Accurate QRP Wattmeters?
Locked
 
|
Hello List,
I've posted my question on QRP-L and here as well- since I will be building a KX-1. I am looking for good ways to measure power output from my KX-1 while I am building it. What first came to mind was to set up my Tek 492 analyzer on a 2 dB scale and then use a 30 or 40 watt (high power) attenuator to measure CW power. I have several Bird 43's but have never seen Bird slugs for QRP LF, MF or HF. I think a competing company may have a through wattmeter with HF but I forget the lowest scale of that one. I have read the E-Ham reviews for the Oak Hills QRP wattmeter- 300 Khz to 54 MHz and 100mW, 1W and 10W scales- still thinking over the reviews. Comments on the accuracy of using the Tek 492 method, and on other accurate wattmeter options? 73 Jay W6CJ AAR9QM _______________________________________________ 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 |
|
|
Measure V p-p into an accurate 50 ohm dummy load with a decent o-scope. Power is then V^2/400.
At 01:45 PM 7/3/2005, J. Coote wrote... >Comments on the accuracy of using the Tek 492 method, and on other accurate >wattmeter options? _______________________________________________ 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 |
|
|
In reply to this post by J. Coote
The Elecraft Mini-Module DL1 Dummy Load has test points that allow you to
use a DMM to measure out put. I can't imagine anything in that price range being more accurate 73, KI4DGH Chuck Gehring -----Original Message----- From: [hidden email] [mailto:[hidden email]]On Behalf Of J. Coote Sent: Sunday, July 03, 2005 12:46 PM To: [hidden email] Subject: [Elecraft] Accurate QRP Wattmeters? Hello List, I've posted my question on QRP-L and here as well- since I will be building a KX-1. I am looking for good ways to measure power output from my KX-1 while I am building it. What first came to mind was to set up my Tek 492 analyzer on a 2 dB scale and then use a 30 or 40 watt (high power) attenuator to measure CW power. I have several Bird 43's but have never seen Bird slugs for QRP LF, MF or HF. I think a competing company may have a through wattmeter with HF but I forget the lowest scale of that one. I have read the E-Ham reviews for the Oak Hills QRP wattmeter- 300 Khz to 54 MHz and 100mW, 1W and 10W scales- still thinking over the reviews. Comments on the accuracy of using the Tek 492 method, and on other accurate wattmeter options? 73 Jay W6CJ AAR9QM _______________________________________________ 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 |
|
|
In reply to this post by J. Coote
Jay,
I may have answered this already on QRP-L, but I find the most accurate way to determine power output is to use a good 50 ohm resistive load (check it with an antenna analyzer or use the Elecraft DL1). Measure the RF voltage across the 50 ohm load (RF Probe reads in Vrms while a 'scope will show you Vp-p), then calculate the power. I use this procedure to calibrate or check wattmeters. I don't trust any wattmeter (including a Bird) until I have verified that it is reading correctly - some can be off by as much as 20% and still meet their specs (2 watts on a 10 watt scale, 20 watts on a 100 watt scale), and I can get MUCH closer than that with my known good dummy load. 73, Don W3FPR > -----Original Message----- > > Hello List, > I've posted my question on QRP-L and here as well- since I will > be building > a KX-1. > I am looking for good ways to measure power output from my KX-1 while I am > building it. > What first came to mind was to set up my Tek 492 analyzer on a 2 dB scale > and then use > a 30 or 40 watt (high power) attenuator to measure CW power. I > have several > Bird 43's > but have never seen Bird slugs for QRP LF, MF or HF. I think a competing > company may > have a through wattmeter with HF but I forget the lowest scale of > that one. > I have read > the E-Ham reviews for the Oak Hills QRP wattmeter- 300 Khz to 54 MHz and > 100mW, 1W and 10W > scales- still thinking over the reviews. > > Comments on the accuracy of using the Tek 492 method, and on > other accurate > wattmeter options? > > 73 > Jay > W6CJ > AAR9QM > No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.323 / Virus Database: 267.8.8/37 - Release Date: 7/1/2005 _______________________________________________ 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 |
|
|
In reply to this post by J. Coote
Jay, the Tek 492 will do the job IF you have an accurate way of calibrating it and IF you know exactly the attenuation at all frequencies of interest of the attenuator you will be using. I'm not familiar with the '492... I have a 7L13, and on the 2dB scale the divisions are .4dB.. which are pretty big steps. Don is right about the dummy load method, but first you have to determine the actual Z of the dummy load at all frequencies if you want to be within a couple percent. The resistors in the Elecraft dummy load are 5% metal film, so statistically, the average Z will probably be better than 5%, but unless you can measure it, you won't know. You also have to take into account the diode drop in the Elecraft to wring out the last bit of accuracy. Anything better than 5% absolute power accuracy, BTW, is wishful thinking on the part of manufacturers. Be advised too that even the Birds are rated at 5% of FULL SCALE... meaning ~ 10% of half-scale if that's where your reading happens to be... and that's best case with a purely resistive load. In develping my LP-100 wattmeter kit (more on my website), I learned a lot about power accuracy. It's a very elusive thing. My meter is accurate within a couple % of the calibrating standard at any power level from .1 milliwatt to 2500 watts... but ultimately, the accuracy of the standard determines the overall accuracy of the meter. In my shop, I can measure power to better than .001dB on a relative (not absolute) basis with my HP VNA, but it still all comes down what you're measuring against. One thing I can do, and have done for my own use is create Z vs. freq charts for all my precision loads (and Cantenna and other non-precision loads as well). These charts are accurate to better than 1%. As part of my LP-100 project, I plan to offer a 50W precision dummy load using thick film metal power resistors mounted on a heatsink to allow easy calibration of the meter. It would be a nice addition to any shack. I will provide a custom chart of Z vs. frequency for each one. It will be similar to the Elecraft DL1 in operation, but will use precision parts and come with the custom charts. I am also thinking of making a version of the dummy load with digital readout for power that comes already calibrated. It would be considerably simpler than the LP-100, and would not be a thru-line device, so would not measure SWR, etc. In the meantime, if you have a DL1 and want me to run a custom chart for you, send it with return postage and I will chart it for you. Larry N8LP www.telepostinc.com/n8lp.html J. Coote wrote: >Hello List, >I've posted my question on QRP-L and here as well- since I will be building >a KX-1. >I am looking for good ways to measure power output from my KX-1 while I am >building it. >What first came to mind was to set up my Tek 492 analyzer on a 2 dB scale >and then use >a 30 or 40 watt (high power) attenuator to measure CW power. I have several >Bird 43's >but have never seen Bird slugs for QRP LF, MF or HF. I think a competing >company may >have a through wattmeter with HF but I forget the lowest scale of that one. >I have read >the E-Ham reviews for the Oak Hills QRP wattmeter- 300 Khz to 54 MHz and >100mW, 1W and 10W >scales- still thinking over the reviews. > >Comments on the accuracy of using the Tek 492 method, and on other accurate >wattmeter options? > >73 >Jay >W6CJ >AAR9QM > > >_______________________________________________ >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 |
|
|
In reply to this post by Chuck Gehring
Chuck and all.
Can you tell me if you need to use an RF probe along with the DL-1, or is the circuitry built into the DL-1 and you can just use the DMM probes? Thanks. Tom WB2QDG ----- Original Message ----- From: "Chuck Gehring" <[hidden email]> To: "J. Coote" <[hidden email]>; <[hidden email]> Sent: Sunday, July 03, 2005 5:10 PM Subject: RE: [Elecraft] Accurate QRP Wattmeters? > The Elecraft Mini-Module DL1 Dummy Load has test points that allow you to > use a DMM to measure out put. I can't imagine anything in that price > range > being more accurate > 73, KI4DGH > Chuck Gehring > > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]]On Behalf Of J. Coote > Sent: Sunday, July 03, 2005 12:46 PM > To: [hidden email] > Subject: [Elecraft] Accurate QRP Wattmeters? > > > Hello List, > I've posted my question on QRP-L and here as well- since I will be > building > a KX-1. > I am looking for good ways to measure power output from my KX-1 while I am > building it. > What first came to mind was to set up my Tek 492 analyzer on a 2 dB scale > and then use > a 30 or 40 watt (high power) attenuator to measure CW power. I have > several > Bird 43's > but have never seen Bird slugs for QRP LF, MF or HF. I think a competing > company may > have a through wattmeter with HF but I forget the lowest scale of that > one. > I have read > the E-Ham reviews for the Oak Hills QRP wattmeter- 300 Khz to 54 MHz and > 100mW, 1W and 10W > scales- still thinking over the reviews. > > Comments on the accuracy of using the Tek 492 method, and on other > accurate > wattmeter options? > > 73 > Jay > W6CJ > AAR9QM > > > _______________________________________________ > 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 _______________________________________________ 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 |
|
|
Tom,
I believe I can answer that - the only thing you need with the DL1 is a DVM and you can either use the formula or the graph from the manual to determine the power. In other words, yes the circuitry is built into the DL1, but a caution, you will find the formula a bit different than the normal because the diode probe circuitry is connected across half the load rather than across the full 50 ohms. 73, Don W3FPR > -----Original Message----- > > Chuck and all. > > Can you tell me if you need to use an RF probe along with the > DL-1, or is > the circuitry built into the DL-1 and you can just use the DMM probes? > > Thanks. > Tom > WB2QDG > > No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.323 / Virus Database: 267.8.8/37 - Release Date: 7/1/2005 _______________________________________________ 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 |
«
Return to Elecraft
|
1 view|%1 views
| Free forum by Nabble | Edit this page |