http://elecraft.85.s1.nabble.com/Re-K3-receiver-noise-questionable-test-results-tp4192141p4193476.html
> measurements on an FT-1000 - perhaps with the INRAD filter. I am
All measurements were made at the speaker output for consistency.
settings. FT-1000MP Mark V was measured with both the analog
and DSP (100-3100 Hz setting) detectors.
2.40=-5, 3.20=-6).
Note the K3 audio amplifier is the cleanest hands down. The other
-100 dBV). Except for what appear to be artifacts of the ADC
... Joe, W4TV
> -----Original Message-----
> From: Don Wilhelm [mailto:
[hidden email]]
> Sent: Saturday, December 19, 2009 5:14 PM
> To:
[hidden email]
> Cc:
[hidden email]
> Subject: Re: [Elecraft] : K3 receiver noise - my test results (long)
>
>
> Joe,
>
> I think you may have hit on some major part of the "problem" here. I
> measured the passband (and out of passband) response of my K3
> and my K2,
> Yaesu FT-900 and Yaesu FT-817. All measurements were with the SSB
> filter in all transceivers, and the K3 DSP width was set to
> maximum. My
> K2 has the 2.4 kHz filter and the Yaesu transceivers have the
> stock SSB
> filter.
>
> The test setup consisted of an Elecraft broadband noise generator
> feeding that receiver and the output was observed with
> Spectrogram. The
> receiver gain controls were adjusted to place the peak in-passband
> response at -30 dB.
> I also connected an antenna and listened to several signals
> participating in a 40 meter roundtable, and made my own 'quality of
> sound' assessment.
>
> Several things became apparent as a result of these tests.
> 1) the K3 in-passband response is almost flat - from 500 Hz
> to 2500 Hz
> it showed less than 1 dB variation.
> 2) All the other passband responses were down about 5 dB at
> 500 Hz and
> essentially flat from 1 kHz to 1600 Hz, then began a gradual falloff,
> being down 3 dB at 2 kHz, down 8 dB at 2.5 kHz, the Yaesus
> were down 17
> dB while the K2 was down 36 dB (this is the effective high end of the
> passband). So within the passband, there is a rolloff
> similar to that
> which you suggested for the receive EQ settings on all but the K3.
> 3) The response outside the passband on the low end was also
> interesting. The K3 at 200 Hz was only down 3 dB, but
> dropped steeply
> at lower frequencies (I do not have the low frequency mod on my K3).
> The K2 was down 26 dB at 200 Hz while the Yaesus were down 20 dB.
> 4) On he high frequency side out of the passband, the K2 and K3 had
> almost no audio response that showed on Spectrogram - in other words
> greater than 60 dB down from the passband peak. The Yaesu FT-900 had
> audio artifacts that were only 44 dB down at 4 kHz and for the FT-817
> were only 35 dB down. At 5 kHz the FT-900 had audio content
> at -50 dB
> and the FT-817 had content only 40 dB down.
>
> Summary of my observations - the in-passband response of both Yaesu
> filters and the K2 filter tapered off above 1800 Hz, similar
> to a "pink
> noise" response, while the K3 response was remarkably flat with very
> steep filter skirts. The skirt slope of the other filter
> passbands were
> more gentle.
>
> On the high frequency end, both Yaesu transceivers had considerable
> audio content while the K2 and K3 content was much lower.
>
> My conclusions: I am not certain what K3 owners are
> perceiving as noise
> any more than I had been before these tests. The flatter
> passband of
> the K3 may be sub-consciously perceived as being more 'harsh', but I
> could not equate that to 'noise'. The other filters with a high end
> in-passband response that drops off similar to a "pink noise"
> response
> *could* be causing a perception of additional noise *if* their local
> noise has significant content in the 2 kHz to 3 kHz range -
> yes, the K3
> will make this section of the audio spectrum louder than the other
> receiver I measured. The "audio hiss" is not coming from the high
> frequency spectrum outside the passband because in that area,
> the K3 and
> the K2 are much more quiet than the others measured.
>
> It would be interesting (at least to me) for someone to make similar
> measurements on an FT-1000 - perhaps with the INRAD filter. I am
> especially interested to know if the in-passband response shows a
> similar taper at 2 kHz and above, and what is the response for the
> FT-1000 above the filter passband.
>
> For those trying the "pink noise rolloff", my measurements
> suggest that
> you should set the RX EQ bands from 100 Hz through 1600 Hz at
> 0 dB, 2400
> at -3 dB, and 3200 at -5 dB. The 50 Hz band can be set at -16 dB for
> the reasons Joe has stated.
>
> 73,
> Don W3FPR
>
> Joe Subich, W4TV wrote:
> > If one is going to attempt to mimic the "pink noise" behavior,
> > there is no need to bother with the low frequency boost. It
> > simply puts more strain on the audio amplifier, increasing the
> > amount of IMD products, with little or no aural benefit. A
> > better RX EQ configuration with essentially the same perceived
> > sound:
> >
> > 50: -16 dB (reduce sub-vocal noise and hum)
> > 100: 0 dB
> > 200: 0 dB
> > 400: 0 dB
> > 800: 0 dB
> > 1600: -3 dB
> > 2400: -5 dB
> > 3200: -6 dB
> >
> >
> >