Building the Ensemble RXTX: testing the PA stage
- I am getting 43.4 mV & 42.00 mV across R48 & R49 respectively.
This is more than 10% difference.
I have a problem matching the fets, as my meter shows only two decimal points on the 20v range. The other ranges are 2v and 200 mv !
Is there any other way to match the fets p;ease ?
Lower the drain voltage to get a lower voltage in mv range ?
Check any fet resistance ?
--- In firstname.lastname@example.org, "warrenallgyer" <allgyer@...> wrote:
Oops, I should have said R25...
> Suggestion: check the polarity on C12.
...which would make the associated capacitor C11. It's OK. I even pulled it and tried another. And for good luck, I swapped C15 and C16. No change in behavior.
> The behavior you describe at R26 is not right. Any differential behavior among the four op amps will cause exactly the symptoms you are showing; modulation by the input audio.
> Warren Allgyer - W8TOD
> --- In email@example.com, "warrenallgyer" <allgyer@> wrote:
> > One of us is confused and there is a high probability it is me. I have been thinking you were using the 10KHz tone on the "Line Out" input to the RXTX. If you do this it should result in a CW carrier at full power, 10 KHz from the CFGSR indicated frequency. It will be either plus or minus 10 KHz depending on the setting of the IQ jumper. If the IQ phase and gain balances are off then you will see the lesser image 10 KHz on the other side and it should null out with gain and phase adjustments. The resulting carrier should be pure, single frequency with no sidebands. There should be no output at all on the CFGSR frequency.
You have it right. CFGSR indicates 21.1 MHz, 10kHz single tone into the "Line Out" input on the RXTX. The image does null depending on the IQ phase/gain settings.
> > Somehow your 10KHz tone is modulating the CFGSR frequency instead of just mixing with it. So what you appear to have is an AM signal centered around the CFGSR frequency with appropriate 10 KHz sidebands, instead of a CW signal at CFGSR +- 10KHz.
> > I used that tone generator some time ago but I don't remember the application. I think for such tests you will find that Rocky 3.7 has much more capability and it integrates the PTT, frequency control, and tone generation in one package. As a bonus, Rocky includes a two-tone test generator that allows true IMD measurement.
Unfortunately, Rocky isn't playing nice with my soundcards on Windows 7. I'll try some more if I get chance tomorrow night.