Baluns & wires & feeders (oh, my!)
Locked
 
|
I have been following the 135 ft flattop thread with interest. I was running my K1 into a 40m wire vertical via 100 ft of RG8x. After doing some loss calculations, that seemed pretty silly, so I set out for a more efficient. arrangement. I just put up a 40m folded dipole (same diameter wires) fed with 300 ohm window line. My K1 (with internal atu)tuned it well, but rf reeked havok on the K-40 keyer and such, so I used the BL2(4:1) balun and all seems well (probably time to do maintenance on the shack rf grounding system). My question is this: Is there a way to measure the insertion loss of the balun? Perhaps setting up my scope to do a differential measurement on the output of the balun w/ a 300ohm dummy load? Also, I could rig a way to sweep the antenna/window line with the antenna analyzer.
Any suggestions? 72s, Pete wd4lst Pete Axson WD4LST 17901 NE 18th Ave Citra, FL 32113 _______________________________________________ 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 |
Re: Baluns & wires & feeders (oh, my!)
|
|
[hidden email] wrote:
> I have been following the 135 ft flattop thread with interest. I was running my K1 into a 40m wire vertical via 100 ft of RG8x. After doing some loss calculations, that seemed pretty silly, A 100 feet of RG8X is a looser for QRP. > so I set out for a more efficient. arrangement. I just put up a 40m folded dipole (same diameter wires) fed with 300 ohm window line. My K1 (with internal atu)tuned it well, but rf reeked havok on the K-40 keyer and such, so I used the BL2(4:1) balun and all seems well (probably time to do maintenance on the shack rf grounding system). My question is this: Is there a way to measure the insertion loss of the balun? Perhaps setting up my scope to do a differential measurement on the output of the balun w/ a 300ohm dummy load? Also, I could rig a way to sweep the antenna/window line with the antenna analyzer. > A balun wound on a toroid can have no more than 5% loss at 100 Watts. Just relax and use your antenna. It might be hard to load on 40 and 20 Meters but it should work ok. 73 Karl K5DI > Any suggestions? > 72s, > Pete > wd4lst > > > Pete Axson > WD4LST > 17901 NE 18th Ave > Citra, FL 32113 > > _______________________________________________ > 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 |
Re: Baluns & wires & feeders (oh, my!)
|
|
In reply to this post by wd4lst
You could measure power accuratly using the scope and a dummy load.
Measuring power at the load with a 300 ohm dummy load and balun and then, in a seperate test, measuring it with a 75 ohm load and no balun would give you a rough idea of balun losses. This would show balun losses if they were fairly large. I have never been successful using a scope to measure differential rf voltages because of the rf voltage that gets into the scope through sneak paths that you do not intend. Anytime you float a scope (measuring relative to a point that is not absolute ground) you will start to display rf voltage where "there is none" due to stray rf fields in the environment. Don K7FJ My question is this: Is there a way to measure the insertion loss of the balun? Perhaps setting up my scope to do a differential measurement on the output of the balun w/ a 300ohm dummy load? Also, I could rig a way to sweep the antenna/window line with the antenna analyzer. > Any suggestions? > 72s, > Pete > wd4lst > _______________________________________________ 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 |
Re: Baluns & wires & feeders (oh, my!)
|
|
In reply to this post by Karl Larsen
Sorry, I just can not understand why that should be so. I have managed to
heat very large toroid baluns to the point where wire insulation melted just by driving a 100 watts or so into an extreme SWR. Perhaps you are assumming a simple 1:1 choke balun? A 4:1 voltage balun can easily have extremely high circulating currents within the balun that will cook it in a hurry under high swr feedline conditions. Don K7FJ > A balun wound on a toroid can have no more than 5% loss at 100 Watts. > Just relax and use your antenna. It might be hard to load on 40 and 20 > Meters but it should work ok. > > 73 Karl K5DI > _______________________________________________ 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 |
Re: Baluns & wires & feeders (oh, my!)
|
|
In reply to this post by wd4lst
There is a simple way to measure the efficiency of a balun, make two of
them and connect them "back to back". Measure the power fed to them and the corresponding output power. Obviously this doesn't take a mismatched antenna into account. _______________________________________________ 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 |
Re: Baluns & wires & feeders (oh, my!)
|
|
Dave G4AON wrote:
> There is a simple way to measure the efficiency of a balun, make two of > them and connect them "back to back". Measure the power fed to them and > the corresponding output power. Obviously this doesn't take a mismatched > antenna into account. > I did just that about this 5 years ago. I used two MFJ tuners connected by the 4:1 baluns in each. I fed one from my MFJ Antenna Analyser and hooked a 50 ohm resister to the other tuner. I measured the voltage across the resistor with a RF probe. Alas I can't locate the paper where I wrote down the results. Over the bands the loss was around 10-15% I recall and I thought that was about what I expected. 73 Karl K5DI _______________________________________________ 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 Dave, G4AON
I ask this as a question - Putting baluns or UN-UN back to back checks that
both have the same ratio and can check efficiency if they are transformers such as what is used on beverages. How does this check if it is working well as a balun? As an example, a straight piece of coax with ferrite beads on it could be treated as one or two baluns back to back. But just checking power at the end versus power going in would seem to check the efficiency of the coax but not tell you how much, if any RF was on the outside of the shield. Please correct me if I am all wet. 73, N2TK, Tony -----Original Message----- From: [hidden email] [mailto:[hidden email]]On Behalf Of Dave G4AON Sent: Saturday, October 07, 2006 2:54 AM To: [hidden email] Subject: Re: [Elecraft] Baluns & wires & feeders (oh, my!) There is a simple way to measure the efficiency of a balun, make two of them and connect them "back to back". Measure the power fed to them and the corresponding output power. Obviously this doesn't take a mismatched antenna into account. _______________________________________________ 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 |
Re: Baluns & wires & feeders (oh, my!)
|
|
N2TK, Tony wrote:
> I ask this as a question - Putting baluns or UN-UN back to back checks that > both have the same ratio and can check efficiency if they are transformers > such as what is used on beverages. How does this check if it is working well > as a balun? As an example, a straight piece of coax with ferrite beads on it > could be treated as one or two baluns back to back. But just checking power > at the end versus power going in would seem to check the efficiency of the > coax but not tell you how much, if any RF was on the outside of the shield. > Please correct me if I am all wet. > Hi Tony, you missed the question. We assumed the balun's were made properly. The task was to measure the loss through them. 73 Karl > 73, > N2TK, Tony > > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]]On Behalf Of Dave G4AON > Sent: Saturday, October 07, 2006 2:54 AM > To: [hidden email] > Subject: Re: [Elecraft] Baluns & wires & feeders (oh, my!) > > There is a simple way to measure the efficiency of a balun, make two of > them and connect them "back to back". Measure the power fed to them and > the corresponding output power. Obviously this doesn't take a mismatched > antenna into account. > _______________________________________________ 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 |
|
|
Tnx Karl. Yes I must have missed the first part. Yes this will work for
measuring the loss. 73, N2TK, Tony -----Original Message----- From: Karl Larsen [mailto:[hidden email]] Sent: Saturday, October 07, 2006 9:54 AM To: N2TK, Tony Cc: 'Dave G4AON'; [hidden email] Subject: Re: [Elecraft] Baluns & wires & feeders (oh, my!) N2TK, Tony wrote: > I ask this as a question - Putting baluns or UN-UN back to back checks that > both have the same ratio and can check efficiency if they are transformers > such as what is used on beverages. How does this check if it is working well > as a balun? As an example, a straight piece of coax with ferrite beads on it > could be treated as one or two baluns back to back. But just checking power > at the end versus power going in would seem to check the efficiency of the > coax but not tell you how much, if any RF was on the outside of the shield. > Please correct me if I am all wet. > Hi Tony, you missed the question. We assumed the balun's were made properly. The task was to measure the loss through them. 73 Karl > 73, > N2TK, Tony > > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]]On Behalf Of Dave G4AON > Sent: Saturday, October 07, 2006 2:54 AM > To: [hidden email] > Subject: Re: [Elecraft] Baluns & wires & feeders (oh, my!) > > There is a simple way to measure the efficiency of a balun, make two of > them and connect them "back to back". Measure the power fed to them and > the corresponding output power. Obviously this doesn't take a mismatched > antenna into account. > _______________________________________________ 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 |
RE: Baluns & wires & feeders (oh, my!)
|
|
The usual approach to measuring the loss of any device like this is to
measure the heat. Basic physics - the first law of thermodynamics - tells us that the energy going into the device will equal the energy going out. The question is how much of that energy emerges as RF. In this case there is only one other significant form of energy involved: heat. (Yes, if the device is arcing over there will also be light and sound, but I'm assuming it *seems* to be working okay; no arcing and buzzing <G>.) So you put the device into a very well insulated test chamber. Dense urethane foam is commonly used for this. Then it is operated under the exact conditions you want to evaluate (high SWR through a BALUN at normal power levels, etc.) and the heat rise in the chamber is noted on an accurate thermometer over a specific period of time. Then you can calculate how many watts of RF were turned into heat. Not into doing the math? You can figure it out empirically by putting a resistor in the box with the device, let the whole thing return to ambient after measuring the temperature rise over time operating the device under test. Then do not apply RF to the balun (or tuner or whatever you're testing) but instead put DC current through the resistor sufficient to raise the temperature the same amount in the same time. The power dissipated by the resistor (volts times current) will be equal to that lost from the balun, ATU or whatever. Obviously, it might take several runs to find the exact value but you can learn something very useful from a limited test. For example, if you run 10 watts through a balun and the temperature goes up 2 degrees in 10 minutes, then you put 1 watt through the resistor and note that the temperature goes up more than 2 degrees in 10 minutes, you've demonstrated that the loss is less than 1 watt, since that amount of loss would cause a faster temperature rise. Does all that sound like a little bit "much" for a test on a quiet Saturday afternoon? That's why most Hams ignore the whole issue, hoping that the losses aren't too high. That's easy to do since in most on-air operating, especially on HF, a loss of even 10 dB is hard to spot unless once can do side-by-side testing with a distant station. So unless the losses are truly large, we'll never know for sure they are occurring. And if they are, we notice that the balun feels warm, the cores of the toroids cracked, or it arced over, Hi! On the other hand, arranging these experiments and working through them are a wonderful way to better understand not only Ham radio, but your equipment and physics as well. Ron AC7AC _______________________________________________ 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 wd4lst
Great Idea - thanks for pointing me to the obvious <GR>.
Just as I was contriving a highly complex solution to a non existent problem!! Besides, one could always use another balun. 73s Pete > > From: Karl Larsen <[hidden email]> > Date: 2006/10/07 Sat AM 07:07:13 CDT > To: Dave G4AON <[hidden email]> > CC: [hidden email] > Subject: Re: [Elecraft] Baluns & wires & feeders (oh, my!) > > Dave G4AON wrote: > > There is a simple way to measure the efficiency of a balun, make two of > > them and connect them "back to back". Measure the power fed to them and > > the corresponding output power. Obviously this doesn't take a mismatched > > antenna into account. > > > I did just that about this 5 years ago. I used two MFJ tuners > connected by the 4:1 baluns in each. I fed one from my MFJ Antenna > Analyser and hooked a 50 ohm resister to the other tuner. I measured the > voltage across the resistor with a RF probe. > > Alas I can't locate the paper where I wrote down the results. Over > the bands the loss was around 10-15% I recall and I thought that was > about what I expected. > > > 73 Karl K5DI > > _______________________________________________ > 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 > Pete Axson WD4LST 17901 NE 18th Ave Citra, FL 32113 _______________________________________________ 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 |
Re: Baluns & wires & feeders (oh, my!)
|
|
Hi Guys, if there are several who want to measure the two MFJ balum tuners loss on several bands, I can do it and will be glad to do it and report back. I will do it just like I did it when I measured MFJ tuner loss. You can see what I do by clicking on MFJ on my web page at: http://www.zianet.com/k5di/ 73 Karl [hidden email] wrote: > Great Idea - thanks for pointing me to the obvious <GR>. > Just as I was contriving a highly complex solution to a non existent problem!! > Besides, one could always use another balun. > 73s > Pete > >> From: Karl Larsen <[hidden email]> >> Date: 2006/10/07 Sat AM 07:07:13 CDT >> To: Dave G4AON <[hidden email]> >> CC: [hidden email] >> Subject: Re: [Elecraft] Baluns & wires & feeders (oh, my!) >> >> Dave G4AON wrote: >> >>> There is a simple way to measure the efficiency of a balun, make two of >>> them and connect them "back to back". Measure the power fed to them and >>> the corresponding output power. Obviously this doesn't take a mismatched >>> antenna into account. >>> >>> >> I did just that about this 5 years ago. I used two MFJ tuners >> connected by the 4:1 baluns in each. I fed one from my MFJ Antenna >> Analyser and hooked a 50 ohm resister to the other tuner. I measured the >> voltage across the resistor with a RF probe. >> >> Alas I can't locate the paper where I wrote down the results. Over >> the bands the loss was around 10-15% I recall and I thought that was >> about what I expected. >> >> >> 73 Karl K5DI >> >> _______________________________________________ >> 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 >> >> > > > Pete Axson > WD4LST > 17901 NE 18th Ave > Citra, FL 32113 > > > > _______________________________________________ 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 |
RE: Re: Baluns & wires & feeders (oh, my!)
|
|
In reply to this post by wd4lst
Dave, did you use an antenna analyzer?
I've tried it using two ATU's to evaluate the losses through the tuners, figuring that if the total loss through both of them was acceptable feeding the impedance presented by the feedline, I'd be happy with the loss through one. I first set up the ATU to test for a 1:1 SWR on my antenna like this: RIG -> ATU1 -> ANT Then I disconnected the ATU from the antenna and substituted the second ATU "output". A 50 ohm dummy load was connected to the second ATU. So it all ended up like this: RIG -> ATU1 -> ATU2 -> DUMMY LOAD I carefully adjusted ATU2 for an SWR of 1:1 at the output of the rig again, without touching the settings on ATU1, since ATU losses can vary widely depending upon the load it is "matching". Power was measured at the output of the rig and at the dummy load connected to the second ATU to determine the total loss. It worked, but it demanded a much more accurate means of assessing the SWR than the typical SWR bridge for accurate results. With a typical SWR bridge used for matching to an antenna, I could shown a huge range of "loss" or "low loss" all while the SWR meter stayed at 1:1 - or as close as it was capable of measuring. I did get some good results only using an accurate return loss bridge that can measure SWR to a degree common meters can't approach. Perhaps an "antenna analyzer" also would provide that sort of accuracy. Ron AC7AC -----Original Message----- Great Idea - thanks for pointing me to the obvious <GR>. Just as I was contriving a highly complex solution to a non existent problem!! Besides, one could always use another balun. 73s Pete > > From: Karl Larsen <[hidden email]> > Date: 2006/10/07 Sat AM 07:07:13 CDT > To: Dave G4AON <[hidden email]> > CC: [hidden email] > Subject: Re: [Elecraft] Baluns & wires & feeders (oh, my!) > > Dave G4AON wrote: > > There is a simple way to measure the efficiency of a balun, make two > > of them and connect them "back to back". Measure the power fed to > > them and the corresponding output power. Obviously this doesn't take > > a mismatched antenna into account. > > > I did just that about this 5 years ago. I used two MFJ tuners > connected by the 4:1 baluns in each. I fed one from my MFJ Antenna > Analyser and hooked a 50 ohm resister to the other tuner. I measured the > voltage across the resistor with a RF probe. > > Alas I can't locate the paper where I wrote down the results. Over > the bands the loss was around 10-15% I recall and I thought that was > about what I expected. > > > 73 Karl K5DI _______________________________________________ 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 |
Re: Re: Baluns & wires & feeders (oh, my!)
|
|
Ron, AC7AC wrote:
> I did get some good results only using an accurate return loss bridge that > can measure SWR to a degree common meters can't approach. > > Perhaps an "antenna analyzer" also would provide that sort of accuracy. ----------------------------------------------------- FWIW my MFJ 259-B "antenna analyzer" does not provide the accuracy required, whereas a return loss bridge does. 73, Geoff GM4ESD _______________________________________________ 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 |