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Re: phase noise specifications

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  • Scotty
    Hi Swetterlin and all, When looking at a phase noise graph, always look to see what resolution bandwidth in which they are taking the measurement. You must
    Message 1 of 20 , Jun 24, 2005
      Hi Swetterlin and all,
      When looking at a phase noise graph, always look to see what
      resolution bandwidth in which they are taking the measurement. You
      must convert the measurement BW to a 1 Hz BW for a dBc/Hz number. For
      example, their graph is claiming a phase noise -101.3 dBm/Hz at 10
      KHz. They have their Res BW at 300 Hz. Convert 300 Hz to 1 Hz: 300
      Hz bw= 10Log300= 24.77 This means that the noise power in a 300 Hz
      bandwidth is 24.77 dB greater than the noise measured in a 1 Hz
      bandwidth. The plotted graph line is about -77 dBc at 10 KHz.
      Subtract the 1 Hz bw (in dB) from the graph measurement: -77dBc -
      24.7 dB = -101.77 dBc/Hz. This is how they get their correct number.
      If anyone who wishes to buy and construct this PLL approach using
      the PNP-1500-P22, I will add this option to the software for the
      SSA's. Let me know. Wouldn't mind trying this myself, if I had one,
      of course. You wanna buy several and send me a sample (grin)?
      Cheers, Scotty

      --- In spectrumanalyzer@yahoogroups.com, "swetterlin"
      <swetterlin@m...> wrote:
      > Regarding the PNP-1500-P22. How do they get phase noise measurements
      > of -90,-100 ... when their graphs all show the noise level at 75-80
      > db below the peak?
      >
      > Also, the level of spurs may be more important than the phase noise,
      > since this part would be used broadband and couln't be run through a
      > narrowband filter.
      >
      > Still, it is nice to see that someone is combining the PLL and VCO in
      > a single unit with a simple interface.
      >
      > Sam W
    • swetterlin
      Hi Scotty I tried out the SRD approach and thought I was getting marginal phase noise quality with -85dbc at 1kHz, -95 at 10kHz, but it turns out with the
      Message 2 of 20 , Jun 24, 2005
        Hi Scotty
        I tried out the SRD approach and thought I was getting marginal phase
        noise quality with -85dbc at 1kHz, -95 at 10kHz, but it turns out with
        the bandwidth correction the real numbers are -100 and -110. Not so bad.

        Your explanation makes sense for truly random noise--on a spectrum
        analyzer, as you narrow the RBW the noise drops. But as for spurs,
        which are not random but represent noise at precise frequencies, the
        peak level will not drop as you narrow the RBW--you will just get a
        narrower and narrower peak and the peak will start to stick out well
        above the surrounding noise level. Their data sheet states spurs are
        -60 to -80 dbc depending on step size. Doesn't that level of spurs
        create a problem? For example, if you are tuned to 500MHz and there
        is a -60dbc spur at 1MHz above the tuned LO signal, your IF signal
        will contain a small piece of any signal at 501MHz. If there is no
        actual signal at 500 but a 0dbm signal at 501, it will appear as
        though there is a -60dbm signal at 500MHz.

        Sam W

        --- In spectrumanalyzer@yahoogroups.com, "Scotty" <wsprowls@y...> wrote:
        > Hi Swetterlin and all,
        > When looking at a phase noise graph, always look to see what
        > resolution bandwidth in which they are taking the measurement. You
        > must convert the measurement BW to a 1 Hz BW for a dBc/Hz number. > >
      • william sprowls
        Hi Swetterlin, True, spurs are not noise and are treated as real signals in a spectrum analyzer. If a local oscillator has spurs, they are always relative to
        Message 3 of 20 , Jun 24, 2005
          Hi Swetterlin,
          True, spurs are not noise and are treated as real
          signals in a spectrum analyzer. If a local oscillator
          has spurs, they are always relative to the frequency
          of oscillation. Most spurs created within a PLL are
          harmonics of the phase detector frequency (PDF). If
          the PLL's PDF is running at 300 KHz and the PLL's VCO
          is at 1000 MHz, there will be two spurs, 300 KHz above
          and below the carrier frequency of 1000 MHz, or
          999.700 MHz and 1000.300 MHz. There will also be
          spurs at the harmonics of 300 KHz away from the
          carrier. For example, 1000.3000 MHz (1st harmonic),
          1000.600 MHz (second harmonic), 1001.200 MHz (third
          harmonic), etc. As you go further away from the
          carrier, these spurs will become lower in amplitude.
          Theoretically, if a PLL had a perfect loop bandwidth,
          that is, any frequency above its 0 gain crossover had
          high attenuation, there would be no PDF spurs at all.
          In most cases, and in the SSA, the first PDF spur is
          the only one that can be seen. In the SSA's PLL 1,
          with a PDF of 356 KHz, the PDF first harmonic spur is
          about -70 dBc (relative to the carrier).
          Now, does this create a problem in measurement?
          When there is a real signal entering a mixing action
          with a local oscillator (that has spurs), the
          resulting I.F. signal will have the identical spur
          relationship. Example: If we have a 1000 MHz LO (with
          spurs at 999.7 MHz and 1000.3 MHz) and it is mixed
          with a real signal at 1050 MHz (perfect signal with no
          noise or spurs). The IF freq of 50 MHz will have
          spurs at 49.7 MHz and 50.3 MHz. The IF spur
          amplitudes, relative to the carrier, will have the
          same spur amplitude relationship as it was in the LO.
          In the case of the SSA, the spurs on each side of the
          IF signal will be -70 dBc. So, yes, these spurs can
          cause confusion if you are not prepared to deal with
          them.
          If the LO is mixing with no other signal, there will
          be no spurs created in the IF. As a matter of fact,
          the only thing in the IF will be converted noise.
          Remember, PDF spurs are relative to the carrier. A
          PLL running at a PDF of 300 KHz will NOT produce spurs
          at 300 KHz (relative to 0 MHz) and its harmonics.
          That is, there will be no created spurs at 300 KHz,
          600 KHz, etc. Therefore, if no signal enters the SSA,
          there will not be a PDF spur shown on the Graph.
          In the case of the SSA, the dynamic range
          (amplitude) is about 80 dB. If a very large (and
          clean) signal entered the SSA and created a maximum
          resonse at the top of the scale, the PDF spurs would
          be 70 dB below that. You would see the spur responses
          in the lowest portion of the scale, along with the
          baseline noise.
          I am in the process of changing the SSA software to
          include a "spur test" button. When clicked, the PDF
          will change in frequency. Real signals will remain at
          the same position of the graph, spurs will move or
          dissappear. It is for the operator who is ever in
          doubt whether a signal is real, or it is a spur
          created within the SSA.
          Cheers, Scotty



          --- swetterlin <swetterlin@...> wrote:

          > Hi Scotty
          > I tried out the SRD approach and thought I was
          > getting marginal phase
          > noise quality with -85dbc at 1kHz, -95 at 10kHz, but
          > it turns out with
          > the bandwidth correction the real numbers are -100
          > and -110. Not so bad.
          >
          > Your explanation makes sense for truly random
          > noise--on a spectrum
          > analyzer, as you narrow the RBW the noise drops.
          > But as for spurs,
          > which are not random but represent noise at precise
          > frequencies, the
          > peak level will not drop as you narrow the RBW--you
          > will just get a
          > narrower and narrower peak and the peak will start
          > to stick out well
          > above the surrounding noise level. Their data sheet
          > states spurs are
          > -60 to -80 dbc depending on step size. Doesn't that
          > level of spurs
          > create a problem? For example, if you are tuned to
          > 500MHz and there
          > is a -60dbc spur at 1MHz above the tuned LO signal,
          > your IF signal
          > will contain a small piece of any signal at 501MHz.
          > If there is no
          > actual signal at 500 but a 0dbm signal at 501, it
          > will appear as
          > though there is a -60dbm signal at 500MHz.
          >
          > Sam W
          >
          > --- In spectrumanalyzer@yahoogroups.com, "Scotty"
          > <wsprowls@y...> wrote:
          > > Hi Swetterlin and all,
          > > When looking at a phase noise graph, always look
          > to see what
          > > resolution bandwidth in which they are taking the
          > measurement. You
          > > must convert the measurement BW to a 1 Hz BW for a
          > dBc/Hz number. > >
          >
          >
          >




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        • John Miles
          Well, the UMS-2150-R16 VCOs showed up today from Avnet. Very good service from them, although I still don t know how much I paid for S&H, which scares me!
          Message 4 of 20 , Jun 27, 2005
            Well, the UMS-2150-R16 VCOs showed up today from Avnet.  Very good service from them, although I still don't know how much I paid for S&H, which scares me!
             
            Composite noise comparisons in my hybrid DDS/PLL synth are as follows.  Blue = the UMS part, purple = the Mini-Circuits ROS-2150VW that I normally use for coverage between 1-2 GHz.
             
             
            The marker is at 10 kHz, 3 kHz, and 300 Hz from the 1200-MHz carrier, respectively.  Loop bandwidth is approximately 2500 Hz.
             
            Executive summary is that the UMS VCO's performance is close to identical to the ROS part within and near the loop bandwidth (as expected), but approximately 3 dB *worse* at 10 kHz.  This was NOT expected, given its data-sheet specs.
             
            Actual results at 10 kHz were -90.3 dBc/Hz for the ROS-2150 and -87.3 dBc/Hz for the UMS-2150.
             
            This is not a scientific test -- it only used one sample, and there's a 300-mA DDS chip right next to the PLL circuit on my board that could theoretically raise the noise floor of every part on the board.  However, I did conduct three additional tests to sanity-check the 10-kHz result. 
             
            First, I redesigned the loop filter for 1250 Hz, to make sure that the measurement at the 10-kHz offset was being made well outside the loop bandwidth.  That earned an improvement of about 3 dB, pretty much as expected.  (The equations I use for this synthesizer tend to result in a somewhat wider-than-predicted loop bandwidth.)  The two VCOs were now competitive at 10 kHz from the carrier, but at the cost of a large (4.7 uF) cap in the loop filter and significantly-increased lock times.
             
            Next, I disabled the AD9852 DDS by yanking its clock signal, and fed a 10.7-MHz reference signal directly into the PLL from an HP 8657A signal generator.  This had no effect on the 10-kHz noise level.
             
            Finally, recognizing that the higher power output from the UMS VCO was exceeding the recommended input power spec of the ADF4112 PLL chip's prescaler, I used a larger voltage divider ratio between the VCO and PLL chip to drop the signal by several dB.  This had no effect on either the in-band or out-of-band noise.
             
            I can't condemn the UMS part with 100% certainty, of course, but based on my tests, it offers no significant noise advantage over the Mini-Circuits ROS-2150VW.
             
            -- john, KE5FX
            -----Original Message-----
            From: John Miles [mailto:jmiles@...]
            Sent: Thursday, June 23, 2005 1:12 PM
            To: spectrumanalyzer@yahoogroups.com
            Subject: RE: [spectrumanalyzer] phase noise specifications

            OK, Google finally came through: http://www.vco1.com/UMS.html .  Looks like the part number competitive with the ROS-2150VW is actually the UMS-2150-R16.
             
            This is a 12-volt part (as opposed to the ROS's 5-volt rating.)  It puts out a lot more power (+11 dBm as opposed to +4), and its second-harmonic spec is about 5 dB better.  Pinout *appears* to be the same, although the ROS's layout is pad-oriented while the UMS data sheet seems to be device-oriented.
             
            I called the Avnet 800# on their page at http://www.vco1.com/DomesticSales.html and ordered 5 of them at $27.95 each via credit card.  Very painless process.  That is $2 cheaper than Mini-Circuits' price of $29.95 each for the ROS-2150VW! 
             
            They sound like a no-brainer replacement for anyone who is using the ROS-2150VW and can supply 12V instead of 5V on Vcc.  I will post some noise comparisons next week assuming the parts show up when promised.  Much appreciate the tip!
             
            -- john, KE5FX
             
            -----Original Message-----
            From: spectrumanalyzer@yahoogroups.com [mailto:spectrumanalyzer@yahoogroups.com]On Behalf Of John Miles
            Sent: Thursday, June 23, 2005 12:44 PM
            To: spectrumanalyzer@yahoogroups.com
            Subject: RE: [spectrumanalyzer] phase noise specifications

            Hmm.  Where do you get those UMS-1283-R16 VCOs?  Who makes them?  Same footprint as the ROS-2150VW? 
             
            That's actually a pretty meaningful improvement, but Google seems to be failing me. 
             
            If you have any to sell, and they match the ROS-2150VW's frequency coverage range and PCB footprint, let me know and I will PayPal you for a couple. 
             
            -- john KE5FX
            -----Original Message-----
            From: spectrumanalyzer@yahoogroups.com [mailto:spectrumanalyzer@yahoogroups.com]On Behalf Of S. Cash Olsen
            Sent: Thursday, June 23, 2005 12:37 PM
            To: spectrumanalyzer@yahoogroups.com
            Subject: [spectrumanalyzer] phase noise specifications

            Scotty,

            I am evaluating the specs of some alternative VCO . How much will a 5dB
            better number in the phase noise make in the overall quality of the SSA.
            For example:


            Typ. Phase Noise      1kHz      10kHz      100kHz      1mHz
            ROS-2150VW            -70      -96      -118      -138
            UMS-1283-R16      -75      102      -122      -143

            Is the first or second oscillator more significant in contributing to the
            overall preformance?

            Would this be worth a significant price difference? I so how much, or would
            there be any reason to have a high performance option at some premium in price.

            Cash

          • S. Cash Olsen
            Great work John, so much for that idea. Cash
            Message 5 of 20 , Jun 28, 2005
              Great work John, so much for that idea.

              Cash
            • John Miles
              There are still some things I want to check -- these VCOs have more tuning sensitivity than the ROS parts, so I want to make sure I m not limited by opamp
              Message 6 of 20 , Jun 28, 2005
                There are still some things I want to check -- these VCOs have more tuning sensitivity than the ROS parts, so I want to make sure I'm not limited by opamp output noise.  I use the LT1677, which is pretty quiet, but you never know until you crunch the numbers.  More later, maybe...
                 
                -- john, KE5FX
                -----Original Message-----
                From: spectrumanalyzer@yahoogroups.com [mailto:spectrumanalyzer@yahoogroups.com]On Behalf Of S. Cash Olsen
                Sent: Tuesday, June 28, 2005 6:32 AM
                To: spectrumanalyzer@yahoogroups.com
                Subject: [spectrumanalyzer] UMS-2150 VCO versus ROS-2150VW

                Great work John, so much for that idea.

                Cash

              • John Miles
                I messed around with the synth a little more this morning, and was able to get the 10 kHz noise down to -94.3 dBc/Hz by redesigning it with a passive loop
                Message 7 of 20 , Jun 28, 2005
                  I messed around with the synth a little more this morning, and was able to
                  get the 10 kHz noise down to -94.3 dBc/Hz by redesigning it with a passive
                  loop filter via ADIsimPLL. But that seems to be as good as I can do,
                  regardless of the reference (DDS, HP 8657A, or 10 MHz from the back of the
                  8566).

                  These parts may reach their stated specs under absolutely-ideal conditions,
                  but I was unable to come anywhere near those conditions on the bench.
                  Frankly, some aspects of their claims (e.g., improving the phase noise while
                  at the same time increasing the KVco MHz/V figure) don't pass the sniff
                  test. It would be interesting to see an eval board from Universal Microwave
                  that would allow independent verification.

                  Cash, I *definitely* would encourage you to confirm or dispute my results
                  with your boards, rather than giving up. Send me your snail-mail address,
                  if you like, and I'll send you one of the VCOs. I have four left, and
                  they're unlikely to get used as long as I don't know why the ROS-2150VW
                  beats them!

                  -- john, KE5FX


                  -----Original Message-----
                  From: John Miles [mailto:jmiles@...]
                  Sent: Tuesday, June 28, 2005 7:58 AM
                  To: spectrumanalyzer@yahoogroups.com
                  Subject: RE: [spectrumanalyzer] UMS-2150 VCO versus ROS-2150VW


                  There are still some things I want to check -- these VCOs have more tuning
                  sensitivity than the ROS parts, so I want to make sure I'm not limited by
                  opamp output noise. I use the LT1677, which is pretty quiet, but you never
                  know until you crunch the numbers. More later, maybe...

                  -- john, KE5FX
                  -----Original Message-----
                  From: spectrumanalyzer@yahoogroups.com
                  [mailto:spectrumanalyzer@yahoogroups.com]On Behalf Of S. Cash Olsen
                  Sent: Tuesday, June 28, 2005 6:32 AM
                  To: spectrumanalyzer@yahoogroups.com
                  Subject: [spectrumanalyzer] UMS-2150 VCO versus ROS-2150VW


                  Great work John, so much for that idea.

                  Cash
                • S. Cash Olsen
                  John and group, I was looking for a suitable substitute for the OP27 and came up with the TLE2141CD. Any comments about this part, has anyone tried this one?
                  Message 8 of 20 , Jun 28, 2005
                    John and group,

                    I was looking for a suitable substitute for the OP27 and came up with the
                    TLE2141CD. Any comments about this part, has anyone tried this one?

                    At 08:57 AM 6/28/2005, you wrote:
                    >There are still some things I want to check -- these VCOs have more tuning
                    >sensitivity than the ROS parts, so I want to make sure I'm not limited by
                    >opamp output noise. I use the LT1677, which is pretty quiet, but you
                    >never know until you crunch the numbers. More later, maybe...
                    >
                    >-- john, KE5FX
                    >-----Original Message-----
                    >From: spectrumanalyzer@yahoogroups.com
                    >[mailto:spectrumanalyzer@yahoogroups.com]On Behalf Of S. Cash Olsen
                    >Sent: Tuesday, June 28, 2005 6:32 AM
                    >To: spectrumanalyzer@yahoogroups.com
                    >Subject: [spectrumanalyzer] UMS-2150 VCO versus ROS-2150VW
                    >
                    >Great work John, so much for that idea.
                    >
                    >Cash
                    >
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                  • John Miles
                    Looks OK, but I ve never heard of it; what s the advantage over the OP(A)27? The LT1677 is the best all-around low-noise part I ve seen so far. It is a
                    Message 9 of 20 , Jun 28, 2005
                      Looks OK, but I've never heard of it; what's the advantage over the OP(A)27?  The LT1677 is the best all-around low-noise part I've seen so far.  It is a rail-to-rail OP27.
                       
                      -- john, KE5FX
                      -----Original Message-----
                      From: spectrumanalyzer@yahoogroups.com [mailto:spectrumanalyzer@yahoogroups.com]On Behalf Of S. Cash Olsen
                      Sent: Tuesday, June 28, 2005 4:37 PM
                      To: spectrumanalyzer@yahoogroups.com
                      Subject: RE: [spectrumanalyzer] UMS-2150 VCO versus ROS-2150VW

                      John and group,

                      I was looking for a suitable substitute for the OP27 and came up with the
                      TLE2141CD. Any comments about this part, has anyone tried this one?

                      At 08:57 AM 6/28/2005, you wrote:
                      >There are still some things I want to check -- these VCOs have more tuning
                      >sensitivity than the ROS parts, so I want to make sure I'm not limited by
                      >opamp output noise.  I use the LT1677, which is pretty quiet, but you
                      >never know until you crunch the numbers.  More later, maybe...
                      >
                      >-- john, KE5FX
                      >-----Original Message-----
                      >From: spectrumanalyzer@yahoogroups.com
                      >[mailto:spectrumanalyzer@yahoogroups.com]On Behalf Of S. Cash Olsen
                      >Sent: Tuesday, June 28, 2005 6:32 AM
                      >To: spectrumanalyzer@yahoogroups.com
                      >Subject: [spectrumanalyzer] UMS-2150 VCO versus ROS-2150VW
                      >
                      >Great work John, so much for that idea.
                      >
                      >Cash
                      >
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                    • S. Cash Olsen
                      John, Well I didn t think to look and see what you were using. The OP27 is obsolete and is not or soon will not be readily available. I ll make the LT1677 a
                      Message 10 of 20 , Jun 28, 2005
                        John,

                        Well I didn't think to look and see what you were using. The OP27 is obsolete and is not or soon will not be readily available. I'll make the LT1677 a replacement part for the OP27.

                        Thanks,

                        Cash

                        At 05:46 PM 6/28/2005, you wrote:
                        Looks OK, but I've never heard of it; what's the advantage over the OP(A)27?  The LT1677 is the best all-around low-noise part I've seen so far.  It is a rail-to-rail OP27.
                         
                        -- john, KE5FX
                        -----Original Message-----
                        From: spectrumanalyzer@yahoogroups.com [ mailto:spectrumanalyzer@yahoogroups.com]On Behalf Of S. Cash Olsen
                        Sent: Tuesday, June 28, 2005 4:37 PM
                        To: spectrumanalyzer@yahoogroups.com
                        Subject: RE: [spectrumanalyzer] UMS-2150 VCO versus ROS-2150VW

                        John and group,

                        I was looking for a suitable substitute for the OP27 and came up with the
                        TLE2141CD. Any comments about this part, has anyone tried this one?

                        At 08:57 AM 6/28/2005, you wrote:
                        >There are still some things I want to check -- these VCOs have more tuning
                        >sensitivity than the ROS parts, so I want to make sure I'm not limited by
                        >opamp output noise.  I use the LT1677, which is pretty quiet, but you
                        >never know until you crunch the numbers.  More later, maybe...
                        >
                        >-- john, KE5FX
                        >-----Original Message-----
                        >From: spectrumanalyzer@yahoogroups.com
                        >[ mailto:spectrumanalyzer@yahoogroups.com]On Behalf Of S. Cash Olsen
                        >Sent: Tuesday, June 28, 2005 6:32 AM
                        >To: spectrumanalyzer@yahoogroups.com
                        >Subject: [spectrumanalyzer] UMS-2150 VCO versus ROS-2150VW
                        >
                        >Great work John, so much for that idea.
                        >
                        >Cash
                        >
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                      • John Miles
                        Hmm, I was thinking that Scotty s and my discussion about OP27 replacements was on the SA list, but it looks like we never publicized it. :) Yes, as far as
                        Message 11 of 20 , Jun 28, 2005
                          Hmm, I was thinking that Scotty's and my discussion about OP27 replacements was on the SA list, but it looks like we never publicized it. :)  Yes, as far as I'm aware, the LT1677 is the preferred replacement.  Scotty, did you ever find anything you liked better?
                           
                          -- john, KE5FX
                          -----Original Message-----
                          From: spectrumanalyzer@yahoogroups.com [mailto:spectrumanalyzer@yahoogroups.com]On Behalf Of S. Cash Olsen
                          Sent: Tuesday, June 28, 2005 5:16 PM
                          To: spectrumanalyzer@yahoogroups.com
                          Subject: RE: [spectrumanalyzer] UMS-2150 VCO versus ROS-2150VW

                          John,

                          Well I didn't think to look and see what you were using. The OP27 is obsolete and is not or soon will not be readily available. I'll make the LT1677 a replacement part for the OP27.

                          Thanks,

                          Cash

                          At 05:46 PM 6/28/2005, you wrote:
                          Looks OK, but I've never heard of it; what's the advantage over the OP(A)27?  The LT1677 is the best all-around low-noise part I've seen so far.  It is a rail-to-rail OP27.
                           
                          -- john, KE5FX
                          -----Original Message-----
                          From: spectrumanalyzer@yahoogroups.com [ mailto:spectrumanalyzer@yahoogroups.com]On Behalf Of S. Cash Olsen
                          Sent: Tuesday, June 28, 2005 4:37 PM
                          To: spectrumanalyzer@yahoogroups.com
                          Subject: RE: [spectrumanalyzer] UMS-2150 VCO versus ROS-2150VW

                          John and group,

                          I was looking for a suitable substitute for the OP27 and came up with the
                          TLE2141CD. Any comments about this part, has anyone tried this one?

                          At 08:57 AM 6/28/2005, you wrote:
                          >There are still some things I want to check -- these VCOs have more tuning
                          >sensitivity than the ROS parts, so I want to make sure I'm not limited by
                          >opamp output noise.  I use the LT1677, which is pretty quiet, but you
                          >never know until you crunch the numbers.  More later, maybe...
                          >
                          >-- john, KE5FX
                          >-----Original Message-----
                          >From: spectrumanalyzer@yahoogroups.com
                          >[ mailto:spectrumanalyzer@yahoogroups.com]On Behalf Of S. Cash Olsen
                          >Sent: Tuesday, June 28, 2005 6:32 AM
                          >To: spectrumanalyzer@yahoogroups.com
                          >Subject: [spectrumanalyzer] UMS-2150 VCO versus ROS-2150VW
                          >
                          >Great work John, so much for that idea.
                          >
                          >Cash
                          >
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                        • william sprowls
                          Hi all, Analog Devices AD8671 is also a good replacement for the OP27. I am using one in PLL 1 for the MSA. Its bias and noise specs are actually a little
                          Message 12 of 20 , Jun 28, 2005
                            Hi all,
                            Analog Devices AD8671 is also a good replacement for
                            the OP27. I am using one in PLL 1 for the MSA.
                            Its bias and noise specs are actually a little better
                            than the OP27. However, I see no better results than
                            the OP27. This is due to the 20LogN noise of the PLL
                            chip. It is the prevalent noise contribution in the
                            system.
                            It seems to be pretty hardy, too. I accidently
                            crossed the +20v and -5v lines and it still works
                            fine. Absolutely smoked the LMX 2326.
                            Scotty

                            --- "S. Cash Olsen" <KD5SSJ@...> wrote:

                            > John,
                            >
                            > Well I didn't think to look and see what you were
                            > using. The OP27 is
                            > obsolete and is not or soon will not be readily
                            > available. I'll make the
                            > LT1677 a replacement part for the OP27.
                            >
                            > Thanks,
                            >
                            > Cash




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