The Johnson County Radio Amateurs Club operates two repeaters:

WERH 145.290 MHz Repeater System

These pictures were taken May 11, 2007 to comemmorate two years of operation with the new repeater constructed by Bill Brinker, WA0CBW. Photos courtesy of Bill Gery, KA2FNK.

Photo 1: Inside the repeater cabinet. The repeater consists of a commercial grade receiver and transmitter (2), an RF power amplifier (1), a controller, an S-COMM 7k (3) -- that's the brain that runs the machine, and a metering panel (4) that we can use to check various functions out when we do on-site maintenence. Note that huge heat sink on the power amplifier: This unit is designed for 100 watts continuous-duty transmit. We run it at a conservative 50 watts output. The jumper (arrow) allows us to bypass the S-COMM controller in case it fails.

Photo 2: A look up at the tower as seen from the east. It's about 110 feet high. The 145.29 repeater antenna is the vertical element on the east face of the platform. The other antennas are part of the cell site that we co-inhabit.

Photo 3: This is the duplexer. It consists of four tuned-cavity filters. Its job is to allow the repeater to transmit and receive on the same antenna simultaneously. It is configured as a dual bandpass-bandreject system. The transmitter drives a bandpass tuned to 145.290 MHz, with a bandreject at 144.690 MHz (the receiver's input frequency). The receiver is in turn fed from the second pair of "cans," with bandpass of 144.690 MHz and bandreject of 145.290 MHz. Confused yet? Without these filters, the transmitter's energy would literally blow out the front end of the sensitive receiver. It takes a steady hand (and about $20k in test gear) to properly tune them, and fortunately that doesn't have to happen very often.

Photo 4: This is the frequency response of the receiver's bandpass-bandreject filter (two of the four cans) during the last alignment, which was performed in 1998 at the QTH of NGSG. The horizontal axis is frequency and the vertical axis is amplitude. At the input frequency (144.690 MHz) almost all of the signal passes through; however, very little transmit energy (at 145.290 MHz) is allowed through. The frequency response of the bandpass-bandreject for the transmitter side looks just like this, but it is a mirror-image (left-to-right) as the transmitter produces the 145.290 MHz transmit frequency (which needs to get to the antenna) while the 144.690 MHz input frequency must be suppressed.

Photo 5: Our site shares 120 V power with the cellular base station. This power is emergency-backed by this generator and automatic bus transfer switch.

Photo 6: Bill (WA0CBW) explains the features of the repeater to the assembled club members. In the background you can see part of the KCPL electrical substation that is adjacent to our site.

WERH 443.250 MHz Repeater System

Brief History of the WERH 145.290 MHz Repeater

Our repeater came into existence in 1993, and has lived in several different places before finding its current home.

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