K6BJ UHF MSF5000 Repeater Construction Log

K6BJ 440.925Mhz+ 123.0Hz PL

by Jeff Liebermann AE6KS

This is in WebLog format where the most recent postings are at the top of the page. If you wish to follow the construction in chronological order, please read starting at the bottom of the page.

Mar 13, 2011

One year later, I finally get around to working on the repeater again. The first step was to build a dolly so that I can move the monster around the shop. The MSF500 is really heavy. After re-installing the green Tee and a bit of tuning, everything is back to working again. Efficiency at 10% sucks, but I think we can live with it. Standy power for the CXB is 57w.

Pout   AC Pwr
 30w   330w
 50w   510w
100w   700w

Next step is to check rx sensitivity, make the usual measurement, check for desensitization, attach an antenna, do a field test for a week, and the move the repeater to the K6BJ repeater building. However, if I have time, I might consider a new controller, link port interface to the clubs CAT-1000,

Mar 27, 2010

Installed Secure board and was able to program the SSCB. After some RTFM and numerous screwups, I was able to get the CXB SSCB to play on by simply installing JU13 in the non-default position. Seems to be working now, but busy with other projects.

Mar 14, 2010

I got lucky and won a Secure board on eBay. That should solve the chicken and egg CXB SSCB problem detailed below. Waiting for UPS to deliver.

Mar 13, 2010

There are two MSF5000 UHF repeaters. For no obvious reason, I decided to build up the backup repeater. I also noticed that burning a new EPROM for the original CLB repeater is going to cost $50 each. My guess is about 3-4 burns to get it right. It makes more sense to get a computer programmable CXB SSCB and forget about CLB EPROM's. Well, that was the plan. What can go wrong?

Error dc7

backup repeater

The new CXB SSCB board and expansion tray seem to function, but there's a problem. Both the bootup diagnostics and RSS software complain that they can't read the Secure digital board. That's for good reason as the board was apparently removed by the eBay vendor. The problem is that the brain damaged Motorola RSS software won't proceed beyond complaining that it can't find the Secure baord. The system also boots with an error dc7, resets, and tries again, endlessly. It's a chicken and egg problem. In order to disable the radio from looking for the Secure board, I have to have the Secure board present. I'm stuck. This article explains the problem in more detail.

The programming computah is a Panasonic Toughbook CF-25 MK1 with a Pentium 120Mhz CPU and 80MBytes of RAM (maximum). Not the greatest but it does run the MSF5000 RSS software without needing Mo'Slo.

Mar 07, 2010

Slight diversion into working on the backup MSF5000 repeater. I'm off to a rocky start when I plug in the power supply and blow a fuse. Using a Kill-a-watt meter, I determine that it's drawing far too much power. A clue is that the previous owner had started to remove the power transformer, but stopped. After a few bad guesses, and about 6 blown fuses, I isolate the problem to a shorted IN3493R or R3520PF power diode. In the process of beating on the heat sink with a drift punch and hammer to remove the bad diode, I also manage to destroy the good diode. I eventually find some MR890R diodes in my junk pile, which are under-rated, but will work as long as I don't attach the big power amplifier. Sorry, no photos as this is a temporary kludge and will eventually be replaced by proper diodes.

Mar 01, 2010

Measured and tested internal duplexer. According to various articles on Repeater-Builder.com, sometimes the duplexer works, sometimes it doesn't. I'm close. Installing the Green TEE cable, I get about 3dB of sensitization. Not good, but without any notch filtering, it seems reasonable. Doing some VERY rough measurements and guesswork (at midnight):

+50dBm (100 watts) -80 dB tx noise -65dB filter isolation = -95dBm noise at the receiver input

-102dBm rx sensitivity - -95dBm = -7dB too much noise at the rx input

Not good, but close enough that a notch filter or two should make it work without clobbering the sensitivity. I posted a question to the Yahoo MSF5000 Forum asking for advice and experience.

Feb 28, 2010

Tested various power amplifiers. One works fine, one marginal, one dead, and one on the wrong band. 150 watts out without the filters installed.

PA Check

Putting everything back into the rack, I now get about 90 watts maximum (mostly due to about -4dB cavity losses).

MSF5000 with PA

The problem is where to put the duplexer, repeater controller, and fans. The duplexer can be bolted to the top of the box, but the RC-85 controller is rack mounted with all the connectors towards the back. There's no back door on this cabinet, so it may need to be repackaged and planted on top of the SCM (station control module).

Feb 27, 2010

EPROM burning. I found a suitable repeater eprom image in the MSF5000 Yahoo group files. F1 is at 442.125+ 100.0Hz PL. I also purchased a cheap Willem 5.0 EPROM burner. I was able to burn AMD 2732 EPROM's, but had problems with older Intel EPROM's. Note that 2732 requires VPP=27v while 2732A is VPP=21v.

Willem 5.0

Starting with the receiver, I followed the quick tuning instructions. Everything tuned as expected. Having the TRN5525A injection probe and proper tuning tool kit is a big plus. Other than the VCO tuning, the transmitter required no adjustments. However, without the power amplifier installed, the transmitter shows a short burst of RF, followed by alarm beeps from the speaker. I had to inject 9.2VDC into Pin 4 of the Molex connector to fool the SCM into thinking the PA was working. The driver then delivered about 15 watts. I should just pay the money and order a properly programmed code plug, but am tempted to hack the existing EPROM to the correct frequency and PL.

Feb 15, 2010

Stalled on RF testing waiting for a working code plug EPROM. Meanwhile, I'm ordering manuals, scrounging spare parts, and cleaning up a spare UHF MSF5000 repeater. My EPROM burner appears dead. Argh.

Feb 12, 2010

Replaced more sick electrolytic capacitors. Electrolytics replaced are circled. Device on the right is a Dick Smith ESR (Equivalent Series Resistance) meter. All the capacitors removed were well out of acceptable range for internal resistance. The toggle switch on the left was also replaced (with the wrong length toggle arm). Oops. The 2732A code plug is currently missing so I can't test the full radio. This will need to be programmed initially with the current operating frequency of the repeater (about 460Mhz) and later with the K6BJ UHF frequency and PL.

Station Control Module

Station Control Module.

Feb 7, 2010

Replaced the blown and leaky electrolytic capacitors on the SCM (Station Control Module). According to Repeater-Builder, this is a common problem. I'm awaiting a replacement switch and more capacitors from Digikey.

Feb 6, 2010

I bought a TLN2418A test set on eBay for about $40 plus shipping. Unfortunately, it arrived with a broken switch and filled with fine sand and plaster. The meter was also slightly mangled. Clean and repaired. I also have a TLN2419A, which includes a diagnostics display, but also required some minor repairs. The nice part is that it includes a printed manual, all the cables, and some weird looking tuning tools.

TLN2419A Manual (10MByte PDF)

TLN2418ATLN2419ATLN2419A Inside

TLN2418A and TLN2419A test sets

Jan 30, 2010

JV and I tear apart the UHF repeaters and drag the pieces up about 30 stairs to my shop. Brute force and sweat worked where sanity and a fork lift were lacking. Spent some time cleaning up the box, cleaning and testing the power supplies, and inspecting for damage and missing parts. That's when I found that one of the big transformers was not bolted to the chassis. Replace missing hardware

Jan 16, 2010

JV and I drive to Fiddletown CA and pickup 4 boxes and some spare parts. Two are MSF5000 UHF repeaters. Two are MSR2000 VHF repeaters. None of the boxes are complete and will need considerable work to turn into repeaters.


UHF power amplifierVHF Power Amp

These boxes are HEAVY. My guess is about 150 lbs each, with the 120w RF power amplifier and monster power supply installed.

9 hrs drive and about $40 in gas. The 2ea MSF5000 repeaters, and 2ea MSR2000 repeaters, plus test set, spare boards, and spare UHF amps cost about $800. Ouch but cheap considering that it would cost $100/ea to ship.

Jan 9, 2010

Tried to fix old Micor mobile repeater. Too many problems. Time for a replacement.

Old Micor Repeater

by Jeff Liebermann AE6KS http://802.11junk.com