KPA1500 Solution to the efficiency problem?
Locked
KPA1500 Solution to the efficiency problem?
 
|
It occurred to me that the KPA1500's built in tuner might be of
some help. Here's my reasoning. If we decrease the drive power to lessen the output power but keep the same voltage, the amplifier wants to see a higher load impedance. Here are the results of some quick tests: Base line is the amp set for 1000 watts output and eff is 44% I the set the tuner so the amp "sees" a load of 60 Ohms (actually) 58 Ohms with the values of L and C available. Eff went up to 53%! I then set the tuner to present a 70 Ohm load (actually 68 Ohms). Eff went up to 59%! This was into a dummy load. I realize that, if you're using the tuner to match an antenna, this could be very complicated. If Elecraft could figure some way to give us a choice of voltages for differing power levels, this problem would go away. 73, Roger ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
Re: KPA1500 Solution to the efficiency problem?
|
|
I think I've discovered a fly in my ointment! The efficiency
that the amp displays is based on it's determination of the output power. If the amp is looking into a higher Z load, the indicated power is greater than normal resulting in a higher efficiency reading. Oh well, back to the drawing board! 73, Roger On 8/31/2019 9:32 AM, Roger D Johnson wrote: > It occurred to me that the KPA1500's built in tuner might be of > some help. > > Here's my reasoning. If we decrease the drive power to lessen > the output power but keep the same voltage, the amplifier wants > to see a higher load impedance. > > Here are the results of some quick tests: > > Base line is the amp set for 1000 watts output and eff is 44% > > I the set the tuner so the amp "sees" a load of 60 Ohms (actually) > 58 Ohms with the values of L and C available. Eff went up to 53%! > > I then set the tuner to present a 70 Ohm load (actually 68 Ohms). > Eff went up to 59%! > > This was into a dummy load. I realize that, if you're using the tuner > to match an antenna, this could be very complicated. > > If Elecraft could figure some way to give us a choice of voltages > for differing power levels, this problem would go away. > > 73, Roger > > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [hidden email] Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
|
|
There also seems to be some real-world question. I've been operating
the WW Digi contest this morning, and find that running at 500 watts out vs 1500 watts out,with similar sequences of transmissions there is about a 10-degree difference in temperature as reported by the amp. 73, Pete N4ZR Check out the Reverse Beacon Network at <http://reversebeacon.net>, now spotting RTTY activity worldwide. For spots, please use your favorite "retail" DX cluster. On 8/31/2019 10:15 AM, Roger D Johnson wrote: > I think I've discovered a fly in my ointment! The efficiency > that the amp displays is based on it's determination of the > output power. If the amp is looking into a higher Z load, > the indicated power is greater than normal resulting in a > higher efficiency reading. > > Oh well, back to the drawing board! > > 73, Roger > > > On 8/31/2019 9:32 AM, Roger D Johnson wrote: >> It occurred to me that the KPA1500's built in tuner might be of >> some help. >> >> Here's my reasoning. If we decrease the drive power to lessen >> the output power but keep the same voltage, the amplifier wants >> to see a higher load impedance. >> >> Here are the results of some quick tests: >> >> Base line is the amp set for 1000 watts output and eff is 44% >> >> I the set the tuner so the amp "sees" a load of 60 Ohms (actually) >> 58 Ohms with the values of L and C available. Eff went up to 53%! >> >> I then set the tuner to present a 70 Ohm load (actually 68 Ohms). >> Eff went up to 59%! >> >> This was into a dummy load. I realize that, if you're using the tuner >> to match an antenna, this could be very complicated. >> >> If Elecraft could figure some way to give us a choice of voltages >> for differing power levels, this problem would go away. >> >> 73, Roger >> >> >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> Message delivered to [hidden email] > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [hidden email] Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
KPA1500 Solution to the efficiency problem?
|
|
In reply to this post by Roger D Johnson
"If we decrease the drive power to lessen the output power but keep the same voltage, the amplifier wants to see a higher load impedance."
Is the PA Voltage of the KPA1500 regulated? The KPA500 PA voltage can vary about 20 V (80 V unloaded to 60 V at max PA current). 73, Andy k3wyc ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
Re: KPA1500 Solution to the efficiency problem?
|
Administrator
|
Yes, the 1500 PA voltage is regulated.
73, Eric elecraft.com _..._ > On Aug 31, 2019, at 7:33 AM, Andy Durbin <[hidden email]> wrote: > > "If we decrease the drive power to lessen the output power but keep the same voltage, the amplifier wants to see a higher load impedance." > > Is the PA Voltage of the KPA1500 regulated? The KPA500 PA voltage can vary about 20 V (80 V unloaded to 60 V at max PA current). > > 73, > Andy k3wyc > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [hidden email] Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
|
|
In reply to this post by Roger D Johnson
Totally aside from the power meter issue, what you are doing with the
ATU is like loading a tube amplifier more lightly with the PI network. Lighter loading will improve efficiency, but may result in more distortion. One reason solid state amplifiers are generally less efficient than tube amplifiers is that transistors (including FET's) become extremely nonlinear when they are driven close to saturation. That is, when the voltage across the device is near zero at the bottom of the cycle. As a result, solid state amplifiers have to be loaded more "heavily", to keep the transistors far from saturation. This, of course, results in more dissipation. I haven't tried it, but it's possible the KPA1500 could be loaded more lightly by manually adjusting the ATU values to improve efficiency on CW or RTTY, where linearity isn't a big issue. That might reduce PA temperature a little, though I'm not sure it would be worth the trouble. Given how sensitive the KPA1500 is to small changes in SWR, though, setting this up across a band would be a tedious process. The rather large variations in PA current I see at 1500 W output at a moderate SWR, like 1.3:1, is probably due to the same effect. (A 1.3:1 SWR could be a load impedance of anything from 39 to 65 Ohms.) 73, Scott K9MA On 8/31/2019 09:15, Roger D Johnson wrote: > I think I've discovered a fly in my ointment! The efficiency > that the amp displays is based on it's determination of the > output power. If the amp is looking into a higher Z load, > the indicated power is greater than normal resulting in a > higher efficiency reading. > > Oh well, back to the drawing board! > > 73, Roger > > > On 8/31/2019 9:32 AM, Roger D Johnson wrote: >> It occurred to me that the KPA1500's built in tuner might be of >> some help. >> >> Here's my reasoning. If we decrease the drive power to lessen >> the output power but keep the same voltage, the amplifier wants >> to see a higher load impedance. >> >> Here are the results of some quick tests: >> >> Base line is the amp set for 1000 watts output and eff is 44% >> >> I the set the tuner so the amp "sees" a load of 60 Ohms (actually) >> 58 Ohms with the values of L and C available. Eff went up to 53%! >> >> I then set the tuner to present a 70 Ohm load (actually 68 Ohms). >> Eff went up to 59%! >> >> This was into a dummy load. I realize that, if you're using the tuner >> to match an antenna, this could be very complicated. >> >> If Elecraft could figure some way to give us a choice of voltages >> for differing power levels, this problem would go away. >> >> 73, Roger >> -- Scott K9MA [hidden email] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
«
Return to Elecraft
|
1 view|%1 views
| Free forum by Nabble | Edit this page |