GR1225 12.5 khz spacing problem

johnny1225 · Post by **johnny1225** » Tue Oct 18, 2005 4:06 am

I have (2) UHF GR1225 repeaters that were working fine at 25 khz spacing, got all the coverage they need, finally reprogrammed the repeaters to 12.5 khz and the new cp200 to 12.5 khz spacing. Now they say they have a problem with coverage were they use to get good coverage now is very scratchy or missing the call all together. I was wondering is there something i can do to improve the 12.5 khz spacing like bumping up the devation. Any suggeustions would be appreciated.

thank you

john

Post by **wavetar** » Tue Oct 18, 2005 1:23 pm

Were they always using CP200's, even at the 25KHz spacing?

Todd

johnny1225 · Post by **johnny1225** » Wed Oct 19, 2005 2:15 am

yes always using cp200 even at 25 Khz

Dan562 · Post by **Dan562** » Wed Oct 19, 2005 9:20 am

I think there may be some confusion here. Just because a radio is capable of 12.5 kHz Splinter RF Channels does not mean it's capable of the true Narrow Band Astro Digital Modes being APCO P25 Type I or Type II. I believe the GR1225 is an Analog FM Repeater only!

Nand · Post by **Nand** » Wed Oct 19, 2005 5:57 pm

An un-modulated wide or narrow band un-companded signal should produce the same quieting level. When companding is used, the noise level appears to get better.

If the audio quality is suffering, it likely is that the companding is not matched between the radios and the repeater. Depending on the repeater configuration, it may be best to not use companding at the repeater at all, but do use it for the portables. This will increase the voice quality for narrow band.

There is no need to have the repeater reprocesses the audio, just leave it linear and no repeater gain. I believe one of the manuals for the GR1225 discusses this. If you use the repeater also as a base, then its companding should be turned on.

About companding, according to the Motorola manuals, the TX audio is compressed at a 2 to 1 ratio (2 dB in for 1 dB out) and on the RX end it is expanded again into its original form. Once compressed, the signal is also amplified in such a way that at 40% deviation the signal has the same amplitude as an uncompressed audio signal with the same 40% deviation.

There is no need to have the repeater use companding/expanding when the audio is only repeated. Only if a wire line is used, does the audio need to be expanded / companded.

The repeater, since it does not modify the audio, should appear invisible to the audio.

Nand.

d119 · Post by **d119** » Thu Oct 20, 2005 12:31 am

Dan562 wrote:I think there may be some confusion here. Just because a radio is capable of 12.5 kHz Splinter RF Channels does not mean it's capable of the true Narrow Band Astro Digital Modes being APCO P25 Type I or Type II. I believe the GR1225 is an Analog FM Repeater only!

Sorry to butt in, but where the hell did that come from?

Post by **wavetar** » Thu Oct 20, 2005 4:25 am

d119 wrote:
Dan562 wrote:I think there may be some confusion here. Just because a radio is capable of 12.5 kHz Splinter RF Channels does not mean it's capable of the true Narrow Band Astro Digital Modes being APCO P25 Type I or Type II. I believe the GR1225 is an Analog FM Repeater only!
Sorry to butt in, but where the hell did that come from?

I'm wondering the same thing...nobody said ANYTHING about digital, or APCO...

Todd