This is going to be long, so grab a coffee.
As you know, these radios were really made for 12.5kHz channel operation, it is a bit of a kludge that they do to make them do 25kHz, basically by bonding two 12.5kHz channels together inside the radio… at least, that is what it looks like they are doing.
Here are my notes on alignment… note, I have an HP8920/8921 series test set, so some of the cues in here are for it’s audio filters…
This procedure is for if you are using Asterisk/RTCM to generate PL. (I have a slightly different procedure if you are generating PL in the SLR TX instead).
The SLR5700 is very sensitive to levels… things go sideways when you over-drive the modulator.
There is a note in the Service Manual:
“If the manufacturer of the third party controller specifies that the Tx Audio is not to be pre-emphasized, use Pin 1 instead of Pin 22.” Fact, or fiction?
Here are the pre-requisite conditions:
-using an RTCM/VOTER
-loaded with v1.5/Chuck Squelch/DSP BEW firmware (BEW disabled)
-Intent to support RX PL
-Configured for TX PL
-Configured to fallback to offline repeat
In voter.conf, make sure we have: MAKE SURE YOU EDIT THE RIGHT VOTER CONTEXT IF MORE THAN ONE EXISTS
txctcss = 136.5
;txctcsslevel = 50 ;this is a calibrated value, DO NOT CHANGE
txctcsslevel = 0
txtoctype = phase
Yes, we want to initially set txctcsslevel to 0… we’ll set the level later. We need these settings so that the channel drive configures itself properly for flat audio.
Accessories --> Audio Type --> Flat Unsquelch
-This disables the audio gate to let audio out of the RX pin at all times.
-The “discriminator audio” is clipped and looks (and sounds) more like data than true analog audio.
-Haven’t run that in to an audio spectrum analyzer, but I suspect it is missing a lot of high frequency
spectrum audio, hence maybe requiring the use of BEW.
Pin #2 - External PTT, Active Low, Debounce
Pin #4 - CSQ, Active Low (not used)
Pin #5 - PL/Talkgroup Detect, Active High
Channel 1 - Analog
Channel Bandwidth - 25kHz
Squelch - Normal (no effect, since we’re not using CSQ detect)
MPT1237 - Un-checked (this changes something about the RX audio… so we’ll just leave it alone)
Set the RX Squelch Type to CSQ for tuning. Set to PL, if desired, when done.
Leave TX Squelch Type at CSQ, we’ll generate the PL externally (in the RTCM/VOTER/Asterisk).
RX Audio is from Pin 1 of the DB25.
TX Audio is to Pin 13 (TX Data). This “should” go direct to the modulator… at least it normally would…
Get the RTCM up and running and connected to the host.
JP1 should be IN to disable the 20dB pad.
JP2 should be OUT.
With no signal applied, do the Diode Calibration routine. Insert JP10, then insert JP9.
This will do the Diode Calibration and the Squelch Calibration at the same time.
Wait for the RX LED to stop flashing and go solid.
The console should show the Diode Calibration being written to EEPROM (about 57).
Remove JP10 then remove JP9.
Squelch Calibration should be written to EEPROM (about 45).
Launch the Motorola Tuner. This is where things start getting hinky. The repeater is designed for 12.5kHz, they do some funny business to make it work at 25kHz. Alignment needs to be done at 1.5kHz deviation (60% rated system deviation for 12.5kHz) to get the levels to work right.
Click on Rated Volume.
Feed 460.050 (155.075) with 1kHz @ 1.5kHz in to the RX.
If you scope JP1 in the RTCM, you should see 560mVpp/345mVrms.
In the RTCM console, select 97 to look at the RX bar graph.
Adjust the RX Gain (R35) in the RTCM to get 3kHz lined up… trust me.
Click Write (we’re not going to change the softpot in the repeater, but you have to “write” to exit).
Click on Audio Level.
Set the test set to RX 460.025 (155.025). Note the repeater RX is still configured for 460.050 (155.075)
Send 460.050 (155.075) with 1kHz @ 1.5kHz in to the RX.
Click on PTT Toggle.
This should send the audio through Asterisk and in to the transmitter to be demodulated by the test set.
Filter on the PL in the test set. There shouldn’t be any PL modulation… or very little (like 0.015kHz). If it is more… did you edit the right context in voter.conf?!
Anyways leave that… Back to the level adjustment…
If we set the filters to 300Hz HPF and 15kHz LPF, we can knock out any PL modulation.
Adjust the TX Gain (R61) in the RTCM to get 1.5kHz deviation.
Exit the tuner.
This should get us where we need to be… now some fine tuning.
Let’s go check the offline repeat first.
Disable the GPS by setting it to NMEA instead of TSIP. This will drop the host connection and put us in to offline repeat.
Send an on-channel carrier with 1kHz @ 3kHz in to the receiver and demod the repeater output.
Offline repeat is set for CTCSS with a value around 1500 and De-emphasis Override is 1. If you change the De-emphasis Override, you MUST save the values and reboot for it to take effect!!
We want De-emphasis Override = 1 so that the de-emphasis filter is bypassed and we get flat audio through the RTCM in offline mode. If it is set incorrectly, when you sweep the modulating frequency, the deviation will change.
Set the filters in the test set for 300Hz HPF and 15kHz LPF to strip any PL.
The TX should be modulating around 2.7kHz.
Bump R61 up to give us 3kHz deviation.
Set the filters to measure PL deviation.
Adjust the CTCSS level in the RTCM to get about 0.6kHz.
Now, if we widen the filters to include PL and the 1kHz (<20 & 15), we should get about 3.5kHz composite deviation.
If we sweep the modulating frequency, the deviation changes… this SHOULDN’T happen… but it does. Setting the Offline De-emphasis Override doesn’t seem to make a difference. Since offline repeat should not happen very often, we’ll just leave it. ***There is a bug… if you change De-emphasis override, you MUST save and reboot for it to take effect. We want De-emphasis Override = 1 to bypass the De-emphasis Filter and have flat audio through the RTCM in offline mode. It DOES work properly when De-emphasis Override = 1… the deviation is constant (within TX specs) when the frequency is swept.
Re-enable the GPS to lock back up to the host and send our audio through Asterisk.
Send on-channel with 1kHz @ 3kHz in to the RX.
Filter and measure the PL… change the level in rpt.conf and run astres.sh to restart Asterisk to adjust the PL level for about 0.6kHz. Should be about 47.
Set the test set filters for >300Hz & <15kHz. Check the 1kHz level is pretty darn close to 3kHz (3.1kHz).
Widen the test set filters and check the composite modulation is around 3.6kHz.
Sweep the audio frequency and see that the deviation remains about the same (around 3.6kHz).
It should start to drop when you hit 300Hz. And it will start to roll off gradually when you get above 1.6… but it will dive when you hit about 3kHz, and drop right off at 3.4kHz… that seems to be characteristics of the transmitter.
Finally, set the squelch using R22 on the RTCM by feeding an on-channel signal in to the RX and lowering the level until the squelch closes. Adjust as necessary. A squelch level on the console of about 560 is probably a good place to start. Might need to adjust it tighter in the field.
Don’t crank the squelch too high, weird shit happens! Had it set to 920 and the RTCM would squelch when the frequency was swept up to 2600Hz.
OK! We’re pretty much at the end.
If we are going to use CSQ on RX, we’re done.
If we want to use PL on RX. Program the repeater for TPL on RX, set GPIO 5 for PL Detect, and set the RTCM for External CTCSS Non-inverted.
In fact, you can program the repeater for TPL anyways, and the only side effect is that the RxA and RxB LED’s on the front won’t light on a received signal (since PL isn’t satisfied).
Then, the decision to enable PL decode is entirely done by changing the option in the RTCM.
If CTCSS is enabled in the RTCM and no valid PL is on the received carrier, the RX light on the RTCM will flash at the same rate as the ACT light.
So, give that a go, and see if it clears things up. The key here is aligning the radio in the Tuner, as a 12.5kHz radio, and then let it do its thing when it bonds the channels back in to 25kHz.