The Motorola MSR2000 and Micor Commercial Two-Way Radio Repeaters contain a Squelch Gate Module, which handles the Repeater Logic and Audio Functions. Most repeaters use additional cards to complete the remaining receiver - transmitter logic and audio requirements. The complete "chassis - shelf - cage" then operates as a very rugged repeater system package in Commercial or Amateur Radio (Ham) Service using adjacent mounted transmitter and receiver "strips."

The addition of an external Repeater Controller to a Commercial Repeater Station allows the users and operators many advantages. Features might include Telephone Interconnect (Auto-Patch), Macro Control functions, External Linking Ports, Voice Response and Data Telemetry Functions. There are many brands of Amateur Repeater Controllers made; all have their merits, features and special "bells & whistles".

Two or more very practical methods to connect the MSR-2000 to an External Repeater Controller are available on the net, this conversion requires simple connections to the Squelch Gate Module (card) and the other methods require more invasive (cutting of pc board traces) and or connections to the back plane of the repeater card cage. The package presented here is the complete "Squelch Gate Module Connection Method", which has the advantage of being both brand generic and simple. This modification also works on the Micor Repeater using the exact same Squelch Gate Module connections.

I'll try to quickly provide an overview of the differences between the two basic methods mentioned above. Web sites, which detail the back-plane method can be found many places on the Internet. Many such articles are a reprint of the same original back-plane mods done years ago. The Squelch Gate Module to External Repeater Controller method presented here was originally authored by me. It is now offered to and for the public domain, free and copies of text may not be sold for profit. I simply ask that you retain the source credit on any text you distribute so I can be contacted with/for error corrections, feedback and questions. Onward...

The Squelch Gate Card Method is best described as the simple addition jack plug or direct cable interface to the front plate of the original Squelch Gate Module/Card. The required External Controller audio and logic lines route through the plug/jack pins using simple and clean (often pre-made and low cost) quality shielded computer cables. The added interface cable can be hard-wired (permanent) to the Squelch Gate Module, or connected through a mounted jack & plug assembly such as the common DB-9 (computer style) may be used. All my recent conversions have the interface cable routed through a common Heyco Brand strain relief type grommet (without the DB-9 (actually D-9) jack plug assembly). A picture of a completed hard-wired Module is shown below.

The Same modification is done to both the Motorola MSR 2000 and Micor Repeater Squelch Gate Modules, regardless of model. Indeed, the two cards are exact same electronic circuits... only the plastic edge connector and cage pins differ between repeater types. The mod detailed here also mentions that I have used Micor Squelch Gate Cards in my MSR 2000 Repeaters by removing the cage connection pins from an original Micor Squelch Gate Card and inserting the plastic MSR 2000 edge connector (removed from an unused parts card like the guard tone dectector) onto the Micor card... the card is then an exact copy of the MSR 2000 card and works as such. Quite the money saver if you've ever had to purchase surplus MSR Squelch Gate Cards from surplus Two-Way Radio Equipment Vendors.

All the original repeater/base cards remain in operation if desired or required for the standard original operation. Advantages include use of the many factory options like digital modes controls and spectra-tac voting. The mod is easily reversed or completely removed by the insertion of an unmodified spare Squelch Gate Module (Card). It doesn't get much simpler than that. Best of all, it works very well... I've had units in operation with this mod since the mid - late 1980's.

So take a look at the squelch gate card (module) close-up below. A few simple connections and You're ready to add your own external controller.

The Back-Plane method of adding an external controller involves location and cutting of many pc board traces on the back of the card cage. Most or all of the factory cards are removed and discarded. Any hardware features of the original cards are lost... a physical wiring harness is attached to various points on the back plane and routed to the external controller. In the case of the Micor, the receiver audio squelch board sources the audio and the cos logic. The MSR 2000 repeater requires the R1 Audio Card to source the same functions. The locations for audio and logic are not compatible between the MSR and the Micor for the back plane mod. Things can get messy if one doesn't pay attention. The repeater is not easily restored to factory "stock" operation should the controller fail or require service/updates.

A case is made by some that the back-plane method operates better on the Micor because of the direct connection to the Micor Audio Squelch Board. Reasons given are related to the design and operation of the Audio Squelch Board circuit and it's custom Fast-Slow squelch IC Chip, which works very well. The MSR does not offer the same type R-1 audio squelch board circuit so similar arguments are mute. The mentioned Micor audio-squelch gate chip provides outstanding cos switching speeds (logic) based functions and audio gating. Straightforward connections to the proper locations on the audio squelch gate board provide sources of rapid Carrier Operated Squelch ("COS") audio gating which removes the receiver squelch "crash" often heard in poorly designed repeater systems.

Using different physical hardware and electronic circuits, both described methods end up with very similar results. The Squelch Gate Card has a circuit, which provides the same type audio gate functions and some additional flexibility when properly understood. The "back-plane-boys" dance and sing praise only to the squelch chip on the Micor AS board never wanting to hear that there might be another approach that works just as well. Few if any have even considered/offered up an MSR 2000 Repeater External Controller connection method. The Squelch Gate Card alignment does require you actually read and understand the straightforward alignment steps. Repeater owners and service personal should understand how the hardware operates, not always the case I'm sorry to report. The alignment steps are made up from original circuit operation ext/pictures, which are quite clear and well described. The end result, listener wise for both methods are very short or missing receiver squelch crash noise at the end of every user transmission. Zero or very short receiver squelch crash noise is very much desired.

The overall simplicity and described features of the Squelch Gate Card, controller connection method makes it a very smart and practical first choice. If you have questions or need help, feel free to send me an Email. An easy Email message icon is located at the bottom of this description page. Remember to hit the back button on your web browser to return to the main www.radiowrench.com/sonic page.

Cheers 73's
skipp

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