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Re: What's the most TX power anyone has amplified an RXTX to? Just out of curiosity...

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  • warrenallgyer
    Chris I have built a number of the RXTX Ensembles and one Peaberry and have checked all of them with a spectrum analyzer. I think you need have no worries
    Message 1 of 19 , Nov 16, 2012
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      Chris

      I have built a number of the RXTX Ensembles and one Peaberry and have checked all of them with a spectrum analyzer. I think you need have no worries about taking the Softrocks exciter signal up to high power levels. It is relatively easy to get 50 dB of transmitter image rejection and the harmonics generated by the standard build are better than 40 dB down except for the cases identified in the notes for the low bands of the 80/40, 40/30/20, and 30/20/17 builds. The low bands DO need the external filter but -40 dB is easily achieved without extraordinary measures. I think the stock unit, properly aligned per Robbie's notes, will be fine.

      If you are doing SSB you will want to limit the audio drive so that the unit stays well under one watt out. Otherwise you will get non-linearity and resulting compression. And, of course, you will need to assure the follow-on amplification stages are linear. But I really see no issues. This is a solid clean design when properly aligned.

      Warren Allgyer - W8TOD

      --- In softrock40@yahoogroups.com, Chris Wilson <chris@...> wrote:

      > 16/11/2012 14:36
      >
      > As I said, I was just curious as to how much power people
      > realistically run from these things, and my thoughts were whether they
      > could be made clean enough to be unobtrusive at high power output
      > levels, or whether the fact the majority are QRP tends to hide any
      > nasties from the fellow spectrum users. Is a soundcard based SDR TX
      > bound to be dirtier than a good conventional transmitter? Or can the
      > Softrock RXTX package be amplified to serious levels without becoming
      > unsociable, and without major doctoring?
      >
      > --
      > Best Regards,
      > Chris Wilson. 2E0ILY
      >
    • warrenallgyer
      Tony I think this idea is great. I am a little concerned however about doing it with reduced drive level. I use cheap USB or built in audio cards (walking
      Message 2 of 19 , Nov 16, 2012
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        Tony

        I think this idea is great. I am a little concerned however about doing it with reduced drive level. I use cheap USB or built in audio cards (walking carefully here..... don't want to restart THAT war)... and I have found that the channel to channel levels do not always track that well as you change the overall level. So the relative audio gains at the reduced level may not be the same when you bring the drive back up and, as a result, your image rejection at operating level may suffer.

        Of course you could use external audio pads to reduce the level but that is complicated and they would need to be carefully matched as well.

        My 2 cents.

        Warren Allgyer - W8TOD

        --- In softrock40@yahoogroups.com, "Parks, Tony" <kb9yig@...> wrote:
        >
        > Good Afternoon All,
        >
        > I have done the following several time to null the TX image when using
        > Rocky 3.7 and think it works right but I would be interested in feedback,
        > positive or negative.
        >
        > Rocky 3.7 continues the RX function when in TX with the RXTX Ensemble
        > transceiver. The RX antenna connection is open to the antenna path via Q10
        > biased off. Moreover, the RX antenna connection over to the QSD circuit is
        > shorted to ground by Q11 and the QSD circuit is disabled by the /OE lines
        > of U10 being allowed to be pulled to 5 volts with Q9 off.
        >
        > What I have done is to clip a lead from the top lead of R63 to circuit
        > ground to enable the QSD circuit and get an Rocky RX spectrum display.
        > This allows the use of the Rocky TX balance adjustment to "null" the TX
        > image. It probably is necessary also to reduce the TX level output to keep
        > the RX function from saturating even with the antenna input grounded.
        >
        > Any thoughts?
        >
        > Thanks and 73,
        > Tony KB9YIG
        >
        >
        >
        > On Fri, Nov 16, 2012 at 1:28 PM, kk4dcf <oohay@...> wrote:
        >
        > > **
        > >
        > >
        > >
        > > >
        > > > Maybe, but only if you admit it:) WSPR chat scrolls off the bottom, as
        > > far as I know it gets lost. So I thought I could mention that
        > > > without accusing anybody in particular.
        > > > Don't stop trying, learn what to do. WSPR is good for QRP. Given good
        > > conditions 1 watt will reach everywhere on 40m and above. And
        > > > much less may be used successfully.
        > > >
        > >
        > > I'm certain it was me. The issue was that I built the kit with TX jumpers
        > > crossed and RX jumpers straight for PSDR and then started using linux
        > > instead. I forgot I had done that.
        > >
        > > That mistake points out to me that I do not have the equipment needed to
        > > do this. Especially the most basic testing gear, another receiver.
        > >
        > > The other major issue is that I don't have a viable home antenna. I've
        > > tried a handful of configurations and while I seem to be able to transmit
        > > decently (per WSPR and the 1 QSO I've had in the past week) the receive
        > > performance is terrible (also per WSPR and the 1 QSO). I expect to setup
        > > portable in a good open space next week to try and confirm my issues are
        > > antenna related. If that truly is the case then I'm probably just going to
        > > sell this all off and try again with a commercial rig in a few years when I
        > > move.
        > >
        > > James.
        > >
        > >
        > >
        >
      • Alan
        ... Subject: [softrock40] Re: What s the most TX power anyone has amplified an RXTX to? Just out of curiosity... ... Yes, I also have noticed variations in
        Message 3 of 19 , Nov 16, 2012
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          ----- Original Message -----
          Subject: [softrock40] Re: What's the most TX power anyone has amplified an RXTX to? Just out of curiosity...


          >I am a little concerned however about doing it with reduced drive level. I use cheap USB or built in audio cards (walking carefully
          >here..... don't want to restart THAT war)... and I have found that the channel to channel levels do not always track that well as
          >you change the overall level. So the relative audio gains at the reduced level may not be the same when you bring the drive back up
          >and, as a result, your image rejection at operating level may suffer.
          >

          Yes, I also have noticed variations in gain between channels as the volume slider, or drive slider is changed.
          Image rejection needs to be finally adjusted with these controls set for operation at maximum required output.

          I as hoping that when I tested it would not be necessary to reduce TX output. And wondering if there was a way to even further
          reduce the stray signals getting into the receiver.
          But it will be a while before I try.

          73 Alan G4ZFQ
        • irbsurfing
          Hi Chris, As well as ensuring that the image rejection is adjusted correctly you need to be sure that your soundcard is not emitting significant broadband
          Message 4 of 19 , Nov 20, 2012
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            Hi Chris,
            As well as ensuring that the image rejection is adjusted correctly you need to be sure that your soundcard is not emitting significant broadband noise.

            My setup uses an EMU USB0202 familiar to many, it works well on Rx but on Tx its noise floor is terrible, it has a high noise peak at about 10kHz which will modulate the QSE and give you strong noise peaks on each side of your carrier. Even playing music with good speakers you can hear a hiss (it might be faulty of course!).
            It measures about 20dB worse than an FT-817 in 2.7kHz BW at a 10kHz offset and consequently as it stands I would not use it on the air at all, let alone amplified to the legal limit!
            To fix it I had to change the capacitors in the QSE and add another pole of filtering. Then it was just about acceptable. It really requires some outboard filtering also. Flex Radio had issues like this in the early days and I recommended a filter in the lead from the sound card, the document is still available from their website.
            Not sure how other cards compare but I'm sure that the Delta44 for example, is much better in this respect. If you have a USB0202 find a way to check it first before going on the air!
            Andrew
            G4XZL

            --- In softrock40@yahoogroups.com, Chris Wilson <chris@...> wrote:
            >
            >
            >
            > >
            >
            > > ----- Original Message -----
            > > Subject: [softrock40] Re: What's the most TX power anyone has
            > > amplified an RXTX to? Just out of curiosity...
            >
            > > Another related question may be "What is the largest spurious
            > > signal transmitted from a Softrock, (or other SDR)."
            >
            > > On WSPR "Chat" the other day I came across someone who was
            > > transmitting without having checked his TX IQ was correct. Transmitting
            > > on the wrong frequency.
            > > He also knew nothing about setting TX IQ balance so when the IQ was
            > > set correctly his image may have been only 25dB down.
            > > If he had a fault he could have been transmitting simultaneously on
            > > both frequencies without knowing. The same as "mirrored"
            > > receiving.
            >
            > > A good understanding of what is involved is necessary before
            > > amplifying mistakes. Any soundcard SDR transmitter needs careful
            > > setting by someone who at least understands the basics. A receiver must be used to check.
            >
            > > I sometimes wonder when immediately after building a Softrock
            > > somebody says "I want more power". It took me quite a while to get a
            > > fair understanding of the Softrock and software.
            >
            > > 73 Alan G4ZFQ
            >
            >
            >
            >
            > 16/11/2012 14:36
            >
            > As I said, I was just curious as to how much power people
            > realistically run from these things, and my thoughts were whether they
            > could be made clean enough to be unobtrusive at high power output
            > levels, or whether the fact the majority are QRP tends to hide any
            > nasties from the fellow spectrum users. Is a soundcard based SDR TX
            > bound to be dirtier than a good conventional transmitter? Or can the
            > Softrock RXTX package be amplified to serious levels without becoming
            > unsociable, and without major doctoring?
            >
            > --
            > Best Regards,
            > Chris Wilson. 2E0ILY
            >
          • Alan
            ... Subject: [softrock40] Re: What s the most TX power anyone has amplified an RXTX to? Just out of curiosity... ... Andrew, If it is your 0202 and not
            Message 5 of 19 , Nov 20, 2012
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              ----- Original Message -----
              Subject: [softrock40] Re: What's the most TX power anyone has amplified an RXTX to? Just out of curiosity...


              >
              >
              > Hi Chris,
              > As well as ensuring that the image rejection is adjusted correctly you need to be sure that your soundcard is not emitting
              > significant broadband noise.
              >
              > My setup uses an EMU USB0202 familiar to many, it works well on Rx but on Tx its noise floor is terrible, it has a high noise peak
              > at about 10kHz which will modulate the QSE and give you strong noise peaks on each side of your carrier.

              Andrew,

              If it is your 0202 and not anything else then it must be faulty.
              Many use that, I'm sure it would have been mentioned by now.
              Here http://g4zfq.alotspace.com/RightMarkTests/E-MUTrackerPre%20_%20USB192.htm is my test on a Tracker Pre. This is basically a 0202
              with preamp, not used of course.

              A soundcard must be bad to seriously affect a transmit signal. As long as it is not overdriven I would expect noise and hum to be
              well below the signal level.

              73 Alan G4ZFQ


              Even playing music with good speakers you can hear a hiss (it might be faulty of course!).
              > It measures about 20dB worse than an FT-817 in 2.7kHz BW at a 10kHz offset and consequently as it stands I would not use it on the
              > air at all, let alone amplified to the legal limit!
              > To fix it I had to change the capacitors in the QSE and add another pole of filtering. Then it was just about acceptable. It
              > really requires some outboard filtering also. Flex Radio had issues like this in the early days and I recommended a filter in the
              > lead from the sound card, the document is still available from their website.
              > Not sure how other cards compare but I'm sure that the Delta44 for example, is much better in this respect. If you have a USB0202
              > find a way to check it first before going on the air!
            • irbsurfing
              Hello Alan, Well, as I said mine might be faulty! I was shocked at how bad it was. I will try running the Rightmark Analyser and see how it compares to your
              Message 6 of 19 , Nov 21, 2012
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                Hello Alan,
                Well, as I said mine might be faulty! I was shocked at how bad it was.
                I will try running the Rightmark Analyser and see how it compares to your Tracker Pre, thanks for posting the links. I will report back.
                Thanks,
                Andrew

                --- In softrock40@yahoogroups.com, "Alan" <alan4alan@...> wrote:
                >
                >
                > ----- Original Message -----
                > Subject: [softrock40] Re: What's the most TX power anyone has amplified an RXTX to? Just out of curiosity...
                >
                >
                > >
                > >
                > > Hi Chris,
                > > As well as ensuring that the image rejection is adjusted correctly you need to be sure that your soundcard is not emitting
                > > significant broadband noise.
                > >
                > > My setup uses an EMU USB0202 familiar to many, it works well on Rx but on Tx its noise floor is terrible, it has a high noise peak
                > > at about 10kHz which will modulate the QSE and give you strong noise peaks on each side of your carrier.
                >
                > Andrew,
                >
                > If it is your 0202 and not anything else then it must be faulty.
                > Many use that, I'm sure it would have been mentioned by now.
                > Here http://g4zfq.alotspace.com/RightMarkTests/E-MUTrackerPre%20_%20USB192.htm is my test on a Tracker Pre. This is basically a 0202
                > with preamp, not used of course.
                >
                > A soundcard must be bad to seriously affect a transmit signal. As long as it is not overdriven I would expect noise and hum to be
                > well below the signal level.
                >
                > 73 Alan G4ZFQ
                >
                >
                > Even playing music with good speakers you can hear a hiss (it might be faulty of course!).
                > > It measures about 20dB worse than an FT-817 in 2.7kHz BW at a 10kHz offset and consequently as it stands I would not use it on the
                > > air at all, let alone amplified to the legal limit!
                > > To fix it I had to change the capacitors in the QSE and add another pole of filtering. Then it was just about acceptable. It
                > > really requires some outboard filtering also. Flex Radio had issues like this in the early days and I recommended a filter in the
                > > lead from the sound card, the document is still available from their website.
                > > Not sure how other cards compare but I'm sure that the Delta44 for example, is much better in this respect. If you have a USB0202
                > > find a way to check it first before going on the air!
                >
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