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Cell tower interference

Oldtimer

Oldtimer

Active Member
May 20, 2008
223
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28
75
Stuart Florida
We are gonna buy a house in another month or so.
One we are looking at is approx. 1/4 mile or less from a tv station and cell towers.
Would they help or hinder my cb antenna which will probably be on a say 40' tower itself.
Thanks
God Bless
 

I cannot see why they would help or hinder your CB station. They are not likely to interfere in any way with your station and the towers themselves should have no affect on your TX at that distance away. The good thing is that the off air signal at your neighbors should be incredible and you have no worries about TVI on the local channels. (y)
 
i agree

there should be no attenuation of signal because of the tower. now if you start hearing weird voices.............:LOL:
 
I also agree with the slight possibility of one exception. If the TV transmitter is down in VHF low band (and some still are), there is a chance the visual signal could cause RF desensing in his CB receiver. This can make signals in your receiver appear weaker then normal or weak signals disappear altogether. There is reasonable frequency separation even if the TV transmitter is on channel 2 to prevent this problem in most cases.

The problem is the visual signal is huge in terms of power when you compare it to a normal audio RF channel. The oral signal for a TV transmitter may be 100 KW but the ERP of the visual signal could be around a megawatt! At 1/4 mile away from the tower, depending on it's height and antenna element spacing, he could be approaching the area of maximum signal level.

Typical VHF broadcast antenna patterns at 1000 feet above ground level produce peak RF density on the ground at approximately 1 mile from the tower. Lower towers place this point closer. If the front end in your CB receiver is not selective enough to reject most of this signal, just add a quality low pass filter on the back of your radio to add much more attenuation of the TV signal.
 
Shockwave said:
I also agree with the slight possibility of one exception. If the TV transmitter is down in VHF low band (and some still are), there is a chance the visual signal could cause RF desensing in his CB receiver. This can make signals in your receiver appear weaker then normal or weak signals disappear altogether. There is reasonable frequency separation even if the TV transmitter is on channel 2 to prevent this problem in most cases.

The problem is the visual signal is huge in terms of power when you compare it to a normal audio RF channel. The oral signal for a TV transmitter may be 100 KW but the ERP of the visual signal could be around a megawatt! At 1/4 mile away from the tower, depending on it's height and antenna element spacing, he could be approaching the area of maximum signal level.

Typical VHF broadcast antenna patterns at 1000 feet above ground level produce peak RF density on the ground at approximately 1 mile from the tower. Lower towers place this point closer. If the front end in your CB receiver is not selective enough to reject most of this signal, just add a quality low pass filter on the back of your radio to add much more attenuation of the TV signal.
Click to expand...

On a positive note...you't won't need a grill to cook hotdogs in your back yard. (y)

Not so good...if the station is running 1 megawatt erp being 1/4 mile or less from the antenna puts you at risk for rf exposure. You may want to check out the stations power levels and enter the data into this rf exposure calculator. No worries from the cell towers which are low ppwer.

http://hintlink.com/power_density.htm
 
The most DX fun I ever had was talking on a HT from atop a cell tower. I have taken CB's up with also, of course right now its irrelevant with the sunspot cycle in full force so I cant see a problem.
 
The Missouri City antenna farm with like 14 AM FM TV stations is about 6 to 8 miles south of my house every time I am within 2 miles I get like 4 to 6 db of static. I would say cell towers no I drive by cell towers all the time no problems now AM FM towers yes
 
Shockwave said:
I also agree with the slight possibility of one exception. If the TV transmitter is down in VHF low band (and some still are), there is a chance the visual signal could cause RF desensing in his CB receiver. This can make signals in your receiver appear weaker then normal or weak signals disappear altogether. There is reasonable frequency separation even if the TV transmitter is on channel 2 to prevent this problem in most cases.

The problem is the visual signal is huge in terms of power when you compare it to a normal audio RF channel. The oral signal for a TV transmitter may be 100 KW but the ERP of the visual signal could be around a megawatt! At 1/4 mile away from the tower, depending on it's height and antenna element spacing, he could be approaching the area of maximum signal level.

Typical VHF broadcast antenna patterns at 1000 feet above ground level produce peak RF density on the ground at approximately 1 mile from the tower. Lower towers place this point closer. If the front end in your CB receiver is not selective enough to reject most of this signal, just add a quality low pass filter on the back of your radio to add much more attenuation of the TV signal.
Click to expand...

I had a similar problem back in the eighties when a repeater system was installed above a multi storey building (23 storeys) near where i lived, it used to desense my cobra 148 gtl dx s meter by about 2 s points everytime it was transmitting.

back then i didn't have widebanded receivers to trace what the actual cause was,but as it started as soon as the repeater was put up it was pretty obvious,especially as the cobra was a radio with a reasonably solid front end, there wasn't many cb'ers could touch it (in an area packed with strong cb signals) so it pointed to a local high power transmitter causing it.

also as Donald says many people forget that the low pass filter is bidirectional,it will attenuate any higher frequencies being received as well as those that may be transmitted as harmonics.personally i would always use a quality low pass filter when homebase no matter what the power level i was running, one court visit was enough for me,costly experience.;)
 
I don't live close to any TV stations so can't comment on that part. I do live within a quarter mile of an active cell tower and have experienced some 'noise' from it when it was first set up, but nothing after than. Figured the set-up dealt with a number of issues/frequencies/whatever. But, after the testing was done, it's been quiet.
I'm also within a quarter mile of several public service repeaters/transmitters and they are a different story! Periodic interference from those things on VHF/UHF, but you'd have to know the people who maintain them (nicest way I know of saying that they could use some @#$ "guidance").
None of these things are always 'good'/'bad', they vary a lot for various reasons. Good luck, hope you don't have a lot of 'trash' in the new place.
- 'Doc
 
Before I moved to CA from IL I lived less that 1/8th of a mile from 2 cell towers and I never had any issues with them.
 
Shockwave said:
The problem is the visual signal is huge in terms of power when you compare it to a normal audio RF channel. The oral signal for a TV transmitter may be 100 KW but the ERP of the visual signal could be around a megawatt! At 1/4 mile away from the tower, depending on it's height and antenna element spacing, he could be approaching the area of maximum signal level.
Click to expand...

What visual? What aural?

Analog TV is dead in the USA except for LPTV and boarder blasters.

8VSB looks like wideband noise with a pip carrier.

Get a tube CB and nothing can give you any trouble.
 
Oldtimer said:
We are gonna buy a house in another month or so.
One we are looking at is approx. 1/4 mile or less from a tv station and cell towers.
Would they help or hinder my cb antenna which will probably be on a say 40' tower itself.
Thanks
God Bless
Click to expand...

When you ask would they help, like as in act as a reflector and direct your signal in one direction, i would say no unless if you are within 36 feet of it, which prolly not going to happen.

And when you ask if it would hinder, like as in physically block or attenuate your signal, I would say no again since it is very unlikely that you are within 36 feet for this to happen.

:bdh:
 
Kamikaze said:
What visual? What aural?

Analog TV is dead in the USA except for LPTV and boarder blasters.

8VSB looks like wideband noise with a pip carrier.

Get a tube CB and nothing can give you any trouble.
Click to expand...

True that analog TV is dead in the USA. Because video has a much wider bandwidth then audio it still takes much more power to allow a video signal to propagate the same distance as an audio signal in the same spectrum even with digital. Digital compression does reduce the bandwidth but then again we go and fill it all back up again to transmit in HD or multiple programs on one TX. The mode of transmission has little to do with RF desensing. It is the ERP and frequency of the nearby transmitter.

DTV transmitters still use ERP levels approaching a megawatt. Some are still in VHF low band. Tube radios are just as susceptible to this as solid state. What makes a difference here is how selective the filtering is before the first RF amp in the receivers front end. Things like pre-selectors, bandpass filters, and cavity filters or traps in extreme cases are helpful in correcting this issue. Although, I doubt Oldtimer will need any of this.
 
There are no megawatt DTV stations on VHF. Maybe there should be.

Audio is now muxed into the same datastream as video. They both use the same exact bandwidth.

Tube front ends usually have a very high dynamic range. Much better than the average solid state cb.

Intermodulation of a transistor final by high power VHF signals is a very remote possibility and practically impossible with a cb tube final.

If the housekeeping at the site is bad expect to encounter weird signals from rectification.

Shockwave said:
True that analog TV is dead in the USA. Because video has a much wider bandwidth then audio it still takes much more power to allow a video signal to propagate the same distance as an audio signal in the same spectrum even with digital. Digital compression does reduce the bandwidth but then again we go and fill it all back up again to transmit in HD or multiple programs on one TX. The mode of transmission has little to do with RF desensing. It is the ERP and frequency of the nearby transmitter.

DTV transmitters still use ERP levels approaching a megawatt. Some are still in VHF low band. Tube radios are just as susceptible to this as solid state. What makes a difference here is how selective the filtering is before the first RF amp in the receivers front end. Things like pre-selectors, bandpass filters, and cavity filters or traps in extreme cases are helpful in correcting this issue. Although, I doubt Oldtimer will need any of this.
Click to expand...
 

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