When using Quisk FDX mode, are we seeing the real broadcast spectrum?

[Bill Cox AI6SJ]

In the bscope window, with FDX on, in CWL/CWU mode, when I hit Spot, I hear the CW tone being received, with no antenna on RF1, and a dummy load on ANT.  However, I see all sorts of harmonic noiseon 80m, and on 20m there are a lot of spikes in all bands.

Is it safe to assume that I'm receiving the power spectrum from before the filters, or would I actually transmit all this noise if connected to a real antenna?

Thanks,

Bill

[ron.ni...@gmail.com]

If you are worried about spurious transmission levels, you might want to monitor your transmitter's signal from a separate well-isolated receiver.  My 2 HL2's appear to transmit very clean signals when monitored from a separate HF+ SDR receiver, BUT one can never tell what might happen if a circuit component fails, or the SDR software encounters a new bug.

73,

Ron

n6ywu

[Steve Haynal]

Hi Bill,

Yes, you see your TX signal on RX when in FDX. Note that this is all through incidental pickup. The TR relay is in the TX position so there are only some short RX traces, components and internals of the AD9866 where the TX signal leaks through. This is necessary for PureSignal or predistortion to reduce IMD. See:

https://github.com/softerhardware/Hermes-Lite2/wiki/PureSignal

Although it is helpful, I wouldn't trust the RX data during TX for true harmonic measurements, etc., of your TX signal unless you have a controlled feedback from TX to RX which is strong enough to overcome any incidental pickup. The gateware has LNA settings for both TX and RX which some software utilizes. The idea is to set the LNA at a very low level during TX but feedback some TX to the RX so that you then see a nice strong controlled and clean representation of your TX.

73,

Steve

kf7o

[Bill Cox]

Oh ok.  Thatakea.sense.  IIUC Quisk does not support attenuation in the LNA setting, but I'll try some of the other software packages, or maybe a resistor divider, or maybe just patch Quisk.

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[Bill Cox]

BTW the reason my typos are so bad is I have very poor vision and am typing.on my phone without a screen reader.  Sorry!

[Steve Haynal]

Hi Bill

Quisk has controls for the LNA. The RX LNA setting is the horizontal slider on the main screen near the bottom left labeled RfLna. Usually you want to run this between +12 and +20dB.  Under "Config-> <Your Radio Name> -> Hardware" there is a setting on the right named "LNA during Tx dB." You can set this to a value as low as -12dB. Quisk is one of the few software packages which makes use of the gateware-based RX/TX LNA settings for fast switching.

73,

Steve

kf7o

[Bill Cox]

Got it.  I would like to see the Spectrum went under full load.  So I'm thinking of getting a t connector, and having the 50 ohm dummy load in parallel with a higher resistance path to the RX input.  Does that sound right?

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[Steve Haynal]

Hi Bill,

Yes, the total parallel impedance should still be close to 50 Ohms. 

See the attenuator and attenuator calculator link on this page:

https://github.com/softerhardware/Hermes-Lite2/tree/master/hardware/companions/psfeedback

73,

Steve

kf7o