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Antenna combiner/joiner question
Hello,
I have two antennas that I am trying to combine, and have a question in regards to the best way to do this. The first antenna is a Winegard HD7084P (FM/VHF/UHF lpda) that is hooked to a preamp and tuned in perfectly. I want to add my other antenna (Winegard PR-8800 UHF bowtie) that is also tuned in and points in the opposite direction (almost 180 degrees) to pick up some UHF stations. The two antennas are side by side, but the ends of the elements are about 4 feet apart. When I disconnect the HD7084P from the preamp and connect the combiner and hook the HD7084P to the combiner, the signal strength for HD stations maintains about the same. But when I hook up the second antenna to the combiner, the HD signal strength from the HD7084P drops by 10-40% (depending on the channel). I tried two combiners/splitters and got the same results, one is a RCA brand splitter, the other is a Radio Shack hybrid splitter/combiner. Would something like the Channel Master 0538 or the Winegard CC-7870 work better for this?? I read up and these models mention "high isolation" which I can't seem to find any information on. It seems like a powered combiner would be ideal so that there is no loss at all, but I haven't seen anything like that. I am looking for any suggestions or ideas that anybody might have. I really appreciate all of the help and feedback. Thank you very much, -- Chris |
Antenna combiner/joiner question
Since both antennas cover UHF, point in opposite directions, and are spaced
within a fraction of a wavelength at UHF frequencies and below, it is extremely likely that the phase cancellations of the two antennas causes the drop in signal strength when mixed in a combiner. The solutions are far as I can tell would be to bring both feed lines (coax lines) down to the receiver and switch when you need one or the other, or to filter out UHF content from the log periodic with a step low pass filter, or separate the 2 antennas more, since you appear to be creating a phased array even though you never intended to by the way you are configuring them. Phased arrays deliberately add and subtract RF energy to gain directivity at the expense of attenuation in other directions. Smarty "szilagyic" wrote in message oups.com... Hello, I have two antennas that I am trying to combine, and have a question in regards to the best way to do this. The first antenna is a Winegard HD7084P (FM/VHF/UHF lpda) that is hooked to a preamp and tuned in perfectly. I want to add my other antenna (Winegard PR-8800 UHF bowtie) that is also tuned in and points in the opposite direction (almost 180 degrees) to pick up some UHF stations. The two antennas are side by side, but the ends of the elements are about 4 feet apart. When I disconnect the HD7084P from the preamp and connect the combiner and hook the HD7084P to the combiner, the signal strength for HD stations maintains about the same. But when I hook up the second antenna to the combiner, the HD signal strength from the HD7084P drops by 10-40% (depending on the channel). I tried two combiners/splitters and got the same results, one is a RCA brand splitter, the other is a Radio Shack hybrid splitter/combiner. Would something like the Channel Master 0538 or the Winegard CC-7870 work better for this?? I read up and these models mention "high isolation" which I can't seem to find any information on. It seems like a powered combiner would be ideal so that there is no loss at all, but I haven't seen anything like that. I am looking for any suggestions or ideas that anybody might have. I really appreciate all of the help and feedback. Thank you very much, -- Chris |
Antenna combiner/joiner question
On Mon, 23 Jul 2007 14:27:48 -0000, szilagyic
wrote: I really appreciate all of the help and feedback. Basically, the combiners only work with antennas (lines) that address different frequencies. I'm sure with the right filters and spacing you could combine things in phase, and also instantly detect missile launches from North Korea, but basically you want to run them down separately and put some kind of manual switch between the two sources. .... unless someone can point me to a source of filters that would let him (and me!) combine things on a channel-by-channel basis, ... at reasonable cost. J. |
Antenna combiner/joiner question
On Jul 23, 10:42 am, "Smarty" wrote:
Since both antennas cover UHF, point in opposite directions, and are spaced within a fraction of a wavelength at UHF frequencies and below, it is extremely likely that the phase cancellations of the two antennas causes the drop in signal strength when mixed in a combiner. The solutions are far as I can tell would be to bring both feed lines (coax lines) down to the receiver and switch when you need one or the other, or to filter out UHF content from the log periodic with a step low pass filter, or separate the 2 antennas more, since you appear to be creating a phased array even though you never intended to by the way you are configuring them. Phased arrays deliberately add and subtract RF energy to gain directivity at the expense of attenuation in other directions. Smarty Thanks for the quick reply. Right now the best alternative is the spacing as I only have one downfeed that uses a preamp. What would be the minimum distance between the two antennas that I should use, or is it better to stack these instead, and if so what would be the minimum distance that should be used? Or, would a metal barrier between the two fix this issue with spacing?? I really appreciate the help. -- Chris |
Antenna combiner/joiner question
On Jul 23, 10:42 am, "Smarty" wrote:
Since both antennas cover UHF, point in opposite directions, and are spaced within a fraction of a wavelength at UHF frequencies and below, it is extremely likely that the phase cancellations of the two antennas causes the drop in signal strength when mixed in a combiner. The solutions are far as I can tell would be to bring both feed lines (coax lines) down to the receiver and switch when you need one or the other, or to filter out UHF content from the log periodic with a step low pass filter, or separate the 2 antennas more, since you appear to be creating a phased array even though you never intended to by the way you are configuring them. Phased arrays deliberately add and subtract RF energy to gain directivity at the expense of attenuation in other directions. Smarty Thanks for the quick reply. Right now the best alternative is the spacing as I only have one downfeed that uses a preamp. What would be the minimum distance between the two antennas that I should use for UHF considering VHF doesn't appear to be a problem, or is it better to stack these instead, and if so what would be the minimum distance that should be used? Or, would a metal barrier between the two fix this issue with spacing?? I really appreciate the help. -- Chris |
Antenna combiner/joiner question
"szilagyic" wrote in message ps.com... On Jul 23, 10:42 am, "Smarty" wrote: Since both antennas cover UHF, point in opposite directions, and are spaced within a fraction of a wavelength at UHF frequencies and below, it is extremely likely that the phase cancellations of the two antennas causes the drop in signal strength when mixed in a combiner. The solutions are far as I can tell would be to bring both feed lines (coax lines) down to the receiver and switch when you need one or the other, or to filter out UHF content from the log periodic with a step low pass filter, or separate the 2 antennas more, since you appear to be creating a phased array even though you never intended to by the way you are configuring them. Phased arrays deliberately add and subtract RF energy to gain directivity at the expense of attenuation in other directions. Smarty Thanks for the quick reply. Right now the best alternative is the spacing as I only have one downfeed that uses a preamp. What would be the minimum distance between the two antennas that I should use for UHF considering VHF doesn't appear to be a problem, or is it better to stack these instead, and if so what would be the minimum distance that should be used? Or, would a metal barrier between the two fix this issue with spacing?? I really appreciate the help. -- Chris Hi Chris Is there a reason for not mounting the two antennas "back to back"? Is there an amplifier at one antenna *before* the combiner? If so, why? Jerry |
Antenna combiner/joiner question
Stacking the antennas vertically could work but will create some nulls /
signal attenuation /cancellation in the elevation plane (versus your current problem in the azimuth plane). The elevation nulls can put some signals near the horizon (where you want the antenna to provide its' gain) into a deep trough. The effect would depend on frequency / channel, the physical spacing of the two vertically stacked antennas, and the antenna designs themselves. To get a rough idea about how to avoid these effects either in vertical or horizontal separation of the two antennas, consider that 1 wavelength at the end of the UHF band is very roughly 1 meter long and that it is roughly half that at the high end of the UHF band. A minimum separation of quite a few wavelengths is required before the so-called "near field" effects of the antenna diminish, and I would guess that 10 wavelength = ten meters = about 35 feet would be very adequate for low band UHF and about 17 or 18 foot separation if you were seeing cancellation / attenuation at the high end of the UHF band only. I would NEVER suggest putting metal / insulating plates or surfaces between the 2 antennas since this would act as yet another element to cause attenuation / reflections / etc. You are therefore left the options of spatially separating the antennas on a single mast vertically 17-35 feet apart, or on 2 masts 17 to 35 feet apart. My approach is very conservative and somewhat smaller spacings may work adequately, but this could only be determined by experimentation. A lot has to do with the specific antenna designs, the arrival angles of the desired channels / signals, the coax line lengths and impedance matches, etc., etc., etc. Smarty "szilagyic" wrote in message ps.com... On Jul 23, 10:42 am, "Smarty" wrote: Since both antennas cover UHF, point in opposite directions, and are spaced within a fraction of a wavelength at UHF frequencies and below, it is extremely likely that the phase cancellations of the two antennas causes the drop in signal strength when mixed in a combiner. The solutions are far as I can tell would be to bring both feed lines (coax lines) down to the receiver and switch when you need one or the other, or to filter out UHF content from the log periodic with a step low pass filter, or separate the 2 antennas more, since you appear to be creating a phased array even though you never intended to by the way you are configuring them. Phased arrays deliberately add and subtract RF energy to gain directivity at the expense of attenuation in other directions. Smarty Thanks for the quick reply. Right now the best alternative is the spacing as I only have one downfeed that uses a preamp. What would be the minimum distance between the two antennas that I should use for UHF considering VHF doesn't appear to be a problem, or is it better to stack these instead, and if so what would be the minimum distance that should be used? Or, would a metal barrier between the two fix this issue with spacing?? I really appreciate the help. -- Chris |
Antenna combiner/joiner question
On Jul 23, 2:28 pm, "Jerry Martes" wrote:
"szilagyic" wrote in message ps.com... On Jul 23, 10:42 am, "Smarty" wrote: Since both antennas cover UHF, point in opposite directions, and are spaced within a fraction of a wavelength at UHF frequencies and below, it is extremely likely that the phase cancellations of the two antennas causes the drop in signal strength when mixed in a combiner. The solutions are far as I can tell would be to bring both feed lines (coax lines) down to the receiver and switch when you need one or the other, or to filter out UHF content from the log periodic with a step low pass filter, or separate the 2 antennas more, since you appear to be creating a phased array even though you never intended to by the way you are configuring them. Phased arrays deliberately add and subtract RF energy to gain directivity at the expense of attenuation in other directions. Smarty Thanks for the quick reply. Right now the best alternative is the spacing as I only have one downfeed that uses a preamp. What would be the minimum distance between the two antennas that I should use for UHF considering VHF doesn't appear to be a problem, or is it better to stack these instead, and if so what would be the minimum distance that should be used? Or, would a metal barrier between the two fix this issue with spacing?? I really appreciate the help. -- Chris Hi Chris Is there a reason for not mounting the two antennas "back to back"? Is there an amplifier at one antenna *before* the combiner? If so, why? Jerry Hi Jerry, It would be difficult for me to mount them back to back based on the space where they are mounted, but if this would help our situation then I'd be open to trying it. There is not an amplifier before the combiner. Basically, I have the coax feeds running directly from each antenna to the combiner, which goes to the preamp, which runs down to a splitter, and then to a couple receivers. Thank you! -- Chris |
Antenna combiner/joiner question
"szilagyic" wrote in message ups.com... On Jul 23, 2:28 pm, "Jerry Martes" wrote: "szilagyic" wrote in message ps.com... On Jul 23, 10:42 am, "Smarty" wrote: Since both antennas cover UHF, point in opposite directions, and are spaced within a fraction of a wavelength at UHF frequencies and below, it is extremely likely that the phase cancellations of the two antennas causes the drop in signal strength when mixed in a combiner. The solutions are far as I can tell would be to bring both feed lines (coax lines) down to the receiver and switch when you need one or the other, or to filter out UHF content from the log periodic with a step low pass filter, or separate the 2 antennas more, since you appear to be creating a phased array even though you never intended to by the way you are configuring them. Phased arrays deliberately add and subtract RF energy to gain directivity at the expense of attenuation in other directions. Smarty Thanks for the quick reply. Right now the best alternative is the spacing as I only have one downfeed that uses a preamp. What would be the minimum distance between the two antennas that I should use for UHF considering VHF doesn't appear to be a problem, or is it better to stack these instead, and if so what would be the minimum distance that should be used? Or, would a metal barrier between the two fix this issue with spacing?? I really appreciate the help. -- Chris Hi Chris Is there a reason for not mounting the two antennas "back to back"? Is there an amplifier at one antenna *before* the combiner? If so, why? Jerry Hi Jerry, It would be difficult for me to mount them back to back based on the space where they are mounted, but if this would help our situation then I'd be open to trying it. There is not an amplifier before the combiner. Basically, I have the coax feeds running directly from each antenna to the combiner, which goes to the preamp, which runs down to a splitter, and then to a couple receivers. Thank you! -- Chris Hi Chris The best way to mount your two antennas sure would be to locate each in the region of least sensitivity of the other. That will afford the least amount of influence of one to the other. As I understand it, you have an amplifier that is common to both antennas. You probably have a good reason for doing that. But, why is the amplifier neded between the antenna and the receiver. It appears that you now have "one antenna" that is made in two parts. And there is an amplifier somewhere between the antenna and the receivers. Jerry |
Antenna combiner/joiner question
On Jul 23, 4:13 pm, "Jerry Martes" wrote:
"szilagyic" wrote in message ups.com... On Jul 23, 2:28 pm, "Jerry Martes" wrote: "szilagyic" wrote in message oups.com... On Jul 23, 10:42 am, "Smarty" wrote: Since both antennas cover UHF, point in opposite directions, and are spaced within a fraction of a wavelength at UHF frequencies and below, it is extremely likely that the phase cancellations of the two antennas causes the drop in signal strength when mixed in a combiner. The solutions are far as I can tell would be to bring both feed lines (coax lines) down to the receiver and switch when you need one or the other, or to filter out UHF content from the log periodic with a step low pass filter, or separate the 2 antennas more, since you appear to be creating a phased array even though you never intended to by the way you are configuring them. Phased arrays deliberately add and subtract RF energy to gain directivity at the expense of attenuation in other directions. Smarty Thanks for the quick reply. Right now the best alternative is the spacing as I only have one downfeed that uses a preamp. What would be the minimum distance between the two antennas that I should use for UHF considering VHF doesn't appear to be a problem, or is it better to stack these instead, and if so what would be the minimum distance that should be used? Or, would a metal barrier between the two fix this issue with spacing?? I really appreciate the help. -- Chris Hi Chris Is there a reason for not mounting the two antennas "back to back"? Is there an amplifier at one antenna *before* the combiner? If so, why? Jerry Hi Jerry, It would be difficult for me to mount them back to back based on the space where they are mounted, but if this would help our situation then I'd be open to trying it. There is not an amplifier before the combiner. Basically, I have the coax feeds running directly from each antenna to the combiner, which goes to the preamp, which runs down to a splitter, and then to a couple receivers. Thank you! -- Chris Hi Chris The best way to mount your two antennas sure would be to locate each in the region of least sensitivity of the other. That will afford the least amount of influence of one to the other. As I understand it, you have an amplifier that is common to both antennas. You probably have a good reason for doing that. But, why is the amplifier neded between the antenna and the receiver. It appears that you now have "one antenna" that is made in two parts. And there is an amplifier somewhere between the antenna and the receivers. Jerry Hi Jerry, I have the preamp connected to send the signal from the two antennas down a length of coax and to a 4-way splitter that will supply a few receivers. When I have everything hooked up except for the second antenna, it works out well. What would be your guestimation on how far apart the two antennas should be, if we put them back to back??? Thank you!! -- Chris |
Antenna combiner/joiner question
"szilagyic" wrote in message ups.com... On Jul 23, 4:13 pm, "Jerry Martes" wrote: "szilagyic" wrote in message ups.com... On Jul 23, 2:28 pm, "Jerry Martes" wrote: "szilagyic" wrote in message oups.com... On Jul 23, 10:42 am, "Smarty" wrote: Since both antennas cover UHF, point in opposite directions, and are spaced within a fraction of a wavelength at UHF frequencies and below, it is extremely likely that the phase cancellations of the two antennas causes the drop in signal strength when mixed in a combiner. The solutions are far as I can tell would be to bring both feed lines (coax lines) down to the receiver and switch when you need one or the other, or to filter out UHF content from the log periodic with a step low pass filter, or separate the 2 antennas more, since you appear to be creating a phased array even though you never intended to by the way you are configuring them. Phased arrays deliberately add and subtract RF energy to gain directivity at the expense of attenuation in other directions. Smarty Thanks for the quick reply. Right now the best alternative is the spacing as I only have one downfeed that uses a preamp. What would be the minimum distance between the two antennas that I should use for UHF considering VHF doesn't appear to be a problem, or is it better to stack these instead, and if so what would be the minimum distance that should be used? Or, would a metal barrier between the two fix this issue with spacing?? I really appreciate the help. -- Chris Hi Chris Is there a reason for not mounting the two antennas "back to back"? Is there an amplifier at one antenna *before* the combiner? If so, why? Jerry Hi Jerry, It would be difficult for me to mount them back to back based on the space where they are mounted, but if this would help our situation then I'd be open to trying it. There is not an amplifier before the combiner. Basically, I have the coax feeds running directly from each antenna to the combiner, which goes to the preamp, which runs down to a splitter, and then to a couple receivers. Thank you! -- Chris Hi Chris The best way to mount your two antennas sure would be to locate each in the region of least sensitivity of the other. That will afford the least amount of influence of one to the other. As I understand it, you have an amplifier that is common to both antennas. You probably have a good reason for doing that. But, why is the amplifier neded between the antenna and the receiver. It appears that you now have "one antenna" that is made in two parts. And there is an amplifier somewhere between the antenna and the receivers. Jerry Hi Jerry, I have the preamp connected to send the signal from the two antennas down a length of coax and to a 4-way splitter that will supply a few receivers. When I have everything hooked up except for the second antenna, it works out well. What would be your guestimation on how far apart the two antennas should be, if we put them back to back??? Thank you!! -- Chris Hi Chris I am no expert on TV and FM antennas. I do have some experience with signal splitters and combiners. It just seems logical that you will get the best antenna performance by mounting them "back to back" and as far apart as you can without making a BigJob of it. As I understand the system connections you are using, both antennas are being fed from one amplifier thru a signal splitter. That will be as though you have one antenna thats physically two antennas fed in parallel with a phase lead or lag dependent on the lengths of their coax. If both antennas are well matched, the receiver's signal would drop 3 dB when the second antenna is connected thru that "Signal Splitter", even if the radiation pattern wasnt effected by that second antenna. I think you have a very interesting project here. I also think you will be lucky to solve the "sometimes weak signal" problem using the components you now have. How long is the coax and what kind is it? Jerry |
Antenna combiner/joiner question
On Jul 23, 8:23 pm, "Jerry Martes" wrote:
"szilagyic" wrote in message ups.com... On Jul 23, 4:13 pm, "Jerry Martes" wrote: "szilagyic" wrote in message roups.com... On Jul 23, 2:28 pm, "Jerry Martes" wrote: "szilagyic" wrote in message oups.com... On Jul 23, 10:42 am, "Smarty" wrote: Since both antennas cover UHF, point in opposite directions, and are spaced within a fraction of a wavelength at UHF frequencies and below, it is extremely likely that the phase cancellations of the two antennas causes the drop in signal strength when mixed in a combiner. The solutions are far as I can tell would be to bring both feed lines (coax lines) down to the receiver and switch when you need one or the other, or to filter out UHF content from the log periodic with a step low pass filter, or separate the 2 antennas more, since you appear to be creating a phased array even though you never intended to by the way you are configuring them. Phased arrays deliberately add and subtract RF energy to gain directivity at the expense of attenuation in other directions. Smarty Thanks for the quick reply. Right now the best alternative is the spacing as I only have one downfeed that uses a preamp. What would be the minimum distance between the two antennas that I should use for UHF considering VHF doesn't appear to be a problem, or is it better to stack these instead, and if so what would be the minimum distance that should be used? Or, would a metal barrier between the two fix this issue with spacing?? I really appreciate the help. -- Chris Hi Chris Is there a reason for not mounting the two antennas "back to back"? Is there an amplifier at one antenna *before* the combiner? If so, why? Jerry Hi Jerry, It would be difficult for me to mount them back to back based on the space where they are mounted, but if this would help our situation then I'd be open to trying it. There is not an amplifier before the combiner. Basically, I have the coax feeds running directly from each antenna to the combiner, which goes to the preamp, which runs down to a splitter, and then to a couple receivers. Thank you! -- Chris Hi Chris The best way to mount your two antennas sure would be to locate each in the region of least sensitivity of the other. That will afford the least amount of influence of one to the other. As I understand it, you have an amplifier that is common to both antennas. You probably have a good reason for doing that. But, why is the amplifier neded between the antenna and the receiver. It appears that you now have "one antenna" that is made in two parts. And there is an amplifier somewhere between the antenna and the receivers. Jerry Hi Jerry, I have the preamp connected to send the signal from the two antennas down a length of coax and to a 4-way splitter that will supply a few receivers. When I have everything hooked up except for the second antenna, it works out well. What would be your guestimation on how far apart the two antennas should be, if we put them back to back??? Thank you!! -- Chris Hi Chris I am no expert on TV and FM antennas. I do have some experience with signal splitters and combiners. It just seems logical that you will get the best antenna performance by mounting them "back to back" and as far apart as you can without making a BigJob of it. As I understand the system connections you are using, both antennas are being fed from one amplifier thru a signal splitter. That will be as though you have one antenna thats physically two antennas fed in parallel with a phase lead or lag dependent on the lengths of their coax. If both antennas are well matched, the receiver's signal would drop 3 dB when the second antenna is connected thru that "Signal Splitter", even if the radiation pattern wasnt effected by that second antenna. I think you have a very interesting project here. I also think you will be lucky to solve the "sometimes weak signal" problem using the components you now have. How long is the coax and what kind is it? Jerry We will see what happens, I'll be sure to post the results. I am still debating whether I need a better combiner or if they are pretty universal for quality. The coax from both antennas to the combiner is 6 ft RG-6, with the combiner attached to the preamp with a coupler. Then from the preamp to the 4-way splitter is about 15 ft of RG-6 QS + 20 ft RG-6. From the 4-way splitter to each device is about 15-20 ft RG-6. -- Chris |
Antenna combiner/joiner question
On Mon, 23 Jul 2007 14:27:48 -0000, szilagyic
wrote: Hello, I have two antennas that I am trying to combine, and have a question in regards to the best way to do this. The first antenna is a Winegard HD7084P (FM/VHF/UHF lpda) that is hooked to a preamp and tuned in perfectly. I want to add my other antenna (Winegard PR-8800 UHF bowtie) that is also tuned in and points in the opposite direction (almost 180 degrees) to pick up some UHF stations. The two antennas are side by side, but the ends of the elements are about 4 feet apart. When I disconnect the HD7084P from the preamp and connect the combiner and hook the HD7084P to the combiner, the signal strength for HD stations maintains about the same. But when I hook up the second antenna to the combiner, the HD signal strength from the HD7084P drops by 10-40% (depending on the channel). I tried two combiners/splitters and got the same results, one is a RCA brand splitter, the other is a Radio Shack hybrid splitter/combiner. Would something like the Channel Master 0538 or the Winegard CC-7870 work better for this?? I read up and these models mention "high isolation" which I can't seem to find any information on. It seems like a powered combiner would be ideal so that there is no loss at all, but I haven't seen anything like that. I am looking for any suggestions or ideas that anybody might have. I really appreciate all of the help and feedback. Thank you very much, When you join two antennas, the wavelengths are different for the different channels. Some may cancel each other on your favorite channel and some may be additive on channels you don't care about. You can adjust the lengths of the leads going to the two antennas and change which channels/wavelengths are additive. Try a shorter cable on one of the two antennas. |
Antenna combiner/joiner question
On Jul 23, 10:11 pm, valvejob wrote:
On Mon, 23 Jul 2007 14:27:48 -0000, szilagyic wrote: Hello, I have two antennas that I am trying to combine, and have a question in regards to the best way to do this. The first antenna is a Winegard HD7084P (FM/VHF/UHF lpda) that is hooked to a preamp and tuned in perfectly. I want to add my other antenna (Winegard PR-8800 UHF bowtie) that is also tuned in and points in the opposite direction (almost 180 degrees) to pick up some UHF stations. The two antennas are side by side, but the ends of the elements are about 4 feet apart. When I disconnect the HD7084P from the preamp and connect the combiner and hook the HD7084P to the combiner, the signal strength for HD stations maintains about the same. But when I hook up the second antenna to the combiner, the HD signal strength from the HD7084P drops by 10-40% (depending on the channel). I tried two combiners/splitters and got the same results, one is a RCA brand splitter, the other is a Radio Shack hybrid splitter/combiner. Would something like the Channel Master 0538 or the Winegard CC-7870 work better for this?? I read up and these models mention "high isolation" which I can't seem to find any information on. It seems like a powered combiner would be ideal so that there is no loss at all, but I haven't seen anything like that. I am looking for any suggestions or ideas that anybody might have. I really appreciate all of the help and feedback. Thank you very much, When you join two antennas, the wavelengths are different for the different channels. Some may cancel each other on your favorite channel and some may be additive on channels you don't care about. You can adjust the lengths of the leads going to the two antennas and change which channels/wavelengths are additive. Try a shorter cable on one of the two antennas. This makes sense, but does this apply for antennas that are pointed in opposite directions? I just want to clarify, you are basically saying to alter the cable length by say, a portion of a wavelength (a half of a wavelength?), for one of our favorite channels that is having issues? |
Antenna combiner/joiner question
I am no expert on TV and FM antennas. I do have some experience with signal splitters and combiners. It just seems logical that you will get the best antenna performance by mounting them "back to back" and as far apart as you can without making a BigJob of it. As I understand the system connections you are using, both antennas are being fed from one amplifier thru a signal splitter. That will be as though you have one antenna thats physically two antennas fed in parallel with a phase lead or lag dependent on the lengths of their coax. If both antennas are well matched, the receiver's signal would drop 3 dB when the second antenna is connected thru that "Signal Splitter", even if the radiation pattern wasnt effected by that second antenna. I think you have a very interesting project here. I also think you will be lucky to solve the "sometimes weak signal" problem using the components you now have. How long is the coax and what kind is it? Jerry We will see what happens, I'll be sure to post the results. I am still debating whether I need a better combiner or if they are pretty universal for quality. The coax from both antennas to the combiner is 6 ft RG-6, with the combiner attached to the preamp with a coupler. Then from the preamp to the 4-way splitter is about 15 ft of RG-6 QS + 20 ft RG-6. From the 4-way splitter to each device is about 15-20 ft RG-6. -- Chris Hi Chris I'm surprised that the amplifier is needed. But, you have determined that it does improve reception so I have nothing to add to what you have done. I do submit to you that the high quality splitter/combiner isnt likely to provide you with any improvement in TV reception. When you connect two seperate antennas to one output terminal, like with a splitter, you then have One Antenna that has two feed points. Mount the two antennas "back to back", and dont spend too much money on high quality splitters. Good luck Jerry |
Antenna combiner/joiner question
In article .com szilagyic writes:
On Jul 23, 10:11 pm, valvejob wrote: When you join two antennas, the wavelengths are different for the different channels. Some may cancel each other on your favorite channel and some may be additive on channels you don't care about. You can adjust the lengths of the leads going to the two antennas and change which channels/wavelengths are additive. Try a shorter cable on one of the two antennas. This makes sense, but does this apply for antennas that are pointed in opposite directions? I just want to clarify, you are basically saying to alter the cable length by say, a portion of a wavelength (a half of a wavelength?), for one of our favorite channels that is having issues? Yes, it applies then, too. You may want to look at the result for frequency cancellation with a good spectrum analyzer. Lacking that, and the knowledge of how to understand the results, you may just have to try things and see how they work. Alan |
Antenna combiner/joiner question
In alt.tv.tech.hdtv szilagyic wrote:
| I have two antennas that I am trying to combine, and have a question | in regards to the best way to do this. The first antenna is a | Winegard HD7084P (FM/VHF/UHF lpda) that is hooked to a preamp and | tuned in perfectly. I want to add my other antenna (Winegard PR-8800 | UHF bowtie) that is also tuned in and points in the opposite direction | (almost 180 degrees) to pick up some UHF stations. The two antennas | are side by side, but the ends of the elements are about 4 feet | apart. When I disconnect the HD7084P from the preamp and connect the | combiner and hook the HD7084P to the combiner, the signal strength for | HD stations maintains about the same. But when I hook up the second | antenna to the combiner, the HD signal strength from the HD7084P drops | by 10-40% (depending on the channel). I tried two combiners/splitters | and got the same results, one is a RCA brand splitter, the other is a | Radio Shack hybrid splitter/combiner. Would something like the | Channel Master 0538 or the Winegard CC-7870 work better for this?? I | read up and these models mention "high isolation" which I can't seem | to find any information on. It seems like a powered combiner would be | ideal so that there is no loss at all, but I haven't seen anything | like that. I am looking for any suggestions or ideas that anybody | might have. The simple resistive combiner, which can also be a splitter when wired in reverse, intentionally loses 3db of signal as part of its simple circuitry to be sure the impedances are matched. If the impedances are not matched, things get worse because the joint becomes a point where signals can be reflected, resulting in a number of signal abberations. In addition, a combiner should also isolate the branches from each other. The importance of having this depends on other factors in your design, such as how well the antenna feedpoints match across the frequencies you want to receive. You can get away with a mismatch on the source end if the target end (amplifier) is well matched. But unless the combiner has very high isolation, the two antennas form "ends" opposing each other on the wire, and can result in signal reflections between them. A combiner with 6 db isolation (very simple) will at least reduce those reflections between antennas somewhat. The proximity of the antennas to each other may also warp the pattern they receive in, depending on their design, the exact distance, etc. Even with a combiner of high isolation, when one antenna is picking up the signal only the other antenna should (e.g. the "back lobe" in such a case with antennas almost 180 degrees apart), that can result in two sources of the same signal being merged. Depending on phase difference, that can combine or cancel-out. Both can happen at different frequencies depending on the exact length. The ideal combiner system involves frequency isolation. That is, channel filters only allow each channel to come from one or the other antenna. This is common in well engineered cable headends. But these usually also involve lots of large single channel antennas. If one direction were VHF and the other were UHF, this would be easy as the frequency isolation could be done via a VHF band filter and a UHF band filter. I take it your case does not involve that. Losing signal is almost certainly going to be a part of combining two antennas. Larger antennas can compensate for it. Amplifiers per each antenna may help as well (especially with reflections along the coax). If your channels are intermingled, frequency isolation is going to be very expensive. Your last resort for full signal is two separate feeds to a switch. That can be a nearby switch manually operated, or a switch on the mast that is remotely controlled. But either way, your TV will never see both sets of signals at the same time, and apparently most modern digital tuner systems need to see the whole channel lineup at once on the one RF feed. If an STB is part of your setup, you might consider a 2nd STB for the 2nd feedline, and switch between them. -- |---------------------------------------/----------------------------------| | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below | | first name lower case at ipal.net / | |------------------------------------/-------------------------------------| |
Antenna combiner/joiner question
"szilagyic" wrote in message oups.com... Hello, I have two antennas that I am trying to combine, and have a question in regards to the best way to do this. The first antenna is a Winegard HD7084P (FM/VHF/UHF lpda) that is hooked to a preamp and tuned in perfectly. I want to add my other antenna (Winegard PR-8800 UHF bowtie) that is also tuned in and points in the opposite direction (almost 180 degrees) to pick up some UHF stations. ........................................... Over the past 50 years several antenna manufacturers have come up with kluged arrangements to do what you propose. None worked, except in a few special cases where the signals were very strong. What you need is an antenna rotator, or a second antenna with its own feedline. When you combine the outputs of two antennas without appropriate filters, not only is there a chance of signal cancellation, but you will also quite likely have a severe echo problem. Tam |
Antenna combiner/joiner question
Tam/WB2TT wrote:
"szilagyic" wrote in message oups.com... Hello, I have two antennas that I am trying to combine, and have a question in regards to the best way to do this. The first antenna is a Winegard HD7084P (FM/VHF/UHF lpda) that is hooked to a preamp and tuned in perfectly. I want to add my other antenna (Winegard PR-8800 UHF bowtie) that is also tuned in and points in the opposite direction (almost 180 degrees) to pick up some UHF stations. .......................................... Over the past 50 years several antenna manufacturers have come up with kluged arrangements to do what you propose. None worked, except in a few special cases where the signals were very strong. What you need is an antenna rotator, or a second antenna with its own feedline. When you combine the outputs of two antennas without appropriate filters, not only is there a chance of signal cancellation, but you will also quite likely have a severe echo problem. Tam I wanted the same set up as you did using a Winegard HD8200P (combo) & HD9095P (UHF). In the end I unhooked the UHF in the HD8200 and get VHF (from the 8200) from one direction and UHF from another direction. I could not combine the two and receive a good UHF signal. I will say that my HD9095P does recieve one channel 180 deg from where it is pointed. You might want to play with the UHF reflectors (try folding them down some maybe) to get more 180 deg. signal. |
Antenna combiner/joiner question
szilagyic wrote:
Hello, I have two antennas that I am trying to combine, and have a question in regards to the best way to do this. The first antenna is a Winegard HD7084P (FM/VHF/UHF lpda) that is hooked to a preamp and tuned in perfectly. I want to add my other antenna (Winegard PR-8800 UHF bowtie) that is also tuned in and points in the opposite direction (almost 180 degrees) to pick up some UHF stations. The two antennas are side by side, but the ends of the elements are about 4 feet apart. When I disconnect the HD7084P from the preamp and connect the combiner and hook the HD7084P to the combiner, the signal strength for HD stations maintains about the same. But when I hook up the second antenna to the combiner, the HD signal strength from the HD7084P drops by 10-40% (depending on the channel). I tried two combiners/splitters and got the same results, one is a RCA brand splitter, the other is a Radio Shack hybrid splitter/combiner. Would something like the Channel Master 0538 or the Winegard CC-7870 work better for this?? I read up and these models mention "high isolation" which I can't seem to find any information on. It seems like a powered combiner would be ideal so that there is no loss at all, but I haven't seen anything like that. I am looking for any suggestions or ideas that anybody might have. I really appreciate all of the help and feedback. Thank you very much, -- Chris I wanted the same set up as you did using a Winegard HD8200P (combo) & HD9095P (UHF). In the end I unhooked the UHF in the HD8200 and get VHF (from the 8200) from one direction and UHF from another direction. I could not combine the two and receive a good UHF signal. I will say that my HD9095P does recieve one channel 180 deg from where it is pointed. You might want to play with the UHF reflectors (try folding them down some maybe) to get more 180 deg. signal. |
Antenna combiner/joiner question
Chris,
"Back to Back" mounting only makes sense if you either can rotate the entire array with a rotor or if the signals you are trying to receive are coincidentally 180 degrees apart on the compass from your receiving location using a fixed (non rotating) array. The log periodic array you are using no doubt is highly directive, and the bow tie at UHF is, even with a reflector element added to the UHF bowtie dipole, an asymmetrical figure eight. The cancellation effects will still occur at UHF until you get the two antennas physically separated, either horizontally or vertically. The combiner and coax length / mismatch issue is far less important. Smarty "Jerry Martes" wrote in message news:3Rdpi.12267$U47.3415@trnddc08... I am no expert on TV and FM antennas. I do have some experience with signal splitters and combiners. It just seems logical that you will get the best antenna performance by mounting them "back to back" and as far apart as you can without making a BigJob of it. As I understand the system connections you are using, both antennas are being fed from one amplifier thru a signal splitter. That will be as though you have one antenna thats physically two antennas fed in parallel with a phase lead or lag dependent on the lengths of their coax. If both antennas are well matched, the receiver's signal would drop 3 dB when the second antenna is connected thru that "Signal Splitter", even if the radiation pattern wasnt effected by that second antenna. I think you have a very interesting project here. I also think you will be lucky to solve the "sometimes weak signal" problem using the components you now have. How long is the coax and what kind is it? Jerry We will see what happens, I'll be sure to post the results. I am still debating whether I need a better combiner or if they are pretty universal for quality. The coax from both antennas to the combiner is 6 ft RG-6, with the combiner attached to the preamp with a coupler. Then from the preamp to the 4-way splitter is about 15 ft of RG-6 QS + 20 ft RG-6. From the 4-way splitter to each device is about 15-20 ft RG-6. -- Chris Hi Chris I'm surprised that the amplifier is needed. But, you have determined that it does improve reception so I have nothing to add to what you have done. I do submit to you that the high quality splitter/combiner isnt likely to provide you with any improvement in TV reception. When you connect two seperate antennas to one output terminal, like with a splitter, you then have One Antenna that has two feed points. Mount the two antennas "back to back", and dont spend too much money on high quality splitters. Good luck Jerry |
Antenna combiner/joiner question
In alt.tv.tech.hdtv szilagyic wrote:
| This makes sense, but does this apply for antennas that are pointed in | opposite directions? I just want to clarify, you are basically saying | to alter the cable length by say, a portion of a wavelength (a half of | a wavelength?), for one of our favorite channels that is having issues? No antenna perfectly eliminates the back lobe. Some just do better than others (like a solid parabolic dish). The bow tie antenns will receive some signal in the reverse direction. If that back lobe reception on one combines out of phase with the front lobe of the other, it will reduce the total sign somewhat. -- |---------------------------------------/----------------------------------| | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below | | first name lower case at ipal.net / | |------------------------------------/-------------------------------------| |
Antenna combiner/joiner question
On Jul 24, 7:50 pm, wrote:
In alt.tv.tech.hdtv szilagyic wrote: | This makes sense, but does this apply for antennas that are pointed in | opposite directions? I just want to clarify, you are basically saying | to alter the cable length by say, a portion of a wavelength (a half of | a wavelength?), for one of our favorite channels that is having issues? No antenna perfectly eliminates the back lobe. Some just do better than others (like a solid parabolic dish). The bow tie antenns will receive some signal in the reverse direction. If that back lobe reception on one combines out of phase with the front lobe of the other, it will reduce the total sign somewhat. -- |---------------------------------------/----------------------------------*| | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below | | first name lower case at ipal.net / | |------------------------------------/-------------------------------------*| Would some of these 'jointennas" reduce the interference / interaction? They're not cheap but as much a s a cable bill. http://www.warrenelectronics.com/ant...Jointennas.htm Did I miss it or did nobody ask what the actual channels in question are? Any idea of the relative signal strengths? How far away? I would think if the antennas are "spectally separated" via diplexers, the cable lengths woun't be all that critical. It also depends on how far apart the channel frequencies are. If you have a 28 and 30 in front and are trying to get a 29 from the back, that will be tough but if it's several channel numbers apart, it is less tough. SO, what are the channels in question? GG |
Antenna combiner/joiner question
On Jul 25, 12:32 am, G-squared wrote:
On Jul 24, 7:50 pm, wrote: In alt.tv.tech.hdtv szilagyic wrote: | This makes sense, but does this apply for antennas that are pointed in | opposite directions? I just want to clarify, you are basically saying | to alter the cable length by say, a portion of a wavelength (a half of | a wavelength?), for one of our favorite channels that is having issues? No antenna perfectly eliminates the back lobe. Some just do better than others (like a solid parabolic dish). The bow tie antenns will receive some signal in the reverse direction. If that back lobe reception on one combines out of phase with the front lobe of the other, it will reduce the total sign somewhat. -- |---------------------------------------/----------------------------------*| | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below | | first name lower case at ipal.net / | |------------------------------------/-------------------------------------*| Would some of these 'jointennas" reduce the interference / interaction? They're not cheap but as much a s a cable bill. http://www.warrenelectronics.com/ant...Jointennas.htm Did I miss it or did nobody ask what the actual channels in question are? Any idea of the relative signal strengths? How far away? I would think if the antennas are "spectally separated" via diplexers, the cable lengths woun't be all that critical. It also depends on how far apart the channel frequencies are. If you have a 28 and 30 in front and are trying to get a 29 from the back, that will be tough but if it's several channel numbers apart, it is less tough. SO, what are the channels in question? GG GG, I came across those Jointennas and they look very interesting. Unfortunately the channels (frequencies) we are trying to get are all spread out. Here's a list anyway: On the first antenna (VHF/UHF/FM) we get channels 2,4,7,9,20,28,50,56,62 (analog), and 14,21,41,43,44,45,52,58 (digital). On the second antenna (UHF only) we get channels 18,23,47,53 (analog), and 34,38,51,57,59 (digital). Just out of curiousity, what is the average loss in dB when using the Jointennas, or does it vary? I haven't been able to find any info on the loss. Thank you very much. There have been some great ideas posted in this thread and we will try various things hopefully soon and see what works. -- Chris |
Antenna combiner/joiner question
On Jul 23, 10:27 am, szilagyic wrote:
Hello, I have two antennas that I am trying to combine, and have a question in regards to the best way to do this. The first antenna is a Winegard HD7084P (FM/VHF/UHF lpda) that is hooked to a preamp and tuned in perfectly. I want to add my other antenna (Winegard PR-8800 UHF bowtie) that is also tuned in and points in the opposite direction (almost 180 degrees) to pick up some UHF stations. The two antennas are side by side, but the ends of the elements are about 4 feet apart. When I disconnect the HD7084P from the preamp and connect the combiner and hook the HD7084P to the combiner, the signal strength for HD stations maintains about the same. But when I hook up the second antenna to the combiner, the HD signal strength from the HD7084P drops by 10-40% (depending on the channel). I tried two combiners/splitters and got the same results, one is a RCA brand splitter, the other is a Radio Shack hybrid splitter/combiner. Would something like the Channel Master 0538 or the Winegard CC-7870 work better for this?? I read up and these models mention "high isolation" which I can't seem to find any information on. It seems like a powered combiner would be ideal so that there is no loss at all, but I haven't seen anything like that. I am looking for any suggestions or ideas that anybody might have. I really appreciate all of the help and feedback. Thank you very much, -- Chris The problem is phasing of the signals at the combiner. You only need to lengthen one feedline from one source prior to the combiner, this will be done by experiment. You could also shorten feedline a little at a time and observe the changing signal levels. You will not get them perfect (due to slightly different frequencies/wavelenghts). You will also effect the impedance 'coupling' slightly which may work in your favor. |
Antenna combiner/joiner question
On Jul 25, 10:44 am, DeanO wrote:
On Jul 23, 10:27 am, szilagyic wrote: Hello, I have two antennas that I am trying to combine, and have a question in regards to the best way to do this. The first antenna is a Winegard HD7084P (FM/VHF/UHF lpda) that is hooked to a preamp and tuned in perfectly. I want to add my other antenna (Winegard PR-8800 UHF bowtie) that is also tuned in and points in the opposite direction (almost 180 degrees) to pick up some UHF stations. The two antennas are side by side, but the ends of the elements are about 4 feet apart. When I disconnect the HD7084P from the preamp and connect the combiner and hook the HD7084P to the combiner, the signal strength for HD stations maintains about the same. But when I hook up the second antenna to the combiner, the HD signal strength from the HD7084P drops by 10-40% (depending on the channel). I tried two combiners/splitters and got the same results, one is a RCA brand splitter, the other is a Radio Shack hybrid splitter/combiner. Would something like the Channel Master 0538 or the Winegard CC-7870 work better for this?? I read up and these models mention "high isolation" which I can't seem to find any information on. It seems like a powered combiner would be ideal so that there is no loss at all, but I haven't seen anything like that. I am looking for any suggestions or ideas that anybody might have. I really appreciate all of the help and feedback. Thank you very much, -- Chris The problem is phasing of the signals at the combiner. You only need to lengthen one feedline from one source prior to the combiner, this will be done by experiment. You could also shorten feedline a little at a time and observe the changing signal levels. You will not get them perfect (due to slightly different frequencies/wavelenghts). You will also effect the impedance 'coupling' slightly which may work in your favor. The whole point of a diplexer (jointenna) is to filter out individual channels so that 'phasing' is no longer an issue for combining the feeds. The actual insertion loss of a jointenna should be aound 1 dB on a pass through channel GG |
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