I've been trying to follow the setup instruction for Squelch setting, SW2 down, green lights etc. I can only get the green light to flash slowly even through I have bird clip #1 installed (booster)
See https://allstarlink.github.io/user-guide/troubleshooting/ on how to ask a good question to obtain the quickest and best assistance
What radio are you connecting to the RTCM?
What pins are you using for audio?
What firmware is the RTCM using (in the very top of the screen when it boots)?
What jumper/switch positions do you have set?
What test equipment do you have available?
Lee
Lee,
Radio Motorola MT500
telnet in and serial number shows but no firmware for the RTCM appears. Understand that may indicate an older version firmware.
Jumper JU 1 in JU2 out. Did the SW2-1 on and initiated the device. LD1 goes solid but flashes about every 10 seconds. SW2-1 off. SW2-2 on, radio on with no antenna. Three hundred mv measured at DB9 Pin 3. Menu item 12 =1, Menu item 13 =0, LD3 flashes slow. COR on pin 4 pulled low, LD3 still flashes slow. Menu 98 - Current Peak Audio 53600. Squelch Noise gain =0, diode cal =0, sq lvl = 262
Equipment = scope, voltmeter, IFR1200 Service Monitor.
Bob k6mby
Hi Bob,
Where are you pulling "discriminator" audio out of the MT500?
You'll only see the firmware version when you first boot the unit, or it MAY be on the status menu (98):
System Re-Booting...
VOTER Client System Version 3.10 1/11/2026, AllStarLink, Inc.
Enter Selection (1-19,81-82,97-99,i,o,s,r,q,d) : 98
S/W Version: 3.10 1/11/2026
System Uptime: 76.3 Secs
Squelch noise gain = 0 and diode cal = 0 tells me that the squelch initialization didn't complete (obviously), as well as the diode calibration (temperature compensation) didn't run.
Once you have initialized the device with SW2-1, you shouldn't touch that again (unless you want to reset it to defaults).
I would power it off. Turn SW2-1 and SW2-3 ON, power it up, and wait for the green LD1 to come on solid.
Power it off. Turn SW2-1 and SW2-3 OFF.
Power it on again, and check that there is now a value in the diode cal field.
Power it off, turn on SW2-2, and power it on, and see what the squelch calibration does by watching the green LD3 LED.
If it flashes slow, and never goes solid, the audio level is too low, so insert JP1, and try again.
If it flashes fast, and never goes solid, the audio level is too high, so remove JP1 (if installed), and try again.
You may need to wait up to a minute for it to calibrate. It can take it a while to iterate through the steps of the soft pot and measure.
Once you get a solid LD3, you should be good to turn SW2-3 off. Check that you have a non-zero value for Squelch Noise Gain.
JP1 is the only one that should affect squelch calibration.
JP2 is used in conjunction with setting the receive audio level. It adds/removes a 20dB pad on the input amp (at least it should, if it was built off the VOTER design...).
Give that a go, and let me know what you find.
Lee,
Found the S/W version. V3. dated 3/24/2021
I will ask Bryon, KW1C, exactly where he picked up the disc output. He insists, however, it is before any filtering and the high frequencies should be there.
JP1 out
SW2-1 and 3 on, power on, LD1 goes solid. Power off. Read 98. Diode value 43.
Power off, SW2-1 and 3 off, SW2-2 on, LD3 after 20 seconds flashes at a rate of 1 every 4 seconds. After a minute or two LD3 flashes at a rate of 1 every 1 second but never goes solid on.
Repeat the process with JP1 in and the outcome is exactly the same.
Bob K6MBY
Ok, well at least that is a recent version of firmware. 
Glad the diode cal worked.
The 300mV you measured, was that with the radio connected to the RTCM at the time? The RX Input pot is probably a 100k load to ground, which may affect your discriminator level if you were measuring without the RTCM connected (there's also some additional AC impedance that may come in to play too).
It sounds like the level is too low. More specifically, there is not enough high frequency noise being detected to measure and calibrate.
Any specific reason you're trying to use a 50 year old HT?
The 300mv is measured with the RTCM connected to the radio.
Why the MT500? Because we had them. Small enough to fit in the outdoor box we have. Low receive drain.
Open to a different UHF receiver suggestion.
For a test, I am going to drag out an Icom 7000 and pick the disc audio off the ACC jack.
Lee,
Same story with the Icom 7000. About 500 mv noise from the 9600 baud pin 4 data jack. I can see the noise on the scope at the DB9 pin 3, Can adjust R36 via menu 97 to about 3/4 scale.
Bob k6mby
R36 has nothing to do with the squelch calibration. That is strictly for actual receive audio level. R36 gets adjusted with a 1kHz @ 3kHz deviation tone on the receiver to get it to match 3kHz on the bar graph in the CLI.
Just confirming, you're doing the squelch calibration with NO signal on the receiver, and no antenna? It needs raw discriminator noise. Any signal on the receiver will make it "quiet", and therefore there will be no (or very little) DC noise voltage to measure.
I don't have schematics of the RTCM (since it was built by a third party), the closest we have are the VOTER schematics which it was built off of. You can find that here:
That will give you an idea of how the signal flows. Sheet 2 shows how the RXIN splits to go to the squelch noise/RSSI measurement (top branch), and the receive audio path (lower branch).
"NVOLT" is the DC squelch/RSSI voltage that is sent to the uC for processing. I don't know if the RTCM has an equivalent TP3 to measure the voltage.
The squelch/RSS branch effectively rectifies the incoming signal to produce a DC voltage. "Noisy" signals will have lots of high frequency AC components, so when rectified they produce a "large" DC voltage. The stronger the signal, the quieter it is, so the less "AC" noise available, so the smaller the rectified DC voltage (NVOLT).
This explains some of the logic about what it is doing during calibration:
I don't know what those softpot values translate to for actual NVOLT readings... have never gone down that rabbit hole.
Lee,
No antenna on the MT500, no signal applied via IFR. Try on Icom 7000 same as before. No solid LD3.
Found a boxed Yaesu FT 7900. 500 mv on data out pins. LD3 goes solid!! Power off. SW2-2 off. Power on. LD3 on solid.
On with the rest of the calibration.
Bryon revised the tap point for the discriminator and could only get .1 volt. Looking at building an amp to get it up to .5 v.
Thanks for your help and direction.
Bob k6mby
Sequim, WA
Glad you seemed to have figured things out (insufficient discriminator level).
I had a peek at the MT500 schematic. It looks like true discriminator output is on U4 Pin 3, but it is VERY low (like around 35mVrms). So, you'd need to buffer and amplify it to make it usable.
Personally, I'd be using a radio from this century. A 50 year old radio is surely going to have some questionable capacitors in it, especially if it saw lots of use. That is going to impact all sorts of performance, both RX and TX.
Good luck in your adventures!
Well, this was just the first step so there is more to figure out as we move on to actually trying to put this receiver in place and get it connected to the far end repeater. I heard what I though may have been your call testing on the repeater yesterday... 441.125. Most of the path is over water and the repeater is on a hill.
Yes, U4 Pin 3 is where we tapped but as you say, very low audio.
Agree, if we could find a small radio, pre surface mount, that we could get sufficient voltage, that would be a good thing.
BTW. we are not transmitting with the MT500. This is just a receiver for voting. Going to need to go through the same process at the repeater end. A Motorola SLR5700
Bob k6mby. 441.125 + tone 100 - call is actually W7FEL on the repeater.
Nope, wasn't me you heard. I could probably hit it from here, but haven't tried.
As for "small" radios, I have used Maxtrac/Radius/GM300/M120 series in the past with success for satellite receivers. Smaller would be the CDM-1250/1550 that should also work. I think the ICOM F-5021/6021 series should work, as they are very similar to the FR5000 repeater, which I have also used with a VOTER/RTCM.
There should be information on how to line up an SLR5700 floating around. If you can't find it, let me know. I have used both the VHF and UHF in the past as a repeater with the VOTER/RTCM, but there are a number of "gotchas" when lining them up, considering they are inherently a 12.5kHz radio (which affects some of the tuning procedures) and they don't have true analog discriminator audio (it is digitally processed, very much like the Quantar, but it does work).
Found your May 2020 writing on how to set up RTCM Squelch and the SLR5700. Now that is something to look forward to!!
Bob k6mby