Advanced Repeater Systems

KA9RIX Repeater System

I received my Amateur Radio License when I was working for American Antenna (K40 fame) in the Chicago area in 1984.  Back then you had to go to the FCC Office to take your test and they only gave them twice a year.  I was happy to pass my five words per minute code test and earn my KA9RIX call Technician License.

Since, I have upgraded to Extra and mainly operate on VHF and UHF with D-Star, EchoLink and now AllStar.  My main interest is building Repeaters and Linking.

In the 1990's we had a RF Linked Repeater System which covered the West Coast of Florida from: Naples, Ft. Myers, Arcadia, Sarasota, Bradenton, St. Petersburg, Dunedin, Tampa, Lakeland and sometimes into Miami with twelve 2m and 440 repeaters.

After the loss of sites, interest, cellphones, the Internet, family, work, fire 
and Silent Keys, the system is much smaller but links to the world with D-Star and EchoLink.  (Use KA9RIX B and KA9RIX G for Access) 

My Main Repeaters are:

    53.050, -1 MHz, 103.5, linked on AllStar
    145.390, 203.5, St. Petersburg, linked on AllStar

    444.175, 203.5, St. Petersburg

    444.725, 103.5 Madeira Beach, linked on AllStar

    444.500, D-Star, Madeira Beach, usually on REF-030C

    444.4625, D-Star, Madeira Beach, usually on REF-001C

    147.285, D-Star, Clearwater, usually on REF-030C (The D-Star Blowtorch)

    444.075, DPL 546, St. Petersburg, linked to Madeira Beach

    444.3375, 203.5, Dunedin, linked to Madeira Beach

    444.275, 203.5, Palma Sola (west of Bradenton)


Above is the KA9RIX Micor D-Star Repeater on 444.500 in the same rack with the analog 444.725 Micor located at Madeira Beach.  WaCom UHF duplexer and Telewave receiver multicoupler are at the top.  Bottom is a 2m WaCom duplexer for the back-up 145.390 repeater.  The black box is a Satoshi D-Star Node Adapter.  D-Star repeater system utilize the V2 Node Adapters which made superior repeater controllers.

My repeater rack is always a mess because it is always changing, which is why I prefer these open racks. The cabinet to the right is a 1954, 250-watt, Motorola Sensicon base station on 52.525 MHz. Back in the 1980's my brother Mike, KB4ABE, was living in Gainesville, and we linked our UHF repeaters with remote bases on 51.4 MHz. (We bought the radios from a Florida veterinarian who was later convicted and sent to prison for having his wife killed.) His repeater was located on the University of Florida Shans Hospital. I used this Motorola as my remote base with a vertical yagi at 50 ft. and he had a 100-watt RCA with a yagi at about 150 ft. Sometimes it actually worked and we could talk using our UHF handy talkies from St. Petersburg to Gainesville- quite a novelty for the pre-cellphone, pre-Echolink, D-Star era!

Below is the repeater tower on Madeira Beach.  The top Antenna is a forty year old Decibel Products DB-411.  It has four, DC grounded elements mounted on one side for 9 dBd offset gain and is the tower lightning rod.  It is connected to the primary repeater transmitter and a receiver multicoupler.  The Antenna to the right is a DB-404, a two, dual element array with 3 dBd gain.  It is used as the secondary repeater transmit antenna. 


The white Antennas are Comet and Diamond dualband antennas for the 2m back-up repeater, 2m D-Star repeater receiver and general amateur use.  The all metal top-mounted DB-411 provides lightning protection for these antennas. (Never mount Comet or Diamond antennas at the top of a tower!) The yagi at the bottom is the D-Star link antenna to the main St. Petersburg repeater site.

Most of my repeaters are General Electric Exec II and Motorola Micors mobile radios with several Icom and Kenwood mobile radios.  Most are in the 15 to 45 watt range.  I prefer to use low power for the reduced heat, power consumption and cooling requirements which greatly improve reliability and on UHF it is hard to tell the difference.

The UHF Micor Mobile Radios, in my opinion, are the best radios to make a 440 ham repeater.  Motorola probably stopped making them because they were expensive to produce.  A basic one channel, carrier squelch, medium power Micor sold for $1600 in 1972!  They seem to last forever and no radio manufactured since has come close to the standard features found in these over-engineered radios.

The UHF Micor came with a transmitter circulator, ceramic power amplifiers that can be modified to produce 1 and up to 100 watts, a unique transmit offset oscillator that allows a single channel element to generate both receive and transmit frequencies (with a simplex option), a direct FM modulator for DPL (works great for D-Star), modular design, separate receiver and transmitter units, and the famous Micor fast squelch, among others. 

Unfortunately the same can't be said about the VHF Micors which uses PNP RF power transistors.  The 25 to 65 watt versions are pretty good but the 90, 100 and 110 watt version are notoriously unreliable and often generate spurious, are prone to failure and burn-out for no apparent reason.  I've tried everything to resolve these issues, but what works on one doesn't work on another.  Motorola had problems with them too judging by the numerous revisions, modifications, and added and deleted components over the years.  There is simply too much gain, power and heat on the small power amplifier board.  It is not uncommon for these to produce over 160-watts with the power control set wide-open on the bench.

The VHF receiver requires major modifications to the front-end helical filters and some multiplier parts changes to convert them to 2m.  Once converted the receivers work well for 0.5 microvolt sensitivity, which isn't that great, but I've put some of them in RF hell (or intermod alley) and they do just fine!

For VHF operation I prefer the GE Exec II.  They are easy to modify and extremely reliable and the transmitters can be modified for D-Star.  The Mastr II is ok, but they use a lot of fragile custom hybrid modules and the chassis doesn't have as good of isolation for full-duplex operation.  Regardless, I have built plenty of Mastr II repeaters that work just fine.

Below is a repeater system in a GE Mastr-Pro cabinet with a 30-watt VHF Micor on the top shelf, a back-up 15-watt UHF Micor on the middle shelf and a 2m duplexer below.  This UHF repeater receives on a multicoupled DB-420 that feeds a UHF Motorola Micor dual mode D-Star/analog repeater in the small Motorola cabinet to the right.  The UHF Micor uses a single Motorola 1501 bandpass-bandreject cavity and transmits on a Comet GP-9 dualband antenna which is diplexed with the 2m repeater.  The repeater controller is an Advanced Computer Control RC-85 housed in the Data Signal box on the middle shelf.

The power supply is a Motorola MSF ferro-resonant unit rated at 30 amps.  The ferro power supplies are the best power supplies for repeater service.  I find them at hamfests surprisingly cheap these days.  For some reason amateurs are afraid of them, don't know what they are, or don't like their characteristic buzz and poor efficiency.  However, the saturated core design of a ferro are virtually immune to power surges and spikes which is why Motorola, GE, EF Johnson and other commercial repeater manufacturers used them.  Notice the large power transformer, choke and filter capacitors, this thing was built to last. 

I bought this ferro (marked "BAD") at the Bradenton (Tampa Bay) hamfest from a Motorola guy for $10. I found that the factory forgot to install the ground wire to the filter capacitors which caused the voltage to wander up. I grounded the filter caps and the unit works perfectly.

The VHF Micor has been in repeater service for over 25 years without a single failure.  And it was in mobile service likely 10 years before that.  Maybe that's why Motorola quit making the Micor, because they just go on and on...

It uses the popular ARS Transmitter Control (front) and Audio Delay Boards (rear) and a vintage 1993 ARS CW IDer (mounted on the other side).

The 2m duplexer is one of my favorites, an old Sinclair bandpass-bandreject unit with direct DC grounded loops.  They don't make them like this anymore because this design cost more to build. Like the Micor, these old units are better than anything you can get today.

These can take lightning and keep on duplexing.  Notches are set by adjusting the sleeve capacitors similar to the WaCom design.  However, the WaCom, which is an excellent duplexer, does not have DC grounded coupling loops.  Lightning flows through them like water right into your repeater!  Make sure you are using a Polyphaser with your WaCom duplexer.

Also shown here is the 2m/440 diplexer that combines the UHF transmitter,
via the BPBR Cavity, with the 2m repeater and feeds a Comet GP-9 dualband 2m/440 antenna.

Below is the UHF repeater antenna, a Decibel Products DB-420, which is one of the best 440 MHz antennas available.  It is an eight bay, dual element array, producing 9 dBd of omni-directional gain at 444 MHz.  (My favorite is the DB-413, which has eight single elements mounted on one side of the mast which produces an offset pattern with 12 dBd of gain)

These antennas are virtually lightning proof with all elements DC grounded to the mast.  They are on a long, two-part aluminum mast and can be a  quite a handful to install without help and/or a gin pole.  This one is connected to the Micor dual-mode D-Star/analog repeater and was purchased new from Tessco in 1986 for around $500.  Designed for the 450-470 MHz range, this antenna has a 1.4:1 VSWR on 444 MHz.  The antenna is fed with 50 ft. of 1/2" Heliax with the base of the Antenna about 120 ft. above ground level. 

Behind it, barely visible, is a Comet GP-9 dualband antenna used for the 2m repeater and the back-up UHF repeater transmitter.  This GP-9 has been on-the-air for over 20 years and still performs very well.  Don't let anyone tell you these antennas (and the similar Diamond and generic versions) are not good antennas, I have used many of these and for the money, you can't beat them.  Just don't make them a lightning rod by mounting them to the top of a tower or building.  At this site, the DB-420 takes the lightning strikes and protects the lower GP-9.

Below are a pair of DB-408's, the little brother of the DB-420, with 6 dBd omni Gain and slightly more in the offset pattern with the elements in-line.  The DB-408 is a Compact, Lightweight, easy to install antenna.

These particular antennas are on the Homeland security medical service which appear on just about every hospital in Florida.

Below is a custom DB-408 I put together when I ran out of antenna mounts on this building.  I took the phasing harness and elements off the bottom half of an old DB-410 (the predecessor of the DB-420) and with the help of some big hose clamps, mounted them on an existing building conduit. (Note the upside down element feeds)

The antenna is used for the repeater system control link and works perfect despite being mounted close to the roof wall.

Below is the dual-mode D-Star/analog UHF Micor repeater installed in a short Motorola cabinet.  (The tan colored dust covering everything is from the building, not sure where it comes from, but it is everywhere...)

This is a 45-watt unit with two cooling fans.  This radio has also been in almost continuous trouble-free operation for over 25 years.  A Motorola MSF Ferro Power Supply is in the bottom of the cabinet.  The Analog mode is accessed by DPL code 546.  The unit has an a vintage 1993 ARS CW IDer Board. 

For the D-Star mode, it uses the popular ARS DRC Stand-Alone D-Star Repeater Controller which utilizes the CMX589A GMSK modem chip from CML that detects and locks on the D-Star GMSK waveform, a digital delay that delays the header and data stream (while the CMX589A detects the GMSK waveform and keys the transmitter, so no data is lost) and retransmits the data via a GMSK data pump.  It works quite well.  It is linked to the D-Star Gateway via a radio link connected to the 444.500 repeater on Madeira Beach and the 145.260 repeater in Largo, FL.

The duplexer is a compact Telewave 6-cavity notch type (in rear).  The receive side goes into a bandpass cavity, to an ARR-432 preamp (the BEST preamp for repeater service, provided it is protected by a bandpass cavity), then to a UHF Micor 6-pole helical filter (pulled from an old UHF Micor receiver strip and modified with 50 ohm I/O coax) and finally to a 4-way receiver multicoupler (top).  Because the multicoupler has about 12 dB of gain, I put the Micor helical to provide some loss (6 dB) and provide a sharp bandpass response.  The helical, duplexer, bandpass filter and ARR preamp set the overall system noise figure to less than 3 dB.  All coaxes are double-shielded.  This set-up is very sensitive and works well in the high RF environment.  System sensitivity is outstanding with handheld coverage up to twenty miles and mobile coverage up to forty miles.  Not bad for a 120 ft. site.

As of yet no one does D-Star as well as Icom.  DSP boards, Hot-Spot Boards that use Dutch Star firmware and Hot-Spot boards from Satoshi still have technical issues and bugs that hopefully will be solved one day that will allow these solutions to operate in fades as well as ICOM.

Most of the time I am linked to the Georgia Southeast Reflector 30 Charlie.  Pretty good bunch.  Using one of my Radio Interface Adapters, I often link Reflector 30C audio on one of my analog repeaters.

EchoLink seems to work well although the audio quality isn't that good, but it is ok.  Enjoy talking to friends who live far away.  Currently I am experimenting with an AllStar node, audio is much better and plan to upgrade the system soon.

An engineer friend of mine, Ron Wright, N9EE, who owns Micro Computer Concepts, and builts and sells repeaters and controllers, installed an ARS DRS board in an VHF MSR-2000.  The repeater transmits on an antenna at 500 feet on a tower in south Pasco County Florida.  He also operates the popular 146.640 repeater with an antenna located over 1000 foot.  Below is a picture of his repeaters (left and center).

Below is Ron's 146.640 Motorola MSR-2000 repeater and Wacom duplexer installed in a 6-foot Motorola cabinet.  Ron's repeaters have outstanding coverage of the entire Tampa Bay area.


I hope this site has been informative and if you have any questions, please feel free to send me an e-mail.



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