Re: QRP Labs xciever with SSB capability
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this difference of 15 dB in favour to the drain modulation compared to the gate modulation raises some hopes.
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Reading the article from the link about the measured IMD3 I realised the result of the gate modulation was only -5dBc and the statement that everything over -25dBc was bad. I agree with that. There was also a statement mentioning the power level at which the measurement was done. Also OK.
VK2IHL actually said regarding IMD3:
? -40dBc/IMD3 Excellent
? -30dBc/IMD3 Good
? -20dBc/IMD3 Poor
? -10dBc/IMD3 Very poor
But there is some room for confusion, between whether you consider the ARRL style measurement dB relative to PEP (I admit I always used this method), or dBc relative to the strongest tone level.??
? But I am confused with your stating the absolute results of IMD3 in dBm without stating the power level of the original signals. Does it mean that the end result in dBc could be even better or the power cold be higher? Perhaps this was only a lapsus in units.
Yes, sorry, I mis-reported VK2IHL's results, my apologies. Indeed check:
and all his units are correctly stated in dBc. So it should be -20dBc not dB.? It's all there on the VK2IHL page. I was just reporting on that.?
FYI - my own measurements and evaluation of gate bias modulation vs drain modulation was done while I was researching and designing QMX 18 months' back, at that time as far as I am aware, I had not come across?VK2IHK's page so I was not influenced by his findings (not that his findings would have necessarily influenced me in any event, as there is all sorts of stuff all over the internet and anything that one sees has to be taken with a pinch of salt).? ?
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