How can I integrate a legacy analog console into a Telex RoIP system?
Legacy TRC (Tone Remote Control) consoles send analog voice and signaling tones down copper pairs to control remote radios. In a system conversion from copper to RoIP, the IP-223 is able to convert the console signals into data, which is sent across the network to a far end IP-223 in Tone mode. This IP-223 re-constitutes the data back into analog signals, and sends them to the tone remote adapter/control station transmitter. (The console end IP-223 must be configured for Console mode to perform this conversion)
Receive audio is likewise digitized by the radio end IP-223, and sent across the network back to the Console mode IP-223, which again converts the data back into analog audio that is played back as console receive audio.
Configuration of the IP-223s
Jumpers MUST be configured correctly for the unit to work. An incorrect jumper setting can waste hours of unnecessary troubleshooting time. Consult your application notes and manual to determine the correct jumper settings for your application. We recommend that you double check them.
It is also important to be sure that the Console mode IP-223 2175 Hz PTT Notch filter is ON. This prevents two sets of 2175 tones being sent to the radio end of the system (one from the Console mode IP-223 and one from the Tone mode IP-223), which will create a beat frequency, and thus create impossibly unstable tone decoding.
When converting a legacy tone console to a Telex RoIP system, it is necessary to connect the console outbound audio (TX pair) to the IP-223 RX pair (dB-25 pins 12 and 24), and the console inbound audio (RX pair) to the IP-223 TX pair (dB-25 pins 13 and 25).
The Parallel Console checkbox in Per Line settings must be checked when using Console Mode.
All Function Tones that will be used need to be enabled.
Tone and Frequency durations, frequencies and magnitudes must match the radio end TRC decoder requirements
Connection in 2 Wire or 4 Wire?
If a choice of 2 Wire or 4 Wire configuration is available, there is no doubt that 4 Wire is the best option. With separate TX and RX audio paths, the possibility of random loud RX signals audio causing TX decoder to falsely recognize as a TRC tone burst, is eliminated. This problem is commonly manifested by erratic momentary mode changes from RX to TX modes while receive traffic is active. This can even cause the radio to change channels randomly as decoder thinks it is supposed to change channels.
4 Wire also normally provides better audio quality and more stable levels over time, especially when long runs of copper leased lines are used, and the false decoding issue is not a factor in 4 Wire.
Figure 1 - Tone Remote Control (TRC) Burst
Most consoles use standard TRC levels and frequencies based on a LLGT (Low Level Guard Tone, sometimes called Hold Tone) of -20 db. The voice audio portion of the signal normally occupies a level window of approximately -20 to 0.0 dB.
Motorola consoles often use a slightly lower TRC level window…a LLGT of about -30 dB. The voice window will also be correspondingly lower. This will require a slightly lower LAM level setting in the IP-223 than the typical -35 dB. The IP-223 is normally able to work reliably with a Motorola legacy console if aligned carefully.
If you are unable to obtain consistent TRC keying, verify that your console is sending standard tone frequencies, durations and levels that match what the radio is expecting.
Dead key the console (PTT with no voice) and measure the LLGT with a Transmission Test set or TIMS Test Set on the console TX pair.The LLGT should be stable at approximately -20 dB, or with some Motorola consoles, -25 dB to -30 dB. Adjust accordingly to present this level to the input of the IP-223.
Perform a loud voice test and see that the peaks do not exceed approximately 0.0 dB. The IP-223 should consistently display “CTX F1” at all voice levels from quiet to maximum peak.If the levels peak at greater than 0.0 dB, the IP-223 “CTX F1” display may drop out. This can be caused by excessive peak levels at the input of the IP-223 CODEC. If this happens, slightly reduce the input level.The IP-223 gains may be adjusted via software, or a hardware pot.
It is good practice to do a quick check of the digital output level going out onto the network with the Telex “VU Meter” program. The bar graph deflection should be peaking in the range of about ½ to ¾ of full scale.
Transmitter deviation should be checked for correct values with a console voice test. Receive levels should be in approximately the same level range as transmit, to provide acceptable volume at the console.
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