[Elecraft] Duty Cycle of FT8 #Elecraft
The complete FT-8 cycle is 30 seconds of which 12.63 seconds is the actual transmitting period. Therefore (12.63/30)*100 = 42.1%. As to backing down the power, the measured performance on my KPA500 indicates the highest dissipation does occur at lower power levels. On 20M at 500 watts output the dissipation is 368.0 watts for an efficiency of 57.6%, while at 200 watts the dissipation if 388.7 watts for an efficiency of 34.0%. I've concluded, with my KPA500, reducing the output power is not advantageous with regard to amp performance. Based on published data in the manual, the duty cycle at 500 watts is 100% for 10 minutes, and 5 minutes of standby. Applying the same concept, then (10/15)*100 = 66.6%. Clearly FT-8 at 500 watts output is well below the duty cycle rating of the KPA500. I suggest one do the same measurements for the KPA1500 and find out what the real numbers might be and publish the results. To be fair, one needs an accurate power meter and a known good 50 ohm resistive load and a little math. 73 Bob, K4TAX On 11/13/2023 8:03 AM, elecraft-requ...@mailman.qth.net wrote: Message: 1 Date: Fri, 10 Nov 2023 09:27:18 -0500 From: Pete Smith N4ZR To:ws...@groups.io, Elecraft List Subject: [Elecraft] Duty Cycle of FT8 #Elecraft Message-ID:<261a35c3-7996-433a-833a-b0a1e7cb2...@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed I started operating FT8 while my KPA-1500amp was out for repair.? Now it's back and raising a question: Operating with just my K-3, set at 100 watts, I would see 100 watts indicated on its meter through the whole 15-second FT8 transmission..? When I drive my amp, it only needs 30 watts for full CW power (on 24 MHz),? but the amp indicates 1200 watts input for the whole FT8 transmit cycle.? I'm wondering if I should back off to protect the amp,considering the duty cycle is so high - on the other hand, the temperature reading profile of the amp seems to be pretty much the same as on CW. 73, Pete N4ZR __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Duty Cycle of FT8 #Elecraft
Ten kilometers! Wow, that’s DX! I know that you meant 10,000 miles, but to the global readership most ops will read it as “10 km“ first. 73, Kevin Sent from my iPhone > On Nov 10, 2023, at 11:15, Victor Rosenthal wrote: > > I don't have a kpa1500, but I recall someone from Elecraft saying that > since the efficiency decreases when power is reduced, backing off the power > does not reduce the heat load. > > Victor 4X6GP > >> On Fri, Nov 10, 2023, 16:28 Pete Smith N4ZR wrote: >> >> I started operating FT8 while my KPA-1500amp was out for repair. Now >> it's back and raising a question: >> >> Operating with just my K-3, set at 100 watts, I would see 100 watts >> indicated on its meter through the whole 15-second FT8 transmission.. >> When I drive my amp, it only needs 30 watts for full CW power (on 24 >> MHz), but the amp indicates 1200 watts input for the whole FT8 transmit >> cycle. I'm wondering if I should back off to protect the >> amp,considering the duty cycle is so high - on the other hand, the >> temperature reading profile of the amp seems to be pretty much the same >> as on CW. >> >> 73, Pete N4ZR >> __ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:Elecraft@mailman.qth.net >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> Message delivered to k2vco@gmail.com > __ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to mcqui...@sfu.ca __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Duty Cycle of FT8 #Elecraft
Hi Jim, I've experienced a 10% drop in output as the finals warm up, which doesn't ultimately make a large difference, but can be compensated if desired (a percentage of 1 dB). It can run legal limit on all bands; but into a SteppIR, because of the transformer/balun in play not being efficient at 6M, limit the output to no more than 1 KW (ask me how I know). I use the default speeds, but I'm also uncomfortable with it going above 65C, so I step in at that point and boost the fans. 73, Rick nk7i On 11/10/2023 11:34 AM, Jim Brown wrote: I've been told by someone who knows that 1) it is normal for MOSFet devices to lose efficiency as they heat; 2) the KPA1500 can run WSJT modes at rated power except on 6M, where it's best to not run much more than 1 kW for long TX sessions, like meteor scatter. It's an issue un-related to the the MOSFets; and 3) to use default fan settings and let the amp adjust upward as needed. 73, Jim K9YC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to rick.n...@gmail.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Duty Cycle of FT8 #Elecraft
On 11/10/2023 6:27 AM, Pete Smith N4ZR wrote: I started operating FT8 while my KPA-1500amp was out for repair. Now it's back and raising a question: Operating with just my K-3, set at 100 watts, I would see 100 watts indicated on its meter through the whole 15-second FT8 transmission.. When I drive my amp, it only needs 30 watts for full CW power (on 24 MHz), but the amp indicates 1200 watts input for the whole FT8 transmit cycle. I'm wondering if I should back off to protect the amp,considering the duty cycle is so high - on the other hand, the temperature reading profile of the amp seems to be pretty much the same as on CW. I've been told by someone who knows that 1) it is normal for MOSFet devices to lose efficiency as they heat; 2) the KPA1500 can run WSJT modes at rated power except on 6M, where it's best to not run much more than 1 kW for long TX sessions, like meteor scatter. It's an issue un-related to the the MOSFets; and 3) to use default fan settings and let the amp adjust upward as needed. 73, Jim K9YC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Duty Cycle of FT8 #Elecraft
The duty cycle of FTx is 43.3% and may be less than RTTY or PSK depending on the transmit:receive ratio; or long winded SSB. I've run the KPA1500 at or near legal limit into a resonant antenna on Ftx, for hours at a time without issues. It will warm the shack and I suggest headphones, the fan can make some noise. The lower output that you run, the less efficient the amp is, which is total power used (presented as heat) to output power. Sometimes (30M), that's the cost (the K3/4 won't produce the US legal limit of 200 watts, without the amp). 73, Rick nk7i On 11/10/2023 11:14 AM, Victor Rosenthal wrote: I don't have a kpa1500, but I recall someone from Elecraft saying that since the efficiency decreases when power is reduced, backing off the power does not reduce the heat load. Victor 4X6GP On Fri, Nov 10, 2023, 16:28 Pete Smith N4ZR wrote: I started operating FT8 while my KPA-1500amp was out for repair. Now it's back and raising a question: Operating with just my K-3, set at 100 watts, I would see 100 watts indicated on its meter through the whole 15-second FT8 transmission.. When I drive my amp, it only needs 30 watts for full CW power (on 24 MHz), but the amp indicates 1200 watts input for the whole FT8 transmit cycle. I'm wondering if I should back off to protect the amp,considering the duty cycle is so high - on the other hand, the temperature reading profile of the amp seems to be pretty much the same as on CW. 73, Pete N4ZR __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to k2vco@gmail.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to rick.n...@gmail.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Duty Cycle of FT8 #Elecraft
I don't have a kpa1500, but I recall someone from Elecraft saying that since the efficiency decreases when power is reduced, backing off the power does not reduce the heat load. Victor 4X6GP On Fri, Nov 10, 2023, 16:28 Pete Smith N4ZR wrote: > I started operating FT8 while my KPA-1500amp was out for repair. Now > it's back and raising a question: > > Operating with just my K-3, set at 100 watts, I would see 100 watts > indicated on its meter through the whole 15-second FT8 transmission.. > When I drive my amp, it only needs 30 watts for full CW power (on 24 > MHz), but the amp indicates 1200 watts input for the whole FT8 transmit > cycle. I'm wondering if I should back off to protect the > amp,considering the duty cycle is so high - on the other hand, the > temperature reading profile of the amp seems to be pretty much the same > as on CW. > > 73, Pete N4ZR > __ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to k2vco@gmail.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Duty Cycle of FT8 #Elecraft
I’ve been running my 1500 at 12-1300w out on FT8 when chasing rare dx, which results in numerous cycles until I work the station I’m calling. My SWR is always below 1.5:1, and I have no need to inject the tuner except on 160 where I’ll lower the power as a precaution. Have had no issues with the 1500. It handles the load well. 73, Lou W0FK Lou Laderman Sent from my mobile device On Nov 10, 2023, at 8:27 AM, Pete Smith N4ZR wrote: I started operating FT8 while my KPA-1500amp was out for repair. Now it's back and raising a question: Operating with just my K-3, set at 100 watts, I would see 100 watts indicated on its meter through the whole 15-second FT8 transmission.. When I drive my amp, it only needs 30 watts for full CW power (on 24 MHz), but the amp indicates 1200 watts input for the whole FT8 transmit cycle. I'm wondering if I should back off to protect the amp,considering the duty cycle is so high - on the other hand, the temperature reading profile of the amp seems to be pretty much the same as on CW. 73, Pete N4ZR __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to llader...@icloud.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
[Elecraft] Duty Cycle of FT8 #Elecraft
I started operating FT8 while my KPA-1500amp was out for repair. Now it's back and raising a question: Operating with just my K-3, set at 100 watts, I would see 100 watts indicated on its meter through the whole 15-second FT8 transmission.. When I drive my amp, it only needs 30 watts for full CW power (on 24 MHz), but the amp indicates 1200 watts input for the whole FT8 transmit cycle. I'm wondering if I should back off to protect the amp,considering the duty cycle is so high - on the other hand, the temperature reading profile of the amp seems to be pretty much the same as on CW. 73, Pete N4ZR __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
