WR1ABM Avon Repeater
- Category: Ham Radio
- Created: Monday, 25 July 2011 23:38
- Last Updated: Monday, 21 January 2019 06:05
- Written by Rick Swenton
- Hits: 5834
These are some old slides taken in the 1970s at the 28-88 repeater in Avon CT. One of these days I will orgaize this page into a formal presentation with explanations and names of the people.
The WR1ABM 2 Meter repeater was in Avon CT back in the 1970s and 1980s on 146.28 MHz in, 146.88 MHz out. The repeater was located on Deercliff Road in Avon with a 120 foot guyed tower similar to Rohn 25.
The original repeater was all vacuum tubes and consisted of a Motorola Sensicon A receiver and a GE Progress Line transmitter running about 40 watts out. Digital electronics and microprocessors were in their infancy then. The repeater had a Morse Code identifier built with RTL Digital Logic: Resistor-Transistor Logic whch was before the more familiar TTL Transistor-Transistor Logic chips. The WR1ABM callsign in Morse Code was stored in a diode matrix where a diode represented a digital bit in the code pattern. However, because the digital circuits were pure digital (and not BCD - the diode matrix was not Base 10) the arrangement of the diodes had to be determined using a Karnaugh Map. I actually used Karnaugh Maps in college in my Digital Electronics courses! This was all done to minimize chip count and reduce cost. Later we used BCD to Decimal decoders and the diode matrix was organized just like the Morse Code dots and dashes. Before microprocessor controllers our identifiers used EPROMS to store the morse code.
The control system was three simple relay timers: one to keep the transmitter keyed for 5 seconds after the input signal stopped (the tail timer), one to key the Morse Code ID every 10 minutes, and one to shut off the transmitter if there was an input signal longer than 3 minutes (the Time Out timer). These were needed to comply with FCC rules.
The second generation VHF system was a modified Johnson commercial transceiver and a KLM amplifier. Dave, K1THP designed and built the original TTL logic controller but we still used that old identifier! The solid state system reduced the amount of space needed inside the cabinets.
The ICRC UHF repeater then on 442.85 / 447.85 MHZ was a modified RCA Series 1000 donated to the club by Vinnie, W1DNI. This was all solid-state and ran about 60 watts output.
The repeaters had a huge array of lead-acid storage batteries for emergency power. Remote control was done with two dedicated telephone lines (alarm pairs) between the repeater and the trustee's house. Using these lines we applied different polarities of DC to perform various functions and we ran the Autopatch audio on them too. Because the repeater site was not a residence it was prohibitively costly to get a phone line there. So we put the phone line at the trustee's house and ran the phone audio up and down the alarm circuits using a hybrid at the house. A hybrid is like an audio duplexer. It splits a 2-wire telephone into a 4-wire configuration with separate tansmit and receive audio paths.