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RE: [Flexradio] Turning off the AGC

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  • KD5NWA
    Thanks, should not steps 1 and 2 be switched for maximum accuracy? ... Cecil Bayona KD5NWA www.qrpradio.com I fail to see why doing the same thing over and
    Message 1 of 6 , Oct 27, 2005
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      Thanks, should not steps 1 and 2 be switched for maximum accuracy?

      At 05:36 PM 10/27/2005, you wrote:
      >Measuring MDS is a simple procedure on the SDR-1000 with PowerSDR software.
      >The software calculates the RMS noise power within the 3dB bandwidth of the
      >filter so you can read it directly on the meter when the radio is connected
      >to a dummy load. You do have to accurately calibrate the radio with a known
      >signal source and the image rejection must be properly adjusted.
      >
      >So do the following:
      >
      >1) Calibrate the radio with a signal generator
      >2) Null the image
      >3) Set the filter bandwidth to 500 Hz
      >4) Attach a dummy load
      >5) Set the RX meter to Signal Avg
      >6) Read the meter and that is your MDS
      >
      >There is NO AGC in these measurements because they are measured before AGC.
      >
      >73,
      >Gerald
      >
      > > -----Original Message-----
      > > From: FlexRadio-bounces@...
      > > [mailto:FlexRadio-bounces@...] On Behalf Of KD5NWA
      > > Sent: Thursday, October 27, 2005 3:20 PM
      > > To: eric@...
      > > Cc: softrock40@yahoogroups.com; 'Flex Radio'
      > > Subject: Re: [Flexradio] Turning off the AGC
      > >
      > > I'm not trying to measure the noise floor, I'm trying to
      > > measure the lowest discernible signal "MSD"
      > >
      > > A voltage reading on a meter by itself means nothing since
      > > it's not being compared to a known quantity.
      > >
      > > The procedure is;
      > >
      > > Run the radio at maximum gain with a 500 Hz filter Measure
      > > the Audio output with a RMS meter, and a 1 micro-volt signal
      > > in the pass-band, set for maximum audio output.
      > > Remove the 1 microvolt signal and measure the Audio output
      > > with the meter Do some simple math with the two figures and
      > > you come up with MSD rating of the radio.
      > >
      > > But for this to be accurate the radio must be running at
      > > maximum gain, not minimum gain. Once you have that figure you
      > > can figure out the noise floor in dB.
      > >
      > > What I would need to know what is the maximum gain that the
      > > software would use while listening to weak signals.
      > >
      > > At 02:35 PM 10/27/2005, Eric Wachsmann - FlexRadio wrote:
      > > >Cecil,
      > > >
      > > >If you are trying to measure the noise floor of the unit,
      > > the easiest
      > > >thing to do is to just connect a dummy load, open the
      > > software and put
      > > >it in 500Hz BW. Look at the multimeter (might help to put it in Sig
      > > >Avg. mode). This is the effective noise floor of the unit (assuming
      > > >that it is higher than the sound card noise floor).
      > > >
      > > >To answer your question more specifically, turning the AGC
      > > to Fixed and
      > > >setting the Fixed Gain on the Setup Form to 0dB will effectively set
      > > >the processed audio to have no gain, variable or otherwise. The
      > > >spectrum and multimeter are both before the AGC however.
      > > >
      > > >
      > > >Eric Wachsmann
      > > >FlexRadio Systems
      > > >
      > > > > -----Original Message-----
      > > > > From: FlexRadio-bounces@...
      > > > [<mailto:FlexRadio-bounces@flex->mailto:FlexRadio-bounces@flex-
      > > > > radio.biz] On Behalf Of KD5NWA
      > > > > Sent: Thursday, October 27, 2005 12:50 PM
      > > > > To: Flex Radio
      > > > > Cc: softrock40@yahoogroups.com
      > > > > Subject: [Flexradio] Turning off the AGC
      > > > >
      > > > > I want to try to measure the noise floor of my SR-40
      > > setup and will
      > > > > need to have the AGC completely turned off.
      > > > >
      > > > > If I turn off the AGC of the Flex software will it really
      > > completely
      > > > > turn off all forms of variable gain?
      > > > >
      > > > >
      > > > > Cecil Bayona
      > > > > KD5NWA
      > > > > www.qrpradio.com
      > > > >
      > > > > I fail to see why doing the same thing over and over and
      > > getting the
      > > > > same results every time is insanity: I've almost proved it isn't;
      > > > > only a few more tests now and I'm sure results will
      > > differ this time
      > > >...
      > > > >
      > > > >
      > > > >
      > > > > _______________________________________________
      > > > > FlexRadio mailing list
      > > > > FlexRadio@...
      > > > >
      > > http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz
      > >
      > > Cecil Bayona
      > > KD5NWA
      > > www.qrpradio.com
      > >
      > > I fail to see why doing the same thing over and over and
      > > getting the same results every time is insanity: I've almost
      > > proved it isn't; only a few more tests now and I'm sure
      > > results will differ this time ...
      > >
      > >
      > >
      > > _______________________________________________
      > > FlexRadio mailing list
      > > FlexRadio@...
      > > http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz
      > >
      > >
      >
      >
      >
      >--
      >No virus found in this incoming message.
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      >Version: 7.1.362 / Virus Database: 267.12.5/150 - Release Date: 10/27/2005

      Cecil Bayona
      KD5NWA
      www.qrpradio.com

      I fail to see why doing the same thing over and over and getting the
      same results every time is insanity: I've almost proved it isn't;
      only a few more tests now and I'm sure results will differ this time ...
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