This page is all about modifying radio equipment for a better way to pass signals for long-distance links and other uses,
starting with the COR/Audio board. If any of the drawings are not clear a better copy is available for a modest cost of handling.
COR/Audio board Ver. 5.3 with a browser
COR/Audio board Ver. 5.3 in pdf
COR/Audio board Ver. 6.5 in pdf
COR/Audio board Ver. 6.5 Notes on parts placement
COR/Audio board Ver. 6.5 Schematic
Component side Ver. 6.5 Layout
Solder side Ver. 6.5 Layout
Motorola Mitrek area - Lot's of information
Most of these documents are in PDF for easy viewing with any O/S. Also, some of them are large in size:
Mitrek conversion to Repeater or link in PDF
Frequency options in PDF
Details on the antenna ports in PDF
Spec sheet on RG-405 coax Beldon part number of 1671A
Preselector repair in PDF
Operation manual in PDF
Motorola Micor area - Lot's of information (including Spectra-Tac)
Micor transmitter for repeater service in PDF
Transmitter supplement for the above in PDF
SRG Interface diagram for above(mobile)unit
Compa station Transmitter supplement for the above in PDF
Micor receiver conversation in PDF
Spectra-TAC Interface SRG version block and level
Spectra-Tac supplement (goes with above document)in PDF
Spectra-Tac PL Module (goes with above document) in PDF
Micor squelch theory discussion in PDF
COR board version 5.4 for Micor Spectra-Tac downlink in PDF
Repeater equipment
Evaluation for the LDG electronics voter.
IDer boards Documentation by Karl Shoemaker
Repeater operation General information
Other equipment
MX-350 Portable radio for UHF links
MX-350 channel element OEM information - just the one page
Maxar radio Just a few notes
GE for repeater operation in PDF
Audio Standards Flat, conventional and compressed audio-level standards
Microphone discussion by Tomi Engdahl
Direct F.M. a Midland 13-509, or most any transmitter
Midland 13-509 Full story on F.M. and repeater conversions for 1 1/4 meters
Wilson 1 1/4 meter radio For the model T2202SM HT.
Johnson PPL6060 Stability notes
Kenwood mobile radio evaluation and notes for the TM-V71A radio
FCU Fan Cooling Unit used to cool transmitters used in some SRG projects
I.C.M. Past services (closed now)
T600 FRS radio
RVS-8 A voter that was used a few years ago for SRG
JPS A voter that is used for SRG
IFR 7550A battery replacement
When performing FM conversions to PM equipment this modulation index chart may be helpful which can be viewed
here here
Occasionally, the Author needs to measure receiver sensitivity (20 db quieting method) in a location other than in front of the equipment.
Hauling an expensive AC volt meter up the tower is not the first choice.
Recently, he found a low-cost self contained sound level meter (SLM) from the vintage days of Radio Shack. It has a built-in battery.
It has 10-db step sensitivity which is perfect for this type of measurements.
With a simple (temp-prototype) modification a higher impedance input was added across the "cal" pot. This did not affect the other functions of this meter.
For now a set of pins where installed which connects directly to the Micor TAC receiver service module as shown here.
These wires hanging out of a meter is a bad way to operate.
In 2024, after some deliberation the Author decided on RCA jacks and plus for testing. A simple adapter can be had to convert that to the pins for the Spectr-TAC service modual pins.
Calibration for this unit was confirmed with a HP 3555 meter. Both meters where clipped in parallel for this task.
A note about the documents; recently they are starting to be converted to PDF for a couple reasons; this solves the issue with html pages (with images) being displayed on various browsers (with other variables) and
generally is smaller in file size. This is especially true for a MS-Word document (with images) compared to the size of the same document in PDF. PDFs are easy to download to your PC for later viewing.
Note: Many of these projects are in the R-n-D stage, therefore, are subject to change and improvement without notice.
They are intended to get the experienced builder in the right direction and not necessarily for the beginner.
Tip: Some are PDF's therefore, to save time you can right click on the link and "save as" to your PC for local (and faster) viewing.
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