Yes DYI and mdd, I want the wider audio BW but it’s going to be some slogging. If I could do it at the client/host level, then at maybe it could pass back locally before it passes to the rest of the code (still beyond me until I look into the source code.
NR9V, Thanks! That answers a LOT OF QUESTIONS
That is EXACTLY the tech spec I was looking for. And it is consistent with what I would expect.
I Screenshot a test from my HP8920 sig gen to an RTL-SDR driving direct into audacity and those are similar levels. In particular at 12dB sinad, the 3kHz 60% alignment level blows out to around 140% because of the noise component…
NR9V has another thread about his “Audio Clip LED feature addition in ASL3” and that got me thinking about the actual headroom versus radio audio.
Basically
3kHz 60% col 34 -12.9dBFS or 23% in linear scale
5kHz 100% col. 51 -9.4dBFS or 34%
? ?% col 150 0 dBFS or 100% at the digital clipping level.
15kHz 300% col 150 0dBFS 100% clip level.
So have a look at the pics.
Picture below… next post…
Here you can see the Bessel Zero at 2.4kHz, and audacity running behind. The RF input is via the HP8920… Also for THIS discussion, NOTE THE HP8920 FM NOISE FLOOR!. only -48dB, Sucks! (RTL-SDR contributes some though) Squelched, the SDR is down around -90
Now I do a bit of labels: trace the 3kHz and 5kHz and 12dB sinad back to the linear scale on the LEFT.
Compare that 3kHz deviation at say -60dBm versus the 12dB SINAD point. YOU NEED that HEADROOM!
Also, I ran some audio from my kenwood F6 and of course it’s a bit hot and has a few mild peaks at 7kHz deviation. Take it with a grain of salt, as we dont know what the channel EQ or de-emph flatness.
Also note here. The -90dB muted level prints back as -147dB once we pass from 16 bit to uLaw and back. Everything lower than about -86dB (the 13.5bit uLaw bottom) goes to complet 16 bit zero.
THAT could be a feature… to exploit… Say put a Behringer MDX2600 and use the expander gate…
I like that you are using transformers, I’ve long used the XICON TL 016 1:1 telephone coupler transformer, and those can sound MUCH wider than telco grade IF THE TERMINATION is well above 600z, say 4.7k to 20k.
They have several quirks. LOW Freq’s will saturate rather quickly. So while 1kHz can be 3Vrms, down at 67Hz it’s more like 300mV before saturation. At high frequency, without normal loading, the top end goes out to 30 to 60kHz and typically has a big PEAK.
So if you have any ultrasonics (ie DAC Hash!), it’s a good idea to either put a zobel, (beyond the scope here), or at least a simple RC pass filter.
I have a couple of Jensen 11-SSP or TRW brand SAT-109 real transformers for testing. Those actually have the faraday tape winding and work a LOT better for noise suppression, say from an H-bridge audio out circuit.
Have you put the Retrevis radio AF out on a fast scope? Is it still via linear chips or is it using a Class D type H-bridge circuit? that isz: Is it any quieter with the AF shorted during the hang time?
The scope picture in post #1 above has a snippet of muted audio, I assume that is what the spectral view is on top. Taking the -95dB in the audio passband and adding in 35dB (ie, Log10 (3k) = 34.5dB puts the scope noise floor at -60 = -95 + 35 just eyeballing the trace.
I suspect your Retrevis radio doesn’t mute as well as the CM108 noise floor. The bigger question is its spec for “residual FM hum and noise” on receive as well as transmit.
BTW, for an extra $150 you can get a piece of crap Behringer MDX2600 and use the expander gate. I’m joking of course. (I’ve actually used those in radio systems… )
Thanks Guys. This is a big help
KD6OVS