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Re: Softrock 40 Based SDR Update

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  • w7qjq
    Good job Bryce.. You can take advantage of the sig gen to get the BPFs working. Are you going to use a crystal LO or a Si570 or something else? When you get
    Message 1 of 10 , Oct 27, 2011
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      Good job Bryce.. You can take advantage of the sig gen to get the BPFs working. Are you going to use a crystal LO or a Si570 or something else?
      When you get things sorted more, make an effort to determine if Rocky is able to perform Image Rejection properly... this will confirm that both I and Q signals are present and are being processed correctly by your sound card.

      I can't answer about the saved audio files as I have no experience with that.

      Good luck with your exams...

      73 Sid W7QJQ
      Oklahoma


      --- In softrock40@yahoogroups.com, Bryce Salmi <bstguitarist@...> wrote:
      >
      > Sid,
      > It works! I replaced the Op Amp and may have found a shorting solder.
      > It's very neat and I know that the BPF I built is not working well. The
      > bands may be crappy but I am receiving much better signals on 80M than I am
      > on 40M. I'll have to tidy this up and rebuild the BPF. We'll see if I can
      > get it done in a few weeks as I have the GRE's coming up shortly! (still in
      > college).
      >
      > The LO I am using at this time is an old HP8654A signal generator, it's
      > not great, but it gets the job done for the moment.
      >
      > I'll follow up this email with another detailing some interesting things
      > I noticed. Also, is there a way to easily change the directory the saved
      > audio files go to? I cannot see the saved filed when I navigate to the
      > directory. Thanks again for the help.
      >
      >
      > Bryce S.
      > KB1LQC
      >
      >
      > On Tue, Oct 25, 2011 at 9:07 PM, w7qjq <sbjknox@...> wrote:
      >
      > > **
      > >
      > >
      > >
      > > Well, there is something amiss with the I section. 1.82 V is not
      > > good...opamps don't work like that. So, my guess is either a bad opamp or
      > > some problem with the components associated with the I section. If you have
      > > the I output connected to the pc and the 1u coupling cap was leaky or
      > > shorted, this might explain the wrong voltage measurement.
      > >
      > > I can understand that you are anxious to see some 40m signals in Rocky.
      > > *If* the I section is bad and *if* the Q section is not being poisoned by
      > > the bad I section, here is something that you can try that will at least
      > > tell you if the remainder of the circuit is working. You will not have image
      > > rejection but you should see a bunch of 40m activity. Connect the Q output
      > > to the pc sound card input (probably best to not connect I at this point).
      > > You will need a reasonable antenna connected to the xfmr primary (no
      > > BPfilter, just straight into the xfmr) ... a long piece of wire *AND* an rf
      > > ground. Or a balanced antenna which needs no rf gnd. And/or you can set your
      > > sig gen near 7056 KHz (28224 / 4), feed it into the xfmr primary, and look
      > > for a signal on Rocky. A 1mV signal is about s9+26dB, ie, a huge signal, You
      > > should see the 'real' signal and the image spaced equally around the center
      > > of the spectrum and as you tune the sig gen both should move in opposite
      > > directions.
      > >
      > > 73, Sid W7QJQ
      > > Oklahoma
      > >
      > >
      > > --- In softrock40@yahoogroups.com, Bryce Salmi <bstguitarist@> wrote:
      > > >
      > > > Sid,
      > > > I just measured the voltages again but this time with a 28.224 MHz LO
      > > > input into my comparator.
      > > >
      > > > I Op Amp
      > > >
      > > > Inv_In: 2.18V
      > > > Non_Inv_In: 2.18V
      > > > Output: 1.82V
      > > >
      > > > Q Op Amp
      > > >
      > > > Inv_in: 2.19V
      > > > Non_Inv_In:2.17V
      > > > Output: 2.18V
      > > >
      > > > Bryce
      > > > KB1LQC
      > > > On Tue, Oct 25, 2011 at 10:11 AM, w7qjq <sbjknox@> wrote:
      > > >
      > > > > **
      > >
      > > > >
      > > > >
      > > > >
      > > > >
      > > > > --- In softrock40@yahoogroups.com, "KB1LQC" <bstguitarist@> wrote:
      > > > > >
      > > > > > Sid,
      > > > > > As for #1 I originally had no transformer attached at all and
      > > obtained no
      > > > > results. is there a way to attached the antenna correctly without the
      > > > > transformer. Should I just attached the antenna and ground to the two
      > > input
      > > > > resistors (10 Ohms). Wouldn't I still need to apply the DC bias to the
      > > > > inputs of the tayloe detector. In the original Softrock 40 design the
      > > 5V
      > > > > supply is divided between the two 10K resistors R17 and R18 and then
      > > applied
      > > > > to the center tap of the secondary winding.
      > > > > >
      > > > > > For #2, I am measuring with no LO input (figured I'd get a steady
      > > state
      > > > > measurement):
      > > > > >
      > > > > > Q Op Amp (Baseband signal present)
      > > > > >
      > > > > > Inv_In: 2.41V
      > > > > > Non-Inv_In: 2.41V
      > > > > > Out: 2.42
      > > > > >
      > > > > > I Op Amp (Baseband signal not present)
      > > > > >
      > > > > > Inv_In: 2.15V
      > > > > > Non-Inv_In: 2.42V
      > > > > > Out: 1.74V
      > > > > >
      > > > > >
      > > > > > Please let me know if there is anything else I can provide.
      > > > > >
      > > > > >
      > > > > > Thank You,
      > > > > >
      > > > > > Bryce
      > > > > > KB1LQC
      > > > > >
      > > > > > --- In softrock40@yahoogroups.com, "w7qjq" <sbjknox@> wrote:
      > > > > > >
      > > > > > >
      > > > > > >
      > > > > > > --- In softrock40@yahoogroups.com, "KB1LQC" <bstguitarist@> wrote:
      > > > > > > >
      > > > > > > > I also forgot to mention that the DC voltage on the output pin of
      > > the
      > > > > Q Op-Amp is 2.2V (this one works) and the DC voltage on the output pin
      > > of
      > > > > the I Op-Amp is 1.77V (this has the constant signal seen in (
      > > > >
      > > https://picasaweb.google.com/lh/photo/6dD2W-pWv54SvuWtFq30yuX-14c5teRmthMEi_jgxqg?feat=directlink
      > > ).
      > > > > Hopefully this helps.
      > > > > > > >
      > > > > > > > Bryce
      > > > > > > > KB1LQC
      > > > > > > >
      > > > > > >
      > > > > > > 1) You have not yet showed how the xfmr is connected. As I earlier
      > > > > suggested, omit the BPF until you get the basic Rx working.
      > > > > > >
      > > > > > > 2) 1.77V is not a what should be there. Please provide measured
      > > voltage
      > > > > values for the inv, non_inv, and out for both I and Q sides of the
      > > opamp and
      > > > > also for each terminal of the xfmr.
      > > > > > >
      > > > > > > 73, Sid W7QJQ
      > > > > > > Oklahoma
      > > > > > >
      > > > >
      > > > > Bryce, the xmfr must be connected as shown on the SoftRock40 schematic.
      > > It
      > > > > provides three essential functions:
      > > > >
      > > > > 1) Produces 0 and 180 degree rf signals to feed the detector.
      > > > >
      > > > > 2) gives DC isolation from the antenna to the detector/opamp. The 2.5V
      > > at
      > > > > the center-tap sets the operating point for the detector/opamp(the
      > > > > center-tap is bypassed so as to be at rf gnd).
      > > > >
      > > > > 3) Impedance matching and some band-pass action (which is indicated by
      > > the
      > > > > different component for different bands).
      > > > >
      > > > > When things are working properly, you should measure the 2.5V at the
      > > > > detector and opamp pins. Your measurement for the Q section of the
      > > opamp
      > > > > looks ok... the values for the I section are not right alyho I am not
      > > clear
      > > > > on why you measure one with LO operating and the other with no LO (??).
      > > What
      > > > > does the I section measure *with* the LO operating?
      > > > >
      > > > > It is possible that either the detector or the opamp is defective. Or
      > > that
      > > > > there is a wiring problem (which includes a solder blob somewhere).
      > > > >
      > > > > 73, Sid W7QJQ
      > > > > Oklahoma
      > > > >
      > > > >
      > > > >
      > > >
      > >
      > >
      > >
      >
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