K3 2 tone 3rd order dynamic range at 2 KHz tone spacing

[Dave, G4AON]

I've been looking at the performance of my K3 using a buffered fixed
crystal oscillator, hybrid coupler and Marconi 2018 signal generator...
I've noticed a strange phenomenon where the two tone dynamic range
appears to be approximately 10 dB worse at 2 KHz spacing with the 400 Hz
8 pole filter than with the 2.8 KHz 8 pole filter (90 dB and 100 dB
respectively). At 5 KHz the range is 100 dB with either filter. Altering
the width control from 400 Hz to 450 Hz and back again switches the
filters, the audible effect of the spurious signal being there or not,
is quite striking. Both upper and lower 3rd order products behave the
same, I also get the same results with the Marconi signal generator on
the high side or low side of the crystal oscillator.

Anyone with a pair of signal generators and a hybrid coupler care to
check their K3 and see if they obtain the same results? I'm assuming the
reason is ripples in the passband of the 400 Hz filter many dBs down the
passband.

73 Dave, G4AON
K3/100 #80
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[dj7mgq]

Hi Dave,

My K3 shows an IMDR3 of between 110dB and 105dB with slight variations
from the upper to lower side. This with the 400Hz roofing filter and
400Hz DSP filter at spacings of 100, 50, 20, 15, 10, 5 and 2kHz on the
20m band. Last week our quick and dirty first look also gave us numbers
in the same ballpark: IMDR3 of 106db at 20 and 5kHz and 104db at a
spacing of 2kHz.

We did find some spurs, last week, which were coming from one of the HP
signal generators, which slightly confused us at first. The spurs were
very far down, but they were there.

vy 73 de toby
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[N2TK]

Tnx for info. Is this with the preamp off?
73,
N2TK, Tony

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Toby Deinhardt
Sent: Thursday, December 27, 2007 4:41 PM
To: Dave G4AON
Cc: [hidden email]
Subject: Re: [Elecraft] K3 2 tone 3rd order dynamic range at 2 KHz tone
spacing

Hi Dave,

My K3 shows an IMDR3 of between 110dB and 105dB with slight variations
from the upper to lower side. This with the 400Hz roofing filter and
400Hz DSP filter at spacings of 100, 50, 20, 15, 10, 5 and 2kHz on the
20m band. Last week our quick and dirty first look also gave us numbers
in the same ballpark: IMDR3 of 106db at 20 and 5kHz and 104db at a
spacing of 2kHz.

We did find some spurs, last week, which were coming from one of the HP
signal generators, which slightly confused us at first. The spurs were
very far down, but they were there.

vy 73 de toby
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[dj7mgq]

> Tnx for info. Is this with the preamp off?

Yes.

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[Jan Erik Holm]

Would be nice to see measurements with preamp
both on and off.
Also please note what the MDS is.

Happy New Year / Jim SM2EKM
-------------------------------------------------
[hidden email] wrote:
>> Tnx for info. Is this with the preamp off?
>
> Yes.
>

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[dj7mgq]

> Would be nice to see measurements with preamp
> both on and off.
> Also please note what the MDS is.

TRX               PRE on     PRE off
IC-781 (500Hz)   -141 dBm   -133 dBm
K3 (400Hz)       -138 dBm   -134 dBm

both in 20m Band, mode CW


vy 73 de toby


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[Jan Erik Holm]

Thanks Toby, I suspect the IMDDR3 wouldn´t
change much between PRE on and off then.

73 Jim SM2EKM
-------------------
Toby Deinhardt wrote:

>> Would be nice to see measurements with preamp
>> both on and off.
>> Also please note what the MDS is.
>
> TRX               PRE on     PRE off
> IC-781 (500Hz)   -141 dBm   -133 dBm
> K3 (400Hz)       -138 dBm   -134 dBm
>
> both in 20m Band, mode CW
>
>
> vy 73 de toby
>
>
>

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