++++++++++++++++ From: "Lyle Johnson" To: "Robert Fanfant" , "Jim Larsen - AL7FS" , "elecraft" Subject: RE: [Elecraft] AL7FS K2 building progress success. Date: Mon, 20 May 2002 07:25:06 -0700 Hello Rob! > Can anyone briefly explain the steps required to measure my K2 receive > sensitivity? I have a calibrated HP 8460B, a Tek TDS 220 and a voltmeter. The ARRL web site (www.arrl.org) has an explanation of how they do all the tests, I believe. You can do it in a couple of ways. One is to hook up your sig gen to the K2, tune it in, tighten up the receive filter to the one you want to listen through, then crank down the sig gen until you can't easily discern the signal is there and call it the sensitivity. Or, you can put an attenuator in line from your sig gen to the K2 - I put the attenuator at the K2 end - this ensures the generator sees a 50-ohm load. I usually use a 10dB attenuator, but use whatever you have that's 6 dB or more, or make one. This is fairly important, since few rigs are really 50-ohm loads and the sig gen calibration can be off a fair amount - as much as 6dB comes to mind - if it isn't seeing 50 ohms. Then, set the bandwidth to 500 Hz or so - that seems to be the default the ARRL tries to use. Kill the AGC if you can and set the volume to some level well below maximum so you ensure the audio stages are linear, not near their maximum output. Measure the audio signal level using an RMS voltmeter. Stare at it awhile until you are satisfied you have a reading that is the average. Since you are hearing noise, the meter will not be steady. Write this value down. IF you have a 4 to 8 ohm resistor you can plug into the external speaker jack and read the voltage across it, that's even better, since a speaker is not necessarily a constant load across its frequency range - but that depends on how much of a purist you are. The speaker itself ought to be just fine. Now tune the sig gen to the frequency you are tuned to and get a reasonable pitch tone, somewhere in the middle of the filter passband. Then turn the signal generator level down until the voltmeter is reading twice the power (ah! that's 70% more voltage, remember the relationship between volts and watts). Note the signal generator reading and don't forget to take into account the attenuator. This level is referred to as the Minimum Discernible Signal, or MDS. Yeah, you can hear a signal weaker than this, but this makes it measurable for comparison purposes. That's probably a longer answer than you wanted! Enjoy! Lyle KK7P ++++++++++++++++++++ From: "Lyle Johnson" To: "Lyle Johnson" , "Robert Fanfant" , "Jim Larsen - AL7FS" , "elecraft" Subject: RE: [Elecraft] AL7FS K2 building progress success. Date: Mon, 20 May 2002 07:32:56 -0700 > Then turn the signal generator level down until the voltmeter is reading > twice the power (ah! that's 70% more voltage, remember the relationship > between volts and watts). Make that 41% more voltage...sorry. Lyle KK7P +++++++++++++++++++++ To: elecraft at mailman.qth.net Date: Mon, 20 May 2002 16:03:11 -0700 From: k6se at juno.com Subject: [Elecraft] Putting K2 #2622 thru its paces I enjoyed working some EU on 20m SSB last night. Also worked 5B4/UA9MA on Cyprus in a pileup on CW. Today I compared the K2 receiver with my FT-1000MP for weak signal detection on CW. I did this same test four years ago, comparing the FT-1000MP with a TS-830S, a TS-870S, an IC-775DSP, and an IC-756. Initially the FT-1000MP was stock, without the INRAD front-end mod. Here are those results: 1st place = TS-830S and TS-870S 2nd place = FT-1000MP 3rd place = IC-775DSP 4th place = IC-756 After installing the INRAD front-end mod in the FT-1000MP, it took over 1st place. To achieve the best S/N ratio, the narrowest selectivity for each receiver being tested was used, as follows: FT-1000MP = 250/250 Hz xtal IF filters + 60 Hz DSP filter. . TS-830S = 250/200 Hz xtal IF filters + VBT tuned to approx 50 Hz passband. TS-870S = 50 Hz IF (radio is strictly DSP). IC-775DSP = 250/250 Hz xtal IF filters + 80 Hz APF. IC-756 = 250/250 Hz xtal IF filters + 80 Hz APF. All tests were run with a quick-switch configuration using the 10-meter beacon station in Long Beach, CA as the steady test signal. The beam was rotated so that the signal was barely detectable. Today I did the same test with the K2 vs. the FT-1000MP. The K2 now is in 1st place. With the beam rotated so that the signal is no longer discernible on the FT-1000MP, it is still copiable on the K2. This is even with the improvement of having a 125 Hz xtal filter in the 2nd IF of the FT-1000MP now. During the test, the K2 was set at 0.10 kHz BW with AF2 selected. The other day I ran the same test on 160m using the third harmonic of a local BC station on 610 kHz as the test signal (I can switch my 160m array to make this steady signal quite weak). Four years ago, the test results with the other rigs were the same as on 10 meters (the FT-1000MP being best). Comparisons between the FT-1000MP and the K2 on 160 meters show them to be equal in weak signal detection on that band. 73, de Earl, K6SE +++++++++++++++++++ From: ZarubaJr at aol.com Date: Wed, 14 Aug 2002 23:12:10 EDT Subject: Re: [Elecraft] K2 RX not working OK To: dl4yao at web.de Cc: elecraft at mailman.qth.net Hello Chris, Do you have an oscilloscope and signal generator available to use? That would make trouble shooting easier, but if you don't, here is what I would check. 40 Meter RX - Examine the pads for L25 and L26 VERY closely, with a magnifying glass. If you see a small black ring around the lead, that means there is some residue from the lead tinning process that is preventing good contact. Remove the leads, clean them very well, then re-install. PREAMP - Basically, the same trouble shooting method as above, the component to check is T6. I've worked on several K2's with similar troubles, and the toroid inductors in the low pass filter section are the first place to look for trouble. I had a similar problem with the K2 I own, and that was the fix for me. If you have a scope and sig gen, set the generator for 7 MHz and inject the signal at the antenna connector. With the scope, verify your signal level at P6 pin 2. Next, look for signal at K12 pin 7, then K12 pin 8, both pads of L26, both pads of L25, K12 pin 3, K12 pin 4. If you have the same amplitude of signal to this point, then the 40 meter low pass filter is probably OK. If at any time you have a loss of signal, or reduced amplitude, back up to the last point of good signal and start verifying the components in between. If you follow the signal flow indicated on the schematic, you should eventually come to the point where your signal is lost, and that would be the area to check more thoroughly. I would also recommend waiting a day or two (go to the gasthaus and sit at the stamtisch) before beginning the troubleshooting session, to give you a fresh perspective of the problem. Sometimes, we spend too much time with our toys, and we don't see the problems, but when we come at it after a rest, troubles are easier to spot. Good Luck, and let me know how it works out. If you need more help, let me know. If this does fix your K2, go to your local gasthaus and have a fine pils for me :) 73, John AA2BN (ex - DA1ZJ) ++++++++++++++++++++ From: "Christoph Rheker" To: Subject: Re: [Elecraft] K2 RX not working OK Date: Thu, 15 Aug 2002 23:29:34 +0200 Many TNX to N0SS, K4ZM, AA2BN, DL8BAG and PE1MHO for their responses. It's working OK now. Error was: 1. T6 not installed correctly. 2. D3 installed in wrong direction. Now sensitivity easily matches my TS870. First results quite impressive... Good thing is, by trouble shooting these issues I always learn something. Bad thing is, it makes me stay up late! For tonight I will follow AA2BN's suggestion and enjoy a good beer.--)) 73 de Chris, DL4YAO ----- Original Message ----- From: "Christoph Rheker" To: Sent: Thursday, August 15, 2002 12:26 AM Subject: [Elecraft] K2 RX not working OK > Hello friends, > > I have just completed my K2 to the step where the 40m RX > works, page 61. > > All tests so far were OK like described in the manual. > > However, it seems the RX is deaf. On my Kenwood I am receiving > signals with S9+ which are just S5 on my K2. > > Also when activating the PRE AMP the signals get weaker! Huh?? > > Seems there is something wrong. I have spent a few hours checking > but couldnt find anything. > > Any idea would be helpfull. > > Mni Tnx de Chris, DL4YAO ++++++++++++++++++