Thanks to a generous donation from W5JTT, the Wilson County Amateur Radio Club now has a UHF repeater! It is a high quality EF Johnson commercial machine and needs a little TLC before it goes on the air.
Currently, the machine is set up for TX on 461.800 MHz and RX on 466.800 MHz. I need to find a lot of missing information on the components. So far, I've been unable to locate any model, serial number or documentation for several of the major components. Here is what I have so far:
|
Subsystem |
Manufacturer |
Model |
Serial |
Documentation |
| Controller | EF Johnson | (unknown) | (unknown) | Needed |
| Receiver | EF Johnson | (unknown) | (unknown) | Needed |
| Exciter | EF Johnson | (unknown) | (unknown) | Needed |
| Amplifier | EF Johnson | (unknown) | 1943 | Needed |
| Preamplifier | Lunar Industries | PAG 467 | 825911 | Not found, but OK |
| Duplexer | Decibel Products | 532-4001-004 | 126241 | Similar found |
| Power Supply | (unknown) | (unknown) | (unknown) | Not critical |
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Controller
The controller will probably need to be replaced with something that has more capabilities. As far as I can tell, the only capabilities the current one has are repeat on/off, timeout timer and CTCSS tones. It consists entirely of a few analog circuits with no logic that I can identify.
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Receiver
The receiver is crystal controlled with sockets for two crystals. One is populated at this time and that is for the 466.800 receive frequency. A new crystal will be needed and we'll need to find documentation for the realignment procedure. The receiver has a cast chassis with no top or bottom covers. Instead, it is installed in a metal box with an RF trap and feedthrough capacitors for the incoming cable.
We're fortunate that the receiver is designed to use a crystal on the fundamental frequency and not some fraction that would require attending resonant circuitry like a Motorola Mitrek unit. This simplifies the task of recrystalling the unit.
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Exciter
Like the receiver, the exciter is built into the same type of cast chassis, but it has top and bottom covers, so there is no outer shielding box. The chassis are built to house both the receiver and exciter/transmitter, but the fact that Johnson kept them physically separate speaks to their intent to guarantee the maximum isolation between them. Very nice design decision.
The exciter too is a crystal controlled unit, so we'll need to order an appropriate crystal and find documentation for the realignment procedure.
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Amplifier
The final amplifier is a beefy monster with a truly massive heat sink. I haven't opened it up yet, but it looks like it just needs some minor cleanup of external corrosion on the cover plates. The model number and specs are not yet known though. The serial number tag indicates that it was rebuilt at some time.
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Preamplifier
Although I can't find any data on the preamp, it is a very nice little unit and is simple to characterize through measurement. See my Preamplifier Measurements article for details.
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Duplexer
More exciting to me than the exciter (heh heh), the duplexer is a top quality unit. There is a fair amount of corrosion on the connectors, the connector screws and the tuning rods, so some very delicate TLC will be needed before the assembly can be safely retuned. In its current configuration though, it is a fantastic performer.
If you're interested in these things, don't miss my Duplexer Measurements article.
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Power Supply
I know nothing about the power supply at this time. There is significant corrosion on the transformers, capacitors and chassis. Before powering it up, I'll need to test the capacitors for ESR and get my hands on a varactor to bring up the input voltage slowly while watching for problems. At this time, it seems like all the capacitors will need to be replaced. Even if they currently work, they're very old and have been subject to a lot of corrosion, so their future longevity is very questionable.
You can see the power supply in the photo above of the amplifier.
