Re: [Elecraft] KX1 speaker output with superimposed oscillation
Hi Dave, Thanks to you. IHope Bob can tell us, with the modeling of the LM386, why this strange behaviour. From the knowledge point of view, the technique "try and error" is not the best way, we would like to know more... . Now, my KX1, at the LM386's speaker output, pin 5, has the original RC network (10 Ohm + 100 nF) to ground plus one 68 nF to ground also. I even tried to put the 68 nF in parallel with the original 100 nF but it did not worked. Neither with a value of 100 nF, so finally I installed the 68 nF capacitor directly to the output and ground, allways with short leads (I learned this after several years working with RF techniques :)). 73, Paco _ Grandes éxitos, superhéroes, imitaciones, cine y TV... http://es.msn.kiwee.com/ Lo mejor para tu móvil. ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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: [Elecraft] KX1 speaker output with superimposed oscillation
Hi Bob, Finally, I got it !. It is related with "the RC network connected between the output pin 5 and ground, required to keep the amplifier stable at high frequencies at different loads", as you mention on your previous post. I checked the RC network and I even installed a new one: same behavior. If I removed this RC network completely, the oscillation now started with lower volumes !. Using the technique "try and error", the problem was solved with a capacitor of 68 nF in parallel with this RC network, that is, just from pin 5 to ground. No more high frequency oscillation with different loads !. By the way, the DC voltage at pin 5 was half the supply: 3 V. I even installed a short leads 10 uF tantalum across the supply of U4, without positive results. I don't know the reason of this behaviour, maybe, as you say on your post, is due to the high gain of this stage (46 dB). Who knows... . Many thanks Bob and have a good day. 73, Paco _ Descarga gratis la Barra de Herramientas de MSN http://www.msn.es/usuario/busqueda/barra?XAPID=2031&DI=1055&SU=http%3A//www.hotmail.com&HL=LINKTAG1OPENINGTEXT_MSNBH ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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] KX1 Output Power & Harmonic Rejection
Hi to all, After "alignment and Test - Part III", I got more power on 20 m (3.8 W) than 40 m (3.2 W). As the manual says, for best harmonic rejection, it should be the opposite (0.3...0.6 W more power on 40 m). Following some previous posts (thanks Don), I checked very carefully all the components, soldering, relay K2 working OK and even the complete TX path from the DDS output to the BNC connector. So, as the manual says, I "squeezed" L2 on the lower pass filter, in order to get the best harmonic rejection. Here are some tests I've made (all measurements at 12 V & with OUTPUT POWER MOD done; NO TUNER): 1. L2 turns not squeezed (according Fig. 16 on the manual) a) 40 m - output power: 3.17 W - current drain: 490 mA - 2nd harmonic: 44 dB - 3rd harmonic: 62 dB b) 20 m - output power: 3.77 W - current drain: 623 mA - 2nd harmonic: 54 dB - 3rd harmonic: 56 dB 2. L2 turns squeezed to 75 % (now, 0.3 W more power on 40 m) a) 40 m - output power: 3.06 W - current drain: 585 mA - 2nd harmonic: 58 dB - 3rd harmonic: 59 dB b) 20 m - output power: 2.74 W - current drain: 563 mA - 2nd harmonic: 48 dB - 3rd harmonic: 56 dB Comments: with L2 turns well spaced I get: more power on 20 m and even a better harmonic rejection. At 40 m, the current drain is lower, and even the harmonic rejection is 44 dB for the 2nd harmonic, it is between specs (40 dB). tests done at 9 V (with L2 squeezed): harmonic rejection results similar to 12 V tests. all tests done with Rohde & Schwarz CMTA-54 Radiocommunication Analyzer & Tektronix 495 P Spectrum Analyzer. So, in my case, for my KX1 s/n 1881 and with output power mod done (R11 = 4.7 Ohm; R30 = 33 Ohm), I will left L2 "not squeezed" !!. Hope this helps. 73, Paco _ Moda para esta temporada. Ponte al día de todas las tendencias. http://www.msn.es/Mujer/moda/default.asp ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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: [Elecraft] KX1 speaker output with superimposed oscillation
Hi Bob, Hate to say it, but it has the same behaviour with the new value of 4.7k for R21: the audio signal shows the parasitic oscillation just on the negative peaks, even with a 10 uV RF level. In any case, many thanks !. 73, Paco _ Acepta el reto MSN Premium: Protección para tus hijos en internet. Descárgalo y pruébalo 2 meses gratis. http://join.msn.com?XAPID=1697&DI=1055&HL=Footer_mailsenviados_proteccioninfantil ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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: [Elecraft] KX1 speaker output with superimposed oscillation
Hi Don First of all, thanks for your answer. Well, I have checked it also with a signal generator: the output signal at R3 (AF Gain) & R5 junction is always a clean 2,2 Vpp 600 Hz tone, with RF levels of 10 uV till 500 uV, except at close or maximum volumen. I this case, even with a 10 uV RF level, the strange oscillation is present, just on the negative peaks, as I told on my first post. At RF levels above 500 uV the signal is clearly distorted (almost square, even at minimum volume) due to overload, I think this is normal. At levels below 10 uV, the audio level is lower also, so no problem with this artifact. It is quite strange cause it works fine with a resisitive load of 8 Ohm, but not with a 8 Ohm speaker. ?? Again, many thanks. 73, Paco _ ¿Estás pensando en cambiar de coche? Todas los modelos de serie y extras en MSN Motor. http://motor.msn.es/researchcentre/ ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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] KX1 speaker output with superimposed oscillation
Hi to all, The scope shows a superimposed high frequency oscillation just on the negative peaks of the audio signal. It produces a distorted and annoying audio when the signal peaks, specially when listening a loud station on the external speaker. This happens when the volume is close to or at maximum volume. I fails just with Panasonic RP-HT60 20 Ohm headphones and external 8 ohm speaker (both work fine with my K2). It works OK with Panasonic earbud type headphone and with an external 8 Ohm load !!. I have re-check every component all around LM386 audio amp: values are OK, soldering fine. It doesn't matter if the KX1 is working with external power (7-12 V) or batteries. At 12 V the RX current drain is about 35 mA (minimum volume). I raises to 71 mA at maximum volume with the external 8 Ohm resistor, and 75 mA with the external 8 Ohm speaker. Hope somebody can help me. Thanks in advance. 73, Paco Barros _ Acepta el reto MSN Premium: Protección para tus hijos en internet. Descárgalo y pruébalo 2 meses gratis. http://join.msn.com?XAPID=1697&DI=1055&HL=Footer_mailsenviados_proteccioninfantil ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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
