[Elecraft] : K3 receiver noise - my test results (long)
Don Wilhelm
w3fpr at embarqmail.com
Sun Dec 20 00:41:57 EST 2009
Joe,
Fine business on those measurements, and thank you for providing the
data. I note that all except the K3 show the taper from 1600 Hz to the
upper passband edge that follows something similar to a "pink noise"
spectrum. The K3 is flat without EQ. It is interesting that the K3
Norm does show some falloff, but not nearly as much as either the
FT-2000 or the MK V or IC-706.
I am ready to conclude that the K3's ultra-flat in-passband response is
the cause of several of the "noisy" responses. That can be easily
handled by shaping with the RX EQ if one desires. I do data modes
frequently, and prefer the flat response of the K3.
The audio response above the filter passband apparently has less
influence than I had originally expected.
73,
Don W3FPR
Joe Subich, W4TV wrote:
>> 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.
>>
>
> Here are some measurements using Spectrogram and broadband noise:
>
> FT-2000 --- MK V --- IC-706 ------ K3 ------
>
> Analog DSP MKIIG Norm BW=4 EQ
>
> 50 -34 -44 -49 -46 -35 -7 -35
> 100 -31 -24 -27 -40 -18 -6 -18
> 200 -17 -10 -9 -21 -5 -2 -5
> 300 -6 -4 -4 -11 -1 0 -1
> 400 -3 -2 -1 -5 0 0 0
> 600 -2 -1 0 -1 0 0 2
> 800 -1 -1 0 0 0 0 1
> 1000 -1 -1 0 -1 0 0 0
> 1200 0 -1 0 -2 0 0 0
> 1400 0 0 0 -1 0 0 -2
> 1600 -1 -2 -1 -2 0 0 -3
> 1800 -2 -3 -2 -3 0 0 -4
> 2000 -5 -5 -2 -4 -1 0 -5
> 2200 -7 -6 -3 -6 -2 0 -7
> 2400 -8 -8 -4 -8 -2 0 -8
> 2600 -10 -10 -6 -15 -3 0 -9
> 2700 -23 -13 -7 -27 -4 0 -10
> 2800 -34 -19 -11 -31 -8 0 -14
> 2900 -41 -32 -24 -33 -18 0 -24
> 3000 -50 -43 -36 -35 -58 0 -60
> 3100 -42 -67 0
> 3200 -58 0
> 3300 0
> 3400 0
> 3500 0
> 3600 -1
> 3700 -2
> 3800 -4
> 3900 -5
> 4000 -13
> 4100 -34
> 4150 -66
>
> All measurements were made at the speaker output for consistency.
> All measurements were made in USB mode with the default filter
> settings. FT-1000MP Mark V was measured with both the analog
> and DSP (100-3100 Hz setting) detectors.
>
> The two additional K3 measurements are 1) FM filter, BW=4.00
> and FC=2.00 and 2) "NORM" using the "pink EQ" settings (1.60=-3,
> 2.40=-5, 3.20=-6).
>
> Note the K3 audio amplifier is the cleanest hands down. The other
> transceivers had noise floors at about -120 dBV (IC-706 mkIIg was
> -100 dBV). Except for what appear to be artifacts of the ADC
> clock at 4, 8, 12, 16, 18 and 20 KHz the K3 out of band audio
> noise is <140 dBV.
>
> 73,
>
> ... Joe, W4TV
>
>
>
>
>
>
>
>
>
>> -----Original Message-----
>> From: Don Wilhelm [mailto:w3fpr at embarqmail.com]
>> Sent: Saturday, December 19, 2009 5:14 PM
>> To: lists at subich.com
>> Cc: elecraft at mailman.qth.net
>> 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
>>>
>>>
>>>
>>>
>
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