Central Idaho Amateur
Radio Club
     
CIARC VHF 2-Meter Repeater & 33cm Link Back-bone Specification
CIARC VHF 2-Meter Repeater & 33cm Link Back-bone Specification
Overview

A completely new 2-meter VHF FM Repeater was constructed in the spring of 2012 with the goal of improving the repeater performance and reliability. Other goals include adding a UHF linking back-bone, located on the 33cm UHF Amateur Service band, to provide extensibility to the VHF repeater by enabling linking with other off-site repeater systems and to enable locating capabilities remotely when those capabilities are incompatible with the repeater site. The new repeater also includes anti-intermodulation technologies toward providing a cleaner RF environment at the repeater site.

Operational frequencies for the VHF FM Repeater and UHF FM Link are as follows:


CIARC VHF Repeater & Link Frequencies
Receive Frequency MHz Transmit Frequency MHz Access
147.6200 147.0200 CTCSS 100.0 Hz
902.2250 927.2250 DCS 023

Repeater Components

The major components of the new repeater system include:

Repeater System Block Diagram

The following block diagram depicts radio frequency signal paths, audio frequency signal paths and control routing within the repeater.

The repeater utilizes separate antennas for the 2-meter and 33cm Amateur Service bands. The antennas are routed, using short coaxial jumpers, to a diplexer that is mounted in close proximity to the two antennas to enable use of a common feed line for both the 2-meter and 33cm radios. Use of a single feed-line reduces both the weight and wind load presented to the tower structure.

Duplexers for both 2-meters and 33cm enable use of a single antenna per band.

Isolators are installed between the duplexers and the transmitters for both the 2-meter and 33cm bands. The Isolators are a directional coupler, which present a highly attenuated signal path for radio frequency energy emanating from other transmitters and that enters the antenna system. Such radio frequency energy, if unattenuated, can enter the transmitter and mix with the transmitter frequency to produce undesired frequencies, known as Intermodulation Products, that are then radiated back out to the antenna. Installation of Isolators, in conjunction with the band-pass filtering that is provided by the Duplexer, acts to attenuate radio frequency energy and significantly reduce or eliminate Intermodulation Products from being produced by the transmitter.

Audio that is detected at either the 2-meter and 33cm receiver is mixed and then is routed to both the 2-meter and 33cm transmitters.

Off-site repeater systems, remote radios or Voice Over Internet Protocol (VOIP) interfaces are thus able to be linked to the repeater system by having these facilities receive the 33cm down-link frequency or transmit on the 33cm uplink frequency. Link capabilities are intended to support remote interfacing with fixed stations only.

The control signals are comprised of Carrier Operated Switch (COS), Constant Tone Coded Squelch System (CTCSS) Decoder State, Digital Codec Squelch (DCS) Decoder State and transmitter Push To Talk (PTT). These signals are routed through the repeater controller, which includes a Dual Tone Multi-Function (DTMF) decoder that enables remote control of repeater control functions. The repeater controller is programmed to perform automated Morse identification, to apply limits to the duration of transmission, to route audio signal paths between the receivers and transmitters, and to implement a squelch tail timer only on the VHF transmitter.

DTMF control is available using either the 2-meter or the 33cm receiver, providing redundancy in control access.

Not depicted on the block diagram is a battery back-up power system. When operating on battery back-up, the VHF Power Amplifier that is connected between the TK-705D VHF transmitter and the EMR VHF Isolator, will not be powered. This results in reduced VHF transmitter power in favor of a longer sustained operational life when operating on battery power.

The transmit output power from the Kenwood TK-705D VHF transmitter has been reduced to a setting that results in an output level of 50 watts from the KLM-PA15-80 power amplifier. Although the KLM-PA15-80 is rated at 80 watts, the power level was reduced to accommodate the higher duty cycle use of a repeater transmitter and in the interest of long term reliability.



Kenwood TK-705D Specification

Kenwood TK-705D Specification
General
Frequency Range 146 to 174 MHz
Receiver
RF Input Impedance 50Ω
Sensitivity 0.20µV for EIA 12 dB SINAD
0.30µV for 20 dB Quieting
Squelch Sensitivity 0.25µV
Modulation Acceptance ±7 KHz
Selectivity -80 dB
Intermodulation -75 dB
Spurious and Image Rejection -90 dB
Frequency Stability ±0.0005 from -30°C to +60°C
Transmitter
RF Power Output 2 W adjustable to 5W
RF Output Impedance 50Ω
Spurious Harmonics -70 dB
Modulation F3E, ± KHz for 100% at 1000 Hz
Audio Distortion 1.0% at 1000 Hz
Frequency Stability ±0.0005% from -30°C to +60°C

Kenwood TK-941 Specification


Kenwood TK-941 Specification
General
Frequency Range RX 935-941 MHz (NOTE: The PLL VCO of the link receiver has been adjusted to lock within the Amateur Service at 927.2250 MHz)
Frequency Range TX 896-902 MHz, 935-941 MHz (NOTE: The PLL VCO of the link transmitter has been adjusted to lock within the Amateur Service at 902.2250 MHz)
Receiver
RF Input Impedance 50Ω
Sensitivity 0.25µV for EIA 12 dB SINAD
Modulation Acceptance ±3.5 KHz
Selectivity -60dB
Intermodulation -65dB
Spurious & Image Rejection -75dB (Excepts 1/2 IF)
Transmitter
RF Power Output 15W
RF Output Impedance 50Ω
Spurious & Harmonics -60dB
Modulation F3E, F1D, F2D
FM Noise -40dB
Frequency Stability ±0.00015%

EMR Dual-Port VHF Isolator Specification


EMR Dual-Port Isolator Specification
Power Input (max) Watts 125
Impedance 50Ω
Insertion Loss (dB) 0.45 (maximum)
Isolation (dB) 70 (minimum)
Return Loss (dB) Not specified
VSWR 1.22:1
Temperature -30°C to +60°C

DB Products ACJ Series Dual-Port UHF Isolator Specification


DB Products ACJ Series Dual-Port Isolator Specification
Power Input (max) Watts 150
Impedance 50Ω
Insertion Loss (dB) 0.2 (maximum)
Isolation (dB) 50 (minimum)
Return Loss (dB) 19
VSWR 1.22:1
Temperature -30°C to +60°C

Wacom WP-639 Duplexer Specification



Wacom WP-639 Duplexer Specification
Tuning Range 144-174 MHz
Minimum Frequency Separation 0.6 MHz
Maximum Power Input 350 Watts
Insertion Loss 1.5 dB at 0.6 MHz separation
Attenuation (TX/RX Frequencies) 80 dB at 0.6 MHz separation
Attenuation (minimum) 50 dB at 0.6 MHz Separation
Maximum VSWR 1.5:1
Temperature -30°C to +60°C
Number of Cavity Filters 4

Wacom WP-494 Duplexer Specification



Wacom WP-494 Duplexer Specification
Tuning Range Any 25MHZ band within 800-960 MHz
Minimum Frequency Separation 25 MHz
Maximum Power Input 175 Watts
Insertion Loss 1.0 to 2.0 dB (adjustable)
Attenuation (TX/RX Frequencies) >80 dB at 25 MHz separation (interpolated)
Maximum VSWR 1.5:1
Temperature -30°C to +60°C
Number of Cavity Filters 4

Repeater Photos


Repeater Cabinet Front



Repeater Cabinet Rear
Measured VHF Repeater Performance

Measured repeater performance and operational settings are as follows:


2m Repeater Performance
Parameter Measurement
Receiver Sensitivity 0.18 µV for -12 dB SINAD
Squelch Threshold 0.05 µV
Receive Duplexer Attenuation 1.6 dB
Effective Receive Sensitivity (Duplexer Loss) 0.23 µV for -12 dB SINAD
TK-705D Transmitter Output Power 4.3 W
KLM PA15-80BL Amplifier Output Power 50.0 W
EMR Isolator Output Power 40.0 W (0.97 dB loss)
Duplexer Output Power 27.5 W (1.62 dB loss)
TK-705D Repeat Audio Deviation 5.0 KHz
TK-705D ID'er Audio Deviation 1.5 KHz

The following power measurements were made, with observations in battery power and commercial power operating modes, at each point along the transmit signal path. No measurable loss was detected at the lightning arrestor. All measurements are expressed in watts.


2m Repeater Power Measurements
Power Source Kenwood
TK-705D
Transmitter
KLM
80-Watt
Amplifier
Isolator Duplexer
Commercial 4.3 50.0 40.0 27.5
Battery 4.3 4.3 3.7 2.6

Note that for the VHF Effective Radiated Power (ERP) calculations below, the transmitter power output that was measured at the end of the signal chain comprised of the isolator, duplexer, diplexer and lightning arrestor. Only the feed-line loss and the antenna gain were required to complete the ERP calculations.


2m Repeater Operating Parameters
Power
Source
Power
Output
Watts
Antenna
Gain dBd
Duplexer Rx
Insertion
Loss dB
Duplexer Tx
Insertion
Loss dB
Isolator Tx
Insertion
Loss dB
Feed-line
Loss dB
Total Tx
Loss/Gain dB
Total Rx
Loss/Gain dB
ERP
Watts
Commercial 27.5 +6.0 -1.5 -1.5 -0.5 -0.4 +3.6 +4.1 165
Battery 2.6 15

Operational Settings

Operational settings are as follows:

2m Repeater Operational Settings
Parameter Setting
Transmitter Timeout Timer 10 minutes
Transmitter ID Timer 10 minutes
Transmitter Squelch Tail Timer 2 seconds

DC Power Budget

The following table depicts the worse case 12-volt power supply budget. Note that the 80-watt amplifier is being driven to only 50-watts, while the TK-705 transmit power level that drives the 80-watt amplifier has been reduced to 4.3-watts, and will result in a reduced current consumption relative to the worse case requirements.


12-Volt Power Supply Budget
Component Receive (Amps) Transmit (Amps)
Kenwood TK-705 (Repeater Transmitter) 0.70 7.00
Kenwood TK-705 (Repeater Receiver) 0.70  
Kenwood TK-981 (Downlink Transmitter) 1.00 7.00
Kenwood TK-981 (Uplink Receiver) 1.00  
Link Communications RLC-1 Repeater Controller    
KLM PA15-80BL 2-Meter VHF Amplifier   10.00
Fans (3X) 0.45 0.45
TOTAL 3.85 24.45

When running on battery, the 80-watt amplifier is not powered. The battery power supply budget is then reduced to:


12-Volt Battery Budget
Component Receive (Amps) Transmit (Amps)
Kenwood TK-705 (Repeater Transmitter) 0.70 7.00
Kenwood TK-705 (Repeater Receiver) 0.70  
Kenwood TK-981 (Downlink Transmitter) 1.00 7.00
Kenwood TK-981 (Uplink Receiver) 1.00  
Link Communications RLC-1 Repeater Controller    
Fans (3X) 0.45 0.45
TOTAL 3.85 14.45

VHF Predicted Coverage

The following image depicts the predicted VHF coverage when operating with commercial power from Lookout Peak on No Business Mountain.



The following image depicts the predicted VHF coverage when operating with battery power from Lookout Peak on No Business Mountain.



UHF Predicted Coverage

The following image depicts the predicted UHF coverage when operating from Lookout Peak on No Business Mountain.