Antenna Height

[SouthernRoller]

Hello, I'm trying to determine is their any recommended height for base scanner antennas? I have heard the proper height for a base CB ant. is roughly 36 feet. I am wondering does anything like this apply to scanner antennas? I was messing around today and dropped my mast from 20 ft down to 18 ft and it cut what i was receiving almost in half...So that got me to wondering if there was any certain height i need to reach?
Thanks...

 

[jwt873]

For transmitting antennas, it's best to get at least 1 wavelength off the ground. (The wavelength of the CB band is 11 meters which converts to 36 feet). This is to ensure the antenna radiation pattern behaves as expected and doesn't get distorted. But, that's a 'minimum' recommended height. It won't hurt to go higher.

The simple rule is "The higher the better". Consider that VHF/UHF, the signals don't go much past the horizon. The higher you get the farther you can 'see'.

 

[SCPD]

Above the foilage

Like the previous poster said, the higher the better.

The best thing to strive for is to get above the trees. This can be a tall order (no pun intended) since, at least around me, that requires an antenna 80' off the ground. But 10' below the top of the trees, and 10' above the tree tops truly makes a night and day difference.

 

[br0adband]

You already proved it to yourself in your impromptu testing just by adjusting the mast 2 feet so, that's the answer:

There is no one size fits all, it depends on what frequencies you're intending to monitor (or transmit on but that's an entirely different thread with antenna lengths involved as well as cabling lengths too) and then basically doing more testing to see what works best on several fronts:

1) you (because some folks can't mount antennas in high locations without assistance or professional work)
2) what you're monitoring (because none of us really monitor the same things overall and the frequencies/wavelengths are extremely relevant)
3) the equipment you're working with.(because sometimes the equipment - including the antenna(s) itself/themselves can make all the difference)
4) the situation itself (because you could be used a building or house mounted mast, a standalone, something in a tree, or something inside an attic, etc)

So, do some testing, push what you've got now up to the maximum safe extension and see how it performs on what you're monitoring or transmitting on and then adjust as necessary or make changes to the hardware itself. At some point you'll find the best configuration for your intended purpose.

 

[SOFA_KING]

Hello, I'm trying to determine is their any recommended height for base scanner antennas? I have heard the proper height for a base CB ant. is roughly 36 feet. I am wondering does anything like this apply to scanner antennas? I was messing around today and dropped my mast from 20 ft down to 18 ft and it cut what i was receiving almost in half...So that got me to wondering if there was any certain height i need to reach?
Thanks...

There are "hot spots" and "not spots" (as I call them) concerning mounting locations. Too many technical reasons for this that it would be overkill to mention, so I won't.

What I used to do was walk around my potential mounting locations with a portable listening to distant stations (in multiple directions, as that shifts around too). When I found the hot spots where reception was best, I would make note of it and mount my antenna(s) there. Of course you cant always mount antennas in just any spot, but you can move them up or down in places you can mount an antenna and at least find the best height for that mounting location....or put up a big tower and have great reception guaranteed.

Your 2' experiment was a valuable lesson. Play...and enjoy the learning experience.

Phil

 

[902]

Usually the reason putting it up a little higher works better is because you've cleared some kind of obstruction or clutter that blocked you from "seeing" that signal. The radio horizon is a little further than light and passes through some materials, but is scattered by others, so it's not exactly like light, but it's a good analogy to use.

In general, the higher and further away from things - especially sources of noise (computers, fluorescent and LED lights, switching power supplies) the better. The kind of antenna you use matters a lot, too. Different types work better for different situations. Scanners also work on a very wide range of frequencies. An antenna pretty much should be resonant on the frequency band you are trying to listen to.

I have had very good luck listening to the 33 MHz fire channels using a CB antenna. It's a little off, but when conditions are right, they still come booming in. A CB antenna might work okay for higher frequencies, like 46 MHz. For VHF, UHF, and 800 MHz, I'd want to use another antenna that's more suited for the frequency range. Also, if there's one particular place I want to listen to, I'd put a Yagi (beam) antenna up pointing at it. Look at it as having a toolbox full of tools. There's a right one for the job. That goes for heights, too.