KX1 Spring Tune Up
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Its spring and I am getting ready for some backpacking with my KX1 so I
thought I would take the time to tweak/tune/analyze/hot rod my baby. The rig is fully loaded. 4 bands, ATU and the SMD CW TUNING AID. I have several projects on the agenda. 1. Scope analysis 2. Dummy load construction with DVM RF measurement capabilities. Or just buy the Elecraft dummy load! 3. Possible tweaking of the existing hardware. 4. Exploring the possibility of increasing the power output to a full 5 watts. Just for the record, the KX1 is working FB on all bands and the readings on the rig are all within specs! Well, one thing at a time. I have hooked up my scope a dummy load consisting of six, 5 watt Milwaukee 300 ohm sand resistors in parallel. These resistors were given to attendees at hands on session of my local radio club. I was dubious about the resistor choice as I understand that these are wire wound and that is not appropriate for a dummy load. Sure enough, when comparing the SWR of the homemade dummy load, my MFJ-9895 and a BNC ½ watt 50 ohm terminator I found that the homemade load showed different SWR readings at 80, 40, 30 and 20 meters. While the MFJ and BNC terminator showed 1.0 SWR on the rig. The MFJ also showed the 1.0 on all four bands its SWR meter. Well, for convenience sake made I made my first scope connection on the homemade dummy load at 3.550 MHz. BATTERY NO LOAD = 12 VDC ON DVM. CONNECTED TO KX1 11.9 VDC ON DVM KX1 BAT FUNCTION = 11.7 VDC ON RECEIVE SCOPE PPV RIG WATTS RIG SWR CALCULATED WATTS 32 2.9-3.0 1.1 2.559 I calculated the power out by this formula. ((32 x .3535) (32 x .3535)) / 50 11.312 x 11.312 = 127.961 127.961 / 49.2 = 2.6.00 My DVM and the scope both show the same frequency! The scope had been calibrated when I bought it. The self calibration function shows the same measurements as when I bought it. So, I have two questions for the group at this point! 1. Are my measurements consistent with what a KX1 would be likely to put out? 2. Am I correct in thinking that the resistors in the homemade load are not the best choice? For what it is worth, I have found several articles on the web re: dummy loads and also looked at the schematic for the Elecraft dummy load and all indications are that sand style, rectangular, wire round resistors are not appropriate! It is true that my measurements confirm this, but as my construction technique was rushed, I do not want to assume anything! If my measurements pass the smell test I am going to trace the RF path of the KX1 end to end in order to establish a baseline! At that point, I will decide whether to try tweaking the KX1 or to continue home brewing a dummy load with power metering capabilities like the Elecraft dummy load! Thanks in advance for all your expert advice/admonitions! Jack, AE6GC, KX1 #1403, K3-100 #1433 ______________________________________________________________ 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 |
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I have reformatted the text and corrected an error. Sorry for the
inconvenience. Its spring and I am getting ready for some backpacking with my KX1 so I thought I would take the time to tweak/tune/analyze/hot rod my baby. The rig is fully loaded. 4 bands, ATU and the SMD CW TUNING AID. I have several projects on the agenda. 1. Scope analysis 2. Dummy load construction with DVM RF measurement capabilities. Or just buy the Elecraft dummy load! 3. Possible tweaking of the existing hardware. 4. Exploring the possibility of increasing the power output to a full 5 watts. Just for the record, the KX1 is working FB on all bands and the readings on the rig are all within specs! Well, one thing at a time. I have hooked up my scope to a dummy load consisting of six, 5 watt Milwaukee 300 ohm sand resistors in parallel. These resistors were given to attendees of a "hands on session" of my local radio club. I was dubious about the resistor choice as I understand that these are wire wound and that is not appropriate for a dummy load. Sure enough, when comparing the SWR of the homemade dummy load, my MFJ-9895 and a BNC ½ watt 50 ohm terminator I found that the homemade load showed different SWR readings at 80, 40, 30 and 20 meters. While the MFJ and BNC terminator showed 1.0 SWR on the rig for all bands. The MFJ also showed the 1.0 on all four bands on its SWR meter. Well, for convenience sake made I made my first scope connection on the homemade dummy load at 3.550 MHz. BATTERY NO LOAD = 12 VDC ON DVM. CONNECTED TO KX1 11.9 VDC ON DVM KX1 BAT FUNCTION = 11.7 VDC ON RECEIVE SCOPE PPV RIG WATTS RIG SWR CALCULATED WATTS 32 2.9-3.0 1.1 2.559 I calculated the power out by this formula. ((32 x .3535) (32 x .3535)) / 49.2 ohms (Measured on my DVM) 11.312 x 11.312 = 127.961 127.961 / 49.2 = 2.6.00 My DVM and the scope both show the same frequency! The scope had been calibrated when I bought it. The scope's self calibration function shows the same measurements as when I bought it. So, I have two questions for the group at this point! 1. Are my measurements consistent with what a KX1 would be likely to put out? 2. Am I correct in thinking that the resistors in the homemade load are not the best choice? For what it is worth, I have found several articles on the web re: dummy loads and also looked at the schematic for the Elecraft dummy load and all indications are that sand style, rectangular, wire round resistors are not appropriate! It is true that my measurements confirm this, but as my construction technique was rushed, I do not want to assume anything! If my measurements pass the smell test I am going to trace the RF path of the KX1 end to end in order to establish a baseline! At that point, I will decide whether to try tweaking the KX1 or to continue home brewing a dummy load with power metering capabilities like the Elecraft dummy load! Thanks in advance for all your expert advice/admonitions! Jack, AE6GC, KX1 #1403, K3-100 #1433 ______________________________________________________________ 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 ______________________________________________________________ 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 |
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In reply to this post by Jack
Jack,
Several comments. First, I would *not* recommend that you run the KX1 power up to 5 watts - keep it at 4 watts max. The zener in the PA output may break down if you connect to a high SWR load, as may the capacitors in the Low Pass Filter - they are only rated at 50 volts, and a high SWR load may cause that rating to be exceeded. Better to keep the power down than to have the KX1 break on you just when you want to use it most. 4 watts with a 13.8 volt power source is about what I expect of a KX1 with the KXB3080 option, and that will be only on 80 and 30 meters. 40 and 20 will be lower, but I expect at least 3.3 watts on 20 with that 13.8 volt supply. The power output with lower DC voltages will be lower. Your 2.56 watts is a small bit on the low side with a 12 volt supply. Secondly, check any dummy load with an antenna analyzer at the frequency of interest so you know what you are dealing with - if it is good, it will have only a resistive component and zero reactance - anything other than that renders it of lesser value for valid measurements. If you want a good dummy load that is light in weight, mount a 50 ohm Caddock thick film power resistor on a heat sink salvaged from a defunct computer CPU cooler. The 15 watt unit is Mouser 684-MP915-50 - it is a 1% resistor, and the 50 ohm resistors are good for RF usage (other values may be capacitive). When mounted with only its leads to a BNC connector, it will be flat up through 222 MHz or more. Your 'scope measurement of the Peak to Peak RF voltage is good as long as you are using a 10X probe on the 'scope - connect the probe to your 'scope's calibrator and make certain the probe is properly compensated. If you want a quicker way to calculate the power, square the peak to peak voltage and divide by 400, and you will have the power directly without going through conversions. The derivation of that formula is an exercise for the student, but I have posted the derivation on this reflector before. One easy to remember data point is that 40 volts peak to peak is equal to 4 watts. 73, Don W3FPR Jack Regan wrote: > Its’ spring and I am getting ready for some backpacking with my KX1 so I > thought I would take the time to tweak/tune/analyze/hot rod my baby. > > > > The rig is fully loaded. 4 bands, ATU and the SMD CW TUNING AID. > > > > I have several projects on the agenda. > > > > 1. Scope analysis > 2. Dummy load construction with DVM RF measurement capabilities. Or > just buy the Elecraft dummy load! > 3. Possible tweaking of the existing hardware. > 4. Exploring the possibility of increasing the power output to a full 5 > watts. > > > > Just for the record, the KX1 is working FB on all bands and the readings on > the rig are all within specs! > > > > > > Well, one thing at a time. > > > > I have hooked up my scope a dummy load consisting of six, 5 watt Milwaukee > 300 ohm “sand” resistors in parallel. > > These resistors were given to attendees at hands on session of my local > radio club. I was dubious about the resistor choice as I understand that > these are wire wound and that is not appropriate for a dummy load. > > > > Sure enough, when comparing the SWR of the homemade dummy load, my MFJ-9895 > and a BNC ½ watt 50 ohm terminator > > I found that the homemade load showed different SWR readings at 80, 40, 30 > and 20 meters. While the MFJ and BNC terminator showed 1.0 SWR on the rig. > The MFJ also showed the 1.0 on all four bands its’ SWR meter. > > > > Well, for convenience sake made I made my first scope connection on the > homemade dummy load at 3.550 MHz. > > > > BATTERY NO LOAD = 12 VDC ON DVM. > > CONNECTED TO KX1 11.9 VDC ON DVM > > KX1 BAT FUNCTION = 11.7 VDC ON RECEIVE > > > > SCOPE PPV RIG WATTS RIG SWR CALCULATED WATTS > > 32 2.9-3.0 1.1 2.559 > > > > I calculated the power out by this formula. > > > > ((32 x .3535) (32 x .3535)) / 50 > > 11.312 x 11.312 = 127.961 > > 127.961 / 49.2 = 2.6.00 > > > > My DVM and the scope both show the same frequency! The scope had been > calibrated when I bought it. The self calibration function shows the same > measurements as when I bought it. > > > > So, I have two questions for the group at this point! > > > > 1. Are my measurements consistent with what a KX1 would be likely to > put out? > 2. Am I correct in thinking that the resistors in the homemade load are > not the best choice? > > > > For what it is worth, I have found several articles on the web re: dummy > loads and also looked at the schematic for the Elecraft dummy load and all > indications are that “sand” style, rectangular, wire round resistors are > not appropriate! > > > > It is true that my measurements confirm this, but as my construction > technique was rushed, I do not want to assume anything! > > > > If my measurements pass the smell test I am going to trace the RF path of > the KX1 end to end in order to establish a baseline! > > > > At that point, I will decide whether to try tweaking the KX1 or to continue > home brewing a dummy load with power metering capabilities like the Elecraft > dummy load! > > > > Thanks in advance for all your expert advice/admonitions! > > > > Jack, AE6GC, KX1 #1403, K3-100 #1433 > > 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 |
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