Are there a set of mods for the KNB1 similar to this? My TS450Sat had a very effective noise blanker and the K3 works wonders on the noise at my home QTH but the K1 blanker could really use a bit more work. Not sure what it needs ATM but it could be fun trying to find it..
~Brett On Wed, 2009-07-08 at 00:17 -0400, Don Wilhelm wrote: > Steve, > > I suggest that you build the KNB2 first and see if it is effective for > the noise you have to deal with. Normally, the gating level is not the > problem, but the blanking pulse width can be varied (G3ULB mod) to > handle other noise pulses. > > The stock KNB2 is quite effective for impulse noise of the automotive > ignition type. Yes, if you have other types of noise sources that you > must deal with, try either (or both) of these mods to see if it helps in > your situation. Similarly, your proposed change for Q3 may make a > difference too, so try it out. There is nothing wrong with a bit of > experimentation. What I am encouraging you to do is build the KNB2 as > "stock" first, and then experiment from there. The actual beta of > several 2N2222As that I have measured is in the range of 100, so your > proposed transistor change may make no difference. > > 73, > Don W3FPR > > NU7B wrote: > > Joe: > > > > I just ordered a KNB2 and looked at DL7MAJ's modification. In looking at the > > schematic, it seems like the shortest time constant for the one-shot is > > above 10 µs. The DL7 mod noted that Q2 was being loaded by the base of Q3 - > > possibly there is a load transient associated with charging C11,12. The > > 2222A has a fairly low beta, and Q3 has no RE, so its base current could be > > fairly high. Raising the beta seems like it would reduce the loading on Q2. > > > > I'll measure the beta on what comes with the KNB2. I've got 2n3904 (B=100) > > and 2n5089 (B=400), so I may substitute. The 5089 has a lower fT of 50 MHz, > > but for a 10µs pulsewidth, it should be fine. > > > > Steve NU7B > > > > > ______________________________________________________________ > 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 ______________________________________________________________ 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
