+++++++++++++++++++++ Continuation of K2 L34 Tuning +++++++++++++++++++++ Reply-To: From: "Ron D'Eau Claire" To: "'Dave Sergeant'" , Subject: RE: [Elecraft] Re:L34 adjustment Date: Thu, 31 Oct 2002 08:50:36 -0800 OOps, I bet you were using a narrow bandwidth setting, Dave. My apologies. I rewriting my procedure quickly, I left out the instruction to select a wide bandwidth. If you narrow down the bandwidth, you will start reading a "peak". That's because the filter suppressing the wide-band noise. At wide bandwidth settings, peaking the "birdie" suppresses the background noise producing a dip in the AGC voltage reading where the birdie is strongest and the signal-to-noise ratio is best. At narrower settings the AGC won't see the wide band noise and reacts only to the birdie. I have a hunch you were using a narrow enough bandwidth to be reading the 'peak'. I set mine with a bandwidth of at least 1.6 kHz. If you have the SSB module installed, the OPT1 filter is best. I am sorry for the confusion. BTW, several ops pointed out that it is actually easier to get a DMM probe clip on R4 nearer the bottom of the control board looking in from the top. It's almost directly below R2 and the other resistors. at the top. That does work just as well. Ron AC7AC K2 # 1289 I have just tried readjusting L34 according to the DMM method suggested by Ron. My Fluke 77 only reads to two decimal places... I found with the core two turns down from the top the reading was 3.75V. It drops to a minimum of 3.67V with the core right at the top, but I cannot screw it any further to confirm it really is the minimum. Possibly I need to reduce C182 slightly to give me more range? I have always had the feeling that my K2 was lacking somewhat in gain as I found I always needed to have the preamp on (which causes intermod products on 40m and 30m here in Europe). With L34 readjusted it certainly sounds a little livelier. When I have time I will check its sensitivity with my Gould generator (with calibrated attenuator). 73s Dave G3YMC K2 #2498 ++++++++++++++++ Reply-To: From: "Ron D'Eau Claire" To: "'peter barville'" , Subject: RE: [Elecraft] Re L34 Adjustment Date: Fri, 1 Nov 2002 09:26:24 -0800 Okay, Mia Culpa "big time"! After Peter in England and Ron in New Zealand both had trouble duplicating my L34 adjustment, I spent my coffee time this morning digging through the Elecraft archives for Gary Surrency's original "procedure" that was trying to recall. I turned up the applicable part of his message quoted by someone else back on October 17, 2000 under "A few questions about C182 and the alignment of L34". Here's what Gary is quoted as having written: >7. If L34 does not have a definite but broad peak, then inspect C182 to >see if it is a 180pF cap. 270pF was used in the earlier kits, and in some >cases C182 must be lowered to 150pF or less. The peak is easiest to see >on a DMM, connected to the LM380N-8 side of R20 on the Control Board. Set >it for AC volts and tune to the 7.0MHz birdie. I suspect that is the message I was remembering. Note that he is NOT measuring the AGC voltage as I did, but is measuring the audio output from the audio amplifier - just what those using Spectrogram are doing but by using a DMM the peak is perhaps a bit easier to 'see'. Making the adjustment by monitoring the AGC voltage works for me. I'm guessing as to why it shows up as a dip in the voltage on wide bandwidths and a peak on narrow bandwidths. I can see the "noise" hump clearly on Spectrogram if I'm watching the audio spectrum while doing the adjustment. The "peak" in the response is when the noise is pretty evenly distributed across the passband around the 'base' of the spike on spectrogram that is the 7 MHz birdie. In any event, my apologies for have gotten Gary's procedure wrong. I'll print this one out and add it to my fat envelope of "mods and notes for keeping the K2 in top form!". But first, I need a crowbar to get my foot out of my mouth... Ron AC7AC K2 # 1289 --------- Now I admit to being really confused. I do not notice any point of L34's travel where it produces a dip in the R2 reading. I'm still not clear how it can. If L34 is adjusted in order to peak the birdie, then surely the AGC volts will increase. Maybe (for some reason) I don't have enough adjustment available on my L34, but I see no point at which the birdie becomes strong enough to suppress the noise. Even if it did, then the AGC voltage the birdie generates would have to be initially equal to, and then greater than, that generated by the noise (otherwise it isn't going to suppress the noise). So where/how can a dip occur? -- 72, peter g3xjs +++++++++++++++ Date: Fri, 1 Nov 2002 21:21:20 +0000 To: elecraft at mailman.qth.net From: peter barville Subject: [Elecraft] Re L34 Adjustment Ron AC7AC wrote: >Okay, Mia Culpa "big time"! >After Peter in England and Ron in New Zealand both had trouble >duplicating my L34 adjustment, I spent my coffee time this morning >digging through the Elecraft archives for Gary Surrency's original >"procedure" that was trying to recall. I turned up the applicable part >of his message quoted by someone else back on October 17, 2000 under "A >few questions about C182 and the alignment of L34". ---------------- Thanks for spooling back through the archives Ron, and coming up with the original posting. I think it will be worth my while trying a smaller value for C182 (150pF, or less) and then maybe I *will* see a definite peak. Either way, time spent inside the K2 is FUN! It seems the subject of L34 runs, and runs, and runs ... ;-) -- 72, peter g3xjs +++++++++++++++++ From: "John Huffman" To: "Elecraft" Subject: Re: [Elecraft] My K2 - Is this normal? Date: Fri, 14 Feb 2003 17:33:56 -0500 Many thanks to all that responded! What a great list. > > First, the IF alignment on page 41, L34's slug peaks at the bottom of the > > can, not 1 to 1.5 turns below the top as in the manual. OK? I redid L34 using Spectogram where I could watch both the birdie and the background noise. It's not a sharp peak, but its a better ratio than at the bottom. > > Second, while receiving every once in a great while the display will show > > the power or keyer speed for a split second. OK? It appears this is not uncommon and not a cause for concern. Thanks to all! 73 de NA8M John ++++++++++++++++++ From: "John Huffman" To: "Wallace, Andy" , "Elecraft" Subject: Re: [Elecraft] L34 -- is this what it sounds like? Date: Sat, 15 Feb 2003 13:56:41 -0500 Andy - That was my experience when I went back to redo L34. The peak remained and I tuned to get the hiss as low as possible. There was no dip, but it averaged just a bit lower near the top of the can. 73 de NA8M John ----- Original Message ----- From: "Wallace, Andy" To: "'Elecraft'" <> Sent: Saturday, February 15, 2003 1:08 PM Subject: [Elecraft] L34 -- is this what it sounds like? > OK, the recent talk about L34 made me go back and take > a look at it with Spectrogram. > > If I tune in the birdie at 7 MHz, I hear it quite clearly. > It shows up as a nice peak in Spectrogram, when I center > it carefully in the filter (at the sidetone freq). > > If I set the volume level such that the birdie peak is > at -10 dB, then the shoulders of the bandpass are down > around -50 dB. > > What I hear, when I tune L34 down from the top to the bottom > of the can, is an increase in hiss volume which then sweeps > down in frequency. This seems to match what shows on Spectrogram. > I don't see the birdie peaking any higher at all. > > Is L34 this subjective? To me, the s/n ratio seems to be best with > L34 almost at the top of the can, but I am surprised I am not seeing > any kind of "peaking" of the birdie signal strength. > > Andy > _______________________________________________ > Elecraft mailing list: Elecraft at mailman.qth.net > You must be a list member to post to the list. > Postings must be plain text (no HTML or attachments). > See: http://mailman.qth.net/mailman/listinfo/elecraft > Elecraft Web Page: http://www.elecraft.com > > +++++++++++++++++ From: "Wallace, Andy" To: "'Peter Halpin'" Cc: "'Elecraft'" Subject: RE: [Elecraft] L34 -- is this what it sounds like? Date: Tue, 18 Feb 2003 08:38:37 -0500 > -----Original Message----- > From: Peter Halpin [mailto:halpin at keyaccess.nl] > > Ermm.....you do have the AGC switched off?? Pete (and everyone) -- yes, I forgot to mention I had the AGC off when I was using Spectrogram to look at the birdie/L34 adjustment. What I experienced was hiss/noise going up and down in pitch and level, but the birdie level remained perfectly steady. (It was centered in the filter passband also.) By the way, it might be nice to have an Elecraft-only cut-down version of Spectrogram, just for aligning filters (set FFT and sample rate, markers, etc.) for a reduced price. Perhaps even ordering a floppy from Elecraft's own site....just an idea! Andy ++++++++++++++++++