Re: What makes a digital voice capable repeater dv capable?
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Hi Skyler,
You are correct on the disc > FM audio. And correct about no filtering.? I am suspicious on requirement of the frequency tolerance to be +/- 150 hz. ? That may be more for the potential narrow band mode co channel interference rather than a demodulation requirement. ? If your repeater or remote can do Out = In level and its flat from 20 hz to 3+ KC, in my experience you have no issues passing Fusion.? You also need to make sure any RX-TX audio propagation is properly addressed.?? You can't clip off the front or back end of the transmission.??
I have a user that occasionally uses fusion on the analog remote base. (with my permission of course)
Andy WJ9J
Well first, you need flat audio. Directly or as closely tied to the discriminator and modulator as possible. Filtering will prevent digital signals from making it through.?
Correct me if I¡¯m wrong or add to this list, but this is what I believe is important in a radio to work over digital:?
¡ªFrequency stability: you need to be on frequency by probably +-150Hz for best decode in comparison with +-500Hz for FM analog.?
¡ªNo filtering: you need to remove PL filters and emphasis / de-emphasis because this will distort the bits.
¡ªPhase response: the phase of the base and signal must not deviate over the frequency range of the baseband signal. This is what has been explained to me why the quantars don¡¯t do DMR.?
¡ª modulation balance: each side of the waveform must be balanced. Feed a square wave into the baseband and the demodulated signal must not be a ramp looking thing, it must look like a flat square wave.?
¡ª QuickT-R response (only applies to Tier 2 DMR and phase 2 P25 client side, not repeater side)? The radio must switch between transmit and receive multiple times per second without distorting the signal on either end. Sometimes this is an issue with radios using a DC offset and a blocking ?capacitor to block that because the capacitor takes time to kick in.?
On Mon, Jan 11, 2021 at 12:41 PM wj9jrg < wj9jrg@...> wrote: Well, you can, and if the repeater audio is good enough (like simplex is) it actually works (Fusion does on my system, even through the remote base). ? But that will probably make the repeater owner mad if they designate it as analog only.
Andy WJ9J
On Mon, Jan 11, 2021 at 12:30 PM Ron Wright via <lt_wright_flg= [email protected]> wrote: No one can normally not just transmit digital voice thru a FM analog repeater.
For DSTAR the receiver side of making an analog repeater work is easy, just take the digital signal off the recvr disc.? But for the xmtr need to use direct FM of the modulator.? There are filter and shaping circuits in a typical FM analog transmitter that will distort the digital signal.
DSTAR is just ones and zeros, looks like a rounded off square wave.? One can easily see it on the rcvr disc.? Also for DSTAR the modulation level needs to be set proper.
C4FM (DMR, P25 & Fusion) are more analog signals, but still the transmitter would distort these signals if not applied properly between the rcvr and xmtr.
73, ron, n9ee/r
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