Thatsclear
Member
- Joined
- Oct 25, 2019
- Messages
- 108
If I am looking at putting an antenna up. How high should I go? 20 feet, 30 feet? Is there a huge difference between an antenna at 20 feet vs 30 feet or not really? Reception wise? Thanks!
Antenna height
- Thread starter Thatsclear
- Start date
- Status
The answers vary widely depending on what frequencies you will be using. The difference between 20 and 30 feet at some frequencies will be minimal... at other frequencies it could make a huge difference. So we need more info - what antenna are you planning to use and for what frequencies / bands will it be used?
racingfan360
Member
- Joined
- Dec 19, 2005
- Messages
- 1,191
Usually the higher the better especially the higher the frequency you go. But remember cable losses increase significantly with higher frequency, so you really want a higher antenna height and a small high-quality cable run.
Thatsclear
Member
- Joined
- Oct 25, 2019
- Messages
- 108
Thanks for the help! It’s only for vhf/uhf and I’m using a diamond x30a. It’s a dual band.
What range do you expect to achieve?
HI Thatsclear,
Although it is a simplification, try this:
It can give estimates of range vs antenna height.
Height is your friend, as long you don't suffer to much loss from the coax run.
Although it is a simplification, try this:
It can give estimates of range vs antenna height.
Height is your friend, as long you don't suffer to much loss from the coax run.
Thatsclear
Member
- Joined
- Oct 25, 2019
- Messages
- 108
I was hoping to at least get 50 miles with 30 feet in the air. Not sure if that’s possible? I’m curious what do public safety radio systems do? How high do they usually have their towers?
mmckenna
I ♥ Ø
It depends on the system you want to listen to, and how it is designed. 50 miles at 30 feet is going to be difficult unless their transmitters are up really high.
The frequency coordination and FCC licenses are designed for them to cover a certain area. Since towers are expensive and so is feedline, they put a lot of effort into putting the best coverage they can into the are that is needed. Wasting money and energy trying to cover something 50 miles outside their jurisdiction would not likely happen unless you are really lucky.
Tall towers are the way to do it. That's what a TV station or FM broadcast station would do. But they have the money for it and their goal is to blanket as much of the local population as possible with their advertising.
Not so for public safety agencies.
Likely they have one tower in the center of their coverage area, or multiple lower towers.
Before you spend a lot of money on this, find a local building/parking garage and take your scanner up there and see if you can hear them. If you can't, no amount of antenna is going to make a difference.
jim202
Member
One item that hasn't been mentioned is what do you have around you? Trees can act as huge attenuation to the frequency your trying to listen to. The higher the frequency, the more attenuation.
This is why you will find that most public safety radio repeaters are located on the highest piece of land that could be found in the area the radio system needs to cover. Then a tall tower is used to get the antenna as high as needed to make sure the coverage is provided. Just how tall the tower needs to be can be computer predicted for the coverage needed.
To put this in a receive point for a scanner, if you live in a gully, your not going to hear much. If you live on a hill, your in a good location. But again, the foliage around your antenna will play on how well you can hear.
The true test is to try an antenna at the peak end of your roof on a bracket on the roof face board and see what you can hear. If you get what you want, your done. If not, it starts to get expensive putting up a tower. Don't forget the longer the coax cable between the radio and the antenna will come into play here. The higher the frequency of interest, the higher the coax cable loss will be. Long runs of coax may require a larger, lower loss cable.
One point to consider is to remember that most newer homes have insulation with a foil backing. This acts as a partial shield to radio signals. If you have aluminum siding, this makes it even worse.
If you do mount an external antenna, don't forget to ground it for lightning protection. That's a whole different discussion.
Jim
This is why you will find that most public safety radio repeaters are located on the highest piece of land that could be found in the area the radio system needs to cover. Then a tall tower is used to get the antenna as high as needed to make sure the coverage is provided. Just how tall the tower needs to be can be computer predicted for the coverage needed.
To put this in a receive point for a scanner, if you live in a gully, your not going to hear much. If you live on a hill, your in a good location. But again, the foliage around your antenna will play on how well you can hear.
The true test is to try an antenna at the peak end of your roof on a bracket on the roof face board and see what you can hear. If you get what you want, your done. If not, it starts to get expensive putting up a tower. Don't forget the longer the coax cable between the radio and the antenna will come into play here. The higher the frequency of interest, the higher the coax cable loss will be. Long runs of coax may require a larger, lower loss cable.
One point to consider is to remember that most newer homes have insulation with a foil backing. This acts as a partial shield to radio signals. If you have aluminum siding, this makes it even worse.
If you do mount an external antenna, don't forget to ground it for lightning protection. That's a whole different discussion.
Jim
- Status
Similar threads
