I stand corrected. I made an assumption, probably incorrectly, that the reason they had a second tuner was that the first did not successfully tune the antenna. They just decided to put the bandpass filter between the two tuners, which would have provided a mismatch at both the filter input and output. I just used a mismatch at the output as an example. I just provided an example of filter performance degradation with even what would be considered a reasonable SWR.
I prefer Jack's solution of bypassing the internal K3 tuner. I do have a situation where my antenna tuner can't tune my antenna on 160. Rather than try to use two tuners in series with the requisite losses, I added a shunt inductor on a big ferrite core to provide most of the required inductance for a match. It gets hot. 73, Mark W7MLG On Fri, Jul 5, 2019 at 10:57 AM David Gilbert <xda...@cis-broadband.com> wrote: > > I think you misread the situation. The question isn't whether to put a > single antenna tuner between the antenna and filter versus putting it > between the rig and the filter. The question is whether putting an > ADDITIONAL tuner (the one internal to the K3) at the input of the filter > is a good idea. And to me it seems the answer is yes. > > I think we all agree that the right feed impedance and load impedance > for a filter is important. And as I pointed out, not just for power > handling, but also for the filter to actually filter as it was intended. > > 73, > Dave AB7E > > On 7/5/2019 10:18 AM, Mark Goldberg wrote: > > I could not let this go. I've done a lot of work with bandpass filters. > The > > mismatch will degrade the filter. > > > > For an example, I used Elsie, which is a filter calculator. Using the > > example 20 Meter bandpass filter, the passband loss is about .25 dB with > > matched 50 ohms in and out. Changing the output impedance to 38+j12 (38 > > ohms plus 135 nH inductor at 14.15 MHz, about 1.5:1 SWR), the passband > > losses increase to about 0.4 - .44 dB and vary more over the band. > > > > Here are the schematics and plots, anyone is welcome to check my > > calculations, as I do make mistakes! > > > > > https://drive.google.com/file/d/1kj31IL_px6nVyRadW4nOi_c6FLgyaRyk/view?usp=sharing > > > > The loss in the filter will almost double. For 100W in, the loss goes > from > > about 6W to about 10W. So, it is not a good idea. A worse match will > result > > in even more losses, perhaps overheating and destroying the filter. > > > > 73, > > > > Mark > > W7MLG > > > > On Fri, Jul 5, 2019 at 8:32 AM Don Wilhelm <donw...@embarqmail.com> > wrote: > > > >> Rich, > >> > >> Yes and no. With 2 antenna tuners in-line, there will be a bit more > >> loss due to inductor winding resistance, but other than that, it should > >> do harm. > >> > >> Several bandpass filters indicate that they should be between the rig > >> and the tuner (so the bandpass filters are not run at a high SWR). > >> If the power rating of the bandpass filter is marginal with respect to > >> the rig power, then I would observe that caution. Refer to the bandpass > >> filter specs. > >> > >> 73, > >> Don W3FPR > >> > >> On 7/5/2019 10:57 AM, Rich wrote: > >>> To minimize emails direct replies would be nice. I searched the web > and > >>> could not find an answer. I know there are a ton of smart folks on > >>> this list so I thought I would ask. > >>> > >>> On Field Day at typical setup is : > >>> > >>> K3 (or any radio) - bandpass filter - External Antenna Tuner - > Antenna > >>> > >>> So the antenna was tuned via the external tuner, but saw a guy then > >>> using the K3 ant tuner to touch up the SWR between the radio and the > >>> bandpass filter. Is that an acceptable practice? > >>> > >> ______________________________________________________________ > >> 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 marklgoldb...@gmail.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 xda...@cis-broadband.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 marklgoldb...@gmail.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
