Re: [Repeater-Builder] Antenna Phasing Question
On Wed, 10 Mar 2010, afa5tp wrote: I have three (3) Antel [BCD 80010] 806-900 mHz vertical antennae that I would like to mount on the three legs of my tower for omni pattern (Rec. only). Several questions come to mind. 1.) At the rated frequency, how many inches should the side arm place the ant. from the tower? 1/4 wavelength from a large plane reflector, mounted in the middle of the reflector. 2.)What would be the best way to phase the antennae? I have a Andrews three port Splitter, and will use LDF4-50A for feedline. I would suspect the length of the pigtail from each antenna to splitter is going to be critical...or not, for receive only? 33% to each side, 120-degrees electrical length (I think). And be sure your tower can take the windload of sheet aluminum on all faces for 1.5 wavelengths below and above the omnis. Look at a feed arrangement for a big wheel antenna that has three petals instead of four. -- Kris Kirby, KE4AHR Disinformation Analyst
RE: [Repeater-Builder] Antenna Phasing Question
As far as phasing the antennas around the tower, it can't be done. Well it can but you will end up with more nulls and a worse pattern than you started with. The problem is that most signals will arrive at more than one antenna. Because they are different distances apart to the mobile there will be a time difference between the two. So you say ok, I will just make the phasing harness that same length as the antennas are apart. That would work great for one specific direction. But what happens when that mobile moves to a new azimuth location? Then there will not be the same distance to him between the two antennas as there was when you made the phasing harness. Now you have a new time difference between arriving signals but you have the same length phasing lines. The result is that the combined signals are no longer in phase so you have less gain. If the two signals fall out of phase then they will cancel. You have a big null in the pattern there. 73 Gary K4FMX -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:Repeater- buil...@yahoogroups.com] On Behalf Of afa5tp Sent: Wednesday, March 10, 2010 12:31 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Antenna Phasing Question Hello Folks I have three (3) Antel [BCD 80010] 806-900 mHz vertical antennae that I would like to mount on the three legs of my tower for omni pattern (Rec. only). Several questions come to mind. 1.) At the rated frequency, how many inches should the side arm place the ant. from the tower? 2.)What would be the best way to phase the antennae? I have a Andrews three port Splitter, and will use LDF4-50A for feedline. I would suspect the length of the pigtail from each antenna to splitter is going to be critical...or not, for receive only? BTW..How good of an antenna is the Antel BCD 80010? Many thanks for any guidance and wisdom. Tim Hardy W7TRH/AFA0TP Vashon Is. Wa. Yahoo! Groups Links
RE: [Repeater-Builder] Antenna Phasing Question
I have three (3) Antel [BCD 80010] 806-900 mHz vertical antennae that I would like to mount on the three legs of my tower for omni pattern (Rec. only). Several questions come to mind. 1.) At the rated frequency, how many inches should the side arm place the ant. from the tower? 2.)What would be the best way to phase the antennae? I have a Andrews three port Splitter, and will use LDF4-50A for feedline. I would suspect the length of the pigtail from each antenna to splitter is going to be critical...or not, for receive only? Any time you start to try to phase omni antennas like you're describing, you're going to end up with nothing like the omni pattern you're hoping to achieve. You'll have deep nulls all over the place, it's just a bad idea. If you were willing to run the three antennas to three separate feedlines and feed three separate receivers and vote between them, that would make more sense, but passively combining the three antennas into one feedline is going to yield extremely disappointing results. You're better off with a single omni and eating whatever tower nulls you end up with... BTW..How good of an antenna is the Antel BCD 80010? I'm using a BCD87010, which is the 870-960 MHz 10 dBd omni with the standard 1.25 degrees of downtilt on a ham repeater in Philly. It works well and is built well. Bought it from Tessco a few years ago. Receive performance is impaired by all of the Part 15 junk, but that's not the fault of the antenna. The BCD800 series is 806-900 MHz; I don't think I'd want to use it in the ham band if that's your intention, I'd get an 870 series. --- Jeff WN3A
Re: [Repeater-Builder] Antenna Phasing Question
Everyone who voiced an opinion. I see the error of my ways! I shall use only (1) antenna! Just want to rec. a better signal from a 800 trunking transmitter, about 30 mi. distant. Thanks guys, for setting me straight! Best Regards, Tim Hardy W7TRH/AFA0TP Vashon Is. Wa. - Original Message - From: Jeff DePolo j...@broadsci.com To: Repeater-Builder@yahoogroups.com Sent: Wednesday, March 10, 2010 10:50:38 AM GMT -08:00 US/Canada Pacific Subject: RE: [Repeater-Builder] Antenna Phasing Question I have three (3) Antel [BCD 80010] 806-900 mHz vertical antennae that I would like to mount on the three legs of my tower for omni pattern (Rec. only). Several questions come to mind. 1.) At the rated frequency, how many inches should the side arm place the ant. from the tower? 2.)What would be the best way to phase the antennae? I have a Andrews three port Splitter, and will use LDF4-50A for feedline. I would suspect the length of the pigtail from each antenna to splitter is going to be critical...or not, for receive only? Any time you start to try to phase omni antennas like you're describing, you're going to end up with nothing like the omni pattern you're hoping to achieve. You'll have deep nulls all over the place, it's just a bad idea. If you were willing to run the three antennas to three separate feedlines and feed three separate receivers and vote between them, that would make more sense, but passively combining the three antennas into one feedline is going to yield extremely disappointing results. You're better off with a single omni and eating whatever tower nulls you end up with... BTW..How good of an antenna is the Antel BCD 80010? I'm using a BCD87010, which is the 870-960 MHz 10 dBd omni with the standard 1.25 degrees of downtilt on a ham repeater in Philly. It works well and is built well. Bought it from Tessco a few years ago. Receive performance is impaired by all of the Part 15 junk, but that's not the fault of the antenna. The BCD800 series is 806-900 MHz; I don't think I'd want to use it in the ham band if that's your intention, I'd get an 870 series. --- Jeff WN3A
