Distance

[Alpha432]

Forgive me if this is in the wrong forum but I think it is an easy answer for someone more knowledgeable than me. How come I can pick up a city like Auburn Hills FD, 50+ - miles from my house, but systems like the 800mhz Downriver Mutual Aid system, Western Wayne, Livonia etc I can only pick up only if I am in that genaral area and not when I am 50 miles away from them?? Does that make sense? Why can't I get these systems from a long distance away but I can recieve others from upwards of 60 miles away?

[consys]

The higher the frequency the more "line of sight" it becomes. The primary reason is that higher frequencies tend to pass through the atmosphere, where lower ones reflect back. I wasn't specific about a what frequs do which because it varies with a large number of factors. Anything that affects the earths atmosphere, or its' magnetic field has an effect on signal propigation. I live in an area that gets heavy fog and that has a noticeable effect.

Higher frequencies are attenuated more by tree leaves and building materials than lower freqs. Most radios are less sensitive to higher frequencies as well.

Other physical factors play a role as well. The antenna for the 800Mhz system I'm most interested in is on the other side of a small hill about four miles from me, and I use a directional outside antenna with some gain to listen to it. But the county fire system in the VHF band- I can disconnect the antenna and still hear them.

[MacombMonitor]

Antenna tower height, on the transmitter site, can be a big factor. If it's high enough, it eliminates most everything that's blocking that "line of site" signal path, that everyone is always talking about. How much R.F. wattage is applied to the antenna can make a big difference as well.

[n211cr]

Being line of sight as well, the height of each antenna can make a huge difference. The larger the area served usually the larger the antenna height, along with the terrain factors. Also their setup can play a factor if they are using directional antennas on the outskirts of the area being covered, rather than an omni directional sending signal in all directions.

[Josh]

I can typically receive downriver from anywhere in the county, and as far north as around 12 mile road.

I find that signal is often covered up and radios desensed by cellular towers, namely NexTel. But in the 868 range, either is anyone's guess.

-Josh

[Alpha432]

Originally Posted by Josh

I can typically receive downriver from anywhere in the county, and as far north as around 12 mile road.

I find that signal is often covered up and radios desensed by cellular towers, namely NexTel. But in the 868 range, either is anyone's guess.

-Josh

12 mile? That is pretty far. I come home from work in Oakland county at 9 mile and southfield road and It doesn't even pick it up at all. It usually picks up at around Warren Rd and Southfield comming into Dearborn. I cannot fully recieve Western Wayne from my home in Allen Park. It is very digitally choppy at best. What type of scanner and antenna do you have Josh?

[Josh]

half-wave 800Mhz (6 inch) whip on an XTS3000

If you use the Radio Shack 6 inch 800Mhz whip deal that they sell, you should see noticeable difference. I've been able to receive Downriver from the Royal Oak area, I-75 and 12 mile, those vicinities. With the mobile antenna, I got as far as around 15 mile and I75 before it became too broken up to attempt to listen to, but alas the Oakland County system is there and in-place.

-Josh

[Alpha432]

I am using the Radio Shack 800mhz antenna on a Uniden 296D. On my mobile antenna I use an Antennex Multiband antenna. The Downriver system is choppy from Oakland county in West Bloomfield. Also the livonia FD system and Western Wayne system is very hard to pick up from the W.B. Maybe I am just in a crowded area. I would love to be able to recieve the Downriver system from up there.