CDM Repeater LLC Dean Martinson — K9QB | Brooklyn, Wisconsin 📞 608-886-5073 ✉ cdmrepeater@gmail.com 🌐 cdmrepeater.com How a CDM Repeater System is Built and Tuned A CDM repeater system is not a pair of mobile radios wired together. By the time a system leaves CDM Repeater LLC, each radio has been extensively modified, converted to wideband operation, and individually aligned to one specific frequency. This page explains what was done and why it matters. Where These Radios Start CDM Repeater LLC builds its systems around the Motorola CDM-series commercial two-way radio platform. From the factory, these are mobile radios designed to cover the entire 222–225 MHz band as a general purpose narrowband mobile unit. Out of the box, a stock CDM radio on 220 MHz is narrowband only. Motorola never produced the CDM-series in a wideband configuration for the 220 MHz amateur band. The stock filters, firmware, and codeplug are all narrowband from the factory. Before any repeater build work can begin, the radio must be converted to wideband operation — a modification Motorola never offered, performed exclusively by CDM Repeater LLC. Wideband Conversion — Hardware, Firmware, and Codeplug CDM Repeater LLC performs a full wideband conversion on every radio in the build. This is not a software setting — it requires physical hardware changes combined with firmware and codeplug modifications. All three must be correct for the radio to operate properly as a wideband repeater exciter or receiver. Front End Filters Stock front end bandpass filters are removed and replaced with wideband alternatives, opening the receiver front end for proper performance on the 220 MHz band. IF Filters Intermediate frequency filters are replaced to match the wideband conversion. Stock IF filters are too narrow for reliable repeater receive performance. Firmware Flash The radio firmware is reflashed to enable wideband operation. Stock Motorola firmware limits the radio to narrowband mobile operation — the firmware modification unlocks it for the wideband repeater application. Codeplug Configuration In addition to the firmware, the codeplug is configured for wideband operation. Both firmware and codeplug must be correct — one without the other will not produce a properly functioning wideband receiver. The Transmitter Radio — Precision Exciter The transmitter radio in a CDM repeater system is no longer a mobile radio. It is a dedicated RF exciter centered on a single frequency and calibrated to drive the external power amplifier at exactly the right level. All of the following are set using professional service monitor equipment and stored in the codeplug. TX Deviation Audio deviation is set precisely for the repeater application. Too high causes splatter and adjacent channel interference. Too low produces weak, thin audio on the output. TX Power Output The exciter is calibrated to a maximum of 700 milliwatts output — the design input level for the external RF amplifier. Exceeding this level over-drives the amplifier and will cause component failure. Oscillator Alignment The reference oscillator is aligned to minimize frequency error at the programmed frequency. This alignment is frequency-specific — moving the radio to a different frequency without realignment degrades frequency accuracy. Audio Levels TX audio drive levels are set for flat, clean modulation at the repeater frequency. These are not mobile radio settings. The Receiver Radio — Maximized for One Frequency A stock CDM mobile radio on receive is a compromise — it has to work reasonably well across the entire 222–225 MHz band. A CDM Repeater LLC receiver has been converted and aligned to perform at its best on one frequency. The difference in receive sensitivity and audio quality is significant. Receive Sensitivity The receiver is aligned and peaked for maximum sensitivity at the programmed receive frequency. This level of performance is not achievable across a wide band — it requires centering on one frequency. Frequency Error The reference oscillator is corrected for minimum frequency error at the receive frequency. Off-frequency signals are rejected more effectively. Audio Levels Receive audio output is set for clean, consistent levels into the controller and node interface. Squelch Alignment Squelch threshold is set for the repeater application, not mobile use. The RF Power Amplifier The external RF amplifier is designed around a specific input drive level of 700 milliwatts from the exciter. The amplifier is not tolerant of over-drive. If the exciter output exceeds the design input level — which can happen if the codeplug is reprogrammed and calibration is lost — the amplifier will be damaged. This is not a warranty failure. It is the result of operating outside design specifications. Any change to the radio codeplug without a full realignment can result in TX power output exceeding the amplifier input specification, causing amplifier failure. Frequency Changes Because every radio in a CDM repeater system is individually calibrated to its programmed frequency, a frequency change is not a simple codeplug edit. It requires a full realignment of both radios on the new frequency using a service monitor — deviation, power output, oscillator alignment, receive sensitivity, and audio levels all need to be reset. CDM Repeater LLC will perform all frequency changes. Contact us with your new frequency pair and we will return calibrated radios ready to install. Do not attempt to reprogram the radios yourself. Codeplug Password Protection — Effective July 1, 2026 Effective July 1, 2026, all CDM Repeater LLC systems ship with the radio codeplugs password protected. This policy was implemented to protect customers from accidental calibration loss and the equipment damage that can result from it. In the past, well-intentioned attempts by customers or their technical staff to make simple changes — such as a frequency or callsign update — resulted in the codeplug being written back without the calibration data intact. Because the CDM platform stores all alignment parameters inside the codeplug, any write operation that does not include the original calibration data resets the radio to factory defaults. The result is low deviation, incorrect power output, degraded receive sensitivity, and in documented cases, amplifier failure due to excess drive power. Password protection prevents programming software from writing to the radio without authorization. It is not intended to restrict your use of the repeater in any way — it is a safeguard that protects your investment and ensures the system continues to perform as it left our bench. For any required changes — including frequency updates, tone changes, or callsign updates — contact CDM Repeater LLC. We will make the changes, recalibrate, and return the radios ready to install. This service is available to all customers regardless of warranty status. Programming Rules ✗ Do not connect RSS, CPS, or any Motorola programming software to the radios in this system. ✗ Do not clone or copy a codeplug from another radio into this system. ✗ Do not attempt to change frequencies, power levels, tones, or any radio parameters yourself. ✗ Do not allow a third party to reprogram these radios without first contacting CDM Repeater LLC. ✓ Contact CDM Repeater LLC for ALL programming changes including frequency and tone updates. ✓ Allow CDM Repeater LLC to recalibrate after any frequency change — this requires a service monitor. CDM Repeater LLC — Dean Martinson, K9QB Brooklyn, Wisconsin 608-886-5073 cdmrepeater@gmail.com cdmrepeater.com