K2 output @2W
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I am trying to use my K2 to drive a little HFPacker amp I built. The
amp needs 2-2.5W input, but I am having trouble setting the K2 output. For requested levels around 2W, I get 1.5-1.7W as measured by both internal and external wattmeters and a simple RF voltage probe. This is into both a good dummy load and the packer using key down and CALP. My K1 is spot on with output into the amp. When I increase the requested power to 2.2-2.5 W, power out jumps to 3-3.6W, so I am unable to get 2 to 2.5W. Above and below this range, the requested vs actual output is fine. I've read most of the archives about requested vs actual power, but I didn't find anything about too much output at low requested levels. So before digging into this, I thought someone might have some ideas about the problem, if it actually is a problem. Thanks, 73, steve, kx7r _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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Steve,
Remove the KAT2 and the external wattmeter and try the following experiment. Compare the output variation possible from the K2 when driving a 50 ohm dummy load with the K2 output developed when driving the amplifier. If you obtain the same results, blame the K2, but if you find different results, blame the amplifier. Analyze that data first and correct whatever is wrong. You may have to swamp the input of the amplifier to obtain a stable 50 ohm load for the K2. The power control circuitry in the K1 is different than that used in the K2, so a comparison with the K1 will not provide valid conclusions - the K2 will seek to provide an RF voltage across the antenna terminals which matches that required to obtain the requested power into a 50 ohm load. I suspect your amp does not present a constant 50 ohm load to the K2, and the KAT2 and external wattmeter each may be adding its own piece of the action too. With the KAT2 and external wattmeter in line and driving the amplifier, there are just too many variables to deal with and still draw valid conclusions - each element may be contributing to the effects you are seeing. After you narrow things down, you can start adding each piece one at a time and analyze any changes in behavior due to adding that element. 73, Don W3FPR > -----Original Message----- > > I am trying to use my K2 to drive a little HFPacker amp I built. The > amp needs 2-2.5W input, but I am having trouble setting the K2 output. > For requested levels around 2W, I get 1.5-1.7W as measured by both > internal and external wattmeters and a simple RF voltage probe. This is > into both a good dummy load and the packer using key down and CALP. My > K1 is spot on with output into the amp. When I increase the requested > power to 2.2-2.5 W, power out jumps to 3-3.6W, so I am unable to get 2 > to 2.5W. Above and below this range, the requested vs actual output is > fine. I've read most of the archives about requested vs actual power, > but I didn't find anything about too much output at low requested > levels. So before digging into this, I thought someone might have some > ideas about the problem, if it actually is a problem. > > Thanks, > > 73, steve, kx7r > > _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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Along these lines, you can isolate the K2 from the amp by putting a pad between them. You can then run the K2 in a more linear range, and guarantee a good load at all times. I would try 6 dB. Of course, efficiency will suffer. Larry N8LP Don Wilhelm wrote: >Steve, > >Remove the KAT2 and the external wattmeter and try the following experiment. > >Compare the output variation possible from the K2 when driving a 50 ohm >dummy load with the K2 output developed when driving the amplifier. If you >obtain the same results, blame the K2, but if you find different results, >blame the amplifier. Analyze that data first and correct whatever is wrong. > >You may have to swamp the input of the amplifier to obtain a stable 50 ohm >load for the K2. The power control circuitry in the K1 is different than >that used in the K2, so a comparison with the K1 will not provide valid >conclusions - the K2 will seek to provide an RF voltage across the antenna >terminals which matches that required to obtain the requested power into a >50 ohm load. I suspect your amp does not present a constant 50 ohm load to >the K2, and the KAT2 and external wattmeter each may be adding its own piece >of the action too. > >With the KAT2 and external wattmeter in line and driving the amplifier, >there are just too many variables to deal with and still draw valid >conclusions - each element may be contributing to the effects you are >seeing. After you narrow things down, you can start adding each piece one >at a time and analyze any changes in behavior due to adding that element. > >73, >Don W3FPR > > > >>-----Original Message----- >> >>I am trying to use my K2 to drive a little HFPacker amp I built. The >>amp needs 2-2.5W input, but I am having trouble setting the K2 output. >>For requested levels around 2W, I get 1.5-1.7W as measured by both >>internal and external wattmeters and a simple RF voltage probe. This is >>into both a good dummy load and the packer using key down and CALP. My >>K1 is spot on with output into the amp. When I increase the requested >>power to 2.2-2.5 W, power out jumps to 3-3.6W, so I am unable to get 2 >>to 2.5W. Above and below this range, the requested vs actual output is >>fine. I've read most of the archives about requested vs actual power, >>but I didn't find anything about too much output at low requested >>levels. So before digging into this, I thought someone might have some >>ideas about the problem, if it actually is a problem. >> >>Thanks, >> >>73, steve, kx7r >> >> >> >> > >_______________________________________________ >Elecraft mailing list >Post to: [hidden email] >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 mailing list Post to: [hidden email] 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 |
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The HFPacker amp has a 3dB pad on the input so you might need to take
that into account. I use mine with a KAT100 on the output and an internal KAT2. I disconnected the Vrfdet on the KAT100 cable as it has the amp in the gain loop, and the K2 software only knows about the KPA100. With the KAT100 enabled, the KAT2 is put into passthrough mode. The K2 power control seems about the same for me with the amp in or out -- 1.7 gets 1.5, and 2.0 gets 2.5, and there is no choice between, as measured by the KAT2 internal Vrfdet. Leigh / WA5ZNU On Sat, 4 Feb 2006 8:40 am, Larry Phipps wrote: > > Along these lines, you can isolate the K2 from the amp by putting a pad > between them. You can then run the K2 in a more linear range, and > guarantee a good load at all times. I would try 6 dB. Of course, > efficiency will suffer. _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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Steve,
If you are seeing an oscillation of the power output level, you might try reducing the ALC loop gain. One can increase the value of R98 on the RF Board to decrease the gain through the K2 power determining ALC loop. If the value is increased too much, the power output on 10 meters will be reduced, so some experimentation is in order. Increasing R98 is a step sometimes taken when the KPA100 is installed to decrease the 'power hunting' cycle (my terminology), but I have never seen the base K2 need such treatment (the KPA100 adds more gain inside the loop and the loop overshoots). Be aware that this is a condition where the power output varies with a longer keydown (or TUNE) time. If your actual problem is confined to a mismatch between the power requested and the actual power output, then the answer to that problem may be different - in that case, look for something that may cause the load to vary, or something like a bad solder connection in the K2 output detector and its path back to the microprocessor. In my experience, the base K2's power determination is quite stable. If the KAT2 or KAT100 is involved, the wattmeter section of those parts may be providing incorrect data to the K2 microprocessor and cause such behavior. 73, Don W3FPR > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]]On Behalf Of Leigh L Klotz, Jr. > Sent: Saturday, February 04, 2006 12:51 PM > To: Larry Phipps; [hidden email] > Cc: Elecraft; Steve Hostetler > Subject: Re: [Elecraft] K2 output @2W > > > The HFPacker amp has a 3dB pad on the input so you might need to take > that into account. I use mine with a KAT100 on the output and an > internal KAT2. I disconnected the Vrfdet on the KAT100 cable as it has > the amp in the gain loop, and the K2 software only knows about the > KPA100. With the KAT100 enabled, the KAT2 is put into passthrough > mode. > > The K2 power control seems about the same for me with the amp in or out > -- 1.7 gets 1.5, and 2.0 gets 2.5, and there is no choice between, as > measured by the KAT2 internal Vrfdet. > > Leigh / WA5ZNU > On Sat, 4 Feb 2006 8:40 am, Larry Phipps wrote: > > > > Along these lines, you can isolate the K2 from the amp by putting a pad > > between them. You can then run the K2 in a more linear range, and > > guarantee a good load at all times. I would try 6 dB. Of course, > > efficiency will suffer. > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > 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 > > > -- > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.1.375 / Virus Database: 267.15.1/250 - Release Date: 2/3/2006 > > |
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