The transmit and receive radios I have used are Kenwood. The earlier repeaters use a pair of TK-931s, and are stil in service in the Portland and Vancouver metro area. All four repeaters in the greater Austin metro area use TK-941s. My portable repeater also uses a pair of TK-941s. Link radios in the earlier repeaters (Portland/Vancouver) are Motorola Maxtrac and CM-200. The TK-840 is used to link all of the Austin machines.

My early 900 MHz repeaters used modified Motorola cellular power amplifiers. The Motorola cellular 300W (SGTF-1019) PAs were used in the Portland repeaters, and the 150W (SGTF-2520) in the early Austin repeaters. Fans are used on all PAs and on transmit radios. These amplifiers are rated in PEP due to original operation in linear service. Hams have used them for SSB operation too. In FM service, they perform very well. Modifications are not difficult. The bias & control board can be removed and replaced with a LM-7805 +5 V regulator. +24 V is required for collector supply. If the STGF-1019 PA is used, the integrated isolator on each amplifier strip must be bypassed (top frequency for the isolator is 904 MHz). This can be accomplished by either an RG-316 jumper around the isolator, or by removing the puck from the housing and running the jumper through the empty circulator shell. If the SGTF-2520 is used, the isolator is separately mounted in the housing. It can simply be removed. Biasing is the same as with the higher power amplifier.

Since 2013, my preferred power amplifiers for 900 MHz repeaters have been MASTR-III variants. There are two families of these PAs: (1) the GE-Ericsson that have a very heavy cast Aluminum heat-sink and housing, and (2) the M/A-com Harris that have an extruded Aluminum heat-sink with a large fan. The heavy GE-Ericsson PA has a pushpull BJT final and an internal isolator. The M/A-com Harris PA has a pair of LDMOS finals that are quadrature combined and an internal isolator. Both these MASTR-III PAs are very reliable apower amplifiers capable of >100W. I typically set them to run around 75W.

Two power supplies are used in all repeaters: +12V and +24V. My prefered power supply is from the Meanwell 350W series of switching type supplies. Fuse blocks are used to provide fuses on all lines. A dedicated AC power distribution strip is mounted in the cabinet.

Celwave isolators with 100W loads are placed between PA output and duplexer TX input. This is not only for PA protection to mismatch; but for IMD protection (PA final can mix repeater output with other co-located signals).

A LNA with a pre-selector filter is placed between the duplexer port and the receiver input. I have used ARR, Angle Linear, and Minicircuits LNAs. My preference is either Chip Angle's product or the Minicircuits pHEMT product: ZX60-0916LN. A pair (P-PR) of WACOM cavities is my pre-selector preference.

I have used many different types of duplexers. The easiest to get with good performance are the WACOM cavities. That said, I really like the performance offered by dual-combline cellular duplexers. Narda West (Loral) dual-combline duplexers are in all of the Austin 100W repeaters. There are two different types of these. One can be used without modification, the other requires shortening the resonator rods. One of the Austin machines uses a duplexer of this type, while the other two high power Austin repeaters use Narda duplexers that do not require modification. More information about this modification can be found in the files section at the bottom of this page. Steve-WB7BYV and Greg-WB6ZSU have both performed this modification with good results. Greg-KJ6KO also uses Narda West duplexers in NC9RS system.

Link radios all have dedicated Motorola T-1500 (PR) cavities to protect against IMD in both transmitter and receiver circuits from co-located sources.

ICS Linker-IIa controllers were used in the two original Portland repeaters, the four Austin repeaters and in the portable repeater. There certainly are more feature rich controllers available. I use an Arcom RC-210 in my UHF repeater. Given the quantity multiplier, a low cost 2-port controller with full basic features was my solution. (I wasn't looking for a controller to talk to me). The Linker-IIa has worked out well for me. I use it's fan control to also key biasing to the PA. Additionally, I have made a couple of mods such as inhibit PL in the link transmitter during ID, and reduction of tone amplitude range. Please contact me for more info about this. I also use a DTMF controlled relay to toggle power to the controller as a failsafe means of hard rebooting. This can be invaluable in a mountaintop installation in the middle of the winter.

In 2011, I began migratng the 900 MHz network internet linking from EchoLink to Allstar. The *927_TECH* conference server is still maintained and linked into the Allstar 900 MHz network; but, the EchoLink side has become secondary. Allstar is an implementation of asterisk, an open source PBX that runs on Linux. The Linux platform can provide complete multiport repeater controller functionality, thereby eliminating the need for a controller board! The most recent repeaters that I have built do not have hardware controller boards in them. Initially, in 2013, I was building Allstarlink repeaters with with mini-ITX Celeron boards. The results with the mini-ITX builds was very good. Allstar has a range of codecs available (depending on available BW). Linked and repeated audio is superb. Next, ARM processor boards began providing a platform for Allstarlink repeaters. The first of these was the "Beaglebone Black" boards. Results were so good with BBB boards that it was safe to say that ARM processor boards were the future direction for all new builds. By 2015, the Raspberry Pi boards began replacing the Beaglebone Black boards as the prefered platform. This was initially with the RPi 2, followed by the RPi 3 and 4 variants. I have added an Allstar page that may also be of interest: http://k5tra.net/AllstarLink.html . If I can help with information, please feel free to contact me.