I'm after some GPS receivers to sync up two nrg pro3's, maybe some old navmans will do it? could anyone recommend anything where it's easy to get a ref freq I can divide to get 12.5khz?

We use the BBC on 198kHz to provide a source for 9kHz reference for medium wave. The BBC transmitter is synchronised to the National Physical Laboratory and is insanely stable!

Do you have frequency standard stations "down under"? These are usually easy to receive and divide to your required reference frequency.

advice me please what is the the use for ?
can be for two transmiitter on same frequency for one audio to make power down and up
sorry for my clarification

It's just to guarantee that a transmitter is exactly on frequency.

If you want to synchronise two transmitters, it's easiest to phase-lock them to the link frequency or to a control sub-carrier on the link signal (I've used the stereo pilot in the past).

When I was engineering B92 in Belgrade (back in the bad times over there), the authorities wanted complete control of the media, so tried very hard to locate and shut the station down. We used concealed aerials and synchronised transmitters so that direction-finding wouldn't work. Once the technology was sorted out, successful raids fell to virtually zero!

I remember sitting in the window of a flat in a tall block watching the Radio Detection Unit guys going 'round in circles. The only way (eventually) they managed to find a rig was by turning off the power to an area so that the other rig stayed on.... We confounded that by using three then four synchronised rigs! Eventually, they gave up. The country achieved democracy a few years later and B92 still broadcasts, but legally these days!

Albert H wrote:We use the BBC on 198kHz to provide a source for 9kHz reference for medium wave. The BBC transmitter is synchronised to the National Physical Laboratory and is insanely stable!

Do you have frequency standard stations "down under"? These are usually easy to receive and divide to your required reference frequency.

None around here that I know of, we do however have two very tall medium wave towers nearby, there are a bunch of stations all multiplexed into them. One of the stations is the government run "National Radio" on 756khz. Stations on these two towers can be received up and down the country. If I can get two transmitters synced up, I can then apparently use the "single frequency network" feature of Stereotool to feed them.