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sinara-hw / Phaser

Quad channel 1GS/s RF generator card with dual IQ upconverter and dual 5MS/s ADC and FPGA in EEM form factor
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Expected LO level #136

Open FabianSchwartau opened 3 years ago

FabianSchwartau commented 3 years ago

Hi, I just noticed that there is a note in the schematic: "Expected LO level is -10dBm" for the TRF. The datasheet does not say anything about the expected LO value. However, the LO output level is 3 dBm and I would expect the input to expect a similar value. This assumption is also confirmed by TI: https://e2e.ti.com/support/rf-microwave/f/rf-microwave-forum/984697/trf372017-ext_vco-maximum-input-level-of-trf372017 So, is there any reason to use -10 dBm instead that I missed? Otherwise I would recommend to update the note.

gkasprow commented 3 years ago

I think I calculated the power from an input voltage

FabianSchwartau commented 3 years ago

Where did you got that input voltage from? I cannot find anything in the datasheet. Interestingly, when I reduce the LO power below -5 dBm the sideband suppression of the mixer gets significantly worse. At -10 dBm I have less than 30 dB suppression left. LO is at 300 MHz. So I guess -10 dBm is way too low. On the other hand, increasing the level beyond +2 dBm also decreases the sideband suppression. So I guess a value between -4 and +2 dBm is optimal.

gkasprow commented 3 years ago

I took it from this image :) obraz

FabianSchwartau commented 3 years ago

I guess you are talking about the Po=-10dBm value? My guess would be, that this is the output power after the mixer. Especially, as Po is also given in figure 27, which is using the internal VCO.

gkasprow commented 3 years ago

Yes, I wasn't sure if it is VCO Po or IC output

FabianSchwartau commented 3 years ago

OK, then I would recommend updating the schematic note. One may also argue to remove the attenuator in front of the second LO input. Edit: I have not measured the output after the attenuator, yet, but the output signal after the second TRF's mixer is horrible. I get like 15 dB sideband suppression.

gkasprow commented 3 years ago

It makes sense.

gkasprow commented 1 year ago

The attenuator is removed by default. I also removed the schematic note.