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 <[email protected]> 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:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [email protected] ______________________________________________________________ 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 Message delivered to [email protected]
