Setting transmit drive level in SDR Console?

[Bob Edwards]

Hermes Lite 2 and SDR Console version 3.0.26 by G4ELI are a great combination. However I have a question about transmitting with Hermes-lite / SDR Console that might find a more ready answer here than the SDR Console forum. Anyone else using SDR-Console for transmit?:-

1. What does the 'OP power' control in the Receive window Radio section actually control? I am guessing it sets the attenuator after the AD9866 DAC to one of 16 settings.

2. What does the 'Drive' control in the Transmit windows TX section actually control? I am guessing it sets the amplitude of the transmit digital signal into the DAC.

3. What do ADC 75 and ADC 100 on the Hermes Lite front panel indicate when on transmit, running gateware version 72.8? I notice that ADC 100 flashes on if the output power exceeds around 3W, with 'Drive' set around 88.

4. The SDR Console indicator 'TX Overload' flashes on during speech peaks if 'Drive' is set greater than 97.

5. I notice that any OP Power setting has no effect on overload indication - hence suspect it controls the attenuator.

I'm confused by the two levels that are indicated by first 'LED 100' and then 'TX Overload'. At what level should I set the two controls above to obtain maximum linear output from the Hermes Lite? Is SDR Console capable of running Hermes Lite at full rated output - 5W-ish? 

[Bob Edwards]

I've also been trying OpenHPSDR mRx PS v3.5.0 (HL2). When I transmit with this application LEDs ADC 75 and ADC100 do not flash on speech peaks, but they do flash with Console SDR. Can anyone tell me why there should be a difference please? They both seem to deliver around 4W when doing a 'Aaaahh' into the Mic.

[Roger David Powers]

ADC should only operate when converting analog to digital, i.e. receive operation, or maybe when transmit signal is being sampled?

Maybe 'SDR Console' is using ADC to sample TX signal i.e. for 'Pure Signal', whereas OpenHPSDR is not?

Just a guess..

https://github.com/softerhardware/Hermes-Lite2/wiki/External-Connections does not make clear what those LEDs do in RX vs TX mode.

Regards,

RDP

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[Bob Edwards]

Roger,

That sounds quite plausible, SDR Console doesn't yet support pure signal, but it looks like he's turned the channel on in readiness. I needn't take any notice of the ADC75 and 100 LEDs then - the maximum permitted drive is signalled in SDR Console when the 'TX Overload' flashes. Thanks for clearing that up.

[Steve Haynal]

Hi Bob,

I can shed some light at least on the hardware side. Regarding the ADC75 and ADC100 on during TX for some software and not for other, this depends on if the software reduces the RX LNA gain during TX. The HL2 always operates in full duplex whether or not software is making use of that. So RX does pickup your TX signal and the ADC75 and ADC100 LEDs indicate RX clipping. If the LNA gain is at the default +14 to +20 dB range, then you will usually see clipping during TX. Some software (like PowerSDR, piHPSDR and LinHPSDR) have a separate setting for RX LNA gain (or attenuation from +20dB) and the software will switch to that gain setting during TX. Other software (like Quisk) makes use of the the hardware managed TX LNA gain as described on the protocol wiki page to set two gain levels and then let the HL2 do the switching. The hardware managed TX LNA gain is a HL2-specific protocol extension. It appears that SDR Console does not change the LNA gain during TX nor uses the hardware managed TX LNA gain and hence your clipping during TX. Maybe there is a SDR Console setting I am missing though.

One reason for these two gain levels is that PureSignal needs a clean signal from the RX ADC during TX, not one with clipping.

If I recall correctly, closed source SDR Console is prohibited from using PureSignal due to the open source license used by PureSignal . Last I heard Simon was developing his own version of PureSignal.

73,

Steve

kf7o

[Bob Edwards]

Thanks very much for that, Steve, that's useful to know.