K2 BFO Test: BFO low freq is really low
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K2 BFO Test: BFO low freq is really low
 
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I've come to the Alignment and Test, Part II. I think I'm having a problem
under the BFO test. Following the instructions, I switch to 40m, hook up the frequency counter to TP2, and get a reading of 4913.52. The manual says I should get something between 4908 and 4918. So far, so good. Next, I go to the part where you determine the BFO range. After hitting Band+, I get a reading of 4917.54 kHz. The manual says you need >= 4916.3, and it's usually between 4916--4917. Maybe a tad high, but looks good to me. After hitting Band-, I get a reading of 2456.11 kHz. The manual says it must be <= 4912.7 (which it most certainly is) but it is usually about 4909--4912 (which is isn't, by a long shot). This results in a range of 2461.43. The manual says it must be >= 3.6 (which it is, by a lot), but it's typically 4--6 kHz. It looks like I'm meeting the letter of the law based on the >= and <= requirements, but I'm nowhere near the typical ranges on the BFO low freq. and range. Following this test in the manual is some info on what to do if the frequencies are too high or too low: First off, I did not use a frequency counter to adjust C22 on the control board, I used a separate receiver and hooked up a wire from its antenna jack to the 4 MHz crystal, as described in the manual. This resulted in me turning C22 less than 30 degrees counter clock wise (anti clock wise). This seems reasonable to me, so I don't think C22 is off by very much. However, I think I might want to try using a frequency counter, to get a little more accuracy in calibration. Could anybody recommend an affordable frequency counter? I've never shopped around for them, so I have no clue as to the price, etc. The third point mentions I might have shorted out part of L33. Looking under a loupe, I did not see any evidence of a short, and in fact, I can slide L33 underneath R116, it doesn't appear that heating R116 affected L33. The fourth point mentions L33 could be broken. I put my DMM on the tiny leads attached to R116 and got 1.7 Ohms. Does this sound reasonable? The final point says to check the capacitors and diodes in the BFO circuit. After another quick look, this appears to be OK to my eyes. Any help would be appreciated! _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: K2 BFO Test: BFO low freq is really low
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Jason,
Yes, 2456 kHz IS way too low - in fact it is quite out-of -bounds - and is close to only half the frequency that it should be. First thing to check is soldering, then re-check the soldering, and when you are finished, check soldering again. Use the schematic to identify those components in the BFO area and check them carefully for good solder joints and proper values. Be certain the varactor diodes are the correct type, and be certain the crystal the correct one and is properly soldered. The BFO is a VXO type circuit, and if everything is proper, it would be very difficult if not impossible to pull a good crystal by 50% of its frequency. If everything else is correct, you may have a bad crystal (or perhaps it is shorted at the solder joints by excess solder) - consider removing the crystal, cleaning up the solder and putting it back in. Lastly, look for something wrong with either the counter probe or the RF voltage at the BFO test point. It is possible (but not probable) that the voltage is high enough to properly count the frequency at the high end, but drops off at the low end and counts only approximately half the pulses. If you have a 'scope (or build the RF probe included with your K2 kit), it should be able to tell you if the RF voltage is really lower at the low frequency end. The calibration of the 4 MHz reference may cause reading to be off by a bit, but not nearly the difference you are reporting. If you set it with another receiver, you are close enough for now - you can refine it later when you have completed the K2 and are ready to do a precise dial calibration. I recommend using the most recent method of zeroing WWV and comparing the BFO and VCO frequencies (previously known as the N6KR method). Details are on the Elecraft website and can also be found in the K2 dial calibration article on my website www.qsl.net/w3fpr. 73, Don W3FPR ----- Original Message ----- From: "Jason Marten" <[hidden email]> > I've come to the Alignment and Test, Part II. I think I'm having a > problem under the BFO test. > > Following the instructions, I switch to 40m, hook up the frequency counter > to TP2, and get a reading of 4913.52. The manual says I should get > something between 4908 and 4918. So far, so good. > > Next, I go to the part where you determine the BFO range. After hitting > Band+, I get a reading of 4917.54 kHz. The manual says you need >= > 4916.3, and it's usually between 4916--4917. Maybe a tad high, but looks > good to me. After hitting Band-, I get a reading of 2456.11 kHz. The > manual says it must be <= 4912.7 (which it most certainly is) but it is > usually about 4909--4912 (which is isn't, by a long shot). This results > in a range of 2461.43. The manual says it must be >= 3.6 (which it is, by > a lot), but it's typically 4--6 kHz. > > It looks like I'm meeting the letter of the law based on the >= and <= > requirements, but I'm nowhere near the typical ranges on the BFO low freq. > and range. > > Following this test in the manual is some info on what to do if the > frequencies are too high or too low: > > First off, I did not use a frequency counter to adjust C22 on the control > board, I used a separate receiver and hooked up a wire from its antenna > jack to the 4 MHz crystal, as described in the manual. This resulted in > me turning C22 less than 30 degrees counter clock wise (anti clock wise). > This seems reasonable to me, so I don't think C22 is off by very much. > However, I think I might want to try using a frequency counter, to get a > little more accuracy in calibration. Could anybody recommend an > affordable frequency counter? I've never shopped around for them, so I > have no clue as to the price, etc. > > The third point mentions I might have shorted out part of L33. Looking > under a loupe, I did not see any evidence of a short, and in fact, I can > slide L33 underneath R116, it doesn't appear that heating R116 affected > L33. > > The fourth point mentions L33 could be broken. I put my DMM on the tiny > leads attached to R116 and got 1.7 Ohms. Does this sound reasonable? > > The final point says to check the capacitors and diodes in the BFO > circuit. After another quick look, this appears to be OK to my eyes. > > Any help would be appreciated! > > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft Help: > http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
RE: K2 BFO Test: BFO low freq is really low
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In reply to this post by Jason Marten
It looks like the counter is only registering half the frequency and it's
really at 4912 kHz. I don't think it's physically possible for the BFO to oscillate down there. Certainly not under crystal control. C22 won't vary your counter time base enough to cause anything like that sort of error. You can confirm that he counter is working by simply going back to the other end of the range where you read 4917.54 kHz and confirm it still works. I'm really stumped to suggest where it might be happening though. I'd say the counter but if you get a good reading at 4917.54, I don't see how that could be it. Ron AC7AC -----Original Message----- I've come to the Alignment and Test, Part II. I think I'm having a problem under the BFO test. Following the instructions, I switch to 40m, hook up the frequency counter to TP2, and get a reading of 4913.52. The manual says I should get something between 4908 and 4918. So far, so good. Next, I go to the part where you determine the BFO range. After hitting Band+, I get a reading of 4917.54 kHz. The manual says you need >= Band+4916.3, and it's usually between 4916--4917. Maybe a tad high, but looks good to me. After hitting Band-, I get a reading of 2456.11 kHz. The manual says it must be <= 4912.7 (which it most certainly is) but it is usually about 4909--4912 (which is isn't, by a long shot). This results in a range of 2461.43. The manual says it must be >= 3.6 (which it is, by a lot), but it's typically 4--6 kHz. It looks like I'm meeting the letter of the law based on the >= and <= requirements, but I'm nowhere near the typical ranges on the BFO low freq. and range. Following this test in the manual is some info on what to do if the frequencies are too high or too low: First off, I did not use a frequency counter to adjust C22 on the control board, I used a separate receiver and hooked up a wire from its antenna jack to the 4 MHz crystal, as described in the manual. This resulted in me turning C22 less than 30 degrees counter clock wise (anti clock wise). This seems reasonable to me, so I don't think C22 is off by very much. However, I think I might want to try using a frequency counter, to get a little more accuracy in calibration. Could anybody recommend an affordable frequency counter? I've never shopped around for them, so I have no clue as to the price, etc. The third point mentions I might have shorted out part of L33. Looking under a loupe, I did not see any evidence of a short, and in fact, I can slide L33 underneath R116, it doesn't appear that heating R116 affected L33. The fourth point mentions L33 could be broken. I put my DMM on the tiny leads attached to R116 and got 1.7 Ohms. Does this sound reasonable? The final point says to check the capacitors and diodes in the BFO circuit. After another quick look, this appears to be OK to my eyes. Any help would be appreciated! _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Jason Marten
A possible cause of misreading the BFO frequency at TP2 may be due to the K2
frequency counter being insensitive. See Elecraft Builders Alert #21 of October 19, 2004. Recent kits issued with the blue colored MPS5179 used in the K2 frequency counter input circuit have been found to have low sensitivity and should be replaced with the black version of the transistor. It is also worthwhile checking the K2 frequency counter input on the K2 Control Board has the components place correctly and soldered joints are good. The significance of this is that TP2 signal levels are much lower than TP1 or TP3 and where the counter may work on the other TP's, it could fail or become random on TP2. The given voltage in K2 Troubleshooting when measured with the K2 RF probe is between 0.025 and 0.070 V rms which is a much lower level than TP1 where 0.60 to 0.75 V rms is expected and TP3 where somewhere approaching 1V rms can be the norm. Checking the setting of C22 and the 4Mhz oscillator with an external frequency counter can have pitfalls. Firstly the counter has to have sufficient accuracy and resolution to fulfil the task. Secondly the external frequency counter, whilst it may have very good accuracy, could load the K2 4MHz oscillator and cause misleading measurements. I found my Racal Dana 9915M bench counter with xtal ovened clock did this and needed to connected via a 10X scope probe to minimise the loading affect. You will note that the K2 frequency counter probe has a 10pF capacitor in series which should reduce the loading effect of the internal counter to a degree. Using the recommended C22 adjustment techniques given by Elecraft and other experts may still be the best solution with a better final accuracy. Regards, Bob, G3VVT _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Don Wilhelm-3
Jason,
Visually check the two transistors that form the preamplifier for the frequency counter (Q9 and Q10, I think). If they have a shiny bluish face on the flat side, Elecraft will send you two replacements (totally black). I had this exact problem caused by low or no gain in the transistors. Just a bad lot apparently. See Elecraft Builders Alert #21 of October 19, 2004. 73, Fred K6DGW Auburn CA CM98lw W3FPR - Don Wilhelm wrote: > > Jason, > > Yes, 2456 kHz IS way too low - in fact it is quite out-of -bounds - and is > close to only half the frequency that it should be. > > First thing to check is soldering, then re-check the soldering, and when you > are finished, check soldering again. Use the schematic to identify those > components in the BFO area and check them carefully for good solder joints > and proper values. > > Be certain the varactor diodes are the correct type, and be certain the > crystal the correct one and is properly soldered. The BFO is a VXO type > circuit, and if everything is proper, it would be very difficult if not > impossible to pull a good crystal by 50% of its frequency. If everything > else is correct, you may have a bad crystal (or perhaps it is shorted at the > solder joints by excess solder) - consider removing the crystal, cleaning up > the solder and putting it back in. > > Lastly, look for something wrong with either the counter probe or the RF > voltage at the BFO test point. It is possible (but not probable) that the > voltage is high enough to properly count the frequency at the high end, but > drops off at the low end and counts only approximately half the pulses. If > you have a 'scope (or build the RF probe included with your K2 kit), it > should be able to tell you if the RF voltage is really lower at the low > frequency end. > > The calibration of the 4 MHz reference may cause reading to be off by a bit, > but not nearly the difference you are reporting. If you set it with another > receiver, you are close enough for now - you can refine it later when you > have completed the K2 and are ready to do a precise dial calibration. I > recommend using the most recent method of zeroing WWV and comparing the BFO > and VCO frequencies (previously known as the N6KR method). Details are on > the Elecraft website and can also be found in the K2 dial calibration > article on my website www.qsl.net/w3fpr. > > 73, > Don W3FPR > > ----- Original Message ----- > From: "Jason Marten" <[hidden email]> > > > I've come to the Alignment and Test, Part II. I think I'm having a > > problem under the BFO test. > > > > Following the instructions, I switch to 40m, hook up the frequency counter > > to TP2, and get a reading of 4913.52. The manual says I should get > > something between 4908 and 4918. So far, so good. > > > > Next, I go to the part where you determine the BFO range. After hitting > > Band+, I get a reading of 4917.54 kHz. The manual says you need >= > > 4916.3, and it's usually between 4916--4917. Maybe a tad high, but looks > > good to me. After hitting Band-, I get a reading of 2456.11 kHz. The > > manual says it must be <= 4912.7 (which it most certainly is) but it is > > usually about 4909--4912 (which is isn't, by a long shot). This results > > in a range of 2461.43. The manual says it must be >= 3.6 (which it is, by > > a lot), but it's typically 4--6 kHz. > > > > It looks like I'm meeting the letter of the law based on the >= and <= > > requirements, but I'm nowhere near the typical ranges on the BFO low freq. > > and range. > > > > Following this test in the manual is some info on what to do if the > > frequencies are too high or too low: > > > > First off, I did not use a frequency counter to adjust C22 on the control > > board, I used a separate receiver and hooked up a wire from its antenna > > jack to the 4 MHz crystal, as described in the manual. This resulted in > > me turning C22 less than 30 degrees counter clock wise (anti clock wise). > > This seems reasonable to me, so I don't think C22 is off by very much. > > However, I think I might want to try using a frequency counter, to get a > > little more accuracy in calibration. Could anybody recommend an > > affordable frequency counter? I've never shopped around for them, so I > > have no clue as to the price, etc. > > > > The third point mentions I might have shorted out part of L33. Looking > > under a loupe, I did not see any evidence of a short, and in fact, I can > > slide L33 underneath R116, it doesn't appear that heating R116 affected > > L33. > > > > The fourth point mentions L33 could be broken. I put my DMM on the tiny > > leads attached to R116 and got 1.7 Ohms. Does this sound reasonable? > > > > The final point says to check the capacitors and diodes in the BFO > > circuit. After another quick look, this appears to be OK to my eyes. > > > > Any help would be appreciated! > > > > > > _______________________________________________ > > Elecraft mailing list > > Post to: [hidden email] > > You must be a subscriber to post to the list. > > Subscriber Info (Addr. Change, sub, unsub etc.): > > http://mailman.qth.net/mailman/listinfo/elecraft Help: > > http://mailman.qth.net/subscribers.htm > > Elecraft web page: http://www.elecraft.com > > > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
RE: K2 BFO Test: BFO low freq is really low
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In reply to this post by G3VVT
Excellent catch by both you and Jim, K4ZM, who replied off line. A flaky
input stage to the counter certainly would fit the symptoms. Please, never be shy about speaking up on the reflector! That's what makes this forum so valuable. It's been nearly four years since I built old number 1289 and I had forgotten about that Builder's Alert. Thanks! Ron AC7AC -----Original Message----- A possible cause of misreading the BFO frequency at TP2 may be due to the K2 frequency counter being insensitive. See Elecraft Builders Alert #21 of October 19, 2004... Regards, Bob, G3VVT _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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