After a trial implementation with SMRC system remote linking using the AllStarLink network, some additional improvements need to be made to the system to facilitate external connectivity.
Due to the legacy configuration of the repeater system and the up/downlink configuration of the experimental AllStarLink node attached to the system, telemetry tones from the James Ridge repeater are passed over the link to Alamo Peak. The net result of this is that telemetry tones for the system are passed over remote links such as AllStarLink and Echolink, which is an undesired practice. Proper repeater system configuration is a system where each individual radio (primary or link radio) emits telemetry without associated tone encoding which prevents the telemetry from being repeated over other radios in the linked system when combined with proper CTCSS settings on other system radios.
Correcting this issue may be paired with a more advanced technological solution which enables CTCSS coding to be used to allow C4FM and analog FM users of the repeater system to both enjoy use of the system without causing unwanted end-user radio traffic to users of the opposite modulation scheme/mode. Integrating an advanced repeater controller at each site will allow multiple CTCSS tones to be used on repeater transmit based on the type of modulation used. End-users can then implement a receive CTCSS (available on virtually every modern FM transceiver) to prevent squelch break unless a received transmission is accompanied by the CTCSS tone suitable to the mode being transmitted.
This functionality is currently being implemented on the Alamo Peak transmitter in a slightly modified manner. Analog FM users who normally monitor the Alamo Peak repeater may filter out unwanted digital transmissions by setting a receive CTCSS of 151.4 Hz in additional to utilizing the normal transmit CTCSS of 151.4 Hz used to access the repeater. C4FM digital transmissions from Alamo Peak utilize no CTCSS tone, and C4FM receivers do not break squelch on receipt of analog FM signals, so mode isolation is currently possible for both C4FM and analog FM users on the Alamo Peak repeater.
Unfortunately, C4FM is currently passed over the system link to both James Ridge and Weed repeaters without the ability to CTCSS segregate those signals. The C4FM is passed through the audio section of the link radios, and as such is not decodable by other C4FM receivers, but is also unable to be filtered using CTCSS tones. As we upgrade the repeaters at James Ridge and Weed to the DR2X multi-mode repeaters, this problem will be corrected and in its final configuration, the system will facilitate co-use by both analog and digital users with minimal interference to each other.
A repeater controller which allows mode segregation via CTCSS tone will also allow the use of non-tone encoded telemetry data, which will make the implementation of analog linking services such as AllStarLink and Echolink clean and technically correct. Stay tuned as we work to implement this solution in coming months.