DMR vs P25

[Project25_MASTR]

I am referring to splitting the frequency into 2, 12.5 split with two 6.25 + 6.25 adjacent "channels"

You shift your center frequency up 6.25 kHz or down 6.25 kHz.

 

[RRR]

I guess what I am trying to say, is even though it looks good on paper, I am pretty sure that is too close to use effectively. Separation is a good thing.

 

[mmckenna]

I guess what I am trying to say, is even though it looks good on paper, I am pretty sure that is too close to use effectively. Separation is a good thing.

Yes, and that's been said a few times in this post.

"Just because you can, doesn't mean you should.".

Yes, it can be done. Yes it's a pain. Yes it's not a good solution. Yes, your frequency coordinator must hate you, or you're a cheap bastard, if you are trying this.

 

[kayn1n32008]

I am referring to splitting the frequency into 2, 12.5 split with two 6.25 + 6.25 adjacent "channels"

In one channel, you would enter the first channel 3.125khz below the 12.5khz centre, select NXDN, select very narrow as bandwidth, select Tx RAN, select Rx RAN. In the second channel, you would enter 3.125khz above the 12.5khz center frequency and do every thing else as above.

You shift your center frequency up 6.25 kHz or down 6.25 kHz.

3.125khz above and below the 12.5khz center

I guess what I am trying to say, is even though it looks good on paper, I am pretty sure that is too close to use effectively. Separation is a good thing.

It requires 0khz separation hybrid combiners. It also requires the repeaters to use the same 10MHz external reference.

You are looking at a minimum of 7dB of loss using a 0khz hybrid combiner.
-100w in would mean less than 25w out.
-50w in would mean less than 12w out.

Where this might make sense, you don't lose both talk paths with a single failure. If you had a repeater failure using DMR, you would lose both talk paths.

Having said that, it's a really expensive way to get 2 talk paths out of a single 12.5khz channel.

 

[kayn1n32008]

I am pretty sure that is too close to use effectively.

S you are willing to spend the money on the filtering and the 10MHz reference(mandatory), it will work.

Separation is a good thing.

350khz or more separation makes filtering potentially cheaper.

 

[Project25_MASTR]

In one channel, you would enter the first channel 3.125khz below the 12.5khz centre, select NXDN, select very narrow as bandwidth, select Tx RAN, select Rx RAN. In the second channel, you would enter 3.125khz above the 12.5khz center frequency and do every thing else as above.

3.125khz above and below the 12.5khz center

It requires 0khz separation hybrid combiners. It also requires the repeaters to use the same 10MHz external reference.

You are looking at a minimum of 7dB of loss using a 0khz hybrid combiner.
-100w in would mean less than 25w out.
-50w in would mean less than 12w out.

Where this might make sense, you don't lose both talk paths with a single failure. If you had a repeater failure using DMR, you would lose both talk paths.

Having said that, it's a really expensive way to get 2 talk paths out of a single 12.5khz channel.

My bad I'm think about how you'd do it on a 800 MHz channel (which are still licensed 25 kHz in the US). I always thought it would be most practical to sub-divide across multiple sites. Keep your spacing but move the splinters to different sites.