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Re: [softrock40] Peaberry V2

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  • Lior Elazary
    It seems like the PCB has room for extra transistors to increase the amplifier gain. Has anyone tried that? Lior. KK6BWA ________________________________ From:
    Message 1 of 2 , May 25, 2013
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      It seems like the PCB has room for extra transistors to increase the amplifier gain. Has anyone tried that?


      From: warrenallgyer <allgyer@...>
      To: softrock40@yahoogroups.com
      Sent: Saturday, May 25, 2013 1:01 PM
      Subject: [softrock40] Peaberry V2

      I have just completed a build of the Peaberry Version 2 for 30/20/17/15 meters. I received the rig on Thursday and spent Thursday night thru Saturday morning (Friday was a holiday in Singapore) doing the build. There is some really nice attention to detail in the kit. I so appreciate the new debug connector since I mangled the original and a replacement on my version 1. An onboard LED is extremely useful in assuring the early operation of the PSoC and PCM chips which have the tiniest pin spacing I have attempted and are really problematic to troubleshoot otherwise.

      The receiver is a big improvement. I am getting nice MDS numbers and the filters are really, really good. I am especially impressed with how far down the 3rd sub-harmonic response is (an 18 MHz receiver hearing stuff from 54 MHz).

      The kit has two gain options. In the standard build the gain is reduced to maximize the large signal handling capability. So you will only see 2-3 dB of noise rise when you connect an antenna. Changing R10-11 to the supplied 5K resistors will increase the sensitivity about 15 dB at the expense of going into overload at S9 + 42 or so. David has said this option is included for use in extremely quiet regions but for most I would recommend the standard setting. Few people live in a quiet enough area to take advantage of the extra gain and receiver performance degenerates quickly in the presence of strong signals even several hundred KHz away when using the high gain setting.

      MDS measured by a 3dB audio increase at the speaker terminals; 2.5 KHz filter bandwidth:

      10 MHz - 112 dBm
      14 MHz - 111 dBm
      18 MHz - 112 dBm
      21 MHz - 109 dBm

      Maximum signal handling performance measured as 1 dB below op amp overload in the receiver:

      10 MHz - 16 dBm (S9 + 57 dB)
      14 MHz - 16 dBm
      18 MHz - 15 dBm
      21 MHz - 14 dBm

      3rd Sub-harmonic response measured by connecting a -40 dBm signal at 3X the LO+1KHz and reading the level in HDSDR after calibration:

      10 MHz - 48 dB (-88 dBm)
      14 MHz - 56 dB
      18 MHz - 58 dB
      21 MHz - 60 dB

      This seems to be a really excellent receiver. The transmitter…… is the standard Softrocks transmitter. Nice power out on 30-17 meters, although I suspect a problem on 15. Like all of the Softrocks the IMD3 at full power is really bad, and much worse with a 12V supply.

      Maximum power out; 13.8 Vdc power supply, 4 volts P-P audio measured at R28

      10 MHz 33.3 dBm (2.1 watts)
      14 MHz 32.9 dBm
      18 MHz 30.4 dBm
      21 MHz 28.7 dBm

      Maximum power out with 30 dB IMD3 suppression

      10 MHz 31.9 dBm (1.6 watts)
      14 MHz 33.5 dBm
      18 MHz 31.1 dBm
      21 MHz 26.8 dBm

      I am going to fiddle with the transmitter and see if I cannot improve it a bit. The driver stage seems to be the main culprit in the IMD3 limitation. I have already discarded C46 and R47. As in the Softrocks, any gain benefit they give is at a severe penalty in IMD3.

      This is a significant step forward in receiver performance and build-ability compared to V1. Congratulations David!

      Best regards,

      Warren Allgyer
      Stealth Amateur Radio from Singapore
      CW, BPSK31, and WSPR on 160 - 10 Meters

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