# RTCM \<-\> CDM1250 Question **URL:** \ **Category:** Archive\ **Created:** [July 10, 2022, 9:08pm UTC](https://community.allstarlink.org/t/rtcm-cdm1250-question/19458 "2022-07-10T21:08:57Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![N4SJW](https://community.allstarlink.org/letter_avatar_proxy/v4/letter/n/898d66/32.png) [@N4SJW](https://community.allstarlink.org/u/N4SJW)\ **Post date:** [July 10, 2022, 9:08pm UTC](https://community.allstarlink.org/t/rtcm-cdm1250-question/19458/1 "2022-07-10T21:08:57Z")
I’m considering experimenting with the RTCM board and Motorola CDM1250. I haven’t used the RTCM yet so have a couple questions: - Is Allstar embedded on the RTCM and if so what version? - If I understand correctly, the RTCM has its own internal squelch but uses external CTCSS detect? - Anyone have any tips in using this combination? tnx, John N4SJW ---
**Author:** ![WB6OZD](https://community.allstarlink.org/letter_avatar_proxy/v4/letter/w/977dab/32.png) [@WB6OZD](https://community.allstarlink.org/u/WB6OZD)\ **Post date:** [July 11, 2022, 3:40pm UTC](https://community.allstarlink.org/t/rtcm-cdm1250-question/19458/2 "2022-07-11T15:40:44Z")
Allstar is not embedded on the RTCM. Instead, the RTCM connects to an existing Allstar node via a UDP data stream. Think of the RTCM as the replacement of a sound card interface with its connectivity over IP instead of USB (but with many more features!). Correct that the RTCM will use the CTCSS detect of the radio. The CDM 1250’s are great to pair with the RTCM. I’m setting up two more for additional voting receivers right now (receive only, no transmit). You can make a great performing repeater out of two CDM’s and an RTCM. ---
**Author:** ![N4SJW](https://community.allstarlink.org/letter_avatar_proxy/v4/letter/n/898d66/32.png) [@N4SJW](https://community.allstarlink.org/u/N4SJW)\ **Post date:** [July 11, 2022, 6:08pm UTC](https://community.allstarlink.org/t/rtcm-cdm1250-question/19458/3 "2022-07-11T18:08:20Z")
Ahhh, ok, so each of the CDMs will have a RTCM then there is, I guess, a raspberry pi at the master site (transmitter) that handles the system. Got it. So if you only have a single site repeater and no remote receivers, then you would have a RTCM and an RPi with the Allstar build? ---
**Author:** ![WB6OZD](https://community.allstarlink.org/letter_avatar_proxy/v4/letter/w/977dab/32.png) [@WB6OZD](https://community.allstarlink.org/u/WB6OZD)\ **Post date:** [July 11, 2022, 7:58pm UTC](https://community.allstarlink.org/t/rtcm-cdm1250-question/19458/4 "2022-07-11T19:58:44Z")
A single site repeater would have two CDM’s and one RTCM going to either a local Rpi or PC or a remote Rpi, PC or cloud server. Also, if you are not doing voting, you do not need to use the GPS. Also note that the RTCM can automatically run in local repeat mode so that your repeater is still functional even if your internet connection to your remote RPi or PC is down.