How to choose the Frequencies and offset For Retevis RT97?
Today we will talk about how to choose the Repeater & Frequencies of Retevis RT97.
If you are going to buy a repeater, maybe you need to have some knowledge of Repeater.
1. Do know what is the history of a repeater?
In the early days of radio invention, the long-distance propagation characteristics of short-wave signals have not been found.
While medium-and long-wave radio communication has limited distance due to earth absorption loss.
Early amateur radio enthusiasm used the manual transfer to expand the range of communication.
The America Amateur Radio Association has so far used the name “Amateur Radio Repeater Alliance” ,
that was left at that time as a testimony to this history.
2. What is the frequency of repeater?
What we usually call the relay frequency refers to the uplink frequency of the repeater.
The so-called “uplink” frequency refers to the transmission frequency of the radio station(Handheld Radio),
while the corresponding “downlink” frequency refers to the transmission frequency of the repeater station,
which is the receiving frequency of the radio station.
Because the “downlink” frequency is usually used to mark the frequency of a repeater,
the downlink frequency is usually called face frequency,
and the corresponding uplink frequency is called “bottom frequency”.
3. What is the offset?
Generally, when using repeater device communications, we will use different transmission and reception frequency,
the difference between transmission and reception frequencies are called “offset”.
The different frequencies are divided into the “uplink offset” and “download offset”.
we usually use the “download offset”, which is transmitting frequency is lower than the receiving frequency,
we take RT97 repeater as an example, the transmission frequency is 462.5550, the receiving frequency is 467.5550, the offset is 5 MHZ.
we call it the “download offset” is 5 MHZ, this is the general amateur radio setting method because some amateur radio difference frequency is fixed,
it is is 5 MHZ.
Of course, there are some special Settings for the difference frequency.
For example, some repeater in Hong Kong is set to 9.850MHz, And some of them are in the United States is 7.6MHZ.
How to choose the Frequencies and offset For RT97?
1. Using Retevis RT97 repeater as an example:
Firstly you need to know what is the frequency of RT97, And what is the offset of RT97.
Above all, you need to know what kind of repeater do you need, and what is the type of RT97, I mean analog or DMR.
2. Secondly, we all know that repeater is not a personal device.
In some areas, if you want to set up a repeater, You need to report to your local radio board at first.
At reporting time, the radio committee will give you a small range of frequencies and let you select one or more frequencies from which to use the repeater legally.
Please Note: The selected frequency areas provided by the radio board are generally at both ends of the UHF, and are not commonly used frequencies.
This is to avoid affecting the use of hot spots.
For example, in various regions of the USA, the frequency band provided by FCC in UHF is 440~450mHz.
You can see the picture as below:
So what is the central frequency of RT97 repeater?
The central frequency of RT97 should be:
Lower frequency(simplex/repeater output, MHz) : 462.625mhz
Upper frequency(repeater input, MHz) : 467.625mhz
This frequency point is the central value of the eight channels of GMRS.
Each repeater station is allowed to fluctuate 1mHz above or below its central frequency.
Using 462.625mhz and 467.625mhz as the central value of the relay station, any one of the eight channels can be used.