An External Controller interface instruction for the Uniden ARU-251 & ARH-231 UHF Repeaters. 
This Revision Feb 2005 (previous revision 06/99)	www.radiowrench.com/sonic 
By: Skipp May P.O. Box 192 Elmira, CA. 95625	Email: nospam4me@juno.com 

You may use this information, free without special permission, provided you do not remove or delete 
any portion of the contents, labels or credits. Thank you. Please read this document through before 
starting your external controller odification/conversion.

Features: 
The addition of an external Repeater Controller to a Commercial or Amateur 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". This modification procedure has the advantage of being generic to most brands 
of external repeater controllers. 

Starting Point, Ground Zero: 
You should have a Uniden ARU-215/ARH-351 Repeater Station in working order, configured for normal 
duplex operation. 

You should have the Service Manuals for your Repeater: 
In February 2005, I plan to make the Uniden Repeater Service Manual available on the www.radiowrench.com/sonic 
web page for free. This is a must have for any repairs and conversion projects.  

Modification Concepts, Description and Scope: 
Repeater Audio, Sub-Tone (CTCSS) Detection and Carrier Operated Squelch "COS" (also known as Carrier 
Operated Relay "COR") functions and logic are routed through the original internal Uniden Repeater 
Board. This is a straightforward modification to insert an external controller into the required 
function and logic paths through an interface cable connected to selected points on the repeater 
board. The added interface cable can be hard-wired (permanent) to the Repeater Board/Module, or 
connected through a mounted jack & plug assembly such as the common DB-9 (computer style) may be used. 

Do not disable the original repeater board time-out-timer! Never rely on the external repeater 
controller to provide a failsafe Transmitter time-out function.  Don't trust an external repeater 
controller to be crash-free (never freeze). 

Getting ready: 
This modification interfaces with the only Repeater Board/Module. You should not remove or modify 
any jumper settings unless you clearly understand their function. Write down (record) the original 
jumper configuration and any changes you make, if possible keep the record with the equipment in a 
logbook. This modification procedure assumes you have a problem free working Uniden Repeater. 

Repeater Controller Basics: The typical external interface connections include the following terms. 

Transmit "PTT" Logic: DC (voltage level) logic sourced from the external controller to the Repeater. 
Receive "COS/COR" Logic: DC (level) logic sourced from the Repeater to the external controller. 
Sub Tone (CTCSS) Logic: DC (level) logic sourced from the Repeater to the external controller.
Transmit Audio: AC voltage (normal transmitter audio) from the external controller to the Repeater.
Receiver Audio: AC voltage (normal receiver audio) from the Repeater to the external controller.

Audio connections are relatively low-level AC voltages. When properly connected as described in this 
text, the receiver audio to the external controller is gated (muted) off with no received signal. 
Muted or gated (silent when off) audio keeps some external controller DTMF (touch tone) controller 
circuits from 
false detecting (falsing-off) or locking onto a specific receiver port during moments of rushing 
no-signal discriminator white noise. 

Logic connections are often DC voltage changes above and below some relative voltage value set in 
the external controller. A high to low ("sink" or "active low") or low to high ("source" or "active 
high") transition supplies receive signal indication and transmitter keying. Refer to your specific 
controller manual for the required voltage threshold value. The typical logic transition voltage is 
often fixed in the controller hardware somewhere from 2.5 to 9 volts dc. Most external controllers 
operate on about +13 volts dc negative ground. 

Getting down to work: 

(Step 1) Receiver audio:  
The audio insertion point is simple. The audio path from the internal control board to the transmitter 
- exciter is broken (opened). The combination audio* from the repeater (internal control) board is 
sent to the external repeater controller, receiver audio input. The wire, which leaves the Uniden Repeater 
internal control board at pin 4 (four) is de-soldered or cut.  The control board side of the cut wire 
is the receiver audio routed to the external controller.  The audio level sent to the external controller 
is set by adjustment VR604 on the control board. Set this control at least 3/4 on/max value to ensure 
enough audio drive to the external controller. My preference is about 80% of max value. The remaining 
unused wire end will be routed to the transmitter audio output from the external controller, described 
in the third step. Note its location and move to step two now. 

*The receiver audio will be gated, have the sub tone removed and de-emphasized by the original Uniden 
Control Board Circuit. All the original Uniden Control Board functions will still operate properly. 
The external controller receives the desired "flat audio" only during a received signal. Gated audio 
keeps the external controller's DTMF Decoder from false decoding from no signal squelch noise.

(Step 2) Receive Signal Indication (COR/COS Logic):  
Modifications for the receiver and transmitter logic functions are preformed in a manner similar to the 
receiver audio connection described above. The wire leading from the Uniden Control Board pin 6 (six) 
to the transmitter (via an internal stop-over at the repeat/local switch) contains the proper functions. 

Cut or de-solder the wire leaving the Control Board and route the control board pin 6 (six) side (end) 
wire (lead) to the Receive COR/COS input of the external controller.  The resting and active receiver 
cos/cor states are used by the Uniden Control Board circuit as active low (most desired).  Well-designed 
repeater controllers often have internal dipswitches, which can be configured to invert the COR/COS 
logic requirements. The original Uniden logic function is active low (or current sink) at pin 6 (six).  
The dipswitch internal to the 7K or equivalent is set for COR/COS active low. The external controller 
front 
panel COS/COR LED will indicate the status when the line from pin (6) six goes active. Should your 
controller not contain the internal logic dipswitch inversion feature (active high or "opposite" logic), 
a simple logic inverter made from a 2N3904, 2N3906, 2N2222a or similar transistor with a 10k current 
limiting base resistor and 220pf disc bypass capacitors can be made up easily. If you need a logic 
line "pull up" for the COS/COR function, a simple 15K (15,000) ohm resistor tied from the logic line 
to the positive dc supply voltage works very well. 

The remaining wire end will be used for the Transmit PTT function in step four.

(Step 3) Transmit Audio:  
The remaining audio wire cut during Step 1 is connected to the external controller Transmit Audio Output. 
Use one extra wire for each dc voltage (logic), transmitter and receiver paths. That is, one ground 
for each voltage and audio path if possible. Most any convenient repeater internal ground point may 
be used but the connections should be made at, on or near the control board. If your using shielded* 
wire, ground the wire lead-foil-braid properly for both audio leads.

The transmitter audio level into the repeater transmitter is set in the external controller using the 
Controller instructions. The repeater local hand mic level is preset and limited by the transmitter. 
Try to avoid adjusting the transmit deviation limiter on the exciter/transmitter unless you have the 
skills and proper test equipment.

(Step 4) Transmit PTT Logic:  
The remaining wire lead from Step (2) two is routed to the transmit PTT output of the external controller. 
The external controller internal logic dip (if available) is set for active low. Grounding this wire or 
"active low" places the transmitter on the air. Transmit timer functions and options will be set by 
program software in the external controller and the original Uniden repeater board circuit.

The original Uniden Repeater drop-out or tail timer board should be set to minimum delay using VR601 
on the control board. The original Uniden Repeater transmit time-out-timer can be disabled by cutting 
jumper J6 on the control board. Cutting the jumper J5 near or next to VR603 on the control board disables 
the time out audio beep oscillator. My first choice is to leave the time out timer enabled and set to 
max time. 

(Step 5) Sub Audible Tone Receive (PL) logic:  
Another cable wire is routed to the external controller tone indicate function. A wire is soldered to 
the collector lead of control board transistor Q601 through a common low power signal diode.  I recommend 
a 1N914 (equivalent to 1N4148) first, but a standard 1N400x series power diode should be fine, just a 
little overkill.  The diode banded end is the cathode, which is soldered to transistor Q601's collector**. 

**Viewing the circuit diagram, note the transistor collector lead is soldered to resistor R621. When Q601 
is on/active the collector lead is grounded, providing a path for LED D610 to light using R621 for LED 
current limiting. You can and should solder to resistor R621 lead on the side, which is connected to Q601. 
Resistor leads are often more rigid and practical soldering points vs. the thinner transistor lead. Solder 
the diode banded-end (cathode) to the collector side of the resistor, transistor collector lead direct or 
the control board pc trace at this location. It just depends on your soldering skills and patience at this 
point. 

The actual sub tone-indicate function cable wire from the external controller is soldered to the diode 
anode-lead (other end in air) just installed on the Q601 collector. If you have the luxury of shrink or 
insulation tube, a small portion over the diode and external controller wire end would be great. The diode 
allows you to isolate and share the active low sub tone logic indication using the Q601 transistor, which 
turns on (sinks) indicator LED D610.  Again: If you need a logic-line voltage "pull up" for the desired 
function, a simple 15K (15,000) ohm resistor tied from the selected logic-line to the positive dc supply 
voltage works very well. 

At this point, install the cable ground wires for each logic function. One end is soldered to ground at 
the control logic board.  Any remaining ends are routed to the external controller logic grounds. Logic 
ground and DC power ground are often the same in most controllers, which is also the case for the Uniden 
Control Board. Use one cable wire from the external controller dc power ground to the Uniden control 
board or same power supply dc ground point.

Sidebars:  If you want to power the external controller using the repeater internal dc supply, you should 
probably not use a traditional pre-made DB-9 serial computer cable. The wire size is often very small and 
may produce erratic controller operation. *I prefer to make my own DB-9 cables using larger multi conductor 
cable, which includes at least one braided ground strand.  Belden makes multi conductor wire of this type. 
As long as you don't exceed about 3 to 6 feet, a quality shielded DB-9 Serial cable works pretty well if 
you power the external controller through a separate cable. Avoid low cost unshielded pre-made computer 
cables if the unit is installed in a high RF location (IE radio/television transmitter sites).

If you make up your own cable, regulated dc for the controller can be used from the supply, which supplies 
the red/white wires leading to the various internal boards from pin seven of the dc power transfer relay. 
Smart people would purchase and install, a common in-line fuse holder with a 1 (one) to 3 (three) amp 3AG 
fuse installed. The fuse assembly would be in the + power lead, secured inside the cabinet and function 
only as a control cable cut (break) line precaution. Don't forget to include the separate fuse holder for 
proper fuse requirements of the external controller, outside the repeater cabinet. The lower value external 
controller power fuse should blow first when a problem occurs.

External Controller Presets:  
Set the external controller transmitter and receiver audio level controls to a mid point. All the external 
controller logic dipswitches should be active low as required for regular operation. 

The Uniden Repeater front panel controls:  The monitor switch position doesn't matter for standard repeater 
operation, only the local speaker. Place the Repeat-Local switch to Repeat. All the panel function switches 
still operate as described in the Uniden Manual.  For normal operation of the sub tone decoder using the 
S-Com 7k (or your controller of choice) internal software, leave the repeater front panel tone/carrier 
squelch switch "S1" in the carrier position. The S1 switch in the "tone position" overrides the external 
controller (7k) tone control software to force a hardware sub tone (ctcss) only operation. If you ever want 
to use carrier squelch, leave S1 in the carrier squelch position and use the power of the external controller 
software.

General guidelines:  
A communications service monitor should be used to set/check the final repeater levels. A strong >10uV receiver 
rf-signal with ~3KHz deviation, 1KHz audio tone is sent to the receiver antenna port. The audio output of the 
receiver (a sine wave) should be seen with a scope display leaving the control board at pin 4 (four) and level 
set at the proper test point inside the external controller. The external controller receive level pot adjustment 
is critical and described in the Repeater Controller Installation Manual. Bad levels will often cause your 
controller too false the audio into mute when the DTMF decoder reacts to excessive audio. The external controller 
front panel LED's (if equipped) should display a received signal and sub tone indication (if sub tone is present 
on the generated test signal).  Once the COS/COR and PL logic is verified, turn off the sub tone from the 
service monitor/signal generator. 

If the external controller receiver audio level input control (pot) does not allow (enough) a proper level at 
the external controller audio test point as described above, adjust VR604 down, toward mid position. External 
controllers often have input op-amp stages, which can then be modified for additional gain (if required). Once 
set, mark the position of the pot with a black, fine point felt pen and leave the receiver audio level adjustment 
alone. Avoid VR604 adjustments after step 1 if possible. Try to obtain enough audio direct from the repeater board, 
modify the repeater controller input gain (stage) if you need more audio at the controller audio input test point. 

Program the external controller for repeater carrier squelch operation after removing the sub tone from the 
generated test signal.   "A desired level setting," is the external controllers transmit level pot set for 
nearly uniform input vs. output.  3KHz deviation of the 1KHz audio tone on the received antenna test signal 
should deviate the transmitter at least 3KHz. Disable the (optional) transmit sub a tone generator by pulling 
IC-605 from its socket on the control board first. Replace it after the regular TX audio test tone audio is 
properly set; make sure the power is off each time. Observe static precautions. Remember, the sub-tone should 
be about 500 to 600Hz deviation, then sum with the regular transmit voice audio deviation when present. Deviation 
values are "plus and minus the indicated number). 

The Real World:  The input and output deviation ratios of any repeater are never linear. Set the external 
controller transmit level pot to give a relative one for one ratio at or around 3.0 to 3.5Khz deviation with 
a 1KHz audio tone. As you adjust the service monitor generated receive test signal deviation, the transmitter 
should try to follow close for deviation values in the 3 to 4KHz range. Otherwise, set it to a compromise 
where you might have a 3.0 to 3.5KHz receiver signal deviate the transmitter 3.8Khz for a slight amount of 
audio compression. When properly set, the transmitter limiter and or receiver IF bandwidth should take care 
of the slightly higher input audio ratio. Also consider the 100 or 200Hz of base-band noise on the transmit 
signal. 

Above 4KHz deviation, many factors play havoc with deviation adjustments, the receiver Bandwidth, IF and Crystal 
Filter response, the external controller audio chain (older ACC 850 Controllers contained an onboard audio 
compressor/compandor), the transmitter audio shaping (pre-emphasize) and transmitter limiter circuits.  Take 
the time to properly record and adjust these values, it's often a choice of your skills, available time, 
equipment resources and preferences. Amateur FM Repeaters should set a realistic maximum transmit deviation 
of 4.8 to 5.5KHz with sub tone. The sub tone should be set around 500 to 600Hz transmit deviation with no 
other audio present. Since most all sub tone decoders will capture/lock well below 150Hz deviation, I prefer 
to set repeater sub tone deviation at 450 to 500Hz deviation.  Repeater Users with low cost radio often have 
little or no sub tone filtering. Hot sub tone deviation levels are unnecessary and heard as annoying hum in 
listeners' ears, causing fatigue. The total deviation is the sum of the sub tone and test tone audio. Restore 
the sub tone after you've set and verified the test tone input output ratios at about 3Khz. The no sub tone 
deviation should track "OK" at lower (less than 3Khz) values, match at 3Khz and compress above 4Khz using the 
transmitter limiter function. . 

That's about it for this revision. 

Please feel free to contact me if you find errors or have specific questions. 


Enjoy... 

Skipp 


Skipp May	P.O. Box 192 Elmira, CA. 95620 (707) 678-4187 nospam4me@juno.com 

This text is made available on the http://www.radiowrench.com/sonic web page.




