Loading ...
Sorry, an error occurred while loading the content.

RXTX as an all band receiver (sort of)

Expand Messages
  • warrenallgyer
    While benchmarking my RXTX 15/17/10 build using the VOM technique that I explained in Post # 77773, I discovered, quite by accident, some interesting responses
    Message 1 of 7 , May 15, 2014
    • 0 Attachment
      While benchmarking my RXTX 15/17/10 build using the VOM technique that I explained in Post # 77773, I discovered, quite by accident, some interesting responses on the lower bands.

      With an input signal of -35 dBm and the LO tuned 10 KHz above the input signal, the 10 KHz audio output from my RXTX measures 0.23 VRMS (-13 dBV) at 28 MHz and 0.14 VRMS (-17 dBV) at 30 MHz. While looking for other artifacts I set my input signal to 14 MHz and tuned that. The audio output measured 0.28 VRMS, a full 2 dB more than at 10 meters! So I decided to run through the LF ham bands just out of curiosity. Here is what I found for response at the lower bands.

      160    -    Nada, zilch, nothing
      80    -    -43 dBV
      40    -    -31 dBV
      60    -    -31 dBV
      20    -    -11 dBV
      17    -    -14 dBV
      15    -    -13 dBV
      12    -    -7  dBV
      10    -    -13 dBV

      This puts the receiver performanceon 80 meters 30 dB below the 10 meter performance. While that is not great, anyone who has a noise level on 80 meters of S5 or higher would theoretically see no difference in performance between the RXTX and another receiver. And the performance just gets better as you get into the higher bands.

      So it would seem that the high band RXTX would make a quite serviceable 80 - 10 meter receiver as well as a 15 - 10 transceiver. Maybe the ideal road trip radio?

      Warren Allgyer
      9V1TD


    • warrenallgyer
      Extending this just a bit. Here are the benchmarks I measured for my other three RXTX. I make no claim that they are optimized or even properly constructed but
      Message 2 of 7 , May 15, 2014
      • 0 Attachment
        Extending this just a bit. Here are the benchmarks I measured for my other three RXTX. I make no claim that they are optimized or even properly constructed but the results seem remarkably similar and I think I would accept them as good except possible the 30/20/17 which looks a bit scotch on overall gain.

        RXTX 80/40
        160    -    -33 dBV
        80    -    -19
        dBV
        40    -    -19
        dBV

        RXTX 40/30/20
        160    -    -34 dBV
        80    -    -21
        dBV
        40    -    -16
        dBV
        30    -    -15
        dBV
        20    -    -16
        dBV

        RXTX 30/20/17
        80    -    -39
        dBV
        40    -    -23
        dBV
        30    -    -23
        dBV
        20    -    -24
        dBV
        17    -    -19
        dBV

        BTW, I am using units in dBV because it is convenient to directly relate that to the input signal level. The receiver audio output should step precisely with the RF input; one dB more RF in should give one dB more audio out. dBV is dB relative to 1.0 volt RMS and is calculated as 20*log(V1/V2).

        I hope this can help someone.

        Warren Allgyer
        9V1TD

      • David Turnbull
        Warren, attached is a plot of the filter response in your 10m RXTX. This seems to follow your numbers. While a loose BPF lets you RX the lower bands it may
        Message 3 of 7 , May 15, 2014
        • 1 Attachment
        • 72 KB
        Warren, attached is a plot of the filter response in your 10m RXTX. This seems to follow your numbers. While a loose BPF lets you RX the lower bands it may also allow, for example, the antenna noise of 30m to swamp weak signals on 10m.

        73 David AE9RB

        On Thu, May 15, 2014 at 3:20 PM, allgyer@... [softrock40] <softrock40@yahoogroups.com> wrote:

        While benchmarking my RXTX 15/17/10 build using the VOM technique that I explained in Post # 77773, I discovered, quite by accident, some interesting responses on the lower bands.

        With an input signal of -35 dBm and the LO tuned 10 KHz above the input signal, the 10 KHz audio output from my RXTX measures 0.23 VRMS (-13 dBV) at 28 MHz and 0.14 VRMS (-17 dBV) at 30 MHz. While looking for other artifacts I set my input signal to 14 MHz and tuned that. The audio output measured 0.28 VRMS, a full 2 dB more than at 10 meters! So I decided to run through the LF ham bands just out of curiosity. Here is what I found for response at the lower bands.

        160    -    Nada, zilch, nothing
        80    -    -43 dBV
        40    -    -31 dBV
        60    -    -31 dBV
        20    -    -11 dBV
        17    -    -14 dBV
        15    -    -13 dBV
        12    -    -7  dBV
        10    -    -13 dBV

        This puts the receiver performanceon 80 meters 30 dB below the 10 meter performance. While that is not great, anyone who has a noise level on 80 meters of S5 or higher would theoretically see no difference in performance between the RXTX and another receiver. And the performance just gets better as you get into the higher bands.

        So it would seem that the high band RXTX would make a quite serviceable 80 - 10 meter receiver as well as a 15 - 10 transceiver. Maybe the ideal road trip radio?

        Warren Allgyer
        9V1TD
      • warrenallgyer
        David An excellent point! And fodder for some more testing as I have just completed a high level, broadband noise generator. What I have in mind bandshaping my
        Message 4 of 7 , May 15, 2014
        • 0 Attachment
          David

          An excellent point! And fodder for some more testing as I have just completed a high level, broadband noise generator.

          What I have in mind bandshaping my noise generator (using some of your existing filter designs) for 7 and 10 MHz and then running up the noise to see what level causes the 10 meter MDS to decline.

          By the way, could I impose upon you to generate the values for one of your great bandpass filters? If you can do the 21-30 frequency range that would be great. If you need to make it more narrow that is fine too but I packaged your filters externally for 80, 60/40, and 30/20 and I find them incredibly useful. I would love to have a complete set.

          Thanks David!

          Warren Allgyer
          9V1TD
        • warrenallgyer
          David Thinking about this more, while I set up for a test, I think antenna noise at 30 meters cannot be an issue. Noise is noise. Noise at 30 meters would have
          Message 5 of 7 , May 15, 2014
          • 0 Attachment
            David

            Thinking about this more, while I set up for a test, I think antenna noise at 30 meters cannot be an issue. Noise is noise. Noise at 30 meters would have no effect on a signal at 10 meters unless it was high enough level to cause blocking. That would be nearly impossible.

            What would be possible would be for a strong 30 meter signal to cause blocking on the 10 meter signals. For the Ensemble series this would require a signal on the order of -20 to -10 dBm. Certainly not impossible and you would be correct in thinking a bandpass filter rather than a low pass filter as used in the Ensembles would help this.

            Warren Allgyer
            9V1TD
          • yl2qn_andy
            Hi, Ensemble RXTX works great WITHOUT RX BPF s/LPF s in range 40m-10m. On 80m band works reasonable well but have some inter-modulation signals. For 160m band
            Message 6 of 7 , May 16, 2014
            • 0 Attachment
              Hi,

              Ensemble RXTX works great WITHOUT RX BPF's/LPF's in range 40m-10m. On 80m band works reasonable well but have some inter-modulation signals. For 160m band do not work in my location - a lot of inter-modulation signals. Sure a good BPF's on front of RX improve performance a lot.

              Regards,
              Andy - YL2QN
            • warrenallgyer
              As they say, The proof is in the pudding I ran a parallel test on 40 meter WSPR from 18:42 to 23:10 UTC. 9V1TD was and RXTX 15/12/10 and 9V1TDR was an RXII
              Message 7 of 7 , May 16, 2014
              • 0 Attachment
                As they say, "The proof is in the pudding"

                I ran a parallel test on 40 meter WSPR from 18:42 to 23:10 UTC. 9V1TD was and RXTX 15/12/10 and 9V1TDR was an RXII HF. Both radios were connected to the same antenna via a 3dB coupler

                Over this 4+ hour period the RXII captured 16 spots. The RXTX missed 6 and had 10 identical spots with the RXII.

                Average received SNR, RXTX vs RXII: 1.2 dB
                Average received SNR on RXII for spots missed by RXTX -27 dB

                In this small sample a 38% miss rate is pretty high but the data is skewed a bit. The spots missed by the RXTX were all from one station, DH5RAE, and all came in at -27 dB on the RXII which, with 1-2 dB margin lost in the RXTX, puts them beyond my detectable noise level.

                On SSB and CW there was no detectable difference between the 2 radios. Quite acceptable performance as a 40 meter receiver by an RXTX 15/12/10.

                Warren Allgyer
                9V1TD
              Your message has been successfully submitted and would be delivered to recipients shortly.