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Stacking Winegard HD-6065P antennas
"Jerry Stuckle" wrote in message ... Jeff is correct. Your error is believing the combiner has 3.5db loss. When splitting a signal, you do have about a 3.5db loss per output, because the signal is halved plus a bit of additional loss. However, when combining the signals, the signal is NOT halved, so you don't have the 3db loss there. You only have about 0.5db loss (more or less, depending on the quality of the combiner and other factors). Let's take an example. Since a combiner is just a splitter turned around, we'll start with the splitter end. Let's feed 2mw to the input of the splitter. This means each output gets 1mw (3db loss) (we could use voltage also, but since power is E^2/R, it's not so straightforward). So now each leg has 1mw on it. Now let's turn the splitter around and make it a combiner and feed two signals, 1mw ea., same frequency, to the inputs to the combiner. Since this is a totally passive device, the effects are reversible. If the signals are 180 degrees out of phase, of course the output is 0. However, if the two signals are in phase with each other, the putout is 2mw. Note there is no 3db loss in the combiner. But of course this assumed a "perfect" combiner, with no losses. In reality, the combiner will have a bit of loss (typically 0.5db as noted above), so the output from the splitter will be slightly less than 1mw and the output from the combiner will be slightly less than 2mw. Does this help clarify things? And yes, phasing harnesses work the same way. The can be either splitters or combiners, depending on how they are used. The advantage is they have less loss; the disadvantage, as noted, is they have a much narrower effective bandwidth. What I am having trouble with is the 'perfect' combiner. The one by Wineguard specs 3.5 db loss and the MiniCircuits I have specs at 3 db plus slightly more depending on frequency. I had forgotten that I built one years ago out of the ARRL Handbook. They give it a spec of 6 db of loss per port. The one I built has that not counting minor errors and loss. Just checked it out. My problem is where are you going to find a combiner for a broad frequency that does not have any large (say over 1 db ) of loss ? Are the ones for the TV frequencies built differant ? For the splitters, I see the 3 db because the signal is going to two places (3 db equals half power as we all know). But then the problem I am having is the extra 3 db that is lossed in the combiner instead of just half of a db or so. Has anyone actually put one on accurate test equipment to see about the loss like I have been trying to do ? I understand phasing harnesses for antennas. They are almost loseless. Only a few feet of coax worth. I have used them on antennas before. They are not usually very broad banded unless the antennas are broad banded and made so the impedance is not the nominal 50 ohms. That is for comercial 4 or 8 dipole arays for VHF/UHF. Lots of 'tricks' used to do that. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com |
#2
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Stacking Winegard HD-6065P antennas
On 1/4/2014 9:23 PM, Ralph Mowery wrote:
"Jerry Stuckle" wrote in message ... Jeff is correct. Your error is believing the combiner has 3.5db loss. When splitting a signal, you do have about a 3.5db loss per output, because the signal is halved plus a bit of additional loss. However, when combining the signals, the signal is NOT halved, so you don't have the 3db loss there. You only have about 0.5db loss (more or less, depending on the quality of the combiner and other factors). Let's take an example. Since a combiner is just a splitter turned around, we'll start with the splitter end. Let's feed 2mw to the input of the splitter. This means each output gets 1mw (3db loss) (we could use voltage also, but since power is E^2/R, it's not so straightforward). So now each leg has 1mw on it. Now let's turn the splitter around and make it a combiner and feed two signals, 1mw ea., same frequency, to the inputs to the combiner. Since this is a totally passive device, the effects are reversible. If the signals are 180 degrees out of phase, of course the output is 0. However, if the two signals are in phase with each other, the putout is 2mw. Note there is no 3db loss in the combiner. But of course this assumed a "perfect" combiner, with no losses. In reality, the combiner will have a bit of loss (typically 0.5db as noted above), so the output from the splitter will be slightly less than 1mw and the output from the combiner will be slightly less than 2mw. Does this help clarify things? And yes, phasing harnesses work the same way. The can be either splitters or combiners, depending on how they are used. The advantage is they have less loss; the disadvantage, as noted, is they have a much narrower effective bandwidth. What I am having trouble with is the 'perfect' combiner. The one by Wineguard specs 3.5 db loss and the MiniCircuits I have specs at 3 db plus slightly more depending on frequency. I had forgotten that I built one years ago out of the ARRL Handbook. They give it a spec of 6 db of loss per port. The one I built has that not counting minor errors and loss. Just checked it out. A perfect combiner (like anything else "perfect") doesn't exist. But it is a very common (and handy) way of specifying how things work. It's used all over the place in EE degree programs, for instance. So you start with the perfect item, then add losses, phase shifts, etc. as they occur to get a "real" part. My problem is where are you going to find a combiner for a broad frequency that does not have any large (say over 1 db ) of loss ? Are the ones for the TV frequencies built differant ? There are good combiners and bad combiners. The commercial grade ones we use typically have 1db loss from 50Mhz to 2Ghz. Note that these are basically splitters which are reversed to form combiners, when necessary. For the splitters, I see the 3 db because the signal is going to two places (3 db equals half power as we all know). But then the problem I am having is the extra 3 db that is lossed in the combiner instead of just half of a db or so. In a good quality combiner, there is no extra 3db of loss. Has anyone actually put one on accurate test equipment to see about the loss like I have been trying to do ? I haven't actually measured it myself, but I do use commercial grade splitters/combiners (not as much any more because a lot of video has gone digital). Typical loss as a combiner is around 0.5 - 0.7 db from 50Mhz to 2Ghz. But you also won't find these at Radio Shack or Best Buy. And there are testing labs out there who do test these things; if any of the ratings were off, the manufacture would quickly lose credibility in commercial circles. I understand phasing harnesses for antennas. They are almost loseless. Only a few feet of coax worth. I have used them on antennas before. They are not usually very broad banded unless the antennas are broad banded and made so the impedance is not the nominal 50 ohms. That is for comercial 4 or 8 dipole arays for VHF/UHF. Lots of 'tricks' used to do that. Phasing harnesses are just another form of splitter/combiner. One way they combine; turn them around and they split. That's why they work for both transmitting and receiving. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
#3
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Stacking Winegard HD-6065P antennas
"Jerry Stuckle" wrote in message ... A perfect combiner (like anything else "perfect") doesn't exist. But it is a very common (and handy) way of specifying how things work. It's used all over the place in EE degree programs, for instance. So you start with the perfect item, then add losses, phase shifts, etc. as they occur to get a "real" part. I am awear of that 'perfect' vers 'real world'. Took a 2 year asociate degree in electronics engineering about 40 years ago. Most things are calculated close and then trimmed to take care of the usual 5 to 10 percent differance in components. That is why I was not worried about anything under a DB, but just the parts close to 3 db. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com |
#4
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Stacking Winegard HD-6065P antennas
On Sat, 4 Jan 2014 21:23:14 -0500, "Ralph Mowery"
wrote: What I am having trouble with is the 'perfect' combiner. I feel your pain. Many years ago, I made a similar mistake on the NEC antenna modeling mailing list. I then processed to make a total fool of myself and had to be corrected by the experts. Even so, I still didn't believe it so I built a Wilkinson combiner and bench tested it for loss. I still have the combiner somewhere as a reminder of my mistake. Incidentally, a Wilkinson combiner might be a tolerable solution for combining two FM antenna. The loss is much less than a bifilar wound toroid. I'm not sure if it will work over the entire FM band. I can grind the numbers if anyone is interested. My problem is where are you going to find a combiner for a broad frequency that does not have any large (say over 1 db ) of loss ? Are the ones for the TV frequencies built differant ? There's only so much you can do with passive only designs. The next step up is an active combiner: http://www.rldrake.com/product-ac1686.php 0-3dB gain per port. 54 to 860 MHz. Has anyone actually put one on accurate test equipment to see about the loss like I have been trying to do ? Yep. I have. There's very little loss between the combiner input ports and the "sum" port. However, in the other direction, there's a bit over 3dB loss due to the power splitting. See the specs on the MCL splitter/combiner that you have and try it with a service monitor or generator. Since it works down to 10 MHz, you might be able to do the test with a function generator, a few dummy loads, some T connectors, and an oscilloscope. I understand phasing harnesses for antennas. They are almost loseless. Only a few feet of coax worth. I have used them on antennas before. They are not usually very broad banded unless the antennas are broad banded and made so the impedance is not the nominal 50 ohms. That is for comercial 4 or 8 dipole arays for VHF/UHF. Lots of 'tricks' used to do that. It's low, but the phasing harness loss for stacked vertical dipoles is not zero. I've never calculated or measured it, but this might help: http://www.kg4jjh.com/pdf/2-Meter%20Vertical%20Dipole%20Array.pdf "The phasing harness loss at 150 MHz is calculated to be 0.67 dB." Scaled for 100 Mhz, I would guess about 0.5 dB. Might as well use a combiner/splitter. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#5
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Stacking Winegard HD-6065P antennas
"Jeff Liebermann" wrote in message ... On Sat, 4 Jan 2014 21:23:14 -0500, "Ralph Mowery" wrote: What I am having trouble with is the 'perfect' combiner. I feel your pain. Many years ago, I made a similar mistake on the NEC antenna modeling mailing list. I then processed to make a total fool of myself and had to be corrected by the experts. Even so, I still didn't believe it so I built a Wilkinson combiner and bench tested it for loss. I still have the combiner somewhere as a reminder of my mistake. Incidentally, a Wilkinson combiner might be a tolerable solution for combining two FM antenna. The loss is much less than a bifilar wound toroid. I'm not sure if it will work over the entire FM band. I can grind the numbers if anyone is interested. My problem is where are you going to find a combiner for a broad frequency that does not have any large (say over 1 db ) of loss ? Are the ones for the TV frequencies built differant ? There's only so much you can do with passive only designs. The next step up is an active combiner: http://www.rldrake.com/product-ac1686.php 0-3dB gain per port. 54 to 860 MHz. Has anyone actually put one on accurate test equipment to see about the loss like I have been trying to do ? Yep. I have. There's very little loss between the combiner input ports and the "sum" port. However, in the other direction, there's a bit over 3dB loss due to the power splitting. See the specs on the MCL splitter/combiner that you have and try it with a service monitor or generator. Since it works down to 10 MHz, you might be able to do the test with a function generator, a few dummy loads, some T connectors, and an oscilloscope. I understand phasing harnesses for antennas. They are almost loseless. Only a few feet of coax worth. I have used them on antennas before. They are not usually very broad banded unless the antennas are broad banded and made so the impedance is not the nominal 50 ohms. That is for comercial 4 or 8 dipole arays for VHF/UHF. Lots of 'tricks' used to do that. It's low, but the phasing harness loss for stacked vertical dipoles is not zero. I've never calculated or measured it, but this might help: http://www.kg4jjh.com/pdf/2-Meter%20Vertical%20Dipole%20Array.pdf "The phasing harness loss at 150 MHz is calculated to be 0.67 dB." Scaled for 100 Mhz, I would guess about 0.5 dB. Might as well use a combiner/splitter. -- I understand the idea of using 'perfect' items in electronics, then going for more exect calculations if needed. As most electronic items are often a 5 to 10 percent variation anyway. Often you get a close calculation and build it and trim for the desired results. I did take 2 year course in electronics engineering about 40 years ago for an associates degree, so know about perfect vers real components. The Wilkinson combiner is possiable for relative narrow frequencies. Not sure if building one out of descrete components or full size transmission lines would be broad enough for the whole FM band either. Wild guess it would be about the same if just two pieces of transmission line of the correct impedance and length were used. Isn't the Wilkinson combiner just two pieces of transmission line (or simulated with components) with a resistor across two of the ports to absorbe the diffeance if the loads/sources are not ballanced ? I know what they are and have seen equipment with them in it,but never did much of a study on it. As the subject is combining, I have not looked into the losses of splitting, but it would be 6 db for the simple resistor designs not counting the minor losses. That would be 3 db for the ports and 3 db lost in the resistors. To combind signals you would get the loss of the resistors of 3 db and a fraction of other loss. I am using a HP 8924C for a test set. It has just about everything you can think of for a service monitor. Calibrated from 30 to 1000 MHz but usuable uncalibrated to about a half of a mhz. http://www.amtronix.com/hp8924c60.htm As mentioned the only combiner I have is a MiniCircuits and they spec it at 3 db plus small losses depending on the frequency. That is what I am measuring. The diplexer/combiner will have very low loss. I have checked out 2 of them in the past just to see and the losses were about half a db or so. However that is for frequencies seperated by a very large percentage. Usually one port is a low pass and the other is a high pass filter. Not suited for signals on the same frequency as the origional poster wanted to do. Yes, phasing harnesses on antennas are not totally loseless, but will be mainly whatever the loss of the coax is between the elements. If were the origional poster and there were not too many transmitters near me, I would try a good preamp first. Mast mounted if possiable as it is for receive only. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com |
#6
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Stacking Winegard HD-6065P antennas
On Sun, 5 Jan 2014 00:01:47 -0500, "Ralph Mowery"
wrote: I understand the idea of using 'perfect' items in electronics, then going for more exect calculations if needed. I like to design perfect antennas and circuits as a sanity check to see if it can be done. Then, I throw in the losses and see what happens. It's also a crude form of sensitivity analysis, which tells me which parameters are most important. The Wilkinson combiner is possiable for relative narrow frequencies. Not sure if building one out of descrete components or full size transmission lines would be broad enough for the whole FM band either. Wild guess it would be about the same if just two pieces of transmission line of the correct impedance and length were used. Good guess. Discrete or coaxial performance (loss, isolation, and bandwidth) are about the same. You're also correct that it wouldn't cover the entire FM band. I could do it with a single stage Wilkinson combiner by lowering the Q of the components. However, that will increase the losses, which is not a great idea. Much better is to use a multi-stage Wilkinson combiner: http://www.microwaves101.com/encyclopedia/wilkinson_multistage.cfm It's a common stripline technique. You probably recognize the general pattern: http://www.eee.bham.ac.uk/yatesac/Web%20PDF%27s/Test%20Gear/Wideband%20Wilkinson%20Coupler_1-2%20GHz_Layout.pdf http://www.eee.bham.ac.uk/yatesac/Web%20Pages/Wideband%20Wilkinson%20Splitter%20&%20Combiner.htm Isn't the Wilkinson combiner just two pieces of transmission line (or simulated with components) with a resistor across two of the ports to absorbe the diffeance if the loads/sources are not ballanced ? The resistor is NOT to provide a load in case of an imbalance. It's to provide an impedance match for a 180 degree out of phase path between input/output ports. A signal that tries to go between the two input/output ports has two paths along which it can go. One is down one 1/4 wave coax, and up the other 1/4 wave coax, resulting in a 180 degree phase shift. The other is through the resistor with a 0 degree phase shift. If everything is roughly impedance matched, the signals through the two paths cancel, resulting in very good isolation between ports. As the subject is combining, I have not looked into the losses of splitting, but it would be 6 db for the simple resistor designs not counting the minor losses. That would be 3 db for the ports and 3 db lost in the resistors. Yep, that's correct. http://www.microwaves101.com/encyclopedia/resistive_splitters.cfm To combind signals you would get the loss of the resistors of 3 db and a fraction of other loss. Yep, that's correct. I am using a HP 8924C for a test set. It has just about everything you can think of for a service monitor. Calibrated from 30 to 1000 MHz but usuable uncalibrated to about a half of a mhz. http://www.amtronix.com/hp8924c60.htm http://axfp.org/god-bless-the-hp-8924c-a-tale-and-tutorial-of-the-service-monitor/ Nice. I'm into opening a museum of antique test equipment: http://802.11junk.com/jeffl/pics/home/slides/test-equip-mess.html Yes, phasing harnesses on antennas are not totally loseless, but will be mainly whatever the loss of the coax is between the elements. Nope. A phasing harness is much like the Wilkinson combiner without the balancing resistor. Isolation between antennas would be nice, but kinda futile with the antennas that close. Like the Wilkinson combiner, the cables are odd multiples of 1/4 wave electrical. Like the Wilkinson, such phasing harnesses have a limited bandwidth, where losses increase the further away one gets from resonance. In other words, you can't supply a single number for the losses in a phasing harness. What's needed are numbers for the losses at resonance and at band edges. At this time, I still don't know if a Wilkinson combiner or phasing harness will have sufficient bandwidth to cover the FM broadcast band. That's 20 Mhz bandwidth at 100 Mhz or Q=5. I don't think that's possible. To make my life more difficult, it's not possible to easily model coax cables using NEC2. I've been using a mythical 50 ohm open wire line, which can be modeled. I would recommend either a messy multistage Wilkinson power splitter/combiner, or go the broadband route with a common CATV/FM power splitter/combiner. If were the origional poster and there were not too many transmitters near me, I would try a good preamp first. Mast mounted if possiable as it is for receive only. Preamps are a mixed blessing. With a good antenna, they can pickup signals at impressive distances. However, they can also overload miserably if there is a nearby transmitter on a nearby frequency. The directionality of a Yagi is a big help, but if the nearby transmitter is too close, the amplifier will overload, desensitize, belch intermod, or otherwise cause problems. At best, the tower mounted amp should be used only to compensate for coax losses. Any more gain than that reduces the dynamic range of the system. Therefore, if the coax cables is fairly short, and the cable is low loss, I wouldn't bother with an amplifier. If the coax cable run is long and/or the coax is junk, a tower mounted amp might be worth trying. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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