[Repeater-Builder] Re: Transmitter combining and Multicoupling information.
Harold Farrenkopf [EMAIL PROTECTED] wrote: I was refering to the resonant frequency of just one loop and cable out of the can behaving like a quarter wave shorted stub (or 3/4 wave) for determining the cable length. No problama, for the most part, that's how many/most people select the cable lengths. If one were able to look at the entire cable - cable length - star frequency response over a very wide spectral display... you'd notice the entire star - cable network loss is significant - skewed or tilted higher at the higher side/end of the actual graph/display. In short, the best performance of the network appears to be with the cable lengths slightly shorter than what you would think or see without the wideband spectral view or return loss display. It cam end up being only a fraction of a dB in many cases, but the loss can add up fast in 4-leg combiner networks with even modest improper length cables. This problem seems to be found more often in tx combiners with fairly wide frequency spacings. Add in the crappy square box star from Telewave and you've got what I would call excessive unwanted unneeded tx combiner network loss. 4 dB is high for a single can system isolator type system but it may be better than using a hybrid since it does give a pass response for TX noise. I like to beat up some of the tx combiner mfgrs at IWCE about the actual resultant loss of most tx combiners. But we all end up on the same there is no free lunch page. The actual results in many cases seem to be an as-built project. When someone tries to deviate from even the most generic norm, you can quickly get into trouble as seen with the previous mentioned South American VHF Tx Combiner System (Alex). The out of the box tx combiner doesn't work right and there is/was no obvious reason why... unless you pay attention to the details. I like the newer TX/RX and Sinclair non critical length tx combiners, but they are really not that much different in the loss department. Plus you don't find their bottles (with the dual jack hybrid ports (what ever they want to call them) on ebay nearly as often. :-( My preference now would be 2 to 3 pass can's plus Q cans per frequency into the star so that the isolator doesn't see much of the other close frequency energy to cause IM problems. Harold Yes, it would be nice... but with our good friends at American Tower and simmilar well run companies charging very modest per rack space antenna system hardware mounting prices (per month)... sometimes evil cost vs performance trades have to be made. With extra rack mounted bottles you simply translate the combiner system dB signal loss to the cost of being at an AT site. What's in your walet would be 2dB down... :-( The most common tx combiner is the single bottle to hub/star type. The larger the bottle (in most cases), the better (higher Q). And it all echos back first to the actual frequencies used and their relative spacing. Then on to what you're willing to live with. And as always mentioned, your results will probably vary. cheers, skipp Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: Transmitter combining and Multicoupling information.
--- In Repeater-Builder@yahoogroups.com, skipp025 [EMAIL PROTECTED] wrote: Gareth Bennett garethb@ wrote: I inherited a TX combiner on a radio site that has just grown without any planning and thought involved. That would be about 80% of the combiners systems I've seen. Clint Eastwood called it a Cluster in one of his movies. There are 5x transmitters from 151.5 through to 153.025 with the closest TX to TX spacing being 250 KHz. which borders on almost being too close for a Star layout. Unless the bottles are large and high Q, those two legs prob. have a lot of loss. No, 250kHz is fine for a 5 TX star combiner (with isolators and or more pass cans in series). 10 cans can go down to 60khz. I have seen star combiners that have been fitted with shorted stubs that Appears to be in the vicinity of around 1/8 wavelength... I was hoping that there was some theory or maths to get close to this length. Sure, it is a harmonic trap with the advantage of being a DC shunt. Sinclair's stubs are near open half waves if my memory serves me and are adjusted (trimmed) to present a balance return loss across the span of frequencies used. In the past I have maintained TX star combiners where the combiner itself has been made for a selective frequency band, with capacitive disks inside. (These almost always had shorted stubs fitted to a spare star port). It's nice to have the stub if you have an extra port, but it's not a requirement. I understand the theory of an odd wavelength from the cavity to the combiner (Usually 3/4 wavelength) More often 1/4 wave cable lenghts in the popular 4 port (less than or equal to) combiners when size and cable lengths permit. 5 way will require the 3/4 wave version to get to 5 cavities from the star. But would like to know more theory and if possible the maths that go into proper transmitter combining. I was a systems guy and never got into those details. Look at manufacturer's catalog pictures to see how they do TX star combiners. The loop and cable length presented approximately a 1/4 wave or 3/4 wave shorted stub when you look at it through the star with a tracking generator and spectrum analyser. The resonance I mentioned was a minimal insertion loss or the best VSWR (best return loss) at the middle of your frequencies) Well... each combiner is a trade off based on your frequency list and band of operation. Might be better to go through an example rather than throw a bunch of technoblather out. cheers, skipp Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: Transmitter combining and Multicoupling information.
Harold Farrenkopf [EMAIL PROTECTED] wrote: There are 5x transmitters from 151.5 through to 153.025 with the closest TX to TX spacing being 250 KHz. which borders on almost being too close for a Star layout. Unless the bottles are large and high Q, those two legs prob. have a lot of loss. No, 250kHz is fine for a 5 TX star combiner (with isolators and or more pass cans in series). 10 cans can go down to 60khz. Depends on what you consider usable performance. I'm not fond of 4dB loss right out of the starting gate in addition to all the other gremlins, which tend to pop up in marginal combiner operation. Yes, the Q of the cans make a big difference as well as the number of... but many of the common combiners are single can and a bunch are even reduced size bottles. Sinclair's stubs are near open half waves if my memory serves me and are adjusted (trimmed) to present a balance return loss across the span of frequencies used. Sinclair's Engineering is first rate work. Another applied stub method is always interesting to learn about. More often 1/4 wave cable lenghts in the popular 4 port (less than or equal to) combiners when size and cable lengths permit. 5 way will require the 3/4 wave version to get to 5 cavities from the star. In many cases yes, but I have seen folded versions of combiners where 5 way starrs were used with 1/4 wave cables. The 1/4 wave cable lengths seem to be easier to match. I was a systems guy and never got into those details. I'm a moderate Republican not so happy with the way my current Politcal Party trys to operate. . Look at manufacturer's catalog pictures to see how they do TX star combiners. Catalogs can be very helpful. The loop and cable length presented approximately a 1/4 wave or 3/4 wave shorted stub when you look at it through the star with a tracking generator and spectrum analyser. The resonance I mentioned was a minimal insertion loss or the best VSWR (best return loss) at the middle of your frequencies) The fly in the soup is the minimal insertion loss is not always in/at the middle of the selected frequencies. And the return loss or resonant curve/value is not a uniform shape. cheers, skipp Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [Repeater-Builder] Re: Transmitter combining and Multicoupling information.
Thanks for the feedback and general comments... Very informative and good to have the topic kicked around a bit. As mentioned previously I inherited a TX combiner on a radio site that has just grown without any planning and thought involved. There are 5x transmitters from 151.5 through to 153.025 with the closest TX to TX spacing being 250 KHz. I have seen star combiners that have been fitted with shorted stubs that Appears to be in the vicinity of around 1/8 wavelength... I was hoping that there was some theory or maths to get close to this length. In the past I have maintained TX star combiners where the combiner itself has been made for a selective frequency band, with capacitive disks inside. (These almost always had shorted stubs fitted to a spare star port). I understand the theory of an odd wavelength from the cavity to the combiner (Usually 3/4 wavelength) But would like to know more theory and if possible the maths that go into proper transmitter combining. Thanks again for reading :-) _ Gareth Bennett This e-mail is confidential, if you received this message in error, or you are not the intended recipient, please return it to the sender and destroy any copies. Thank you. - Original Message - From: skipp025 [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Tuesday, May 02, 2006 6:04 AM Subject: [Repeater-Builder] Re: Transmitter combining and Multicoupling information. Harold Farrenkopf [EMAIL PROTECTED] wrote: Easiest way to verify the actual length required is to remove the loop from the can (or adjust it for minimal coupling) and put it in the star with a cable of approximately the correct length and use 2 of the other star ports to measure the resonant frequency of the loop and cable to see if it is in the mid of your frequency spread. Much of the time, the mid frequency is not the most desired location. I'm not sure if you'd actually call or spec the cable/loop combo as a resonant frequency element... although most people might call it one. All the cables would then be the same length to the star if the loops are the same. Not in all cases... also depend on the number of legs in use via the star or equiv device. Also the frequency spread... The open stub would be close to the electrical 1/2 wavelength if required to make the output return loss symmetrical and better. I personally usually do not use a stub and try to make the cables work alone but then again, I am using an Agilent 8753ES network analyser that makes the job very easy. The stub is used if the frequency span is larger or the cables used are not the ideal lengths. The open circuit stub is trimmed to make the return loss symmetrical. Harold I've found the shorted stub used most often, Not only as a trap, but as a much desired (in most cases) dc shunt. I've seen star combiner setups with various caps and or stubs networks on the unused ports. Telewave sells a square box type - star, which I think is real crap. I like the Sinclair Star mucho betta'. cheers, skipp Yahoo! Groups Links Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: Transmitter combining and Multicoupling information.
Gareth Bennett [EMAIL PROTECTED] wrote: I inherited a TX combiner on a radio site that has just grown without any planning and thought involved. That would be about 80% of the combiners systems I've seen. Clint Eastwood called it a Cluster in one of his movies. There are 5x transmitters from 151.5 through to 153.025 with the closest TX to TX spacing being 250 KHz. which borders on almost being too close for a Star layout. Unless the bottles are large and high Q, those two legs prob. have a lot of loss. I have seen star combiners that have been fitted with shorted stubs that Appears to be in the vicinity of around 1/8 wavelength... I was hoping that there was some theory or maths to get close to this length. Sure, it is a harmonic trap with the advantage of being a DC shunt. In the past I have maintained TX star combiners where the combiner itself has been made for a selective frequency band, with capacitive disks inside. (These almost always had shorted stubs fitted to a spare star port). It's nice to have the stub if you have an extra port, but it's not a requirement. I understand the theory of an odd wavelength from the cavity to the combiner (Usually 3/4 wavelength) More often 1/4 wave cable lenghts in the popular 4 port (less than or equal to) combiners when size and cable lengths permit. But would like to know more theory and if possible the maths that go into proper transmitter combining. Well... each combiner is a trade off based on your frequency list and band of operation. Might be better to go through an example rather than throw a bunch of technoblather out. cheers, skipp Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: Transmitter combining and Multicoupling information.
Harold Farrenkopf [EMAIL PROTECTED] wrote: Easiest way to verify the actual length required is to remove the loop from the can (or adjust it for minimal coupling) and put it in the star with a cable of approximately the correct length and use 2 of the other star ports to measure the resonant frequency of the loop and cable to see if it is in the mid of your frequency spread. Much of the time, the mid frequency is not the most desired location. I'm not sure if you'd actually call or spec the cable/loop combo as a resonant frequency element... although most people might call it one. All the cables would then be the same length to the star if the loops are the same. Not in all cases... also depend on the number of legs in use via the star or equiv device. Also the frequency spread... The open stub would be close to the electrical 1/2 wavelength if required to make the output return loss symmetrical and better. I personally usually do not use a stub and try to make the cables work alone but then again, I am using an Agilent 8753ES network analyser that makes the job very easy. The stub is used if the frequency span is larger or the cables used are not the ideal lengths. The open circuit stub is trimmed to make the return loss symmetrical. Harold I've found the shorted stub used most often, Not only as a trap, but as a much desired (in most cases) dc shunt. I've seen star combiner setups with various caps and or stubs networks on the unused ports. Telewave sells a square box type - star, which I think is real crap. I like the Sinclair Star mucho betta'. cheers, skipp Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: Transmitter combining and Multicoupling information.
What band are you dealing with and its frequency spread? The length of cable including the loop's effective length and the star's contribution should equal an electrical odd multiple of a quarter wavelength. Easiest way to verify the actual length required is to remove the loop from the can (or adjust it for minimal coupling) and put it in the star with a cable of approximately the correct length and use 2 of the other star ports to measure the resonant frequency of the loop and cable to see if it is in the mid of your frequency spread. All the cables would then be the same length to the star if the loops are the same. The open stub would be close to the electrical 1/2 wavelength if required to make the output return loss symmetrical and better. I personally usually do not use a stub and try to make the cables work alone but then again, I am using an Agilent 8753ES network analyser that makes the job very easy. The stub is used if the frequency span is larger or the cables used are not the ideal lengths. The open circuit stub is trimmed to make the return loss symmetrical. Harold --- In Repeater-Builder@yahoogroups.com, skipp025 [EMAIL PROTECTED] wrote: Hi Gareth, Gareth Bennett garethb@ wrote: I am appealing to the wisdom of the group for information regarding Transmitter combining (Multicoupling). OK, we'll try to help. I am interested in the maths and formula involved in cable lengths, coaxial stubs, etc for the Star style of TX combining. Yes there is math, but almost every combiner system is an as built based to the overall system requirements and performance trade offs. The cable lengths are based no relative odd 1/4 wave lenghts with lots of things changing the actual length. I have inherited a site that has been added to over the years with different equipment and filter styles. I need to re-build the TX (and RX) side to tidy it all up. The first think you'll need to do is make a spread sheet of your tx and rx frequencies. Each TX leg is like this... TX, Isolator, Cavity filter, 3/4 wavelength coax to star combiner... Nothing flash, just want to know the maths behind it and to fine tune the system There are rules of thumb for the combiner engineering, based on a number of variables... first the frequecy list, second the allowed mix problems are checked, third the materials you have to construct the combiner, fourth the loss or performance trades vs frequency spacing, fifth the actual equipment you'd like to use. Especially the Transmitter coaxial stub information that usually is found on one spare combiner port. Measure the existing stub for open or shorted end. It's most often a harmonic trap/stub, 1/2 the length of the in band quarter wave length. Thanks for reading :-) No problama, it's hard to be specific without more information from you. If you ask Telewave - Sinclair or the Andrew Decibel RF Engineers about making a combiner, they'll want your frequency list first. Sometimes you can make a single antenna do everything, sometimes you split the antennas. In problematic frequency combinations, you might need to have/include both additional tx and rx antennas to avoid system gremlins. When a multi channel pre-configured tx combiner works right out of the box, I would consider the owner and mfgr very good and a bit lucky. Combiners are where I picked up the no free lunch line. In close space combinations, you try to keep the power loss to less than 60%. Also, your results will probably vary... cheers, skipp Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: Transmitter combining and Multicoupling information.
Hi Gareth, Gareth Bennett [EMAIL PROTECTED] wrote: I am appealing to the wisdom of the group for information regarding Transmitter combining (Multicoupling). OK, we'll try to help. I am interested in the maths and formula involved in cable lengths, coaxial stubs, etc for the Star style of TX combining. Yes there is math, but almost every combiner system is an as built based to the overall system requirements and performance trade offs. The cable lengths are based no relative odd 1/4 wave lenghts with lots of things changing the actual length. I have inherited a site that has been added to over the years with different equipment and filter styles. I need to re-build the TX (and RX) side to tidy it all up. The first think you'll need to do is make a spread sheet of your tx and rx frequencies. Each TX leg is like this... TX, Isolator, Cavity filter, 3/4 wavelength coax to star combiner... Nothing flash, just want to know the maths behind it and to fine tune the system There are rules of thumb for the combiner engineering, based on a number of variables... first the frequecy list, second the allowed mix problems are checked, third the materials you have to construct the combiner, fourth the loss or performance trades vs frequency spacing, fifth the actual equipment you'd like to use. Especially the Transmitter coaxial stub information that usually is found on one spare combiner port. Measure the existing stub for open or shorted end. It's most often a harmonic trap/stub, 1/2 the length of the in band quarter wave length. Thanks for reading :-) No problama, it's hard to be specific without more information from you. If you ask Telewave - Sinclair or the Andrew Decibel RF Engineers about making a combiner, they'll want your frequency list first. Sometimes you can make a single antenna do everything, sometimes you split the antennas. In problematic frequency combinations, you might need to have/include both additional tx and rx antennas to avoid system gremlins. When a multi channel pre-configured tx combiner works right out of the box, I would consider the owner and mfgr very good and a bit lucky. Combiners are where I picked up the no free lunch line. In close space combinations, you try to keep the power loss to less than 60%. Also, your results will probably vary... cheers, skipp Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
