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Re: [softrock40] Re: Mini-Circuits

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  • Dave
    Leon: You could try this group or other Yahoo groups such as UHFSDR, ARRLHBC. Dave -WB6DHW
    Message 1 of 19 , Oct 12, 2012
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      Leon:
        You could try this group or other Yahoo groups such as UHFSDR, ARRLHBC.

      Dave -WB6DHW
      <http://wb6dhw.com>

      On 10/12/2012 5:55 AM, electricham@... wrote:
       

      Leon,

      Thanks loads for the feedback! I was wondering about a bulk order and then selling what I didn't need. Do you have a recommendation on where to try to get interest in a batch order from other HAM's or do you just talk to the HAM's you know personally?

      Thanks!
      73

      --- In softrock40@yahoogroups.com, Leon Heller <leon355@...> wrote:
      >
      > On 12/10/2012 04:14, electricham@... wrote:
      > > All,
      > >
      > > I hope this is not too off topic, but I was hoping to get an idea on
      > > where you guys get your Minicircuits parts? Sometimes they offer the
      > > part I need but only in larger quantities. Clearly, this is a problem!
      > > :-) I have seen many kits out there with these parts, so I know I'm not
      > > the only one off Guy out there.
      >
      > I buy what I need direct from MCL UK. On one or two occasions I've
      > bought 50 pieces, and sold the excess to fellow hams, to get the cost
      > down. I didn't have any problems getting rid of them.
      >
      > 73, Leon
      > --
      > Leon Heller
      > G1HSM
      >


    • John
      I was reading one of DG8SAQ s pages http://www.mydarc.de/dg8saq/switchimpedance/index.shtml where he measures the input impedance to the RX mixer. On the same
      Message 2 of 19 , Oct 14, 2012
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        I was reading one of DG8SAQ's pages http://www.mydarc.de/dg8saq/switchimpedance/index.shtml where he measures the input impedance to the RX mixer.
        On the same page he mentions replacing the two 10 Ohm resistors on the mixer inputs with shorting links.
         
        I have just tried this with the folowing result:
         
        With the two 10 Ohm resistors:
         
        Frequency 1.977 MHz
        With a 50 Ohm resistor connected to the SoftRock antenna input HDSDR noise peaks are about -125dB
        With a signal generator set to -93 dBm connected to the SoftRock antenna input the signal peak is about -110 dB 
         
         
        Without the two 10 Ohm resisors:
         
        Frequency 1.977 MHz
        With a 50 Ohm resistor connected to the SoftRock antenna input HDSDR noise peaks are about -125dB
        With a signal generator set to -93 dBm connected to the SoftRock antenna input the signal peak is about -104 dB
         
        This appears to have improved signal + noise / noise ratio by 6 dB
         
        Has anyone else tried this?
         
        John G3UGY
      • David Turnbull
        Hi John, Don t forget that changing these resistor values will alter the filter response. 73 David AE9RB http://AE9RB.com/
        Message 3 of 19 , Oct 14, 2012
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          Hi John,

          Don't forget that changing these resistor values will alter the filter response.

          73 David AE9RB
          http://AE9RB.com/

          On Sun, Oct 14, 2012 at 10:01 AM, John <v321uk@...> wrote:
          I was reading one of DG8SAQ's pages http://www.mydarc.de/dg8saq/switchimpedance/index.shtml where he measures the input impedance to the RX mixer.
          On the same page he mentions replacing the two 10 Ohm resistors on the mixer inputs with shorting links.

        • Alan
          ... Subject: [softrock40] RXTX v6.3 improved signal to noise John, I m no expert but what is the noise you see on HDSDR? I suspect it is op-amp noise.
          Message 4 of 19 , Oct 14, 2012
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            ----- Original Message -----
            Subject: [softrock40] RXTX v6.3 improved signal to noise

            John,

            I'm no expert but what is the noise you see on HDSDR?
            I suspect it is op-amp noise.
            Certainly on lower frequencies antenna noise overcomes this.
            Removing the 10Rs will increase the front end gain without altering the op-amp noise.
            Seems to me that you are measuring the wrong SNR?

            73 Alan G4ZFQ




            >I was reading one of DG8SAQ's pages http://www.mydarc.de/dg8saq/switchimpedance/index.shtml where he measures the input impedance
            >to the RX mixer.
            On the same page he mentions replacing the two 10 Ohm resistors on the mixer inputs with shorting links.

            I have just tried this with the folowing result:

            With the two 10 Ohm resistors:

            Frequency 1.977 MHz
            With a 50 Ohm resistor connected to the SoftRock antenna input HDSDR noise peaks are about -125dB
            With a signal generator set to -93 dBm connected to the SoftRock antenna input the signal peak is about -110 dB


            Without the two 10 Ohm resisors:

            Frequency 1.977 MHz
            With a 50 Ohm resistor connected to the SoftRock antenna input HDSDR noise peaks are about -125dB
            With a signal generator set to -93 dBm connected to the SoftRock antenna input the signal peak is about -104 dB

            This appears to have improved signal + noise / noise ratio by 6 dB
          • John
            Alan, Those 10 ohm resistors before the mixer are dropping precious nanovolts of wanted signal. Worsening signal to noise ratio. John G3UGY From: Alan Sent:
            Message 5 of 19 , Oct 15, 2012
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              Alan,
               
              Those 10 ohm resistors before the mixer are dropping precious nanovolts of wanted signal. Worsening signal to noise ratio.
               
              John G3UGY
               

              From: Alan
              Sent: Sunday, October 14, 2012 7:23 PM
              Subject: Re: [softrock40] RXTX v6.3 improved signal to noise

               


              ----- Original Message -----
              Subject: [softrock40] RXTX v6.3 improved signal to noise

              John,

              I'm no expert but what is the noise you see on HDSDR?
              I suspect it is op-amp noise.
              Certainly on lower frequencies antenna noise overcomes this.
              Removing the 10Rs will increase the front end gain without altering the op-amp noise.
              Seems to me that you are measuring the wrong SNR?

              73 Alan G4ZFQ

              >I was reading one of DG8SAQ's pages http://www.mydarc.de/dg8saq/switchimpedance/index.shtml where he measures the input impedance
              >to the RX mixer.
              On the same page he mentions replacing the two 10 Ohm resistors on the mixer inputs with shorting links.

              I have just tried this with the folowing result:

              With the two 10 Ohm resistors:

              Frequency 1.977 MHz
              With a 50 Ohm resistor connected to the SoftRock antenna input HDSDR noise peaks are about -125dB
              With a signal generator set to -93 dBm connected to the SoftRock antenna input the signal peak is about -110 dB

              Without the two 10 Ohm resisors:

              Frequency 1.977 MHz
              With a 50 Ohm resistor connected to the SoftRock antenna input HDSDR noise peaks are about -125dB
              With a signal generator set to -93 dBm connected to the SoftRock antenna input the signal peak is about -104 dB

              This appears to have improved signal + noise / noise ratio by 6 dB

            • John
              Hi David, The stock band pass filters are broad. The response on the spectrum analyzer and tracking generator looks the same shape as with the
              Message 6 of 19 , Oct 15, 2012
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                Hi David,
                 
                The stock band pass filters are <extremely> broad.
                The response on the spectrum analyzer and tracking generator looks the same shape as with the resistors.
                 
                John G3UGY
                 

                Sent: Sunday, October 14, 2012 7:12 PM
                Subject: Re: [softrock40] RXTX v6.3 improved signal to noise

                 

                Hi John,


                Don't forget that changing these resistor values will alter the filter response.

                73 David AE9RB
                http://AE9RB.com/

                On Sun, Oct 14, 2012 at 10:01 AM, John <v321uk@...> wrote:
                I was reading one of DG8SAQ's pages http://www.mydarc.de/dg8saq/switchimpedance/index.shtml where he measures the input impedance to the RX mixer.
                On the same page he mentions replacing the two 10 Ohm resistors on the mixer inputs with shorting links.

              • Alan
                ... Subject: Re: [softrock40] RXTX v6.3 improved signal to noise ... John, It does not seem that simple to me. My initial thought was After many years of
                Message 7 of 19 , Oct 15, 2012
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                  ----- Original Message -----
                  Subject: Re: [softrock40] RXTX v6.3 improved signal to noise


                  >Those 10 ohm resistors before the mixer are dropping precious nanovolts of wanted signal. Worsening signal to noise ratio.

                  John,

                  It does not seem that simple to me.
                  My initial thought was "After many years of Softrocks how could this be?"
                  6dB is a big difference.
                  From a practical point of view with a Softrock connected to a good antenna what difference will it make?
                  On a sufficiently sensitive low noise receiver SNR is established at the antenna input. Signal/atmospheric etc. noise. Provided the
                  receiver adds no noise the SNR is fixed. Indeed with the lower frequencies an attenuator can be used with no effect on SNR. Tony
                  uses attenuators in the Ensemble RX.

                  Now, maybe on the higher frequencies a Softrock might need to be a little more sensitive. I understand this is sometimes done by
                  using a low noise card and reducing op-amp gain. So why, apart from Tom, has nobody suggested removing the resistors?
                  What are they doing? Is there something else that is degraded if they are removed? Are they an integral part of the mixer?

                  73 Alan G4ZFQ
                • John
                  Alan, If I get a chance I will put the resistors back in and measure the minimum detectable signal and compare. DG8SAQ also mentions that the impedance looking
                  Message 8 of 19 , Oct 15, 2012
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                    Alan,
                     
                    If I get a chance I will put the resistors back in and measure the minimum detectable signal and compare.
                     
                    DG8SAQ also mentions that the impedance looking into the mixer is closer to 50 Ohms without the resistors than with them as measured on his vector network analyzer. 
                     
                    John
                  • Milt Cram
                    ... Hi All, Shouldn t impedance matching be done with reactive components (transformers, capacitors and inductors)? If the 10 ohm resistors are being used for
                    Message 9 of 19 , Oct 15, 2012
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                      On 10/14/2012 12:01 PM, John wrote:
                      I was reading one of DG8SAQ's pages http://www.mydarc.de/dg8saq/switchimpedance/index.shtml where he measures the input impedance to the RX mixer.
                      On the same page he mentions replacing the two 10 Ohm resistors on the mixer inputs with shorting links.
                       
                      I have just tried this with the folowing result:
                       
                      With the two 10 Ohm resistors:
                       
                      Frequency 1.977 MHz
                      With a 50 Ohm resistor connected to the SoftRock antenna input HDSDR noise peaks are about -125dB
                      With a signal generator set to -93 dBm connected to the SoftRock antenna input the signal peak is about -110 dB 
                       
                       
                      Without the two 10 Ohm resisors:
                       
                      Frequency 1.977 MHz
                      With a 50 Ohm resistor connected to the SoftRock antenna input HDSDR noise peaks are about -125dB
                      With a signal generator set to -93 dBm connected to the SoftRock antenna input the signal peak is about -104 dB
                       
                      This appears to have improved signal + noise / noise ratio by 6 dB
                       
                      Has anyone else tried this?
                       
                      John G3UGY

                      Hi All,

                      Shouldn't impedance matching be done with reactive components (transformers, capacitors and inductors)?  If the 10 ohm resistors are being used for impedance matching, they will both attenuate the signal, and contribute noise power.  This will reduce the S/N.  Removing them should improve S/N....?  If necessary, adjust the turns ratio of the input transformer to provide the impedance match.

                      73, Milt
                      W8NUE
                    • John
                      Agreed... John G3UGY Hi All, Shouldn t impedance matching be done with reactive components (transformers, capacitors and inductors)? If the 10 ohm resistors
                      Message 10 of 19 , Oct 15, 2012
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                        Agreed... John G3UGY
                         
                         
                        Hi All,

                        Shouldn't impedance matching be done with reactive components (transformers, capacitors and inductors)?  If the 10 ohm resistors are being used for impedance matching, they will both attenuate the signal, and contribute noise power.  This will reduce the S/N.  Removing them should improve S/N....?  If necessary, adjust the turns ratio of the input transformer to provide the impedance match.

                        73, Milt
                        W8NUE
                      • Milt Cram
                        ... Additional comments regarding the 10 ohm resistors-- I m guessing that the 10 ohm resistors are also used to swamp the variations in the on-resistance of
                        Message 11 of 19 , Oct 15, 2012
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                          On 10/14/2012 12:01 PM, John wrote:
                          I was reading one of DG8SAQ's pages http://www.mydarc.de/dg8saq/switchimpedance/index.shtml where he measures the input impedance to the RX mixer.
                          On the same page he mentions replacing the two 10 Ohm resistors on the mixer inputs with shorting links.
                           
                          I have just tried this with the folowing result:
                           
                          With the two 10 Ohm resistors:
                           
                          Frequency 1.977 MHz
                          With a 50 Ohm resistor connected to the SoftRock antenna input HDSDR noise peaks are about -125dB
                          With a signal generator set to -93 dBm connected to the SoftRock antenna input the signal peak is about -110 dB 
                           
                           
                          Without the two 10 Ohm resisors:
                           
                          Frequency 1.977 MHz
                          With a 50 Ohm resistor connected to the SoftRock antenna input HDSDR noise peaks are about -125dB
                          With a signal generator set to -93 dBm connected to the SoftRock antenna input the signal peak is about -104 dB
                           
                          This appears to have improved signal + noise / noise ratio by 6 dB
                           
                          Has anyone else tried this?
                           
                          John G3UGY

                          Additional comments regarding the 10 ohm resistors--

                          I'm guessing that the 10 ohm resistors are also used to swamp the variations in the "on-resistance" of the switches.  At low HF frequencies, external noise probably dominates the S/N and the resistors "stabilize" the input impedance.  At higher frequencies, it would seem desirable to eliminate, as much as possible, resistors in the input circuitry.

                          73, Milt
                          W8NUE
                        • Kees & Sandy
                          I agree. Any input impedance matching to the antenna will help and the VNA is a good tool to find out, but I assumed those resistors were in there also to
                          Message 12 of 19 , Oct 15, 2012
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                            I agree. Any input impedance matching to the antenna will help and the VNA is a good tool to find out, but I assumed those resistors were in there also to maintain balance between the two inputs. Since you can have some resistance variation between the two FET switches, windings, etc adding 10 ohms will swamp those values. Another approach might be to take a good commercial input RF transformer from someone like Mini-Circuits and use it. You can also parallel FETs to "average" the resistance variation. As Milt suggests, you can adjust the turns ratio and then reduce the 10 ohm resistance so you see 50 ohms with the VNA. Another item that I've found makes a difference is to use bifilar wire for the secondary. Regardless of how much/little you twist the wires, it's not as good as bifilar wire.
                             
                            73 Kees K5BCQ


                            ---------- Original Message ----------
                            From: Milt Cram <w8nue@...>
                            To: softrock40@yahoogroups.com
                            Subject: Re: [softrock40] RXTX v6.3 improved signal to noise
                            Date: Mon, 15 Oct 2012 09:21:55 -0500

                             

                            On 10/14/2012 12:01 PM, John wrote:
                            I was reading one of DG8SAQ's pages http://www.mydarc.de/dg8saq/switchimpedance/index.shtml where he measures the input impedance to the RX mixer.
                            On the same page he mentions replacing the two 10 Ohm resistors on the mixer inputs with shorting links.
                             
                            I have just tried this with the folowing result:
                             
                            With the two 10 Ohm resistors:
                             
                            Frequency 1.977 MHz
                            With a 50 Ohm resistor connected to the SoftRock antenna input HDSDR noise peaks are about -125dB
                            With a signal generator set to -93 dBm connected to the SoftRock antenna input the signal peak is about -110 dB 
                             
                             
                            Without the two 10 Ohm resisors:
                             
                            Frequency 1.977 MHz
                            With a 50 Ohm resistor connected to the SoftRock antenna input HDSDR noise peaks are about -125dB
                            With a signal generator set to -93 dBm connected to the SoftRock antenna input the signal peak is about -104 dB
                             
                            This appears to have improved signal + noise / noise ratio by 6 dB
                             
                            Has anyone else tried this?
                             
                            John G3UGY

                            Additional comments regarding the 10 ohm resistors--

                            I'm guessing that the 10 ohm resistors are also used to swamp the variations in the "on-resistance" of the switches.  At low HF frequencies, external noise probably dominates the S/N and the resistors "stabilize" the input impedance.  At higher frequencies, it would seem desirable to eliminate, as much as possible, resistors in the input circuitry.

                            73, Milt
                            W8NUE

                             

                             

                          • vbifyz
                            ... I agree with Milt. Shorting these resistors will improve SNR, but may degrade image rejection. There is a tradeoff, which is also frequency dependent. 73,
                            Message 13 of 19 , Oct 15, 2012
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                              --- In softrock40@yahoogroups.com, Milt Cram <w8nue@...> wrote:
                              >

                              > Additional comments regarding the 10 ohm resistors--
                              >
                              > I'm guessing that the 10 ohm resistors are also used to swamp the
                              > variations in the "on-resistance" of the switches. At low HF
                              > frequencies, external noise probably dominates the S/N and the resistors
                              > "stabilize" the input impedance. At higher frequencies, it would seem
                              > desirable to eliminate, as much as possible, resistors in the input
                              > circuitry.
                              >
                              > 73, Milt
                              > W8NUE
                              >

                              I agree with Milt. Shorting these resistors will improve SNR, but may degrade image rejection. There is a tradeoff, which is also frequency dependent.

                              73, Mike
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