Home |
Search |
Today's Posts |
#1
|
|||
|
|||
Radio Station Project Inquiry
Hi Engineers,
I'm Starting a new FM Station Project in BENGHAZI - LIBYA which is 60km2 in area, i was advised to use a transmitting system of a 600w Transmitter attached to 4 double dipole antenna (http://www.labelitaly.com/website/akk2.html) as my tower specs are : tower angle 4 leg (leg size = 10 x 10), parameter at 96 m height = 2.5m x 2.5m. attached a picture of my tower. i want to get an omni-directional coverage as my tower is located in the center of the city and I've been told that unless a panel antenna the tower will make a shadow or something like that to the broadcast signal. i want to know if i'm really forced to use a panel antenna in my system, why i can't use a high power regular dipole antenna. and please advice if the transmitter power i'm using will be enough to cover the 60km2 area. hope to find help here. Thanks in advance. |
#2
|
|||
|
|||
Radio Station Project Inquiry
On 3/7/2012 8:56 AM, samersaed wrote:
Hi Engineers, I'm Starting a new FM Station Project in BENGHAZI - LIBYA which is 60km2 in area, i was advised to use a transmitting system of a 600w Transmitter attached to 4 double dipole antenna (http://www.labelitaly.com/website/akk2.html) as my tower specs are : tower angle 4 leg (leg size = 10 x 10), parameter at 96 m height = 2.5m x 2.5m. attached a picture of my tower. i want to get an omni-directional coverage as my tower is located in the center of the city and I've been told that unless a panel antenna the tower will make a shadow or something like that to the broadcast signal. i want to know if i'm really forced to use a panel antenna in my system, why i can't use a high power regular dipole antenna. and please advice if the transmitter power i'm using will be enough to cover the 60km2 area. hope to find help here. Thanks in advance. Why are looking at a flat panel directional antenna when you want a omnidirectional antenna? Mikek |
#3
|
|||
|
|||
Radio Station Project Inquiry
"samersaed" wrote in message ... Hi Engineers, I'm Starting a new FM Station Project in BENGHAZI - LIBYA which is 60km2 in area, i was advised to use a transmitting system of a 600w Transmitter attached to 4 double dipole antenna (http://www.labelitaly.com/website/akk2.html) as my tower specs are : tower angle 4 leg (leg size = 10 x 10), parameter at 96 m height = 2.5m x 2.5m. attached a picture of my tower. i want to get an omni-directional coverage as my tower is located in the center of the city and I've been told that unless a panel antenna the tower will make a shadow or something like that to the broadcast signal. i want to know if i'm really forced to use a panel antenna in my system, why i can't use a high power regular dipole antenna. and please advice if the transmitter power i'm using will be enough to cover the 60km2 area. hope to find help here. Thanks in advance. -- samersaed Nothing attached! You might be able to use a simple sleeve dipole, ground plane, or suchlike at the top of the mast if that's vacant and you can get an antenna that's happy to work as the lightning finial, but the antenna gain will be low to the intended service area; possibly less than 0 dBd, particularly in the case of a ground-plane antenna (upward-tilted VRP: radiation pattern in the vertical plane). For police communication at similar frequencies in the UK, four two-element yagis around a pole were used at the top of the structure, the pole actining as the finial. Usually, two such arrays were stacked vertically. The small radius of such an array gives a good omni HRP (radiation pattern in the horizontal plane). An advantage to using a circular array of panels is that it can be positioned below the top of the structure (e.g. if the top is used for television) and you might achieve a minimum of 0 dBd if the handovers between adjacent panels are well controlled (or fortunate!). At many stations in the UK, a number of tiers of panels are used in order to provide gain and to facilitate a split upper/lower half-array system for resilience. You could try to get the antenna supplier to measure four panels on a stub tower of the same cross-section as your structure, but if you're only buying a one-off they might charge you a premium for perefoming the measurement. It would demonstrate unequivocally what the final system would achieve HRP-wise, although, depending on the height of the stub tower (or time-domain gating, etc.) you might still need to infer the VRP. A service area of 60 km^2 would have a radius of 4.4 km if it were circular - is yours? The required ERP depends on the required minimum field strength at the limit of service. For simple spherical spreading, taking no account of antenna VRPs and reflections/multipath, E=(7/r)sqrt(ERP) ... which can be found in ITU texts and is easy to derive from first principles .... so if you were to use, for example, a minimum field strength of 5 mV/m (stereo, in a large city with lots of sources of interference, using low-gain receiving antennas) at r=4.4 km, then ERP=9.9W. If your service area isn't circular, say it extends out to 10 km in one direction, then to achieve 5 mV/m at 10 km would require ERP = 51.0 watts. A 600 watt transmitter into an antenna system with a net gain of, say -3 dBd (accounting for VRP, HRP ripples, and combiner/feeder/power-splitter loss), would provide an ERP of 300 watts so, in the latter case, a margin of 7.7 dB. This would provide some resilience to multipath fading (although P-P=0, no matter how large P is!). In other words, you probably wouldn't need a higher-powered transmitter in this case - but it does depend on the shape of the service area, and on your definition of 'service'. Hope this helps. Chris |
#4
|
|||
|
|||
Radio Station Project Inquiry
"christofire" wrote in message news "samersaed" wrote in message ... Hi Engineers, I'm Starting a new FM Station Project in BENGHAZI - LIBYA which is 60km2 in area, i was advised to use a transmitting system of a 600w Transmitter attached to 4 double dipole antenna (http://www.labelitaly.com/website/akk2.html) as my tower specs are : tower angle 4 leg (leg size = 10 x 10), parameter at 96 m height = 2.5m x 2.5m. attached a picture of my tower. i want to get an omni-directional coverage as my tower is located in the center of the city and I've been told that unless a panel antenna the tower will make a shadow or something like that to the broadcast signal. i want to know if i'm really forced to use a panel antenna in my system, why i can't use a high power regular dipole antenna. and please advice if the transmitter power i'm using will be enough to cover the 60km2 area. hope to find help here. Thanks in advance. -- samersaed Nothing attached! You might be able to use a simple sleeve dipole, ground plane, or suchlike at the top of the mast if that's vacant and you can get an antenna that's happy to work as the lightning finial, but the antenna gain will be low to the intended service area; possibly less than 0 dBd, particularly in the case of a ground-plane antenna (upward-tilted VRP: radiation pattern in the vertical plane). For police communication at similar frequencies in the UK, four two-element yagis around a pole were used at the top of the structure, the pole actining as the finial. Usually, two such arrays were stacked vertically. The small radius of such an array gives a good omni HRP (radiation pattern in the horizontal plane). An advantage to using a circular array of panels is that it can be positioned below the top of the structure (e.g. if the top is used for television) and you might achieve a minimum of 0 dBd if the handovers between adjacent panels are well controlled (or fortunate!). At many stations in the UK, a number of tiers of panels are used in order to provide gain and to facilitate a split upper/lower half-array system for resilience. You could try to get the antenna supplier to measure four panels on a stub tower of the same cross-section as your structure, but if you're only buying a one-off they might charge you a premium for perefoming the measurement. It would demonstrate unequivocally what the final system would achieve HRP-wise, although, depending on the height of the stub tower (or time-domain gating, etc.) you might still need to infer the VRP. A service area of 60 km^2 would have a radius of 4.4 km if it were circular - is yours? The required ERP depends on the required minimum field strength at the limit of service. For simple spherical spreading, taking no account of antenna VRPs and reflections/multipath, E=(7/r)sqrt(ERP) ... which can be found in ITU texts and is easy to derive from first principles ... so if you were to use, for example, a minimum field strength of 5 mV/m (stereo, in a large city with lots of sources of interference, using low-gain receiving antennas) at r=4.4 km, then ERP=9.9W. If your service area isn't circular, say it extends out to 10 km in one direction, then to achieve 5 mV/m at 10 km would require ERP = 51.0 watts. A 600 watt transmitter into an antenna system with a net gain of, say -3 dBd (accounting for VRP, HRP ripples, and combiner/feeder/power-splitter loss), would provide an ERP of 300 watts so, in the latter case, a margin of 7.7 dB. This would provide some resilience to multipath fading (although P-P=0, no matter how large P is!). In other words, you probably wouldn't need a higher-powered transmitter in this case - but it does depend on the shape of the service area, and on your definition of 'service'. Hope this helps. Chris Another reason for using panel elements is to facilitate horizontal polarisation, which was popular in the UK (but perhaps for a questionable reason) - nowadays, most stations use mixed or vertical polarisation. When the majority of the listener-base is located in vehicles, VP is a better choice principally because of the typical receiving antenna. Chris |
#5
|
|||
|
|||
Radio Station Project Inquiry
On 3/7/2012 3:10 PM, amdx wrote:
On 3/7/2012 8:56 AM, samersaed wrote: Hi Engineers, I'm Starting a new FM Station Project in BENGHAZI - LIBYA which is 60km2 in area, i was advised to use a transmitting system of a 600w Transmitter attached to 4 double dipole antenna (http://www.labelitaly.com/website/akk2.html) as my tower specs are : tower angle 4 leg (leg size = 10 x 10), parameter at 96 m height = 2.5m x 2.5m. attached a picture of my tower. i want to get an omni-directional coverage as my tower is located in the center of the city and I've been told that unless a panel antenna the tower will make a shadow or something like that to the broadcast signal. i want to know if i'm really forced to use a panel antenna in my system, why i can't use a high power regular dipole antenna. and please advice if the transmitter power i'm using will be enough to cover the 60km2 area. hope to find help here. Thanks in advance. Why are looking at a flat panel directional antenna when you want a omnidirectional antenna? Mikek http://www.kathrein.pl/down/as_fmband.pdf |
#6
|
|||
|
|||
Quote:
I'm Forced to use panel antenna cause the person i'm buying the antenna from told me that my tower specs can handle nothing but a panel antenna to get the desired coverage cause if i use another system of antenna the tower will make a shadow to the transmitted signal and that's an information i don't trust, the panel antennas are so expensive and heavy for shipping so i'm asking for a replacement for those antenna that will work with my tower and gets me an omni-directional coverage. can you verify this information? Quote:
Quote:
thanks in advance Last edited by samersaed : March 8th 12 at 10:51 AM |
#7
|
|||
|
|||
Radio Station Project Inquiry
"samersaed" wrote in message ... - Why are looking at a flat panel directional antenna when you want a omnidirectional antenna? Mikek - First sorry that i forgot to attach the picture of my tower, it's attached now in this RAR File : http://www.mediafire.com/?cse8yiyn5d4jtd9 . I'm Forced to use panel antenna cause the person i'm buying the antenna from told me that my tower specs can handle nothing but a panel antenna to get the desired coverage cause if i use another system of antenna the tower will make a shadow to the transmitted signal and that's an information i don't trust, the panel antennas are so expensive and heavy for shipping so i'm asking for a replacement for those antenna that will work with my tower and gets me an omni-directional coverage. can you verify this information? - You might be able to use a simple sleeve dipole, ground plane, or suchlike at the top of the mast if that's vacant and you can get an antenna that's happy to work as the lightning finial, but the antenna gain will be low to the intended service area; possibly less than 0 dBd, particularly in the case of a ground-plane antenna (upward-tilted VRP: radiation pattern in the vertical plane). For police communication at similar frequencies in the UK, four two-element yagis around a pole were used at the top of the structure, the pole actining as the finial. Usually, two such arrays were stacked vertically. The small radius of such an array gives a good omni HRP (radiation pattern in the horizontal plane). - Unfortunately i'm renting a place in the tower which is 80 m high and the parameters of the tower at 96 m high is 2.5m x 2.5m so it's not gonna be small in radius for the antenna system. - A service area of 60 km^2 would have a radius of 4.4 km if it were circular - is yours? The required ERP depends on the required minimum field strength at the limit of service. For simple spherical spreading, taking no account of antenna VRPs and reflections/multipath, E=(7/r)sqrt(ERP) ... which can be found in ITU texts and is easy to derive from first principles ... so if you were to use, for example, a minimum field strength of 5 mV/m (stereo, in a large city with lots of sources of interference, using low-gain receiving antennas) at r=4.4 km, then ERP=9.9W. If your service area isn't circular, say it extends out to 10 km in one direction, then to achieve 5 mV/m at 10 km would require ERP = 51.0 watts. A 600 watt transmitter into an antenna system with a net gain of, say -3 dBd (accounting for VRP, HRP ripples, and combiner/feeder/power-splitter loss), would provide an ERP of 300 watts so, in the latter case, a margin of 7.7 dB. This would provide some resilience to multipath fading (although P-P=0, no matter how large P is!). In other words, you probably wouldn't need a higher-powered transmitter in this case - but it does depend on the shape of the service area, and on your definition of 'service'. - Ok let us Stick to the 600w transmitter, i'm not an expert in waves calculations glad to have such help from you, you can see exactly the picture of the tower and the position of it in this RAR FILE http://www.mediafire.com/?cse8yiyn5d4jtd9 , attached also a placemark from google earth for the tower location in the city, Benghazi's surface has a lot of area exposed to the sea at the north west, and there are hills at the south east, i only want to cover the residental area in between which is a cicule of 15 km of radius, getting a wrong pattern antenna will waste most of my signal into the sea, please recommend me an antenna system which works with the 600w transmitter and the tower specs i mentioned ( tower angle 4 leg (leg size = 10 x 10), parameter at 96 m height = 2.5m x 2.5m ) and also for the geographical charecteristics of the city and also want to get use of the gain of the antenna i will get to strength the signal ( my tower is the one at the left ) thanks in advance -- samersaed I don't have software to read .rar files - perhaps you could provide links to .jpg photos that can be read by Windows without needing to download a reader program. If the aperture you're renting is at 80 m on the 96 m tower then, clearly, you don't have access to the top so you can't use a simple omni-directional antenna. If you mount a half-wave dipole any reasonable distance off the face of a tower with side dimension similar to the wavelength then the resulting HRP will be directional (viz the 'shadow' principle you mentioned, and reflection off it). You may be able to use one or more such directional patterns if your service area isn't uniform around the antenna but if your aim is consistent coverage at all angles around the structure then you will need to mount an antenna off each face, and that's the purpose for which panel antennas have been designed - to achieve controlled hand-over from one panel to the next so ripples in the HRP are minimised. It isn't trivial to predict the radiation patterns of an antenna next to a metal structure and many manufacturers offer sytlised patterns based on averaged measurements. One manufacturer has already been named by amdx and there are many others you can Google (e.g. RFS, Alan Dick, R&S, Harris, etc.). However, since your service area covers a limited arc, bounded by sea and hills, it sounds like you don't want an omni-directional HRP at all - more a precisely-tailored directional pattern. It would probably take range measurements using a stub tower to get that right - but it all depends on how precise you need to be (e.g. on the definition of your coverage criterion). You will need to do some research into this (or pay someone to do it for you) if you don't trust the advice you're being given by a supplier. There may also be regulatory issues to contend with. It goes without saying that you shouldn't base your purchase on anything written in this or any other newsgroup! Chris |
#8
|
|||
|
|||
Radio Station Project Inquiry
On Wed, 07 Mar 2012 14:56:35 +0000, samersaed wrote:
Hi Engineers, I'm Starting a new FM Station Project in BENGHAZI - LIBYA which is 60km2 in area, i was advised to use a transmitting system of a 600w Transmitter attached to 4 double dipole antenna (http://www.labelitaly.com/website/akk2.html) as my tower specs are : tower angle 4 leg (leg size = 10 x 10), parameter at 96 m height = 2.5m x 2.5m. attached a picture of my tower. i want to get an omni-directional coverage as my tower is located in the center of the city and I've been told that unless a panel antenna the tower will make a shadow or something like that to the broadcast signal. i want to know if i'm really forced to use a panel antenna in my system, why i can't use a high power regular dipole antenna. and please advice if the transmitter power i'm using will be enough to cover the 60km2 area. hope to find help here. Thanks in advance. Katherein Scala antennas makes some very nice low power Yagi-Uda transmit antennas. |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Wanted Station master for Repeater project | Swap | |||
Setting up a radio station - Novice inquiry | Broadcasting | |||
Setting up a radio station - Novice inquiry | Broadcasting | |||
Setting up a radio station - Novice inquiry | Broadcasting | |||
Setting up a radio station - Novice inquiry | Broadcasting |