Fw: [softrock40] Re: Dynamic range measurements of SR V6
wb4jfi at knology.net
Mon Oct 2 20:09:54 CDT 2006
----- 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 4) same as (2), post-mixer amplifier has been replaced by a couple of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
> 73 - Marco IK1ODO
Very interesting results. I will be particularly interested in your
measurements of an active integrator version.
73 de Phil N8VB
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