How can one tell how far a radio will go?

[RedPenguin]

Is it possible to estimate how far a radio signal can go, by it's power output or do you have to know much much more?

I thought the more power that you had, normally the further you could go, but I assume that power probably has nothing to do with it.

For example, my local school district uses 25-50W radios, yet you can't hear them up, when you are only 2 streets up.

I'm only .7 of a mile, from one of their school buildings and I can't ever hear them.

Is the lack of a repeater, the primary reason that pickup of these signals is so hard?

 

[zz0468]

Under line of site conditions, you can predict very accurately. You need to know transmitter power output, feedline loss, antenna gain, free space path loss, receive antenna gain, receive feedline loss, and receiver threshold.

Under non line of site conditions, it becomes much more complicated, and can be almost impossible to predict. In those cases, one frequently makes some assumptions or educated guesses about what the additional losses might be and adds that to the free space path loss.

Yeah, transmitter power has something to do with it, but in the grand scheme of things, not nearly as much as you'd think.

 

[gmclam]

Is the lack of a repeater, the primary reason that pickup of these signals is so hard?

It could be. The basic question; can your receiving antenna "see" the transmitting antenna? When a repeater is used, it is high up where it can be "seen". Another factor is the frequency being transmitted on. Some signals are more likely to bounce off of objects and other frequencies will go through them (but perhaps be attenuated).

 

[fireSAR]

how far a radio will go?

Well? it usuall depends on the weight and aerodynamics of the radio, usually the complexity of it as well.

 

[mchart13]

Is it possible to estimate how far a radio signal can go, by it's power output or do you have to know much much more?

I thought the more power that you had, normally the further you could go, but I assume that power probably has nothing to do with it.

I agree with fireSAR it depends alot on the radio, but you kind of answer the question yourself, if your arm or leg (if you're kicking it) has more power, the further it will go

Sorry RedPenguin could not resit that one....

Serious side now... Keep in mind what the building (they are or you are in) is made of and also the surrounding buildings between you and them. Lots of re-bars in concrete or lots of metal studs or metalic film on windows for sun block; Elevator shafts or stairwells can also "muffle/impede" the signal radiation. Maybe the radios per specs can do 25-50 W but are set to LOW and are actually doing lot less or their antenna/wire are faulty due to poor installation or just wear and tear (poorly maintained) over the years.
I mentioned all those "interior obstructions" assuming so because you did not mention that you had line of sight on their antenna (ie it was on their roof or outside the building)

 

[RedPenguin]

Yes

I understand now, I think the reason, the one school you can't pick it up that far, is because I was near a bunch of tall buildings that properly blocked the signal, though I noticed sometimes, it seems like you can't even get some signals literally across the street, LoL.

 

[austinscan1]

How far??

Well? it usuall depends on the weight and aerodynamics of the radio, usually the complexity of it as well.

Is he throwing it, or using a catapult??

 

[fireSAR]

Is he throwing it, or using a catapult??

not sure, I do have plans for a trebuchet. I prefer throwing, after I build the catapult I feel better again.

 

[fireSAR]

Is it possible to estimate how far a radio signal can go, by it's power output or do you have to know much much more?

I thought the more power that you had, normally the further you could go, but I assume that power probably has nothing to do with it.

For example, my local school district uses 25-50W radios, yet you can't hear them up, when you are only 2 streets up.

I'm only .7 of a mile, from one of their school buildings and I can't ever hear them.

Is the lack of a repeater, the primary reason that pickup of these signals is so hard?

Sorry, now for the serious side.

usually its not the power its height, here size matters. if you want to talk distance you need height.

 

[kb2vxa]

I was SO disappointed the first answer wasn't a question, "How far can you throw it?" You guys are alway so slow on the uptake and so late in breaking news it's already broken by the time I read it here.

"For example, my local school district uses 25-50W radios, yet you can't hear them up, when you are only 2 streets up."

You forgot the decimal point, 2.5W for UHF and 5W for VHF is standard portable power. Security and maintainence personnel carry portables that may or may not work through repeaters and in your case they don't or you're not listening to the repeater output frequency. I know some schools that use 10W repeaters inside the building (no outdoor antenna) but most do not, one is not needed to cover so small an area as one building and grounds.

Now if you use a trebuchet you can toss the whole repeater about half a mile! I tried a catapult once but it spun around and scratched the hell out of me.

 

[RedPenguin]

Oh

I got the power output from the FCC site, it says 25W and 50W.

http://wireless2.fcc.gov/UlsApp/Uls...dTcThJcnV!345167823!1339428642?licKey=1949355

If you look on that page, it actually says 25.00 and 50.00.

 

[n2mdk]

That system would be used in vehicles, not sure what it would actually be used for. Doesn't seem to be for a bus system.

 

[ke5fgc]

Just because they are licensed for that much power, doesn't mean they use that much power.

 

[kb2vxa]

Hi again Red,

Your old avatar had everybody confused, now here you go again. (;->) I see two standard repeater pairs with the output of the first being 451.925 located at 196 WESTGATE DRIVE WESTSIDE ELEM JOHNSTOWN, PA CAMBRIA County. The second is 452.300 but it's listed as mobile, very strange. I'm pretty sure the first is a repeater because in addition to mobiles there is a control station, usually the dispatch center.

By the looks of things the repeater (?) is way out on the edge of town in an elementary school and has quite an area to cover so if you're anywhere from Johnstown proper to Lower Yoder you should be able to hear it.

"Doesn't seem to be for a bus system."

Maybe not to you Jerri but that's what it looks like to me. This is the control station which seems to be located in the administration building.
GREATER JOHNSTOWN SCHOOL DISTRICT
222 CENTRAL AVENUE
JOHNSTOWN, PA 15906

 

[DickH]

How can one tell how far a radio will go?

It all depends on which radio and how hard you throw it.

 

[fireSAR]

How can one tell how far a radio will go?
It all depends on which radio and how hard you throw it.

I think we covered that...

 

[RedPenguin]

Ooh

Hi again Red,

Your old avatar had everybody confused, now here you go again. (;->) I see two standard repeater pairs with the output of the first being 451.925 located at 196 WESTGATE DRIVE WESTSIDE ELEM JOHNSTOWN, PA CAMBRIA County. The second is 452.300 but it's listed as mobile, very strange. I'm pretty sure the first is a repeater because in addition to mobiles there is a control station, usually the dispatch center.

By the looks of things the repeater (?) is way out on the edge of town in an elementary school and has quite an area to cover so if you're anywhere from Johnstown proper to Lower Yoder you should be able to hear it.

"Doesn't seem to be for a bus system."

Maybe not to you Jerri but that's what it looks like to me. This is the control station which seems to be located in the administration building.
GREATER JOHNSTOWN SCHOOL DISTRICT
222 CENTRAL AVENUE
JOHNSTOWN, PA 15906

My old avatar?

Actually 222 Central Ave, is actually their High School. Their admin is actually 1091 Broad Street, Johnstown, PA, 15902. I heard from DRuhe that they do actually have a repeater setup between the schools but they don't actually use it unless something major is going on.

So I assume they must use their radios locally at their assigned schools, but when something big happens, they turn on the repeater and all the schools can talk to each other. That's what I gather.

 

[kb2vxa]

Yeah, I remember something about a logo and the Red Penguin Band from somewhere.

Actually a more logical assumption is since from what you're now saying it's not a bus system and they only use radio when something happens if they use it at all anymore. If anything, IF they need portable communications they use cell phones like everybody else these days, there are plenty of current licenses and dusty radios out there.