Scanner Q&A

They come in, sneaking across an international border. Unwanted. Brash and annoying. Demanding to be heard. Only to invade your home and disrupt your peace and quiet.

No matter what you do, you cannot persuade them to leave.

You KNOW what I'm talking about. It happens every year. It's that nasty inversion layer that brings Mexican transmissions into your scanner.

You'll hear them when the weather is warm, calm, and usually on VHF frequencies. While this can happen any time of year, it's more prevalent in the summer.

This is a different phenomena than "Skip" communications. "Skip" usually happens as a result of ionization of the atmosphere by the Sun, while inversion-layer ducting is strictly caused by the weather.

Hopefully this will stave-off the annual "Why am I hearing Mexicans on my Scanner" posts.

Doesn't it also result from the fact there are no limits to their transmission output power? While I was in Mexico a few weeks ago for the Baja 500 we had pretty good seperation while further away from the border. In the border area it was a free for all on our race frequency

I'm no student on Mexican Radio Regulations, but I would think that there are limits on transmitter power for 2-Way radio users. This certainly is true in the Broadcast bands, where the FCC and the Mexican govenrment work closely to prevent interference issues.

Of course, Mexico like many similar countries lack adequate enforcement - and government officials can easily be bribed.

Adding more power does not necessarily equate with more range. There is a point where you can talk out a lot farther than you can hear your mobile units. And all things being equal, the "Radio Horizon" falls off in a predictable manner where lots of transmitter power will only warm up the clouds

Altitude, Terrain, Weather and Solar phenomena will make the biggest difference - in that order. Solar rarely has any effect when you get above the VHF range.

They come in, sneaking across an international border. Unwanted. Brash and annoying. Demanding to be heard. Only to invade your home and disrupt your peace and quiet.

No matter what you do, you cannot persuade them to leave.

Are we really talking about radio waves here?? If I had it my way, I would make it so not even their radio waves could come into this country.....