Good observation, George. The KAT3A indeed does have a bypass relay, while the KAT3 (in the original K3) does not. As I recall, the KAT3 switches the inductors and capacitors out in bypass mode, but does not necessarily provide the best 50 match. This is due to variances in the components and placement from unit to unit. Tuning into a good 50 ohm dummy load can provide a better 50 ohm match, but it has the slight down side of adding a slight amount of loss to the path. In the end they do pretty much the same thing, but if someone wanted to be a real perfectionist (and I’ll admit to that with many things), then tuning into a dummy load will provide an oh-so slightly better match.
The important point here is that it really needs to tune into a known-good 50 ohm resistive load to get what you want. Tuning into the BPF might get you there depending on the output of the BPF. As I stated earlier, I set my K3s to bypass mode for driving either my BPFs or my KPA500s. 73! Jack, W6FB > On Jul 5, 2019, at 12:56 PM, Gmail - George <gdanne...@gmail.com> wrote: > > > > -----Original Message----- > From: Jack Brindle via Elecraft > > ... > > Now having said this, the ATU can also be bypassed in the K3, and that > circuit may provide a proper 50 ohm source/load for the BPF. I would probably > take this approach myself (and in fact do so in my station). The reason I > take this approach is to avoid the small loss that the internal ATU presents. > In contesting, every db matters. > > Note that we are talking nits at this point. Unless the ATU was tuned for a > load quite a bit off 50 ohms resistive, (quite possible), then retuning won’t > make much difference. Perhaps the op had this situation, and thought it > better to return the ATU than to bypass it, or he didn’t even think to bypass > it. The point is, both methods will work, and I doubt he did anything wrong > it performing the tune. > > > Jack, > If I'm not mistaken - the KAT3 is not able to be physically bypassed in a K3 > - don't know in a K3S; but I thought the KAT3A did a physical bypass. > My understanding is that when you bypass the ATU (KAT3), it is merely being > set to a value that cancels the internal L & C of the board. > I would think a tune would not actually actually change much of anything; but > leave it to someone to actually test the true output impedance in both. > > 73 > George AI4VZ > > --- > This email has been checked for viruses by Avast antivirus software. > https://www.avast.com/antivirus > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to jackbrin...@me.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
