+++++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Sun, 12 Nov 2000 19:19:44 -0800 From: Vic Rosenthal Subject: [Elecraft] Blowby mods Is it reasonable to think that changing L11 to a toroid would help reduce filter blowby from very loud in-band ham signals (like a KW down the street) as well? I did it already, so it's too late to make measurements! 73, Vic, K2VCO Fresno CA +++++++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Sun, 12 Nov 2000 16:33:46 -0700 From: Wayne Burdick Subject: [Elecraft] K2: some experimental 20/30 m BPF component values gsurrency at juno.com wrote: > Do you have the 20m BPF values Arjen wants for the 20m band, inlcuding > the -3dB bandwidth? I've modeled some possible new values for the K2's 20/30 m band-pass filter. These should be of interest to anyone who has extremely strong near-band interference on either of these bands. (As far as I know such problems have only been repored in Europe.) There is a small additional loss that may slightly affect peak transmit output power on 20 meters, and WWV at 15 MHz will be somewhat more attenuated. Otherwise these values should work fine, and should have the desired effect of reducing the strength of SW BC stations in the 13-MHz range. The new values are: C19/C25 = 470 pF C22 = 2 or 2.2 pF The filters will need to be re-peaked as explained in the manual, but they'll be very close. To reduce the possibility of the two trim caps getting maxxed out when they're set (C21/C23, on 20 meters), the slug-tuned inductors should be peaked at a somewhat low 30-meter frequency, e.g. 10 MHz rather than 10.1 MHz. Here's a comparison of the old and new filters: 30 m: OLD NEW Loss at 10.1 MHz: 1.5 dB 2 dB -3 dB bandwidth: 1 MHz 0.5 MHz Return loss: 19 dB 18 dB 9.5 MHz (rel. to 10.1): -8 dB -14 dB 20 m: OLD NEW Loss at 14.2 MHz: 3 dB 4 dB -3 dB bandwidth: 0.75 MHz 0.5 MHz Return loss: 14 dB 12 dB 13.0 MHz (rel. to 14.2): -26 dB -32 dB Note the additional 6 dB of rejection in the 13-MHz range (on 20 m) and 9.5-MHz range (on 30 m). A few K2 owners in Europe who have experienced interference will probably be testing this new filter. If you decide to try the filter because out-of-band signals are causing unwanted AGC and S-meter activation, you should first try making RFC11 a toroid as explained in an earlier posting. 73, Wayne