Thanks Guy for the explanations about IMD measurements. I need a signal
broadcast carrier. I was thinking in building a simple Xtal oscillator
73, Ramiro. EA4NZ
> You do know that you cannot do valid IMD sweep measurements with AGC on?
>
> First thing I have to do for any measurements is turn off the AGC and
> set fixed levels. Particularly very fast config of fast AGC won't
> work. It won't be valid for absolute measurements, but the bandwidth
> needs to be at least four times the spacing of the two to prevent AGC
> severely warping the content. And then you will need to provide your
> single tone sweep selectivity EXTERNAL to the K3. Your fast AGC is
> pulling up the IMD tones by changing the RX gain during the sweep.
>
> 73, Guy.
>
> On Wed, Nov 24, 2010 at 3:07 PM, Ramiro Aceves <
[hidden email]
> <mailto:
[hidden email]>> wrote:
>
> Hello all
>
> As David suggested we continue the discussion on the list. I have done
> some new poor man tests, using a local AM carrier on Medium Wave at 917
> KHz. For generating the other tone, I am using the same home made DDS
> generator as before. At this lower frequencies the signal generated by
> the DDS is much more cleaner. The antenna is a 6.5m long dipole on the
> balcony and an open wire feeder as in the earlier tests, but using only
> one half of the dipole by just directly connecting one open wire end to
> the K3 antenna connector. The reasons of doing that is that my T match
> tunner does not work below 1.8 MHz. This eliminates the posibility of
> IMD products produced on the tuner toroids. It does not remove, just in
> case, other no-linearities found everywhere as suggested by (sorry for
> my poor english, I hope you understand me).
>
> 10 Hz spacing, ACG-F:
>
>
http://ea1abz.ure.es/acg-F.png>
>
> Now with AGC-S, notice the strong reduction of IMD:
>
>
http://ea1abz.ure.es/agc-S.png>
>
>
> Now see the AGS-S to AGC-S-soft transition on the middle of the capture:
>
>
http://ea1abz.ure.es/agc-S_vs_agc-soft.png>
>
>
> Now see the IMD at 100Hz spacing, AGC-F to AGC-S transition at the
> middle of the screen:
>
>
http://ea1abz.ure.es/100Hz.png>
>
> Sorry for the poor noise floor, is the Madrid band noise received by the
> antenna. Hi.
>
> I see that the IMD problem is worse with small carrier distances. At 100
> Hz spacing they are much more weaker and not problematic.
>
>
> 73, Ramiro.
>
> EA4NZ
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