K3 Voltage on TX
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I am using the same SamLex supply with the K3s Elecraft power cord that came
with the kit. At 100 Watts key down I can just see the voltmeter move maybe the width of the needle. The readout on the radio does not dim. Earl, K4KAY -----Original Message----- From: Elecraft [mailto:[hidden email]] On Behalf Of Jim Miller Sent: Monday, October 26, 2015 5:09 PM To: Bill Frantz Cc: Elecraft Reflector Subject: Re: [Elecraft] K3 Voltage on TX I was having too much drop with RR as well. I switched to a 1ft line directly to my Samlex 1235M which has been jacked to 14.4v no load. It only moves a few mV when loaded to 20A. IIRC, the cable is now AWG12. jim ab3cv ______________________________________________________________ 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] |
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In reply to this post by Don Wilhelm-4
Seems to me the display on VFO B is accurate enough for this purpose.
Now to make sure of the accuracy along with voltage drop, measure the voltage at the power supply terminals. I would expect the voltage at the power supply terminals and the VFO B display in receive mode to be identical, +/- meter accuracy. As Don said, diodes or no diodes, the objective is voltage drop at the radio between RX and TX full power. I would perceive anything greater than 0.5 volts as shown on the VFO B display is reason for one to investigate the station DC power distribution. 73 Bob, K4TAX K3S s/n 10163 On 10/26/2015 8:02 PM, Don Wilhelm wrote: > Dick, > > If the main interest is the drop in voltage, the 12V jack will work > fine, no matter how many diodes are in series with it. > So you get 10 volts during RX and 9 volts during TX, that is a 1 volt > drop (OK, that is extreme, but hopefully makes the point). > If you are instead looking for the absolute voltage delivered to the > K3, use the VFO B voltage display. > > 73, > Don W3FPR ______________________________________________________________ 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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In reply to this post by Gary Gregory-2
Thanks for all of the great advice. I have made several changes and
here are the results. I wired my radio directly to the PS with AGW 10 probably about four feet. Thus removing the radio from the automatic battery switch over and then from the rigrunner. I now have the following voltages measured with the VFO B display. No fuse in line - 14.2VDC RX 13.6VDC TX Power pole fuse block 30amp bladed fuses 14.2VDC RX 12.8VDC TX Obviously I am not going to leave myself without fuses. So 12.8VDC seems to be the number. My external watt meter reads 107watts out. Thank you all for you help. Rich ______________________________________________________________ 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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If you operate SSB, you might want to run higher voltage at the K3 terminals (e.g. at 14.5V which is below the 15.0V spec) to minimize IMD. This was discussed extensively in 2009 but the following by W4TV is a good summary:
################################ > Is there something critical in the radio that > gives this outcome? Critical adjustment perhaps? > Is it very sensitive what PS we use (ala W4ZV)? Yes, it is very sensitive to power supply voltage. Look at any of the application notes - the one Craig mentions for the P-P RD100HHF FETs is a good example. Decreasing Vcc (or Vdd) by just one Volt will increase the IMD at 100 Watts by 10 dB and decrease the maximum output power by almost 20 Watts. Running the power supply at 14.0 - 14.5 Volts and using a power supply with good dynamic regulation will go a long way to keeping the K3 "clean." ################################# |
Re: Issue Resolved K3 Voltage on TX
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On Tue,10/27/2015 8:46 AM, Bill W4ZV wrote:
> If you operate SSB, you might want to run higher voltage at the K3 terminals > (e.g. at 14.5V which is below the 15.0V spec) to minimize IMD. IMD is just as much a factor on CW as on SSB. CW is really 100% AM of a carrier by a square wave, which we all know is a lot of AF harmonics, the strength of which is dependent on the rise and fall time of the keying waveform. IMD is clearly visible in the sidebands of CW signals on a spectrum display set for very good frequency resolution -- like a P3, and especially a P3 with SVGA. Take a look at http://k9yc.com/P3_Spectrum_Measurements.pdf These data are with power supply voltage in the range of 12.5V. 73, Jim K9YC ______________________________________________________________ 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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In reply to this post by Rich-4
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Hi Jeff,
many thanks for your post regarding the soldering Anderson Plug leads connections. It seems that I should check it too as I have 0.7V drop RX/TX on VFO-B line measurement. (even although I never had any problem regarding the low voltage...) It is good hint for my old timer K3 (#778) although it work like champ now. 73 - Petr, OK1RP
73 - Petr, OK1RP
"Apple & Elecraft freak" B:http://ok1rp.blogspot.com MeWe: https://bit.ly/2HGPoDx MeWe: https://bit.ly/2FmwvDt |
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In general, it would be ideal if there were zero voltage drop. This just
won't be the case in the real world. The VFO-B voltage indication is reliable in terms of the voltage in receive vs. the voltage in transmit. I think it reasonable to accept < 0.5 volt drop or less between RX and TX at 100 watts output. Do consider the regulation of the supply. Measure that with a good DVM at the supply terminals. And here, it is reasonable to expect less than 0.1 volt change between RX and TX at 100 watts. Many of the better supplies will be in the < 0.01 volt range under this condition. If one finds more voltage drop than expected, then further investigation is suggested. Are the terminals properly crimped and soldered on both ends? Are the terminals tight fitting? Is the wire gauge correct for the current demand and length? Are there other devices between the supply and radio that will contribute to voltage drop? These are a few questions to be answered. Better regulation and maintaining a voltage at the radio between 13.5 and 14.5 will make for a cleaner transmitter in respect to transmitted IMD. And that topic was "beat to death" in a previous discussion. If the supply is not well regulated, be sure the voltage at the radio will never exceed 15.0 volts. 73 Bob, K4TAX On 11/5/2015 7:36 AM, ok1rp wrote: > Hi Jeff, > > many thanks for your post regarding the soldering Anderson Plug leads > connections. > It seems that I should check it too as I have 0.7V drop RX/TX on VFO-B line > measurement. > (even although I never had any problem regarding the low voltage...) > > It is good hint for my old timer K3 (#778) although it work like champ now. ______________________________________________________________ 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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