The Johnson County Radio Amateurs Club operates two repeaters:
- The 145.29 (145.29 MHz output / 144.69 MHz input) (that is a negative offset).
- The 443.725 (443.725 MHz output / 448.725 MHz input) (that is a positive offset).
WØERH 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 NØGSG. 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.
WØERH 443.250 MHz Repeater System
- Would anyone like to contribute photos and story to cover this system?
Brief History of the WØERH 145.290 MHz Repeater
Our repeater came into existence in 1993, and has lived in several different places before finding its current home.
- The idea to build a repeater was championed by Roger Bessemer (then KBØIIG, later WØSOB and now SK), and Jim Hundley (KØGKL).
- Tom (NØGSG) designed and built the first repeater using surplus GE Master Progress (hybrid - tube & transistor) equipment.
The club had very little money to spend on a repeater, and in fact Roger Bessemer took up a special collection to get things
rolling. Contributors got a special commemorative certificate.
- The repeater's first home was at the Leawood, KS police department...it didn't stay there for more than a year or so.
- The repeater lived at Roeland Park city hall for several years in the mid 1990s.
- After being in Roeland Park, the repeater lived at the QTH of Jim KØGKL, until about 2000, when Terry Constant WØTLC initiated an
agreement with T-mobile for us to co-reside at the current location.
- We kept the GE Master Progress equipment going until 2005, when Bill Brinker WAØCBW brought the new all-solid state system
on board. In 2004-2005 we were observing a spike in power amplifier failures on the GE system -- and learned that the AC power line was
running about 145 V instead of 120 V, greatly stressing the (vacuum tube) PA components!
- The "new" Motorola repeater system has been providing flawless service since 2005!