Approximate Timeline of Events:
2001.11.04 - The 146.34/94 FM repeater and duplexer were removed for general overhaul and the 145.73 MHz digipeater was relocated to the 170 Ft equpment platform while the IDRL gantry system is being repainted. Additionally, we were asked to remove the equipment from the 220 Ft. level doghouse so that the enclosure could be used for it's original purpose, that is, a tool shed.
2001.12.01 - Efforts are underway to clean the repeater and duplexer for the purposes of corrosion control. Repainting of both cabinets is necessary to prevent further deterioration.
2002.01.01 - The cooling air screens were repaired and reinforced with additonal bracework. A tool box has been added to the top of the repeater cabinet to contain the new CAT-300 controller and power supply. Also a power surge strip was added with the addition for surge protection for the telephone lines.
2002.02.01 - Efforts are underway to collect documentation on the repeater and duplexer. This is proving to be difficult since the units are more than 30 years of age.
2002.03.01 - The card edge extender was repaired and the repeater backplane was thoroughly cleaned. Circuit troubleshooting was begun. It was discovered that the original potentiometers for receiver audio, noise level squelch, and deviation are all suffering corrosion problems. These were replaced.
2002.03.10 - The controller interface board was interconnected with the repeater subchassis. The squelch tail was removed entirely. This was done with a circuit modification to the squelch gate circuit. The squelch tail is now about 20 mS in duration and is almost not noticable by users.
2002.03.15 - The controller interface board was programmed with elementary identifications and functions that are applicable to NLARC operations.
2002.03.20 - The best set of driver and final amplifier tubes were installed. At present, the repeater has a power output of 75 Watts into a 50 Ohm dummy load.
2002.04.01 - Efforts began to understand how to tune the duplexer. After some research it was determined that we have a Sinclar Hybrid-Ring Duplexer. A document that describes how to tune the is located at: Sinclair Duplexer Tuning Instructions. These instructions are a bit non-specific, and are difficult to follow. I have discovered perhaps a simpler way to perform this function, and with simple tools.
2002.05.01 - Some problems remain with intermodulation products keeping the receiver squlech gate open during repeater operation. This was eventually traced to harmonics radiating from a computer monitor. Once this errant signal source was eliminated the repeater began to operate flawlessly.
2002.05.15 - An email was sent addressed to Charlie Stokes (W4PVT) of the SERA organization to request re-coordination of the 146.34/94 repeater at the Hampton VA location.
2002.05.30 - Final efforts are underway to have two telephone lines installed in the third level equipment room.
2002.06.04 - An email was sent addressed to Jim Campbell (W4YM) of the SERA organization to request re-coordination of the 146.34/94 repeater at the Hampton VA location.
2002.06.07 - A new repeater antenna was installed at the 240 foot level in the crow's nest on the east side of the gantry where the strobe light is installed.
2002.06.10 - The 146.34/94 repeater was put back in service. Unfortunately the intermodulation with an adjacent transmitter that operates intermittently on 10 frequencies in the 405-409 MHz band is causing the squelch to open and repeat the digital signals from the other transmitter(s). This problem is being studied closely. The squelch setting for the repeater is currently at 100% to minimize the duration of the interference.
2002.06.14 - The 146.34/94 repeater was removed from service until the intermodulation problems can be resolved.
2002.06.18 - Contacts were made with Ted (708.681.0300) at MDM Radio LTD. to purchase a manual for the repeater. After several photographs were sent in addition to model numbers, Ted came back with a manual part number 68P8100E575 describing a Motrac CVHF BASE C73HMB3100 system. The manual cost $15.00. Further discussions indicate that this system is a modifed base station with a blower on the driver and final tubes to operate as a repeater. This system is not intended to be a continuous duty system. Ted indicated that the tubes and other parts that he might not have are available from RF Parts INC.
2002.06.20 - During a frequency survey on the gantry Jim Jenco (AB7IN) arrvied and co-examined the situation with multiple frequencies appearing on or near the repeater receive frequency with digital modulation when the 146.94 and one of the 407 MHz transmitters are operating simultaneously. We inspected the transmitter house, coaxial lines, and the antennas involved in the digital radio system for any obvious mechanical problems.
2002.06.25 - The repeater manual was received in good order.
2002.07.16 - After returning from an absence, the purchased repeater manual from MDM Electronics was examined and determined to describe the repeater system to a "T". Many thanks to Ted at MDM Radio for his excellent assistance in obtaining proper documentation.
2002.07.18 - A programmable PL tone encoder donated by Jim Jenco (AB7IN) was installed in the repeater receiver and checked for operational effectiveness in the lab.
2002.07.20 - Further measurements indicate the intermodulation problem with the local APCO-25 system is still a major problem.
2002.07.24 - A UHF notch filter has been ordered to supress the 405-409 MHz APCO-25 system signals from entering the duplexer. Several of the APCO-25 system transimit signals are 600 kHZ apart and these appear to be entering the 146.94 PA only to mix and produce a new frequency of 146.34 MHz.
2002.07.29 - An application for frequency coordination was mailed to Jim Campbell of the SERA organization.
2002.07.31 - A radio propagation model for the 146.34/94 repeater was created using the freeware application Radio Mobile V 3.7.8 by VE2DBE.
2002.08.05 - The UHF notch filter from Par Filters was received.
2002.08.07 - The repeater was put back on the air with the Par Filters UHF notch filter (-40dB, or 10000/1 reduction at 405 MHz). The notch filter was located 1/4 electrical wavelength from the TX/RX junction in the duplexer (toward the antenna). The hybrid-ring duplexer was re-tuned. Unfortunately the filter did not eliminate the interfering signal that appears on the intput of the repeater (146.340 MHz) when the 146.94 transmitter and two of the 405.nnn MHz transmitters (5 pairs of frequencies out of the 10 are 600 kHz apart, the rest are 400 kHz and 200 KHz) are transmitting at the same time. The only way to keep the interfering signal from holding up the repeater receiver was to enable the PL on 97.4 Hz. The squelch was set close to the edge in COR mode, and then the repeater was put back on PL access.
2002.08.09 - The repeater refurbishment project is considered complete. Further improvements to the performance of the repeater are necessary to allow good weak signal COR operation.
Web page operations: James E. Byrd
Responsible NASA Official: Richard S. Eckman
