|REPEATER OPERATING PARAMETERS|
|INPUT FREQUENCY MHz||146.900|
|OUTPUT FREQUENCY MHz||146.300|
|CTCSS TONE||123.0 Hz|
The Brundage Mountain 2-meter VHF repeater consists of a Yaesu DR-1X repeater, Telewave T-1560 Dual-Port Isolator, Wacom WP-641 Duplexer, NHRC-4 Repeater Controller, and an antenna yet to be determined (projected to be a 2-Bay Folded Dipole with an orientation of 48°. This orientation is to avoid interference outside of the coverage area, to focus the coverage area to avoid areas out of the primary service area, and to enhance communications capabilities in the back country. A projection of coverage does not indicate any degradation in coverage for CIARC member operators.
|Yaesu DR-1X Repeater Manufacturer Specifications|
|Frequency Stability||±2.5ppm (-4°F to +140°F)|
|Operating Temperature||-4°F to +140°F|
|Receiver Sensitivity -12 dB SINAD||0.2µV|
|Receiver Selectivity||> 65 dB @ 20 kHz offset|
|Transmitter Power Output||50 / 20 / 5 Watts (selectable)|
|Spurious Emission||> 60 dB|
|Wacom WP-641 BpBr Manufacturer Specifications|
|Insertion Loss||-1.5 dB|
|Maximum Power||275 Watts|
|Number of Cavity Filters||4|
|Tuning Range||144-174 MHz|
|Temperature Range||-30°C to +60°C (-22°F to +140°F)|
The Wacom WP-641 Duplexer has been donated by Larry Stokes (N7IBC).
|Telewave T-1560 Dual-Port Isolator Specifications|
|Frequency Band||118-174 MHz|
|Tuning Range||±4 MHz|
|Input Power||100 Watts|
|Insertion Loss||-0.8 dB|
|Isolation||-70 dB (typical) / -60 dB (minimum)|
|Temperature Range||-30°C to +60°C (-22°F to +140°F)|
The above coverage projection represents nearly a four-fold increase in area when compared to operation on 70cm.
The following image shows the insertion loss at the receiver frequency of 146.300 MHz to be -2.1 dB. Additional tuning efforts have failed to reduce the insertion loss to the duplexer specification of -1.5 dB. An insertion loss of -2 dB is at the limit of acceptable performance standards. A possible cause of failure to reach the device specification maximum insertion loss of -1.5 dB may be due to the length of coax cables composing the duplexer cable harness. The receiver will experience attenuation of -0.6 dB greater than expected by specification, and this will result in degrading the receiver performance from 0.200 µV for -12 dB SINAD to 0.215 µV for -12 dB SINAD, and does not represent a significant degradation in receiver performance.
The following image shows the attenuation of the transmitter on the receiver signal path to be -84 dB. Note that the spectrum analyzer noise floor is ≤ -80 dB, and the measurement may not indicate the full amount of attenuation.
The following image shows the insertion loss at the transmitter frequency of 146.300 MHz to be -2.3 dB. Additional tuning efforts have failed to reduce the insertion loss to the duplexer specification of -1.5 dB. An insertion loss of -2 dB is at the limit of acceptable performance standards.
The following image shows the attenuation of the receiver on the transmitter signal path to be -86 dB. Note that the spectrum analyzer noise floor is ≤ -80 dB, and the measurement may not indicate the full amount of attenuation.
The following image shows the insertion loss through the Telewave T-1560 isolator to be -1.3 dB. Note that the isolator specification indicates a maximum insertion loss of -0.8 dB. The isolator is labeled as originally being tuned to 151.4375 MHz, and moving the center frequency down to 144.81 MHz represents a change of frequency of 6.6275 MHz, which represents a move of 2.6275 MHz greater than the specified tuning range of the isolator. This isolator was originally purchased for installation on the No Business 2-meter/VHF repeater at 147.620 MHz, which would have remained within the specified tuning range of the isolator. The realized performance at 146.300 MHz is at the extreme limit of acceptable performance, and it may be prudent to check if the isolator currently installed at No Business Mt can provide better performance when tuned to 144.81 MHz. If the isolator installed at No Business Mt will provide better performance, swapping the isolators would be recommended. Note that excessive isolator insertion loss will reduce the amount of transmitter power that reaches the antenna.
The following image shows the attenuation of transmitter energy when reflected back down the feed-line, or radiated energy from other transmitters, as -61.9 dB. This level of performance falls within the specification of the isolator.
The following two images show the lack of spurious energy at the repeater primary transmit frequency of 144.510 MHz, and at the downlink receiver frequency of 927.225 MHz, which indicates that there should be no interference to the downlink receiver from the repeater transmitter.
The following block diagrams are intended for comparative analysis. For those not familiar with the impact of system losses imposed by a duplexer or isolator, the realized performance can, on face value, appear to be excessively degraded. In reality, and to a point, the system losses are normal, and the realized performance must be compared against the expected worse case performance. What is worrisome is when the realized losses exceed the expected worse case losses. In our case, and in the case of most amateur radio installations where surplus equipment is installed, and where that equipment is not specifically designed to operate on the target frequency, the installed equipment may not achieve the worse case performance indicated in the device specification.
In the case of the isolator, there is a note (in a blue box below the image that depicts the isolator insertion loss) that provides an option that might result in better performance.
In the case of the duplexers, the excessive insertion loss is probably due to cable lengths within the duplexer cable harness. These are constructed with UHF/PL-259 connectors and LMR-400 (or equivalent) coaxial cable. The original frequency pair was 143.275 MHz and 142.325 MHz (just below the amateur 2-meter band). These are currently tuned to a frequency pair of 146.900 MHz and 146.300 MHz. The move up in frequency would require shorter cables. The connectors in the cable assembly cannot be the standard UHF/PL-259 connectors used in everyday use by the average amateur, but must be silver plated in order to avoid injecting noise into the system and to avoid mixing points that can result in intermod interference (to our own repeater or others in the area). Silver plated UHF/PL-259 connectors are more expensive and harder to find, but that is not the largest problem. Without a cable length chart, which would depict the length of each cable in the cable harness vs the frequency of operation, construction of new cables is experimental with respect to length. UHF/PL-259 connectors are nearly impossible to reuse, so if you don't get it right the first time, the cable must be discarded and a new cable would be constructed. Duplexer manufacturers pre-manufacture cables of different lengths, and when a duplexer is ordered for a specific frequency, they just look at a table of cable lengths vs frequency and grab the appropriate cable needed for the frequency specific assembly. There is no option to just order the cables (Wacom is not in business any longer). I'm of the mind that it is not worth my effort, or the club's, to go through the expense and labor to experiment with cable lengths to gain 0.6 dB (which results in a gain of 2.3 watts on low power or 4.6 watts on high power [best case with no isolator], and an increase of 0.05 µV of receiver sensitivity [a change in sensitivity that cannot be measured]).
The block diagram below depicts realized performance with the dual-port isolator included in the repeater configuration.
The block diagram below depicts measured performance with the dual-port isolator included in the repeater configuration.
The following two tables illustrate the Ideal and Actual ERP calculations with the repeater transmitter operating at 25-watts, using an antenna with a gain of 6 dB.