Re: [Elecraft] KX1 : low power
Luc, Before offering any specifics, can you make some RF Voltage measurements during a TUNE operation please? With that information, the problem can be isolated to one stage. Measure the following points for both 40 meters and 20 meters: Q1 gate Q1 Source Q4 base Q5 base Q5 collector Q6 base Q6 collector Please also tell us whether the voltages are peak to peak, zero to peak or RMS values. 73, Don W3FPR luc Favre wrote: Hi all, I got a problem building my KX1: receive is OK, but transmit power is far too low (40 m 2W, 20 m 0,5 W with 13,5 V). Of course, I checked and double checked solders, solder bridges, components and values. BPF and LPF are OK as measured with RF generator and oscilloscope. Output waveform good. Frequency right. Transmit voltages are all OK, but Q7's transmit base voltage is minus 1,1 V (minus) instead of the requested plus 0,7 V. Resistances and other components Q7 circuit are OK? 6V_2T is + 5,5 V. Q7 replaced Q7 without. Any idea will be welcome ! 73 Luc/HB9ABB/F6HJO ___ 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 : low power
Don, Thanks for your quick reply. Following values are Vrms made with Elecraft RF Probe and DDM. (7 MHz value/14 MHz value) Q1 gate : 0.17 / 0.16 Q1 Source : 0.11 / 0.18 Q4 base : 0.10 / 0.18 Q5 base : 0.9 / 1.1 Q5 collector : 4.7 / 6.0 Q6 base : 1.3 / 1.2 Q6 collector : 8.9 / 10.7 I suppose these values are quite consistent. Q5 collector values and Q6 base values seem to have the same relation betwenn them as the impedances (1:3). Am I right ? Thanks for your help. 73 Luc/F6HJO/HB9ABB ___ 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 : low power
Luc, Those RF voltages look normal until one reaches the Q5 collector. Changing R11 to 4.7 ohms (as in the power mod) will likely help, and you can increase R30 to 33 ohms (the remainder of the power mod) if changing R11 does not help enough. I am concerned because you indicated only 0.2 watts output on 20 meters - with 10.7 volts on the collector of Q6 you should have more output than 0.2 watts unless you also have a problem in the low pass filter area - check the number of turns on the toroids and check the values of C46, C47 and C54. Too many toroid turns can reduce the cutoff frequency of the 20 meter lowpass filter down into the 20 meter band and absorb a lot of the signal. When counting toroid turns, count each pass of the wire through the center of the core as 1 turn. 73, Don W3FPR luc Favre wrote: Don, Thanks for your quick reply. Following values are Vrms made with Elecraft RF Probe and DDM. (7 MHz value/14 MHz value) Q1 gate : 0.17 / 0.16 Q1 Source : 0.11 / 0.18 Q4 base : 0.10 / 0.18 Q5 base : 0.9 / 1.1 Q5 collector : 4.7 / 6.0 Q6 base : 1.3 / 1.2 Q6 collector : 8.9 / 10.7 I suppose these values are quite consistent. Q5 collector values and Q6 base values seem to have the same relation betwenn them as the impedances (1:3). Am I right ? Thanks for your help. 73 Luc/F6HJO/HB9ABB ___ 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 - Low Power Output
First, check the soldering carefully. If the solder connections look convex (like a ball on the component lead), the connection did not receive enough heat to flow the solder adequately onto the solder pad. If there is excess solder, wick it away and re-solder with a minimal amount of solder and adequate heat (at least 700 deg F). Watch the solder flow - if it flows out to a thin, almost invisible, edge on both the solder pad and the component lead, that is a good connection. The solder should be a bit concave - if it looks convex, it either has too much solder or did not receive enough heat or both. Check the low pass filter toroids (and T1 and L3 too) to be certain the leads have been well stripped and tinned - if the solder connection looks like a miniature volcano, you have a bad connection and the only cure is to remove the toroid, re-tin the leads and re-solder it - you cannot do a proper job of it while mounted on the board (I have tried many times). These two problems are the root cause for more than half of the repairs I do. It is seldom that I have to replace a part because it failed. If you have questions about how a good solder connection should look, check the drawings in the soldering tutorial on the Elecraft website (and now being shipped with many of the kits). 73, Don W3FPR Oliver Olsen wrote: Hello, I recently constructed a KX1 with the 30/80 meter option board, and I'm having problems with low power out on all bands except 80 meters. On a 13.8V power supply, I'm getting a hair over 3 watts, but only .5 - .7 watts on 20 meters (measured on a 50 Ohm dummy load). ___ 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
