BFO oscillator level
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I did some measurements on the BFO output level on my K2 #2024. On U11 pin 6, I measured LSB: 596mV RMS, USB: 727mV RMS, CW: 577mV RMS, using the RF probe and a DVM. There has always been some BFO leakage into the AGC circuit. When I adjust the S-meter LOW for 1 led lit on LSB, two leds will lit up on USB, (40m band), I suspect this is caused by some leakage from the BFO osc, beeing a little more on USB than on LSB. Is there a simple way to reduce (or equalize) the BFO osc level, say by half? It would still be within specs (see page 11 Appendix E, on manual) Best if the BFO level would not change when the BFO freq is changed. 73, de Matti -- Marteinn Sverrisson TF3MA Langitangi 2 Internet: tf3ma [at] raunvis [dot] hi [dot] is 270 Mosfellsbær http://www.raunvis.hi.is/~tf3ma Iceland _______________________________________________ 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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Matti,
Rather than the BFO leaking directly into the AGC circuit, there is a much greater liklihood that the BFO signal is leaking into the IF amplifier, T7 or the IF crystals themselves, including the crystals on the KSB2 option. Once the BFO finds its way into those circuits, it will be coupled to the AGC input by the normal AGC Input signal path. I would suggest first steps to reduce BFO leakage would be to make certain all the crystal cans are grounded at the base (particularly the BFO and IF crystals) rather than at the top, and that the soldering at the grounding point be good - you should see the edge of the solder taper smoothly out onto the crystal case - if there is a distinct edge to the solder or it looks like a ball on the crystal can, the crystal can did not receive enough heat for a good solder connection. Clip all leads in the product detector and IF amplifier to the minimum possible (including the IC leads). If there is excess solder, it should be removed with solder wick or a de-soldering tool. With plated thru holes, there is no need for a fillet of solder at the connection - if the holes are filled with solder, that is sufficient. Before flush cutting the leads, it may ba a good idea to re-flow the soldering in the area with a soldering iron set to about 750 degrees F (400 C). Good luck. 73, Don W3FPR > -----Original Message----- > > I did some measurements on the BFO output level on my K2 #2024. > On U11 pin 6, I measured LSB: 596mV RMS, USB: 727mV RMS, CW: > 577mV RMS, using > the RF probe and a DVM. > > There has always been some BFO leakage into the AGC circuit. When I > adjust the S-meter LOW for 1 led lit on LSB, two leds will lit up on > USB, (40m band), I suspect this is caused by some leakage from > the BFO osc, > beeing a little more on USB than on LSB. > > Is there a simple way to reduce (or equalize) the BFO osc level, > say by half? > It would still be within specs (see page 11 Appendix E, on manual) > Best if the BFO level would not change when the BFO freq is changed. > > 73, de Matti > -- > Marteinn Sverrisson TF3MA > Langitangi 2 Internet: tf3ma [at] raunvis [dot] hi [dot] is > 270 Mosfellsbær http://www.raunvis.hi.is/~tf3ma > Iceland > No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.446 / Virus Database: 268.18.8/717 - Release Date: 3/10/2007 2:25 PM _______________________________________________ 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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One of questions frequently asked by those who have built my Z90
panadapter kit and use it with a K2 is "what is that blip that I see even with the antenna disconnected?" It is the BFO leaking backwards through the IF chain back to the post-mixer amplifier output. From what I've learned from my customers, it's present in all K2s, and seems to vary from K2 to K2 about 10 dB or so in level. With the receiver input connected to a dummy load or the antenna disconnected, it's visible with a Z90 connected to my K2 at about 25 dB above the noise level, and this level seems to be typical of my customers observations. With an antenna connected, particularly on the lower bands, enough noise is received to mostly hide the BFO leakage signal on the Z90 panadapter. You can see my measured BFO leakage data at http://www.cliftonlaboratories.com/k2_interface.htm. This page also discusses the probably leakage path and estimates the expected leakage level, based on the reverse isolation of the amplifiers in question. Jack K8ZOA www.cliftonlaboratories.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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