Fw: [softrock40] Re: Dynamic range measurements of SR V6

[Terry Fox]

----- Original Message ----- 
From: FRANCIS CARCIA 
To: softrock40 at yahoogroups.com 
Sent: Monday, October 02, 2006 7:32 PM
Subject: Re: [softrock40] Re: Dynamic range measurements of SR V6


I also measured 96 dB dynamic range with my sdr board using a FST3253. At 2.5 KHz spacing 84 dB.My 3 dB MDS was a bit lower using INA163s I was also using a stock sound card. My generators were also a pair of 8640Bs Frank wa1gfz

Phil Covington <p.covington at gmail.com> wrote: 

  --- In softrock40 at yahoogroups.com, Marco <ik1odo at ...> wrote:
  >
  > Hi all,
  > 
  > I performed some more tests on IMD and dynamic range of the SoftRock 
  > V6 (original and modified). Here is a summary of the results.
  > For all measurements, the reference bandwidth is 2.4kHz, the signal 
  > spacing is 15kHz and the frequency is around 7050kHz.
  > 
  > Instuments used: two HP 8640B signal generators, HP 8494A and -B step 
  > attenuators, Olektron power combiner. Levels checked with an HP 8566B 
  > spectrum analyzer. Power bandwidths and S/N measured with a Fluke 
  > 8920A digital RMS voltmeter. All instruments have traceable calibration.
  > 
  > 1) Unmodified SoftRock, Soundblaster USB 16bit audio interface 
  > (16bit, 48kHz, better antialiasing and response than the usual AC97 
  > found in PCs)
  > MDS: -105dBm
  > blocking dynamic range: 96dB
  > IMD3 dynamic range: not measurable (blocking occurs by saturation of 
  > the audio interface)
  > IIP3: -
  > 
  > 2) same as (1), soundcard Audiophile 192 (24bit, sampling at 96kHz)
  > MDS: -110dBm
  > Blocking dynamic range: 100dB
  > IMD3 dynamic range: 93dB
  > IIP3: +29dBm
  > 
  > 3) same as (2), post-mixer amp voltage gain reduced from 500 times 
  > (5kOhm/10Ohm resistors on the opamp) to 90 times (900Ohm/10Ohm)
  > MDS: -110dBm
  > Blocking dynamic range: 110dB
  > IMD3 dynamic range: 96dB
  > IIP3: +34dBm
  > 
  > 4) same as (2), post-mixer amplifier has been replaced by a couple of 
  > OP27G powered from +/-12V. Opamp gain is now 200 times (2kOhm/10Ohm)
  > MDS: -110dBm
  > Blocking dynamic range: 115dB
  > IMD3 dynamic range: 102dB
  > IIP3: +43dBm
  > 
  > My comments:
  > 
  > a) I don't see any saturation in the FST3253 at least up to +10dBm 
  > (not checked over that)
  > b) the IMD products seem to come mainly from the opamp and audio 
  > interface. Low power, low voltage opamps are the limit here
  > c) some front-end gain is advisable to raise the MDS and stabilize 
  > the impedance seen by the mixer, if the opamp and audio interface can 
  > handle the strong signals. Noise from the opamp dominates the noise 
  > floor, of course; measured noise figure here is approx. 30dB
  > d) IIP3 figures appear very good, but the real performance is limited 
  > by the poor image suppression and the 2nd order audio harmonic 
  > generation in the chain. With only two tones at the input the 
  > spectrum becomes a real forest, such that it's difficult to find a 
  > clean spot to see the IMD products. So, probably we have to talk 
  > about SFDR (spurious free dynamic range) or the system. Much harder 
  > than a simple IMD3 measurement.
  > 
  > Next step: to test different mixer topologies (switch followed by an 
  > active integrator, as proposed on the HPSDR group, and some other
  ideas).
  > 
  > 73 - Marco IK1ODO
  >

  Hi Marco,

  Very interesting results. I will be particularly interested in your
  measurements of an active integrator version.

  73 de Phil N8VB





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