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=TX Level Setting=
=Audio=
*Send 1kHz@3kHz on-channel in to the RX
The RTCM/VOTER is totally flexible regarding emphasis. Although the way it is set is completely obscure. It tries to automatically do the right thing for you, which is great most of the time. But when it’s not, it's hard to know what is going on.
If you are changing the COR Type settings, or nodeemp in voter.conf, make sure you save/reboot the RTCM/VOTER every time you make a change... changes are '''not''' effective until the RTCM/VOTER reboots!
==Receiver De-emphasis==
On the RX side the COR Type setting in the RTCM/VOTER determines whether the de-emphasis filter is used for RX audio. 0=Normal means the RTCM/VOTER squelch circuit is in use and it is expecting discriminator audio on the RX pin (to be able to do the squelch action), and therefore it '''will''' provide de-emphasis (audio is routed THROUGH the de-emphasis RC filter circuit) to the receiver audio. COR Type 1=IGNORE COR uses the CTCSS input pin for COR or CTCSS ''logic'' and it then expects de-emphasized receive (line) audio on the RX pin, and therefore will '''not''' provide de-emphasis to the received audio (the RC filter is switched '''out''' and audio passes straight through).
Most of the time, you do NOT need to override the automatic filter selection. However, if you do, and you are sure you have a good reason to, you CAN switch the de-emphasis filter '''out''' of the circuit so that audio passes straight through to the encoder. You would do this by setting the nodeemp=1 option in voter.conf. When you set nodeemp=1, the ''VOTER Protocol'' tells the RTCM/VOTER to switch the filter '''out''', so audio is passed straight through.
==Transmitter Pre-emhpasis==
On the TX side, the RTCM/VOTER expects the repeater to accept ''mic audio''. In other words, the '''repeater''' is providing the pre-emphasis, not the RTCM/VOTER (you are '''not''' directly modulating the TX). This can be overridden by setting CTCSS tone in voter.conf. If a CTCSS tone is defined, the RTCM '''will''' provide pre-emphasis to the audio, and expects that you will be connecting to your repeater's flat audio input (direct modulation).
If you don’t want TX CTCSS tone but '''do''' need pre-emphasis, set an arbitrary (any) CTCSS tone in voter.conf, and set the level to 0. This will force the RTCM/VOTER to pre-emphasize the audio it generates on the TX pin, but it won't actually mix in a CTCSS tone.
==Level Setting==
Setting the audio levels for the RTCM/VOTER is pretty straight forward. Just follow these steps:
*Ensure you have a connection to your host Asterisk server/chan_voter instance
*Send a 1kHz@3kHz on-channel, full-quieting signal in to the repeater's RX
*Set the RX up so it reads 3kHz deviation on the RTCM's built in console meter
*Set the RX up so it reads 3kHz deviation on the RTCM's built in console meter
*Now set the TX level '''pot''' to get 3kHz out of the transmitter (No PL)
*Now set the TX level '''pot''' to get 3kHz out of the transmitter (No PL)
Now change the modulation from 1kHz tone to 800Hz followed by 1.8kHz and verify that the deviation level doesn't change as the tone frequency changes. '''Changing levels indicates a pre/de-emphasis issue.'''
Now change the modulation from 1kHz tone to 800Hz followed by 1.8kHz and verify that the deviation level doesn't change as the tone frequency changes. '''Changing levels indicates a pre/de-emphasis issue.''' You will want to read the above sections on how audio is handled, and figure out where your issue is.
If using PL you have to account for that deviation, unless you filter it out with your IFR (test set).
If using PL you have to account for that deviation, unless you filter it out with your IFR (test set).
That's it!
Optionally, if you are using the built-in "offline repeat" functions, fail the connection to the host Asterisk server, and make sure your repeat audio performs the same as above.
==Crappy Transmit Audio==
Does your repeated audio sounded really bassy, muffled, and not very understandable?
There was a situation where, compared to a typical simplex radio-to-radio transmission, the audio through the repeater (RTCM and Asterisk) was unacceptable. What was discovered was that the RTCM has an internal pre-emphasis function that was disabled. The user had intentionally disabled "txctcss" and "txctcsslevel" in voter.conf because he didn't
want the RTCM transmitting CTCSS (the Quantar was doing that already). He ultimately found a post on the mail list that said enabling txctcss = some valid tone (114.8 in our case) and setting txctcsslevel = 0 would turn on the pre-emphasis function in the RTCM without transmitting CTCSS tones.
He did, and it worked like a charm! Audio now had more treble and was less bassy/muffled. So, future RTCM users, be sure not to comment out txctcss and txctcsslevel in voter.conf!
Just enable and set the level to 0. You'll thank me later.