If you're new to the whole thing of HAM radio this may interest you. Well it interests me and I've been a HAM since I was 16. I knew this but I never saw it visually like this before.

On VHF (2 meters) Amateur Radio operators have put up repeaters. A repeater is a transmitter and receiver usually connected to an antenna(s) very very high. For years a the local 146.88 MHz repeater was at 1,400 feet (if memory serves) on the local PBS antenna tower!

The repeater's job is to receive a transmitted signal on one frequency and then AS IT IS RECEIVING IT transmit that signal out on another frequency.

The "trick" is to do it on the same band so that people can extend the range of their fixed (base) radio, mobile radio, or hand held (walkie talkie).

On 2 meters the frequency "split" (difference between transmit and receive frequencies) is -600KHz. So a repeater that operates on 146.600 for example, would have a receive frequency of 146.000. Now this is just an example!

So the 146.880 MHz repeater mentioned above would have a receive frequency of 146.280 MHz, or 600 KHz less than the repeaters transmit frequency. (0.600 MHz).

The WHOLE reason for this is to allow your minor, to moderate radio installation to have a much greater transmitting and receiving range that it would normally be capable on it's own. Band conditions can make it possible for your radio to transmit and receive hundreds of miles on 2 meters, but those conditions are fleeting and rare. The repeater means you can reliable communicate with the same people everyday, 24 hours a day. All in FM clarity!

A local repeater in Katy, TX, my home, has a graphical image of their repeater coverage.

Now if you were using a 50 watt mobile and quarter wave antenna this is what you'd expect you "coverage" to be. This means you would be able to hear and send to the repeater and be "heard" inside this circle.


If you look to the far right of the circle you can see RF shadows that are being created by the skyscrapers in downtown Houston! The shadow means that the huge metal structure of the skyscraper is blocking, or at least attenuating the transmitted signal from the repeater in Katy, about 20 miles away.

This is the repeater's coverage if you were on a hand held 5 watt