KX3 Tuner Operation at Low Voltages
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My KX3 internal tuner works perfectly at transmit voltages above 10v. Below that value it will initiate tuning but finish at an SWR of between 3 and 6. When this happens if I connect my station 13.6v supply or an external 12v battery supply it will immediately tune to the expected low SWR.
Elecraft tech support was a bit non committal on this issue. They said that 10v was close to the minimum value for the relay drivers to operate properly. This is a bit strange as one does not have to operate long with internal NiMh batteries before the transmit voltage drops below 10v. An easy work around is to perform my portable tuning when I first start operating. Still this seems strange behavior for a rig designed to work on the internal battery pack. Is this normal operation for the internal tuner? If not, then what should I check? I thought that tuning at a lower power might help but the manual states the tuner operates at either 2w or 3w and the value is not under user control. ______________________________________________________________ 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: KX3 Tuner Operation at Low Voltages
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Hi Dean,
The latching relays in the tuner should work just fine at low supply voltages; they run off a voltage regulator, so their coils should see 5 V even when the rig is running from as low as 8 V. I think what you’re seeing is not enough forward power to qualify the SWR readings. If the load impedance you’re working into is low (on a given band), the instantaneous key-down TX current drain will go up and the forward power might drop below the minimum required level for accurate readings. The ATU will skip LC combinations that don’t meet the measurement criteria. The effect could be made worse by batteries that have higher ESR, which varies with state of charge, number of charge cycles, and temperature. Any increase in ESR reduces key-down max power output. To see if the bridge is working correctly, connect the rig to a dummy load, run it from 10 V, turn the ATU off, and check the key-down SWR reading (TUNE) at 0.5 W, 1.0 W, and 2.0 W. Let me know what you find. 73, Wayne N6KR > On Feb 26, 2018, at 4:36 PM, AL7CR <[hidden email]> wrote: > > My KX3 internal tuner works perfectly at transmit voltages above 10v. Below that value it will initiate tuning but finish at an SWR of between 3 and 6. When this happens if I connect my station 13.6v supply or an external 12v battery supply it will immediately tune to the expected low SWR. > > Elecraft tech support was a bit non committal on this issue. They said that 10v was close to the minimum value for the relay drivers to operate properly. This is a bit strange as one does not have to operate long with internal NiMh batteries before the transmit voltage drops below 10v. > > An easy work around is to perform my portable tuning when I first start operating. Still this seems strange behavior for a rig designed to work on the internal battery pack. > > Is this normal operation for the internal tuner? If not, then what should I check? I thought that tuning at a lower power might help but the manual states the tuner operates at either 2w or 3w and the value is not under user control. ______________________________________________________________ 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] |
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Hi Wayne,
Thank you for your prompt response. I have run the test you suggested with the following results. Test Conditions Tuner bypassed, KX 3 connected via 18" commercial RG8X patch cable to dummy load, power via internal Eneloop batteries with three charge cycles since new, frequency 10.136 Mhz, receive battery voltage 10.8v, battery voltage during transmit 10.2v Results .5W SWR no reading (double dashes) 1.0W SWR 1.0 - 1 2.0W SWR 1.0 - 1 Stepping the power up in .1w increments from .5w gave no SWR reading until .8W which was 1.0 - 1 The above test was then run at a frequency of 14.074 with the same results. I then repeated the above tests with two other convenient power sources. An external sealed lead acid UPS battery which gave a receive voltage of 11.0v and a transmit voltage of 10.9v. and my station power supply giving a receive voltage of 13.6v and a transmit voltage of 13.5v. The result of the tests with the alternate supplies were exactly the same. Hence it appears that at transmit voltages from 10.2v to 13.5v, a KX 3 power setting of .8w is required for an SWR measurement to be obtained. The two antennas I was attempting to tune which led to the original question were a 135 foot doublet at 30 feet and a Buddistick mounted to my shop picnic table. The doublet does indeed have a low impedance as you suggest. I have not measured the impedance of the Buddistick. I am quite interested in your analysis of the above results. Should the KX 3 give an SWR reading into a dummy load at .5W output? If so, what can be done to adjust my unit. 73 de AL7CR On Mon, Feb 26, 2018, at 4:57 PM, Wayne Burdick wrote: > Hi Dean, > > The latching relays in the tuner should work just fine at low supply > voltages; they run off a voltage regulator, so their coils should see 5 > V even when the rig is running from as low as 8 V. > > I think what you’re seeing is not enough forward power to qualify the > SWR readings. If the load impedance you’re working into is low (on a > given band), the instantaneous key-down TX current drain will go up and > the forward power might drop below the minimum required level for > accurate readings. The ATU will skip LC combinations that don’t meet the > measurement criteria. > > The effect could be made worse by batteries that have higher ESR, which > varies with state of charge, number of charge cycles, and temperature. > Any increase in ESR reduces key-down max power output. > > To see if the bridge is working correctly, connect the rig to a dummy > load, run it from 10 V, turn the ATU off, and check the key-down SWR > reading (TUNE) at 0.5 W, 1.0 W, and 2.0 W. Let me know what you find. > > 73, > Wayne > N6KR > > > > > > On Feb 26, 2018, at 4:36 PM, AL7CR <[hidden email]> wrote: > > > > My KX3 internal tuner works perfectly at transmit voltages above 10v. Below that value it will initiate tuning but finish at an SWR of between 3 and 6. When this happens if I connect my station 13.6v supply or an external 12v battery supply it will immediately tune to the expected low SWR. > > > > Elecraft tech support was a bit non committal on this issue. They said that 10v was close to the minimum value for the relay drivers to operate properly. This is a bit strange as one does not have to operate long with internal NiMh batteries before the transmit voltage drops below 10v. > > > > An easy work around is to perform my portable tuning when I first start operating. Still this seems strange behavior for a rig designed to work on the internal battery pack. > > > > Is this normal operation for the internal tuner? If not, then what should I check? I thought that tuning at a lower power might help but the manual states the tuner operates at either 2w or 3w and the value is not under user control. > > 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] |
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