Thanks Guy for the explanations about IMD measurements. I need a signal generator to do better tests and get rid of the need of receiving a broadcast carrier. I was thinking in building a simple Xtal oscillator and some attenuators.
73, Ramiro. EA4NZ Guy Olinger K2AV escribió: > 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 <[email protected] > <mailto:[email protected]>> 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 > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] <mailto:[email protected]> > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
