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Re: Building the Ensemble RXTX: testing the PA stage

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  • Orin
    Or I could put a turn back on L2 and L3. I m considering switching to a Cauer filter. I tried SVC Filter Designer and it came up with a design with 26dB of
    Message 1 of 38 , Dec 31, 2012
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      Or I could put a turn back on L2 and L3.

      I'm considering switching to a Cauer filter. I tried SVC Filter Designer and it came up with a design with 26dB of attenuation at 42MHz. That would do the trick. I'd only have to rewind L2 and L3 and change all the capacitors. I searched through the capacitor drawer and I can manage it without having to buy any more capacitors.

      Orin.

      --- In softrock40@yahoogroups.com, "warrenallgyer" <allgyer@...> wrote:
      >
      > Hi Orin
      >
      > If you have ready access to the VNWA then you can tweak the output filter by squeezing (lowers the cutoff frequency) or spreading (raises it) the turns on L2 and L3. The tradeoff will be output power on 10 meters. I was able to get the 15 meter second harmonic down to -40 dB this way and still get 800 mw out on 10. If I adjusted for 1 watt on 10 then I could only get the 42 MHz down to about 34-35 dB.
      >
      > Warren Allgyer - W8TOD
      >
      > --- In softrock40@yahoogroups.com, "Orin" <orin.eman@> wrote:
      > >
      > > It just so happens that I put my Ensemble RXTX on the spectrum analyzer
      > > this morning. Mine is built for 15-10m. I had tuned the low pass
      > > filter for minimum loss, but was rather worried about the 2nd harmonic
      > > on 15m. I was right. I need 13dB more attenuation at 42MHz. Here is
      > > my VNWA sweep of the filter:
      > >
      > > 15-10m Filter tuned vs Elsie
      > > <https://picasaweb.google.com/lh/photo/Ujjps0q183ySKsaP29mDm4LS1FToz1TiC\
      > > JzHAUEj7Cg?feat=directlink>
      > >
      > > and here are the
      > >
      > > 15m and 10m spectra.
      > > <https://picasaweb.google.com/103209697005891839426/December312012?authu\
      > > ser=0&feat=directlink>
      > >
      > > Even with if my filter matched the theoretical, I'd still need 10dB more
      > > attenuation at 42MHz. Perhaps there is something wrong with my PA.
      > >
      > > Orin,
      > > RF hates me.
      > >
    • Orin
      ... Oops, I should have said R25... ... You have it right. CFGSR indicates 21.1 MHz, 10kHz single tone into the Line Out input on the RXTX. The image does
      Message 38 of 38 , Jan 1, 2013
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        --- In softrock40@yahoogroups.com, "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 softrock40@yahoogroups.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.

        Orin.
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