Rattlesnake 550 Repeater – Technical Specifications

Tower:

  • Elevation:  2408 ft. (734 m.) AMSL

Antenna:

  • Model:  Celwave PD455-7 Super Stationmaster Omni (460-470 MHz)
  • Height:  110 ft. (33.5 m.)
  • HAAT:  916 ft. (279.2 m.)
  • Type:  Omnidirectional
  • Overall Length:  19.5 ft
  • Rated Wind Speed:  100 MPH
  • Side Thrust @ Rated Wind:  75 lbf
  • Gain:  10 dBd
  • Bandwidth:  10 MHz
  • Vertical Beamwidth:  7 degrees
  • Polarization:  Vertical
  • Max Power Input:  500 W
  • Electrical Tilt:  0 degrees
  • Lightning Protection:  Direct Ground
  • Termination:  N-Female
  • SWR:  1.1:1  (est.)

Feed Line:

  • 120 ft. of 7/8″ hard line  (Andrew Heliax LDF5-50A or equiv.)

Duplexer:

  • Model:  Motorola T1504A
  • Reference manual:  PDF
  • RX loss:  1.12dB
  • RX isolation:  81dB
  • RX frequency response:  Graph
  • TX loss:  1.15dB
  • TX isolation:  92dB
  • TX frequency response:  Graph

Bandpass Cavity Filter:

  • Model:  Wacom WP-470-1
  • Diameter:  5″
  • Insertion loss:  2.65dB
  • Frequency response:  Graph
  • Documentation:  Tuning Instructions

Preamp:

  • Model:  Advanced Receiver Research P460VDG
  • Gain:  18dB

Receiver:

  • Model:  ICOM IC-F621-2
  • Serial:  01505
  • Sensitivity:  0.25uV
  • Jumper settings:  A,B,E,H closed; C,D,F,G open; HANG open
  • Notes:  eBay purchase (Dec 2019).  100% working.

Transmitter:

  • Model:  ICOM IC-F621-2
  • Serial:  2209618
  • Nominal TX Power:  45W
  • Actual TX Power:  47W
  • Jumper settings:  A,B,C,E,F,G closed; D,H open; HANG open
  • Notes:  eBay purchase. Was originally used in a railroad Locotrol system. Good TX, low RX sensitivity. Replaced pin diodes D3, D5 and RF transistor Q2. Noticed C32 is missing. Suspect this may have been a Locotrol mod to reduce sensitivity.

Transmitter Cooling Fan:

  • Model:  NOCTUA NF-P14s redux-1500 PWM
  • Dimensions:  140 x 140 x 25 mm
  • Input power:  0.2W

Cooling Fan Filter Capacitor:

  • Model:  Sprague 36D7003
  • Value:  4,400uf (nominal), 5,800uF (measured 4/27/2020)
  • Working voltage:  20VDC
  • Surge voltage:  30VDC

Controller:

  • Model:  Communications Specialists TP-3200
  • Jumper settings:  2,5 closed; 1,3,4 open

DC Power Supply:

  • Model:  Astron RS-35M
  • Current:  25A continuous, 35A peak
  • Voltage Range:  11-15V adjustable
  • Output Voltage:  Set to max possible level of 14.11 VDC
  • Role:  Backup battery charging through PWRGate PG40S module.

Backup Battery:

  • Make:  MK Battery
  • Model:  M24 SLD A  (no longer sold)
  • Type:  AGM
  • Weight:  53 lbs
  • Group size:  24
  • Capacity:  79Ah @ 20-hr rate
  • Notes from West Mountain Radio:
    • 3000 10% or 200 50% discharge cycles
    • Deep-cycling of the AGM 79 will significantly reduce the life of the battery.
  • Discharge Testing – June 1, 2020:
    • Test Protocol:
      • Initial State of Charge:  100%
      • Battery Temperature:  70 F
      • Discharge Current:  7.5 Amperes
      • Cutoff Voltage:  10.5V  (0% state of charge)
    • Test Apparatus:  West Mountain Radio CBA II Computerized Battery Analyzer
    • Test Results:  Amp Hours    Watt Hours    Minutes

Power Source Selector:

  • Model:  West Mountain Radio PG40S Super PWRgate
  • AGM Jumper:  Installed as required for an AGM battery
  • Maximum Charge Current:  Set to 10 Amperes  (safely below max charging rate for a 105Ah battery)
  • Recommended Power Supply Voltage:  Ideally 14.5V to ensure AGM battery is charged to 100%
  • Actual Power Supply Voltage:  14.11V  (max possible with Astron RS-35M supply)

Calculations:

  • TX power out of duplexer:  36W
  • Feed line loss:  0.982dB
  • SWR loss:  0.004dB
  • Connector losses:  0.5dB (est.)
  • Total TX signal loss:  1.485dB
  • TX power out of feed line:  26W
  • Effective radiated power (ERP):  256W

Photos: