What Is Your Experience With 7.5 kHz Splinter Isolation

[Birken Vogt]

Finding new frequencies is like hens teeth and we are being suggested to try ones that are right next to other major players that we know are already there and are separated by only 7.5 KC on VHF. We are talking about repeater outputs output-to-output and the contours are only touching on the edges, the repeaters are separated by many miles but they are on major mountains east and west both overlooking the Central Valley of California.

I would like to know if any of you have experience with this. All I have to go on now is that we have one business frequency and another user 7.5 KC off where if I drive into their their territory our repeater gets wiped out on my mobile but for the most part it seems like they play quite well.

It is just that with this new idea, the stakes are much higher and I do not want to tick somebody else off and have to track down many dozens of mobiles and reprogram them.

Is there a dBm isolation figure you use to approximate this?

[Jim202]

Finding new frequencies is like hens teeth and we are being suggested to try ones that are right next to other major players that we know are already there and are separated by only 7.5 KC on VHF. We are talking about repeater outputs output-to-output and the contours are only touching on the edges, the repeaters are separated by many miles but they are on major mountains east and west both overlooking the Central Valley of California.

I would like to know if any of you have experience with this. All I have to go on now is that we have one business frequency and another user 7.5 KC off where if I drive into their their territory our repeater gets wiped out on my mobile but for the most part it seems like they play quite well.

It is just that with this new idea, the stakes are much higher and I do not want to tick somebody else off and have to track down many dozens of mobiles and reprogram them.

Is there a dBm isolation figure you use to approximate this?

You didn't mention for what type of service this is going to be used for.

It is never a good idea to put two big guns on adjacent channels. Most radios do not work well with strong adjacent channel signals. It only takes a slightly high set deviation and that kills it. If you contact the offending operator, they generally just ignore you or tell you to go take a flying leap.

To directly answer you technical request, take a look at the radio receiver specs and see what it gives for adjacent channel rejection. The higher that number the better the radio will play.

Jim