Carolina 440 UHF Link Specifications Guidelines
Radio Equipment/General Operational Specs
Repeaters must have the ability to enable PL tone access, the recommended PL tones to coordinate for UHF repeaters on the link are: 82.5, 88.5, 91.5, 94.8, 100.0, 110.9 and 131.8 hz PL tones are needed in case of interference issues. 100.0 hz is preferred if available per coordination availability. 100.0 Hz is (Common Pool 1) for NC SERA area repeaters.
We prefer tones below 146.2 hz due to the audible hum that is much present above 150 hz. This may be amended depending on coordination requirements. The Raleigh Hub repeater filters user PL and produces PL encode at proper level on the COS (carrier)
Repeaters must have a RF Link to the backbone frequency 446.725 TX with PL encode of 100.0 Hz and a RX of 441.725 in carrier mode (no PL decode), with the ability to do decode of 100.0 hz if the need arises by control or manual jumper.
The 100 hz PL is used for control, AllStar, EchoLink and IRLP linking in case interference may arise. The backbone hub remains in carrier mode 99 % of the time and detects user PL of 100 hz and re-encodes 100 hz on the carrier at a proper level. The backbone has the ability to do true zero hang time, but may be placed in extended hang time mode by a control op for special uses. The backbone hub is a coordinated SERA linking repeater for a linking Hub.
See further under "Technical Radio Specifications" below.
Link antennas at a minimum usually are 5 or 6 element yagi, preferably a commercial grade Yagi, Example: DB Products, Maxrad BMOY-4405 or MYA-4306 that may be tuned for 446 mhz. Feed line should be low loss and at a minimum no smaller than LMR-400 at lengths below 150 feet. RF path study can be done to determine optimum height and direction along with larger feed line recommendations. The RF link must have a full quieting signal into the system.
Link Radio Pass Band Filter (Optional)
A DCI Model: DCI-445-10C band pass filter may be required on the UHF link radio. This is a wide band pass filter that can be installed to eliminate the on the edge signals below 440 and above 450 mhz from interfering. This is mostly needed at high RF Tower sites.
Repeater controllers we use are the Micro Computer Concepts RC-100, ARCOM RC-210, CAT-250 B AND Cat 300 DXL for the repeaters on the link. The Backbone Hub uses an advanced Pacific Research RI-310-e and does all the Magic for the Hub System. High tier controllers are not needed for our outbound linked repeaters, having the ability to disable and enable link radio and repeater is all that is needed. AllStar Rasp-Pi Controllers are also used, when VoIP/Radio IP is needed to establish a link or as a repeater controller.
Repeaters must be enabled to pass DTMF tones over to the RF link. This will give the ability to use AllStar, IRLP, EchoLink, special code access and control of the backbone from the repeater. No voice or CW ID’s are to transmit to the backbone on the link frequency. We prefer no voice announcements on the repeater systems at all other than connection, basic ID, time or controller user functions and reports back from control. The backbone properly ID’s on the system at 20 wpm every 10 minutes of activity while only in use per FCC requirements. Minimum ID parameters on repeaters are programmed and the CW ID level must be less than 1.0 khz deviation in order for voice to be heard over top of an repeater ID. Audio delays are recommended for the repeater only, not the link radios. However some link radios can have special mods to work fluently and usually we have a tight squelch adjustment on the link radio receivers.
Repeater Codes are formulated based on present controllers and user codes on existing repeaters. The repeaters must have the ability to be shut off through the receiver, link radio receiver of other remote control. These enable and disable codes will be available to Control Operators.
We try not to use courtesy tones on the repeaters while linked on the Carolina 440 system. We believe the repeater should come close to actual conversation as possible. When you are on the phone (other than Nextel) or in person, there is no squelch tail burst or courtesy tones and we try not to have them on the UHF repeater system. However, when a tone is needed we will use 2475 hz for 30 to 40 milliseconds duration at a light 0.5 to 0.8 khz. We would rather it be on the Repeater side with a courtesy tone and not on the RF link side.
Time Out Timer Requirements
The TOT on the Backbone Hub is 175 seconds, just under 3 minutes. It may be necessary to program a repeater on the link with an extended TOT if the Link radio RX is timed on a controller. We can assist with this or other programming parameters to eliminate issues on the system with our set of controller templates.
Technical Radio Specifications
The UHF Link mobile radios of choice are the Motorola GM300, M120 and the latest CDM-1250. Acceptable link radios are the Kenwood TK-840 and TK-863G mobile radios, etc. Interface diagrams are available on these radios. The GE MLS mobiles and GE Phoenix have been used on the system, but we presently do not recommend them due to the reliability issues due to age. Link radios should not have an audio delay or a TX hold time enabled, however audio delay boards on the repeaters are recommended to eliminate squelch burst. Usually 62.5 to 125 milliseconds are sufficient audio delay times. A repeaters squelch should be set normal and not loose as to not have a squelch burst over the system. For additional technical info contact one of the Carolina 440 UHF Link System Trustees for guidance.
* These are the general specs and not the complete repeater and tech spec for the repeaters and radios. Amendments may be added here if the need arises.