Carolina 440 UHF Link Specifications Guideline
Radio Equipment/General Operational Specs
Repeaters must have the ability to enable PL tone access, the PL tones to coordinate for UHF repeaters on the link are: 88.5, 91.5, 94.8, 100.0, 110.9 and 131.8 hz PL tones are needed in case of interference issues. 100 hz is preferred if available per coordination availability. 100.0 Hz is (Common Pool 1) for NC 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. 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 Hub.
Link antennas at a minimum will be 5 or 6 element yagi, preferably the Maxrad BMOY-4405 or MYA-4306 both cut for 446 mhz. A 13 element Maxrad cut at 446mhz with N-connector is also available locally in Raleigh, N.C. 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
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.
Repeater controllers we use are the Micro Computer Concepts RC-100, ARCOM RC-210, CAT-200, CAT-250 B AND cat 300 DXL for the repeaters on the link. The Backbone Hub uses an advanced Pacific Research RI-310-e.
Repeaters must be enabled to pass DTMF tones over to the link. This will give the ability to use IRLP, 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. The backbone properly ID’s on the system at 20 wpm every 10 minutes 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.
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 repeaters. However when a tone is needed we will use 2475 hz for 30 to 40 milliseconds duration at 0.5 to 0.8 khz.
Time Out Timer Requirements
The TOT on the Backbone Hub is 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. Acceptable link radios are the GE Mastr II, Kenwood TK-840 and TK-863G mobile radios. Interface diagrams are available on these radios. The GE MLS mobiles have been used on the system, but we presently do not recommend them due to the reliability issues. 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. No speaker audio on link receivers, this is too much drive and will distort the audio passing through other repeaters on 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.