Just a general update on the Voter2. It is feature complete and a couple brave souls are deploying them as beta testers. While in standby mode waiting for any issues that may crop up, I am starting to work on the definition of the standalone version of the Voter2, the Voter2-SA. This will be physically more like the Voter/RTCM in that it will be in its own case with connectors and cables that should be able to connect to most repeaters. If you are interested, the home site for the Voter2 discussions are on Masons Discord server. This should be the link: VOTER Users
I am also working on a plug-in card with an Oven Controlled VCXO and 16-bit DAC that with the GPS 1PPS I hope will provide a stable enough 10MHz reference for simulcast support. I am getting down to 1-3ppb accuracy most of the time, so feel it may be work.
I do have a general request, you can answer here or on Mason's Discord server: For whatever repeater you have, what are the analog IO voltages for Tx and Rx audio? If you could give me the repeater model and voltages (either full scale or for 3KHz deviation is fine) along with a range if the levels are adjustable, that will be helpful in specifying the voltage ranges the Voter2-SA should support.
Hah, I was just getting ready to reach out to you and see where you were at with the "general purpose" version. Glad to hear it is moving forward.
I do have one feature request that I didn't see in the software (unless it has been added), and that is the "BEW" mode that uses "in-band" audio for sampling to calculate the RSSI. It is needed for the radios like the Quantar and SLR5700 that don't have any wideband noise to measure outside ~300-3500Hz (their "discriminator" audio is really a digitally processed representation, not true analog discriminator noise).
The VOTER/RTCM firmware has "BEW" (Baseband Evaluation Window) DSP routines in it to sample take audio samples in the baseband to quantize the noise/RSSI.
@VE7FET Lee: Yes, in theory I do have BEW mode (well, both of them, the attenuated and clipped) implemented in the Voter2. I emphasize in theory as while I've done my best to code up the algorithm and if I do things like bash on the microphone to generate broadband noise I see the algorithm kick in, I'm not sure how to quantitatively test it. Mason (N5LSN) did a great job of getting an AI summary of the BEW code and between that summary and the actual source I should be at least close. Cool part is if smarter people than me find something not quite right it should be fixable. Even cooler part is if someone comes up with a better algorithm, the Voter2 is NOT code space constrained!
I think the biggest nagging concern is my Nyquist filters at 4KHz. That is a hardware limit. While not useful for audio, since my Nyquist filters have some slope to them I will still get so see some energy above 4KHz folded back into the passband. Useful for energy measurement, but clearly not audio!
Well, when you get your more general layout ready to build, I will definitely spin up a few to test.
I have enough Quantars that I can (with a bit of effort) overlay my existing system and do A-B tests on receive performance between the two hardware platforms.
I can't offer much on the DSP/coding side of things... but I hardware I can poke at all day long.
Cool on the AB testing. While a bit nervous about it, one of my Voter2s will be going on a mountaintop soon for the Colorado Connection. The setup will have a Voter2 and Voter wired up in parallel so if something whacky happens they can switch over to the Voter. This is a mountaintop that is inaccessible for long periods during the winter. The Voter2 is pretty stable, but not wanting to gamble that much this early.
Also, for the Quantar do you have the specifications for the Tx and Rx audio levels in whatever format they call out (Vp-p, Vrms, whatever), if it's adjustable, and if it is for 3KHz deviation or something else. Also, if there is an analog RSSI level signal, its specs too.
Sorry for the delay in replying to this... thought I might have a chance to get a Quantar on the bench to test... but I haven't, yet.
The Quantar does not spit out an RSSI voltage... that is a pretty obscure feature in most radios.
Audio output of the Quantar depends on where you are pulling it from. Some folks use the balanced 600ohm wireline outputs... others use the unbalanced output from the 50-pin connector.
Likewise for audio input.
What I can tell you is what the current VOTER/RTCM does.
I did some circuit analysis, and it looks like the VOTER/RTCM wants to see a minimum of 140mVpp of wideband discriminator noise (considering the 9kHz HPF that is in there in the noise/RSSI measurement circuit). The acceptable range to allow calibration seems to be 140mV - 2.3Vpp, with around 350mVpp probably the "sweet spot". Above 2.3Vpp, and the squelch calibration circuit probably won't succeed (too much audio).
That is the critical measurement for the receive side (making the squelch calibration circuit happy). The actual receive audio side is more forgiving, and can be adjusted with the input attenuation pot. If you've got enough audio to calibrate the squelch, you should have enough baseband for normal audio.
On the transmit side, the VOTER/RTCM has a pretty wide range. By default, it should put out about +/-2.5Vpp, as the output op-amp is biased off the 5V rail. Optionally, the output op-amp can be biased off Vin... which would give you about +/-6.5Vpp output... if you need THAT much audio, you're probably doing something wrong.
Hope that helps in your design decisions. If I get a Quantar on the bench, I will try and take some more accurate measurements for it specifically.
