I am trying to prototype a RTCM based voting system with 2 RTCMs.
I am using two JSLM2 Data Radios as transceivers.  
Using HP8920B service monitor to drive the radios.

Good news: I can get both RTCMs and both radios to transmit.  Test tones sound fine. Deviation good.

Bad news: I can't get the RTCMs to register the incoming audio signal.  There is no CTCSS in these radios, so that line is not connected.  I have no COS signal connected either.  Just audio in/out and PTT to the radio.

I have confirmed the radios are receiving and are sending audio to the RTCMs using an oscilloscope.  If anything the audio is way high in level.  I measured 1v peak-to-peak when I think the RTCM is expecting 200mV.  Tried the 20db pad with no effect.  My suspicion is that the RTCM is a high-impedance input so the voltage is floating up in the absence of appropriate load (say from a 600 or 2k ohm).

Second, I never get the green receive light on so I suspect there is actually some squelching or some such going on that is gating the audio signal off.

Third, I have not been able to the the Squelch calibration or Diode calibration to behave.  Does this require the diagnostic cable described in the interface to be used?  The procedure is not documented well.

I would love to see a know working config and wiring setup to confirm what I have done.  

-Doug-

Current settings:

Select the following values to View/Modify:

S/W Version: 1.51 08/08/2017
System Uptime: 2095.0 Secs
IP Address: 192.168.0.75
Netmask: 255.255.255.0
Gateway: 192.168.0.1
Primary DNS: 192.168.0.1
Secondary DNS: 192.168.0.1
DHCP: 1
VOTER Server IP: 104.197.124.184
VOTER Server UDP Port: 667
OUR UDP Port: 667
GPS Lock: 1
Connected: 0
COR: 0
EXT CTCSS IN: 1
PTT: 0
RSSI: 0
Current Samples / Sec.: 8000
Current Peak Audio Level: 112
Squelch Noise Gain Value: 0, Diode Cal. Value: 0, SQL pot 0
Current Time: Sat  Nov 25, 2017  17:14:12.740
Last Rx Pkt System time: <System Time Not Set>, diff: -198435452 msec
Last Rx Pkt Timestamp time: <System Time Not Set>, diff: 0 msec
Last Rx Pkt index: 0, inbounds: 0

1  - Serial # (1162) (which is MAC ADDR 00:04:A3:00:04:8A)
2  - VOTER Server Address (FQDN) (xxx.org)
3  - VOTER Server Port (667),  4  - Local Port (Override) (0)
5  - Client Password (xxx1),  6  - Host Password (xxx2)
7  - Tx Buffer Length (3000)
8  - GPS Data Protocol (0=NMEA, 1=TSIP) (0)
9  - GPS Serial Polarity (0=Non-Inverted, 1=Inverted) (0)
10 - GPS PPS Polarity (0=Non-Inverted, 1=Inverted, 2=NONE) (0)
11 - GPS Baud Rate (4800)
12 - External CTCSS (0=Ignore, 1=Non-Inverted, 2=Inverted) (0)
13 - COR Type (0=Normal, 1=IGNORE COR, 2=No Receiver) (0)
14 - Debug Level (0)
15  - Alt. VOTER Server Address (FQDN) ()
16  - Alt. VOTER Server Port (Override) (0)
17  - DSP/BEW Mode NOT SUPPORTED
18 - "Duplex Mode 3" (0=DISABLED, 1-255 Hang Time) (1/10 secs) (0)
19 - Simulcast Launch Delay (600) (approx 200 ns, 5 = 1us, > 0 to ENA SC)
97 - RX Level,  98 - Status,  99 - Save Values to EEPROM
i - IP Parameters menu, o - Offline Mode Parameters menu
q - Disconnect Remote Console Session, r - reboot system, d - diagnostics