// API callback
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Therefore it has fewer indicators of status than many other transceivers. There isn't really much space for this on the rather small frontpanel. But I felt for a long time felt that it should be possible to put \u003Ca href=\"http:\/\/marc.info\/?l=elecraft\u0026amp;m=103427055228912\u0026amp;w=2\"\u003Eadditional LED indicators\u003C\/a\u003E on the K2 but I wanted to avoid drilling holes in the front panel.  Here is a method based on using small LEDs in the keycaps, see info from \u003Ca href=\"http:\/\/marc.info\/?l=elecraft\u0026amp;m=111288364420209\u0026amp;w=2\"\u003EW3FPR\/KR5L\u003C\/a\u003E, as you can always get replacement key caps from Elecraft.\u003Cbr \/\u003E\n\u003Cbr \/\u003E\nOn \u003Ca href=\"http:\/\/www.w3fpr.com\/\"\u003EW3FPR\u003C\/a\u003E’s recommendation I have used \u003Ca href=\"http:\/\/marc.info\/?l=elecraft\u0026amp;m=111293335927005\u0026amp;w=2\"\u003E2 mm LEDs\u003C\/a\u003E of types HLMP6300 (red), HLMP6400 (orange\/yellow), and HLMP6500 (green). They can be bought from Digikey as well as from ELFA in Northern Europe. The first two of the five LEDs that I have added can be connected from the front panel board without additional wiring to other boards.\u003Cbr \/\u003E\n\u003Cbr \/\u003E\nThis YouTube video shows the three first LEDs, the Zero-Beat Indicator, the Split Indicator, and the Audio Filter On indicator:\u003Cbr \/\u003E\n\u003Cbr \/\u003E\n\u003Cobject style=\"height: 312px; width: 512px;\"\u003E\u003Cparam name=\"movie\" value=\"http:\/\/www.youtube.com\/v\/XkR4VJ6j0Hg?version=3\" \/\u003E\n\u003Cparam name=\"allowFullScreen\" value=\"true\" \/\u003E\n\u003Cparam name=\"allowScriptAccess\" value=\"always\" \/\u003E\n\u003Cembed allowfullscreen=\"true\" allowscriptaccess=\"always\" height=\"312\" src=\"http:\/\/www.youtube.com\/v\/XkR4VJ6j0Hg?version=3\" type=\"application\/x-shockwave-flash\" width=\"512\"\u003E\u003C\/embed\u003E\u003C\/object\u003E \u003Cbr \/\u003E\n\u003Ca name='more'\u003E\u003C\/a\u003E\u003Cbr \/\u003E\n\u003Ca href=\"https:\/\/blogger.googleusercontent.com\/img\/b\/R29vZ2xl\/AVvXsEgJj_U8Ac3koEQz3_W1vv1RMm5_xhlMqe868uJvrlGutqFRhSNNFpS_tsCpG3WyjUN-vBmkWspt_bSbaOUNC_Csm7pzGRsMs5NoD9SqToUo_ig0v2b_-11A0MZV5o1oBv75mcsjTQpV86I\/s1600\/K2-4LEDS.jpg\" style=\"clear: right; float: right; margin-bottom: 1em; margin-left: 1em;\"\u003E\u003Cimg border=\"0\" height=\"123\" src=\"https:\/\/blogger.googleusercontent.com\/img\/b\/R29vZ2xl\/AVvXsEgJj_U8Ac3koEQz3_W1vv1RMm5_xhlMqe868uJvrlGutqFRhSNNFpS_tsCpG3WyjUN-vBmkWspt_bSbaOUNC_Csm7pzGRsMs5NoD9SqToUo_ig0v2b_-11A0MZV5o1oBv75mcsjTQpV86I\/s400\/K2-4LEDS.jpg\" width=\"400\" \/\u003E\u003C\/a\u003E\u003Cbr \/\u003E\nHere is a picture showing all five LEDS including those not shown above, the ones for TX ON and RX ANT ON:\u003Cbr \/\u003E\nThe five LEDs are:\u003Cbr \/\u003E\n\u003Col\u003E\n\u003Cli\u003E\u003Cspan style=\"color: lime;\"\u003E█\u003C\/span\u003E Green indicator in PRE\/ATT – SPOT button to show CW zero-beat. The\u003Ca href=\"http:\/\/la3za.blogspot.no\/2009\/09\/k2-fixed-level-audio-output.html\" target=\"_blank\"\u003E low-power zero-beat indicator\u003C\/a\u003E (\u003Ca href=\"http:\/\/la3za.blogspot.no\/2002\/04\/qrp-zero-beat-indicator-for-elecraft-k2.html\" target=\"_blank\"\u003Eold version here\u003C\/a\u003E) drives the LED cathode directly with anode connected to the line that carries 4.0 V day\/2.7 V night (emitter of Q2).\u003C\/li\u003E\n\u003Cli\u003E\u003Cspan style=\"color: yellow;\"\u003E█\u003C\/span\u003E Yellow indicator in A=B – SPLIT button to show that \u003Ca href=\"https:\/\/folk.uio.no\/sverre\/LA3ZA\/blog\/K2\/N0SS\/k2_rit-split_led_mod_10.pdf\" target=\"_blank\"\u003ESplit\/RIT\/XIT\u003C\/a\u003E is on (requires firmware ver. 2.03d and IOC firmware ver. 1.07 and up). The 2 mm LED is not an ultra bright type so it requires \u003Ca href=\"http:\/\/marc.info\/?l=elecraft\u0026amp;m=106747048026048\u0026amp;w=2\"\u003Ea PNP driver transistor\u003C\/a\u003E.\u003C\/li\u003E\n\u003Cli\u003E\u003Cspan style=\"color: yellow;\"\u003E█\u003C\/span\u003E Yellow indicator in XFIL – AFIL button to show that the audio filter is on. I have several times felt the need for this as I switched to SSB and wondered why the audio was so unintelligible, until I discovered that the audio filter was on. Here is how I did it:\u003C\/li\u003E\n\u003Cul\u003E\n\u003Cli\u003EKAF2 : 180 ohms from pin 7 of U2 controller to pin 4 of P2. P2 connector has been extended from 3 to 4 pins.\u003C\/li\u003E\n\u003Cli\u003ECTRL board: Loose wire from pin 4 of J2 (extended from 3 pins) to Front Panel board\u0026nbsp;\u003C\/li\u003E\n\u003Cli\u003EFront Panel board: Wire to cathode of yellow LED, anode connected to line that carries 4.0 V day\/2.7 V night\u0026nbsp;\u003C\/li\u003E\n\u003C\/ul\u003E\n\u003Cli\u003E\u003Cspan style=\"color: red;\"\u003E█\u003C\/span\u003E Red transmit indicator in MODE – VOX button. It should be driven from a signal which is related to the 8T line, but unfortunately it is not present on the front panel board, only the controller board. Therefore a second loose wire is required between the boards.\u003C\/li\u003E\n\u003Cli\u003E\u003Cspan style=\"color: yellow;\"\u003E█\u003C\/span\u003E Yellow indicator in ANT1\/2 – TUNE button to show that the \u003Ca href=\"http:\/\/marc.info\/?l=elecraft\u0026amp;m=110710874122159\u0026amp;w=2\"\u003ERX ANT is on\u003C\/a\u003E. Since relay K2 on K160RX has two sections which are in parallel for the RX antenna input, one part can be separated and used instead to switch the LED on and off.\u0026nbsp;\u003C\/li\u003E\n\u003Cul\u003E\n\u003Cli\u003ERelay K2 (K160RX) must be unsoldered and traces cut to separate pins 7, 8, and 9 from the RX antenna signal path. Then pin 8 is grounded, and pin \u003Cstrike\u003E\u0026nbsp;9 \u003C\/strike\u003E\u0026nbsp;7 is routed to the LED on the Front Panel Board.\u003C\/li\u003E\n\u003Cli\u003EWire from K160RX runs to pin 7 of P1 on RF board (was AuxBus, but this bus is not used on the Front Panel Board, so it can be cut)\u003C\/li\u003E\n\u003Cli\u003EFront Panel board: Wire from pin 7 of J1 via 180 ohms to cathode of yellow LED, anode connected to line that carries 4.0 V day\/2.7 V night\u003C\/li\u003E\n\u003C\/ul\u003E\n\u003C\/ol\u003E\nThe schematics can be \u003Ca href=\"https:\/\/folk.uio.no\/sverre\/LA3ZA\/blog\/K2\/LA3ZA\/K2Leds_sch.pdf\" target=\"_blank\"\u003Edownloaded here.\u003C\/a\u003E\u003Cbr \/\u003E\n\u003Cbr \/\u003E\nThis was originally written on my old web page\u0026nbsp;in 2005 and has been updated several times since then. This blog post was taken from that page in order to enable discussions relating to modification of the K2 in order to fit these and possibly other LEDs.\u0026nbsp; The first comments are all based on emails I have received with questions and comments,  therefore you will see me as the author of these comments."},"link":[{"rel":"replies","type":"application/atom+xml","href":"https:\/\/la3za.blogspot.com\/feeds\/8224809140700912207\/comments\/default","title":"Post Comments"},{"rel":"replies","type":"text/html","href":"https:\/\/la3za.blogspot.com\/2011\/05\/five-k2-leds-in-buttons.html#comment-form","title":"21 Comments"},{"rel":"edit","type":"application/atom+xml","href":"https:\/\/www.blogger.com\/feeds\/2554001380039969960\/posts\/default\/8224809140700912207"},{"rel":"self","type":"application/atom+xml","href":"https:\/\/www.blogger.com\/feeds\/2554001380039969960\/posts\/default\/8224809140700912207"},{"rel":"alternate","type":"text/html","href":"https:\/\/la3za.blogspot.com\/2011\/05\/five-k2-leds-in-buttons.html","title":"Five LEDs in buttons for the Elecraft K2"}],"author":[{"name":{"$t":"Sverre Holm"},"uri":{"$t":"http:\/\/www.blogger.com\/profile\/08306221557326542499"},"email":{"$t":"noreply@blogger.com"},"gd$image":{"rel":"http://schemas.google.com/g/2005#thumbnail","width":"26","height":"32","src":"\/\/blogger.googleusercontent.com\/img\/b\/R29vZ2xl\/AVvXsEirIUQ4__tBn8iuiGzcRlJEOroeUKkNCZ2mN2DM3rs_2pPUFGIs7a2EtYWIiOikqsFchk8w4XaHx_XyS1g_-i8Kmu46zrppNaF1Xeh-omtKQqjq9tEzjhEobips8DmSvw\/s1600\/sverreholm20.jpg"}}],"media$thumbnail":{"xmlns$media":"http://search.yahoo.com/mrss/","url":"https:\/\/blogger.googleusercontent.com\/img\/b\/R29vZ2xl\/AVvXsEgJj_U8Ac3koEQz3_W1vv1RMm5_xhlMqe868uJvrlGutqFRhSNNFpS_tsCpG3WyjUN-vBmkWspt_bSbaOUNC_Csm7pzGRsMs5NoD9SqToUo_ig0v2b_-11A0MZV5o1oBv75mcsjTQpV86I\/s72-c\/K2-4LEDS.jpg","height":"72","width":"72"},"thr$total":{"$t":"21"}},{"id":{"$t":"tag:blogger.com,1999:blog-2554001380039969960.post-8693050938700157782"},"published":{"$t":"2009-09-27T12:00:00.006+02:00"},"updated":{"$t":"2014-01-27T07:13:42.517+01:00"},"category":[{"scheme":"http://www.blogger.com/atom/ns#","term":"Elecraft"},{"scheme":"http://www.blogger.com/atom/ns#","term":"homebrew"},{"scheme":"http://www.blogger.com/atom/ns#","term":"K2"},{"scheme":"http://www.blogger.com/atom/ns#","term":"zero-beat indicator"}],"title":{"type":"text","$t":"K2 Fixed Level Audio Output"},"content":{"type":"html","$t":"\u003Cdiv class=\"separator\" style=\"clear: both; text-align: center;\"\u003E\n\u003C\/div\u003E\n\u003Cdiv\u003E\n\u003Cdiv class=\"separator\" style=\"clear: both; text-align: center;\"\u003E\n\u003Ca href=\"https:\/\/blogger.googleusercontent.com\/img\/b\/R29vZ2xl\/AVvXsEhu-DgjxX96iTxzF4rEX2sIasCCFAEk8IAbeMO1iJg5IX-nLYnhRs_w5ukxhSE8s7sgYOiL656VgdAfusBR6FUpIxD5mbQhI9Bjkv_pGwsEtBaXJYr2fNNp2G9wUoO9uijZLffm8FWffWw\/s1600\/K2_fpanelboard.jpg\" imageanchor=\"1\" style=\"clear: right; float: right; margin-bottom: 1em; margin-left: 1em;\"\u003E\u003Cimg border=\"0\" src=\"https:\/\/blogger.googleusercontent.com\/img\/b\/R29vZ2xl\/AVvXsEhu-DgjxX96iTxzF4rEX2sIasCCFAEk8IAbeMO1iJg5IX-nLYnhRs_w5ukxhSE8s7sgYOiL656VgdAfusBR6FUpIxD5mbQhI9Bjkv_pGwsEtBaXJYr2fNNp2G9wUoO9uijZLffm8FWffWw\/s320\/K2_fpanelboard.jpg\" height=\"317\" width=\"320\" \/\u003E\u003C\/a\u003E\u003C\/div\u003E\nI started by making a very simple modification for a low level audio output with level that was independent of the AF pot setting. \u003C\/div\u003E\n\u003Cbr \/\u003E\n\u003Cdiv\u003E\nThe next step was to modify my front panel board by adding an audio output (mic plug) via a 25 x audio buffer and a \u003Ca href=\"http:\/\/la3za.blogspot.no\/2002\/04\/qrp-zero-beat-indicator-for-elecraft-k2.html\" target=\"_blank\"\u003Ezero-beat indicator\u003C\/a\u003E which uses the same signal. The added circuit is built Manhattan-style on the upper right on the back of the front panel board, see image. \u003C\/div\u003E\n\u003Cbr \/\u003E\n\u003Cdiv\u003E\nIn this way three things are achieved: \u003C\/div\u003E\n\u003Col\u003E\n\u003Cli\u003E\u003Cdiv\u003E\nThe amplified audio output is independent of the AF pot setting. \u003C\/div\u003E\n\u003C\/li\u003E\n\u003Cli\u003E\u003Cdiv\u003E\nThe zero-beat indicator is also independent of the audio pot setting. \u003C\/div\u003E\n\u003C\/li\u003E\n\u003Cli\u003E\u003Cdiv\u003E\nThe ‘no-wire’ philosophy of K2 is maintained, as there are no wires that need to be run to any of the other boards.\u003C\/div\u003E\n\u003C\/li\u003E\n\u003C\/ol\u003E\n\u003Cdiv\u003E\nThe schematic of the audio buffer and the updated zero-beat indicator is \u003Ca href=\"https:\/\/docs.google.com\/open?id=0B83T7Z3AHnIBZDQ0MDE2YTgtYzVhNy00ZGI0LWE5ODMtYjEwZTY5ZjIzZDZk\" target=\"_blank\"\u003Ehere\u003C\/a\u003E. Note that the zero-beat indicator’s component values have some minor changes from \u003Ca href=\"http:\/\/la3za.blogspot.no\/2002\/04\/qrp-zero-beat-indicator-for-elecraft-k2.html\" target=\"_blank\"\u003Ethe original design\u003C\/a\u003E, that gave a nicer behavior of the display. \u003C\/div\u003E\n\u003Cbr \/\u003E\n\u003Cdiv\u003E\nI also have added an optional signal from the sidetone circuit on the K2's control board (requires a plugable strap between the boards).  This gives a visual check of the zero-beat indicator when you transmit, and it is also nice for demo purposes as both the received and the transmitted CW are output and can be decoded using e.g. a PC.\u003C\/div\u003E\n"},"link":[{"rel":"replies","type":"application/atom+xml","href":"https:\/\/la3za.blogspot.com\/feeds\/8693050938700157782\/comments\/default","title":"Post Comments"},{"rel":"replies","type":"text/html","href":"https:\/\/la3za.blogspot.com\/2009\/09\/k2-fixed-level-audio-output.html#comment-form","title":"0 Comments"},{"rel":"edit","type":"application/atom+xml","href":"https:\/\/www.blogger.com\/feeds\/2554001380039969960\/posts\/default\/8693050938700157782"},{"rel":"self","type":"application/atom+xml","href":"https:\/\/www.blogger.com\/feeds\/2554001380039969960\/posts\/default\/8693050938700157782"},{"rel":"alternate","type":"text/html","href":"https:\/\/la3za.blogspot.com\/2009\/09\/k2-fixed-level-audio-output.html","title":"K2 Fixed Level Audio Output"}],"author":[{"name":{"$t":"Sverre Holm"},"uri":{"$t":"http:\/\/www.blogger.com\/profile\/08306221557326542499"},"email":{"$t":"noreply@blogger.com"},"gd$image":{"rel":"http://schemas.google.com/g/2005#thumbnail","width":"26","height":"32","src":"\/\/blogger.googleusercontent.com\/img\/b\/R29vZ2xl\/AVvXsEirIUQ4__tBn8iuiGzcRlJEOroeUKkNCZ2mN2DM3rs_2pPUFGIs7a2EtYWIiOikqsFchk8w4XaHx_XyS1g_-i8Kmu46zrppNaF1Xeh-omtKQqjq9tEzjhEobips8DmSvw\/s1600\/sverreholm20.jpg"}}],"media$thumbnail":{"xmlns$media":"http://search.yahoo.com/mrss/","url":"https:\/\/blogger.googleusercontent.com\/img\/b\/R29vZ2xl\/AVvXsEhu-DgjxX96iTxzF4rEX2sIasCCFAEk8IAbeMO1iJg5IX-nLYnhRs_w5ukxhSE8s7sgYOiL656VgdAfusBR6FUpIxD5mbQhI9Bjkv_pGwsEtBaXJYr2fNNp2G9wUoO9uijZLffm8FWffWw\/s72-c\/K2_fpanelboard.jpg","height":"72","width":"72"},"thr$total":{"$t":"0"}},{"id":{"$t":"tag:blogger.com,1999:blog-2554001380039969960.post-5194742193458046759"},"published":{"$t":"2002-04-27T00:00:00.000+02:00"},"updated":{"$t":"2017-02-06T23:17:40.149+01:00"},"category":[{"scheme":"http://www.blogger.com/atom/ns#","term":"homebrew"},{"scheme":"http://www.blogger.com/atom/ns#","term":"K2"},{"scheme":"http://www.blogger.com/atom/ns#","term":"QRP"},{"scheme":"http://www.blogger.com/atom/ns#","term":"zero-beat indicator"}],"title":{"type":"text","$t":"QRP Zero-beat Indicator for the Elecraft K2"},"content":{"type":"html","$t":"\u003Ca href=\"https:\/\/blogger.googleusercontent.com\/img\/b\/R29vZ2xl\/AVvXsEheTh04PcEzdleyPKE0XLqclmARDOb2g5pJjS3Z61BTYFWlfR79alSfAphQw4-Q9C8xN0t99a2tG9E7Sb90mpvfkT5SK1WKe5yEpo7G4Rsr7-qjp5IBclNmnuK9m0JxNaVY42bMmBGg9Qk\/s1600\/QRPZero_picture.jpg\" imageanchor=\"1\" style=\"clear: right; float: right; margin-bottom: 1em; margin-left: 1em;\"\u003E\u003Cimg border=\"0\" height=\"200\" src=\"https:\/\/blogger.googleusercontent.com\/img\/b\/R29vZ2xl\/AVvXsEheTh04PcEzdleyPKE0XLqclmARDOb2g5pJjS3Z61BTYFWlfR79alSfAphQw4-Q9C8xN0t99a2tG9E7Sb90mpvfkT5SK1WKe5yEpo7G4Rsr7-qjp5IBclNmnuK9m0JxNaVY42bMmBGg9Qk\/s200\/QRPZero_picture.jpg\" width=\"153\" \/\u003E\u003C\/a\u003EThis is a circuit that builds on KR5L’s zero-beat indicator circuit. He suggested trying a CMOS version of the 567 instead of the standard bipolar version, and here it is: the QRP version of his circuit. It draws only 0.9 mA at 5V compared to about 20 mA\/8V for the original circuit.\u003Cbr \/\u003E\n\u003Cbr \/\u003E\nCompared to the original circuit, C2 and C3 have been divided by about eight, and C1 has been divided by about two, give or take values found in my junk box.\u003Cbr \/\u003E\n\u003Cbr \/\u003E\n\u003Ca name='more'\u003E\u003C\/a\u003E\u003Cbr \/\u003E\n\u003Cbr \/\u003E\nComponent values:\u003Cbr \/\u003E\n\u003Cbr \/\u003E\n\u003Ca href=\"https:\/\/blogger.googleusercontent.com\/img\/b\/R29vZ2xl\/AVvXsEhjT3YKKLXjcQLLlYJps7aM_ukGPhEJ-mD-o3JNlpaZZNL1bdBJZwUmJyejM1x-U7TQ2sVUmMrNKZDGFs3R07TgdglT7q9BQ9iel5Idq5WUQnle8RQ4p1rKFgC3Y8kF6VwWCXSJo5Y1muE\/s1600\/QRPZero_schematics.jpg\" imageanchor=\"1\" style=\"clear: right; float: right; margin-bottom: 1em; margin-left: 1em;\"\u003E\u003Cimg border=\"0\" height=\"197\" src=\"https:\/\/blogger.googleusercontent.com\/img\/b\/R29vZ2xl\/AVvXsEhjT3YKKLXjcQLLlYJps7aM_ukGPhEJ-mD-o3JNlpaZZNL1bdBJZwUmJyejM1x-U7TQ2sVUmMrNKZDGFs3R07TgdglT7q9BQ9iel5Idq5WUQnle8RQ4p1rKFgC3Y8kF6VwWCXSJo5Y1muE\/s400\/QRPZero_schematics.jpg\" width=\"400\" \/\u003E\u003C\/a\u003E\u003Cbr \/\u003E\n\u003Cbr \/\u003E\n\u003Cdiv class=\"MsoNormal\" style=\"margin: 0cm 0cm 0.0001pt;\"\u003E\n\u003Cspan lang=\"EN-US\"\u003EU1 – LMC567 PLL\u003C\/span\u003E\u003C\/div\u003E\n\u003Cdiv class=\"MsoNormal\" style=\"margin: 0cm 0cm 0.0001pt;\"\u003E\n\u003Cspan lang=\"EN-US\"\u003ER1a – 2.2 k\u003C\/span\u003E\u003C\/div\u003E\n\u003Cdiv class=\"MsoNormal\" style=\"margin: 0cm 0cm 0.0001pt;\"\u003E\n\u003Cspan lang=\"EN-US\"\u003ER1b – 5 k pot\u003C\/span\u003E\u003C\/div\u003E\n\u003Cdiv class=\"MsoNormal\" style=\"margin: 0cm 0cm 0.0001pt;\"\u003E\n\u003Cspan lang=\"EN-US\"\u003ER2 – 22 k\u003C\/span\u003E\u003C\/div\u003E\n\u003Cdiv class=\"MsoNormal\" style=\"margin: 0cm 0cm 0.0001pt;\"\u003E\n\u003Cspan lang=\"EN-US\"\u003ER3 – 220 ohm\u003C\/span\u003E\u003C\/div\u003E\n\u003Cdiv class=\"MsoNormal\" style=\"margin: 0cm 0cm 0.0001pt;\"\u003E\n\u003Cspan lang=\"EN-US\"\u003ER4 – 220 ohm\u003C\/span\u003E\u003C\/div\u003E\n\u003Cdiv class=\"MsoNormal\" style=\"margin: 0cm 0cm 0.0001pt;\"\u003E\n\u003Cspan lang=\"EN-US\"\u003ER5 – 390 k\u003C\/span\u003E\u003C\/div\u003E\n\u003Cdiv class=\"MsoNormal\" style=\"margin: 0cm 0cm 0.0001pt;\"\u003E\n\u003Cspan lang=\"EN-US\"\u003EC1 – 0.15 µF\u003C\/span\u003E\u003C\/div\u003E\n\u003Cdiv class=\"MsoNormal\" style=\"margin: 0cm 0cm 0.0001pt;\"\u003E\n\u003Cspan lang=\"EN-US\"\u003EC2 – 1 µF\u003C\/span\u003E\u003C\/div\u003E\n\u003Cdiv class=\"MsoNormal\" style=\"margin: 0cm 0cm 0.0001pt;\"\u003E\n\u003Cspan lang=\"EN-US\"\u003EC3 – 3.3 µF\u003C\/span\u003E\u003C\/div\u003E\n\u003Cdiv class=\"MsoNormal\" style=\"margin: 0cm 0cm 0.0001pt;\"\u003E\n\u003Cspan lang=\"EN-US\"\u003EC4 – 0.1 µF\u003C\/span\u003E\u003C\/div\u003E\n\u003Cdiv class=\"MsoNormal\" style=\"margin: 0cm 0cm 0.0001pt;\"\u003E\n\u003Cspan lang=\"EN-US\"\u003EC5 – 100 µF\u003C\/span\u003E\u003C\/div\u003E\n\u003Cdiv class=\"MsoNormal\" style=\"margin: 0cm 0cm 0.0001pt;\"\u003E\n\u003Cspan lang=\"EN-US\"\u003EC6 – 470 µF\u003C\/span\u003E\u003C\/div\u003E\n\u003Cdiv class=\"MsoNormal\" style=\"margin: 0cm 0cm 0.0001pt;\"\u003E\n\u003Cspan lang=\"EN-US\"\u003E\u003Cbr \/\u003E\n\u003C\/span\u003E\u003C\/div\u003E\n\u003Cbr \/\u003E\nIn addition R3 and C6 have been added. They add a time constant of 0.1 sec or so, but unlike just increasing the output filter capacitor C3, this gives a fade-out when the LED extinguishes, and results in a smoothness to the display much like the indicator on the FT-1000. The value for R3 has been found from the maximum output current of 20 mA of U1, and is obtained if C6 has been charged to 5 V and is then discharged through U1’s output.\u003Cbr \/\u003E\n\u003Cbr \/\u003E\nR5 has also been added for increased sensitivity. I found that my circuit required a little over comfortable speaker level to trigger before R5 was added. Values as low as 270 k can be used and give even higher sensitivity, but also more triggering on noise.\u003Cbr \/\u003E\n\u003Cbr \/\u003E\nThe output is connected to the right-most LED of the K2, an idea that I first heard from W7DZN. The output goes to pin 20 of the DS2 LED array on the Control Board. In the ‘Nite’ setting, the LED is fed from 2.7 V through a 120 ohm resistor, while in the ‘Day’ mode it is fed from 4 V. R4 results in less than 50% of the current in the LED than in the usual S-meter, and makes it easier to see that this segment has a different function.\u003Cbr \/\u003E\n\u003Cbr \/\u003E\nVcc is connected to 5V from the output of U8 on the RF board (across C90 on the underside of the board), and the audio input is connected to the output of the AF power amplifier. The circuit is mounted on the original N0SS\/KR5L PCB.\u003Cbr \/\u003E\n\u003Cbr \/\u003E\nThe frequency can be adjusted to match the sidetone in two ways: By measuring the output of pin 5 with a frequency counter and divide the frequency by two, or by increasing the sidetone level in Test mode until it turns on the LED, and then tune R1b carefully back and forth until one has found the center between the low and high turn-on frequencies.\u003Cbr \/\u003E\n\u003Cbr \/\u003E\nReference: KR5L’s circuit\/PCB:\u0026nbsp;\u003Ca href=\"http:\/\/www.n0ss.net\/kr5l_led_cw_tuning_ind.pdf\"\u003Ehttp:\/\/www.n0ss.net\/kr5l_led_cw_tuning_ind.pdf\u003C\/a\u003E\u003Cbr \/\u003E\n\u003Chr \/\u003E\nThis article was printed in \u003Ca href=\"http:\/\/www.gqrp.com\/\" target=\"_blank\"\u003ESprat\u003C\/a\u003E, Summer 2002 under the title \"\u003Ci\u003EQRP Zero-beat Indicator for the Elecraft K2 (and other transceivers)\u003C\/i\u003E\"\u0026nbsp;and in a German translation as \"\u003Ci\u003EQRP-Zero-Beat-Indikator für den Elecraft K2\u003C\/i\u003E\" in \u003Ca href=\"http:\/\/www.dl-qrp-ag.de\/\"\u003EQRP-Report\u003C\/a\u003E, 3-2002 (Note that R3 was incorrectly labeled 220k).\u003Cbr \/\u003E\n\u003Cbr \/\u003E\nRecently, I moved the zero-beat indicator to a board mounted on the back of the K2's front panel board. I also added an audio buffer for an AF output through the mic plug that is independent of the AF pot setting. The zero-beat indicator uses the same signal, and its indication is therefore independent of audio pot setting. See \u003Ca href=\"http:\/\/la3za.blogspot.no\/2009\/09\/k2-fixed-level-audio-output.html\"\u003EK2 Audio Output\u003C\/a\u003E for details and new pdf-file with schematic.\u003Cbr \/\u003E\n\u003Cbr \/\u003E"},"link":[{"rel":"replies","type":"application/atom+xml","href":"https:\/\/la3za.blogspot.com\/feeds\/5194742193458046759\/comments\/default","title":"Post Comments"},{"rel":"replies","type":"text/html","href":"https:\/\/la3za.blogspot.com\/2002\/04\/qrp-zero-beat-indicator-for-elecraft-k2.html#comment-form","title":"0 Comments"},{"rel":"edit","type":"application/atom+xml","href":"https:\/\/www.blogger.com\/feeds\/2554001380039969960\/posts\/default\/5194742193458046759"},{"rel":"self","type":"application/atom+xml","href":"https:\/\/www.blogger.com\/feeds\/2554001380039969960\/posts\/default\/5194742193458046759"},{"rel":"alternate","type":"text/html","href":"https:\/\/la3za.blogspot.com\/2002\/04\/qrp-zero-beat-indicator-for-elecraft-k2.html","title":"QRP Zero-beat Indicator for the Elecraft K2"}],"author":[{"name":{"$t":"Sverre Holm"},"uri":{"$t":"http:\/\/www.blogger.com\/profile\/08306221557326542499"},"email":{"$t":"noreply@blogger.com"},"gd$image":{"rel":"http://schemas.google.com/g/2005#thumbnail","width":"26","height":"32","src":"\/\/blogger.googleusercontent.com\/img\/b\/R29vZ2xl\/AVvXsEirIUQ4__tBn8iuiGzcRlJEOroeUKkNCZ2mN2DM3rs_2pPUFGIs7a2EtYWIiOikqsFchk8w4XaHx_XyS1g_-i8Kmu46zrppNaF1Xeh-omtKQqjq9tEzjhEobips8DmSvw\/s1600\/sverreholm20.jpg"}}],"media$thumbnail":{"xmlns$media":"http://search.yahoo.com/mrss/","url":"https:\/\/blogger.googleusercontent.com\/img\/b\/R29vZ2xl\/AVvXsEheTh04PcEzdleyPKE0XLqclmARDOb2g5pJjS3Z61BTYFWlfR79alSfAphQw4-Q9C8xN0t99a2tG9E7Sb90mpvfkT5SK1WKe5yEpo7G4Rsr7-qjp5IBclNmnuK9m0JxNaVY42bMmBGg9Qk\/s72-c\/QRPZero_picture.jpg","height":"72","width":"72"},"thr$total":{"$t":"0"}}]}});