++++++++++++++++++++++++++++++++++++++++ Date: Sun, 18 Mar 2001 00:29:27 -0700 From: "David Gilbert" Subject: [Elecraft] K1 AGC Per the advice that a few folks have given on this reflector, I changed C31 (2.2 uF) in the AGC circuit to 1.0 uF. I highly recommend it. The response is quicker on both ends ... less painful when a strong local station decides to call the DX you've been chasing, and recovers quicker when you're trying to hear the who the weaker DX station responded to. Dave AB7E K1 #412 ++++++++++++++++++++++++++++++++++++++++++++++++++ +Date: Sun, 25 Mar 2001 23:52:12 -0500 From: Richard Arland Subject: [Elecraft] K1 AGC Cap Change Last evening I did the "C31 cap change mod" to s/n 0017. I replaced the 2.2 uf with a .47 uf and the difference was amazing. The AGC is much more responsive with the new cap in place. I also experimented with C2: Originally I installed a 100 pf SM. Got lots of tuning range but the rate was extremely fast. Then I settled on a 68 pf SM but, after about 3 months of use, I changed it out for a 50 pf SM. With the 50 pf I get 62 khz of tuning range. It covers from 14.001 to 14.063 and 7.007 to 7.069 khz on 20 and 40 respectively. I don't mind losing the bottom of 40 meters and the tuning is MUCH improved. I may go back and tack a 5 pf SM in parallel with the 50 pf and see if I can get full band coverage on 40, but that is not an urgent priority. 74 Rich K7SZ ++++++++++++++++++++++++++++++++++++++++ Date: Mon, 26 Mar 2001 09:15:47 -0800 From: Wayne Burdick Subject: [Elecraft] Application Note: K1 QSK Modification Some K1 users have reported audible artifacts ("thump") during break-in keying when moderate-to-strong signals are present in the receive passband. This is not a problem in normal QSOs, since presumably you're the only station transmitting. It's more likely when there's heavy QRM, such as during contests: at times, nearby QRM can be heard even when the narrowest filter bandwidth is used. The audible artifacts are only noticeable if you use headphones with good bass response. If you use less-sensitive headphones, or the speaker, you may not notice the effect at all. This application note describes a simple modification that can reduce "thump" by 10-20 dB under high-QRM transceive conditions. Technical details are provided below. Changes Required You'll need a resistor of 150-270 ohms (nominal: 220) and a miniature electrolytic cap of 15-50 uF (nominal: 22). Values are not critical. The two parts will be attached on the bottom of the RF board in the vicinity of Q11 (muting transistor). Use very short leads. 1. Connect the (-) lead of the cap to ground; the nearest available ground pad is the (-) lead of C10 (220 uF). 2. Connect the (+) lead of the cap to one end of the 220-ohm resistor. 3. Connect the other end of the resistor to the drain lead of Q11. This lead also connects to C68 and C73. Technical details: This modification eliminates DC level changes at the input to the LM380 AF amp that are caused by keying of the mute transistor, Q11 (J309). It is these level changes that are perceived as low-frequency artifacts when using headphones with good low-frequency sensitivity. The "thump" is most noticeable when a strong received signal is present, because the DC shift amplitude-modulates the received audio. On power-up, the added capacitor charges up to the DC voltage that's present at pin 5 of the LM386 (U3). From then on, the cap impedes any DC shift at the drain of Q11 that might normally occur during keying of the gate. The resistor is needed to prevent the capacitor from attenuating the audio signal. - --- +++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Mon, 26 Mar 2001 11:28:30 -0800 From: alta Subject: Re: [Elecraft] Application Note: K1 QSK Modification Additional, related mod to consider... I also changed: C68 from 0.1 mf to 0.047 mf C9 from 220 mf to 100 mf Because: In calculating the audio circuit bandwith, it appeared to me that the audio circuit was passing somewhat more bass than necessary for CW. This causes unnecessary load for the .5w-rated speaker and minor additional unnecessary ependiture of energy. With good headphones, the extra bass passes loud thumps and other QRN and QRM that need not be passed to the ear. The above changes reduce the bass response of the K1 audio circuit. The reduced C9 will have larger effect on the 8-ohm speaker, than on 32-ohm headphones. I think this is good, because the speaker isn't good for audio below about 350 Hz anyway. The K1 has one of the cleanest CW sounds I have experienced. For me, reducing the bass response made it even better. This is NOT an "authorized" Elecraft mod, so as always in real life, use your own judgment... ... Reed K1 K7FLY +++++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Tue, 3 Jul 2001 10:45:53 -0600 From: "Rod Cerkoney, N0RC" Subject: [Elecraft] some K1 tweaking notes Folks, Finished up 0197 a few days ago, and am already tweaking it. ;-) For me the AGC is just to slow on the K1 so I changed C31 to 1uF, as I did before on 539, but this time I also changed C67 to 1uF. During last night's ARS Sprint I only had C31 changed out, and noticed that strong nearby stations reduced RX gain a bit too much, while working weaker stations. Other "transient event's" also muted a few code elements on the weaker stations. The jury is out on how this C67 mod will change things, I'll have to wait for more crowded and mixed signal conditions. Limited testing, listening to weak sigs, then keying "the Big Rig" into a D/L, shows some promise. Also, during last night's sprint I found the RIT range too wide. Mine came in at about +/- 4kHz, this is a result of changing C2 [now 56pF] to limit tuning range to about 69kHz. Changing C7 to 22pF yielded +/- 2kHz; 15pF yielded +/- 1.3kHz, JUST RIGHT for me. Another mod I made is a piece of felt behind the tuning knob to add some drag. I bumped the main tuning knob a couple of times and got off Freq, the "felt drag" helps to minimize this. 73, Rod N0RC Ft Collins, CO +++++++++++++++++++++++++++