K5TRA 927 MHz repeater construction & testing


927 MHz repeater panels: TR/RX & link radios, controller, LNA/preselector cavities, & fuse block


Interior of 927 MHz repeater with duplexer, circulator, PA, powersupplies, and link cavity



K5TRA Repeater Construction

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.

Power amplifiers have all been Motorola cellular 300W (SGTF-1019), in the Portland repeaters, or 150W (SGTF-2520) in the 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.

Two power supplies are used in all repeaters: +12V and +24V. My prefered power supply is from the Meanwell 600W 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 are used in the two 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.

During the past several years I have been migratng the internet linking from EchoLink to Allstar. The 927_TECH hub 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. I have built three with mini-ITX Celeron boards. The results have been very good. Allstar has a range of codecs available (depending on available BW). Linked and repeated audio is superb. More recently, a number of the 900 MHz group has been building with "Beaglebone Black" ARM processor boards. Results have been so good with BBB boards that I think it's safe to say this is the future direction for all of us. I have also deployed a repeater using a Raspberry Pi-2 in La Grange TX with results similar to the BBB board. 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.



South Texas Linked 900 MHz Repeaters
927.0125     TPL 225.7 Austin, TX   (N)   (K5TRA)  Linked-927tech
927.0125     TPL 225.7 Pharr, TX   (N5SIM)  Linked-927tech
927.0250     DPL 532 Belton, TX   (WD5EMS)  Linked-927tech
927.0250     DPL 532 Fredericksburg, TX   (K5TRA)  Linked-927tech
927.0375     TPL 141.3 Canyon Lake, TX   (K5TRA)  Linked-927tech
927.0375     TPL 141.3 / D532 input Austin, TX   (Oak Hill)   (K5TRA)  Linked-927tech
927.0375     TPL 141.3 Troy, TX   (WD4IFU / N5SIM)  Linked-927tech
927.0500     TPL 110.9 Round Rock, TX    (WD5EMS)  Linked-927tech
927.0500     TPL 110.9 San Antonio, TX (NW)   (K5TRA)  Linked-927tech
927.0625     TPL 203.5 Georgetown, TX   (K5TRA)  Linked-927tech
927.0625     TPL 203.5 Katy, TX   (N5TM)  Linked-927tech
927.0750     TPL 218.1 San Antonio, TX (SE)   (K5TRA)  Linked-927tech
927.0750     TPL 218.1 Lampasas, TX   (WD5EMS)  Linked-927tech
927.0875     TPL 151.4 Bee Cave, TX   (K5TRA)  Linked-927tech
927.1125     DPL 432 Austin, TX    (K5TRA)  Linked-927tech
927.1250     TPL 103.5 Lago Vista, TX   (K5TRA)  Linked-927tech
927.1375     TPL 131.8 La Grange, TX   (NA5RC)  Linked-927tech
927.1875     P25 (NAC: 293) Austin, TX      (K5TRA)  on P25 network


NOTE:  927.1125,  927.1250  also have alternate inputs: 902.0125  (same PL as standard channel).


North Texas 900 MHz Repeaters
927.0125     TPL 110.9 Azle, TX   (N)   (WB5IDM)
927.0250     DPL 532 Richardson, TX (K5RWK / KE5GDB)  Linked-927tech
927.0375     TPL 110.9 Waxahachie, TX   (WD5DDH)
927.0500     TPL 110.9 Rosston, TX    (W5FKN / KE5GDB)  Linked-927tech
927.0625     DPL 432 Dallas, TX   (N4MSE)
927.0875     TPL 151.4 Fort Worth, TX   (K5SXK)  Linked-927tech
927.1125     DPL 432 Crowley, TX   (W2DB)  Linked-927tech
927.1500     DPL 432 Arlington, TX   (WD5DBB)  Linked-927tech
927.1625     DPL 432 McKinney, TX   (N4MSE)
927.1750     TPL 110.9 Carrolton, TX   (N5KRG)
927.4125     DPL 432 Denton, TX   (N5LS)  Linked-927tech
927.6125     TPL 110.9 Denton EOC, TX   (W5NGU)
927.6625     DMR Denton (Stark Hall), TX   (N5LS)  on DMR network
927.7375     TPL 110.9 Arlington, TX   (W5PSB)


927 MHz FM Links
927 MHz FM presentation - 2018 33cm Repeater database
NC9RS - N Calif  900 MHz Kenwood 902/927 info
*927_TECH*  EchoLink reflector AR902 user group
Narda combline duplexers Austin area 900 MHz repeater coverage
927_TECH linked network guidelines SAW filter boards


Click for current connections

Allstar 41170     -- This is our primary 900 MHz linking HUB

Additional linking is available with the *927_TECH* EchoLink conference server (linked to Allstrar 41170).



Geographic view of 900 MHz network main and satellite hubs:




*927 TECH* EchoLink reflector

While the majority of linking on our 900 MHz repeater network is now via Allstarlink, we still maintain the *927_TECH* EchoLink conference server as a dedicated linking reflector. This is a private conference with a "white-list" (900 MHz group only) for connection. If you have a 927 MHz repeater or link station and would like to get linked in, please contact K5TRA - tom@k5tra.net.




927 MHz P25 REPEATER

I used a pair of TK-981 transcrivers to build a 900 MHz P25 repeater. The TK-981 receiver radio requires several mods. The front-end ceramic filters must be replaced for good sensitivity on 902 MHz. Many TK-981 radios will not receive on 902 MHz because the VCO will not oscillate for frequencies that low. I modify the VCO for repeater receivers by changing 3 surface mount capacitors inside the VCO module. That modification is detailed in the PDF link below. The baseband audio lines must be DC blocked and appropriately padded. The receive pick-off is the standard DEO, discriminator audio. The transmit audio is injected after the DI point in the chain. It was also necessary to set both TX and RX audio as inverted. A Sinclair duplexer, Motorola RX filter and DB-589 were used. Several photos can be seen below:.


TK-981 VCO mod    - FOR 902 REPEATER RECEIVER

P25 Analog_Bridge and P25 Reflector    - "HOW TO" DETAILS




900 MHz P25 REPEATER (with TK-981 radios)









Some mobile installation photos

About 33cm FM

FM on 900 MHz is fun. The culture is very much like 70cm was 45 or 50 years ago. Radios are commercial, primarily Motorola and Kenwood. In 1970, it was Motorola, GE, and RCA. Chatter is usually interesting with some technical content. Activity level is good due to linking with other 900 MHz systems via the *927_TECH* linking reflector. For more info about radios and repeaters, download the "927 MHz presentation" file. Currently, there are more than 400 repeaters in the US on 33cm.