Date: Sun, 4 Mar 2001 21:03:47 -0600 From: "Don Wines" Subject: Re: [Elecraft] Loud Thunk Pop! Hi John, I had the same problem with K1 #123 after I installed the KNB1. The problem didn't appear immediately but appeared a couple of weeks after the KNB1 was installed. I removed the KNB1 and replaced C22 on the main board and, sure enough, the problem disappeared! So I figured it must be caused by the noise blanker. I did a real close inspection of the parts placement and my soldering job on the KNB1 and discovered a missed solder joint on the IC (I don't remember which pin). Soldered it, pulled C22, and replaced the KNB1. Fired it up and still had the popping on T-R. I scratched my head for a while and went to the Elecraft site and found a T-R circuit mod (K1 Builder Alert #1 for the Rev. C board) to improve noise immunity in the T-R circuit. After I made this modification the severe popping problem went away and has stayed away. I'm not a technical guru so I can't explain why this worked. Maybe Wayne can tell us. - ----- Original Message ----- From: "K7FD N7SG" > Am I the only one having a K1 w/ noisy QSK? It seems after I installed the > KNB1, I've amplified a distinct 'thunk' after each character. Temporarily > I've 'disabled QSK' by setting the t-r to 200. This is not the solution I'm > looking for, however. > > The QSK has never been 'smooth as the K2'...but now it's really buggin' > me... > > Thanks for any tips, > > John K7FD ++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Mon, 5 Mar 2001 19:11:56 -0800 From: "K7FD N7SG" Subject: [Elecraft] AGC/QSK Thunkage K1 78 and 52 are both exhibiting a distinct t-r THUNK, as eluded to in a previous post. The K1's do this WITHOUT ATU or NB installed. The NB installation in nr 78 did, however, appear to amplify the THUNK... At any rate, the THUNKING is present without the options. If the frequency is CLEAR while sending, there is NO thunkage. If there is qrm or a pileup, when I send I get the THUNKING on the last character sent as the receiver comes back. The louder the stations on frequency, the bigger the thunk. Delaying the t-r time does not change level of thunking, just the amount. I changed C31 on the RF board (thanks for the info, Rod) to 1.0 uf but this made NO difference. Is it appearing the slow attacking AGC is causing the THUNK? I also tried C31 at .47 uf, but the thunk is there. This is a HEFTY thunk...one that causes eardrums to hurt if the volume is at all high. With the AGC OFF there is no THUNK. Turning the receive volume to lower than comfortable also reduces the thunk intensity...so it's volume related, too. I've thunk about this all day...and still haven't come up with a decent solution... ;) If someone stumbles onto a solution, please let me know. Thunks in advance! John K7FD +++++++++++++++++++++++++++++++++++++++++++++++++ Date: Tue, 6 Mar 2001 06:36:19 -0800 From: "K7FD N7SG" Subject: [Elecraft] Re: Noisy QSK Interesting! Thanks for the info, Robert. In my two K1's here in the shack, both exhibit the exact same qualities. Very quiet and smooth QSK, UNLESS there is back ground QRM...such as dropping your call in a pileup. Then when the receiver comes back after the t-r switch, a loud THUNK as the agc decides what to do. I'm hoping Elecraft will have a clue. Several others have written with the same problem. N0RC and N4BP both switched out C31 with a lower value cap to eliviate this problem and also put a cap in parallel with pins 9 and 10 on RP3 on the RF board. Doc K0EVZ has the same 'noisy attack' on QSK also. So apparently some rigs are prone, others not. Thanks again for the note... 73 John K7FD ++++++++++++++++++++++++++++++++++++++++++++++++ Date: Tue, 6 Mar 2001 20:12:44 -0800 From: "K7FD N7SG" Subject: [Elecraft] Temporary Fix QSK Thunk For those who've written me also expressing problems w/ K1 QSK t-r noise, I've found I can minimize the noise somewhat by using the NB in LO or HI to blank out the thunk. Also, narrowing the filter to its narrowest width helps. Just a temp fix... Strangely, my loudest t-r noise centers around 14.061MHz. Other frequencies are less... John K7FD, K1/78 ++++++++++++++++++++++++++++++++++++++++++++++++ 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 ++++++++++++++++++++++++++++++++++++++++++++++++++