LakeFreak

I thought I would try to give an explanation about repeater codes since it has been a topic lately on the air. I think it is much easier to grasp if you look at it from the point of view of LISTENING. Codes are a way for a radio to IGNORE or REJECT signals that the listening operator DOES NOT want to hear. Any radio with a code set on its RECEIVE frequency will only open the squelch to let the properly coded signal audio “break” through. The code is a key to the lock. The assigned code must be present in the signal from the TRANSMITTING radio to open that lock and for the receiver to hear. Our community repeaters are programmed with that RECEIVE code set and expected so they only engage properly coded transmissions. They reject every other stray transmission that might be occurring on that receive frequency, (467 mHz). We have to put that code in our TRANSMITTING frequency when we program so the repeater will respond to our transmission. When the repeater “hears” you because the code indeed matches, electrical circuit magic instantaneously happens, and the repeater simultaneously re-transmits your message on the designated output channel (462 mHz). But, people listening for your radio signal from the repeater usually are only interested in that particular repeater’s transmissions, not the other noise happening in the background. So, for your benefit, repeaters are usually set with their own TRANSMIT code. If your radio has that matching code set for your RECEIVE frequency requirement, you, too, will only hear that repeater’s properly coded transmission. Your lock has been opened. But if you don’t set a receive code, ALL POSSIBLE signals on that channel will be heard by you, including the repeater signal you want. This code setting also provides a low level of protection against unauthorized people using the repeater or talking to you on your receive frequency, since a person must know the code being used to unlock either radio. Since there are only 8 repeater pair channels, there is a high level of duplication of the frequencies across the region. If they are close together geographically, these codes help keep the overlapping chatter separate, but it’s not perfect. Closing notes: 1) There are a couple hundred possible alpha numeric codes available consisting of two different types: CTCSS and DCS. 2) Not all manufacturers make available all the same codes. 3) It is possible to have any radio “fooled” into “hearing” a non-coded signal if a coded signal comes in at the same time, opening the squelch. 4) Your own radio is not required to have a receive code set, if you want to hear everything possible on the channel. I have done that with our own Gallatin and Grassland repeaters at times. I listen to two repeaters at once, no code. 5) It is possible, but uncommon, for a repeater to have one alpha numeric code for RECEIVE and use a different one for TRANSMIT, so you need to double check on the repeater listings for what is being used. 6) Remember when using the term TRANSMIT and RECEIVE, make sure you understand which radio in the conversation is being referenced. 7) Our community repeaters are “duplex” requiring the use of two frequencies. They listen on one and simultaneously and instantly retransmit our signals on the other. Our radio’s frequencies are “flipped” to do the same. The repeater receive (our transmit) is 5 mHz higher, with the decimal being the same. A radio hiccup (feature?): I noticed when I am scanning, my radio will rest silently on the Gallatin repeater when someone is transmitting on Grasslands, and vice versa, even with my codes set. So, the radio does “know” there is a transmission occurring, but it won’t let the audio come through the squelch without the right code. In my inexperience, it took me a minute to figure out what was going on! That’s why you may still see a receive light on a channel that has a silent radio. I've talked enough! Steve WSGH297