simply and is exactly what I wanted to know! Thanks a ton for taking the trouble to write all that.
We have family coming to stay for a month arriving in a couple of weeks and I promised my wife I'd help get the place ready. In this plan, part of the "work" is my getting an amp I've been poking at for a while finished and off the bench so we can use my shop space to give everybody a little privacy. Hey, it's sort of work . . . . ish. OK, it's not but she's letting me get away with it anyway.
Once it's done I can try doing the tests on my phone and see what we see, though I have to say, I basically trust the technology (in that every technology has cautions you have to respect) and don't have time to go any farther into a brand new field of study just for the fun of it. (It's challenge enough to juggle more than a handful of output transformer details at once, digital is more reach than I care to try!) I'll put the aluminum screens on the windows as you suggested and leave it at that. Thanks again, your reply was just what I hoped for and the TV signal referrence put it in a perspective that made sense to me.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.