Re: [Repeater-Builder] Re: Repeater Antenna Choice
The area served by many of our radio sites (we are in Central Utah), sit at approximately a 12 degree downtilt from the sites. Most of these sites are at 3000-4000' AGL. In some cases, we have opted for lower gain antennas to cover close in areas better. We designate repeaters as local or wide area coverage to account for this. Wide area repeaters get high gain antennas to aim for the horizon (about 50-100 miles out), and local area repeaters get lower gain antennas for about 5-20 miles out. In some cases we opt for directional antennas such as corner reflectors or dipole arrays with all elements on one side of the mast when we want to cover the populated areas better at the expense of the back country. -- Keith McQueen [EMAIL PROTECTED] 801-224-9460 On 11/26/07, Laryn Lohman [EMAIL PROTECTED] wrote: I've not seen overshoot from relatively low AGL sites either. Maybe someone could bring up some examples of this happening, with details? Laryn K8TVZ --- In Repeater-Builder@yahoogroups.comRepeater-Builder%40yahoogroups.com, Nate Duehr [EMAIL PROTECTED] wrote: Agreed. I think what I was trying to say was there were a lot of people stating that the narrower vertical beamwidth/higher gain antennas would shoot over the top of users from a low HAAT site. I don't think that's true at all. Even the high-gain antennas have 6-7 degrees of 3dB vertical beamwidth and in close, I doubt losing 3dB (even when multiplied by the ERP) is really going to show up as a bunch of close-in holes... if you're standing directly under the building perhaps, but once you get that close the loss is nothing. Doing a quick calculation here... Assuming 350' HAAT, 0 degrees of downtilt, and a 7 degree vertical beamwidth: Radio Horizon: 26.46 miles Lower 3dB beamwidth horizon: 1.08 miles Upper 3dB beamwidth horizon: Over the radio horizon Same HAAT, 16 degree vertical 3dB beamwidth: Radio Horizon: 26.46 (same, of course) Lower 3dB beamwidth horizon: 0.47 miles Upper 3dB beamwidth horizon: Over the radio horizon (A difference of .61 miles - covers better in the neighborhood right around the structure, maybe... but the signal would be so strong there anyway...?) But -- I'll admit, we don't do much low-level stuff around here. I'm curious why folks think it makes that much of a difference? I'm with you on liking the dipole antennas... Having read Ron's comment about salt water eating them up, I guess there are probably places where a fiberglass stick would be wanted... but definitely not out here in our dry air at altitude. -- Nate Duehr, WY0X [EMAIL PROTECTED]
Re: [Repeater-Builder] Re: Repeater Antenna Choice
We had a DB-420 style antenna (actually it was made by Signals, but it was folded-dipole design) on our UHF repeater at work. We were constantly having difficulty with portables being able to hit and hold the repeater and they were no more than 1/2 mile out. The local M/A-Com shop kept saying too much antenna. We changed it out to a DB-408 and the problem was corrected. We are in rolling hills and the antenna was about 70' above ground level at a water tank. I plotted the antenna pattern against topographic map data and discovered that the portables were in some deep nulls with the higher-gain antenna. In another instance, a UHF ham repeater on a pretty decent site was using a DB-420 style antenna (I believe it was actually an Antenna Specialists version). It worked great out at the horizon, but closer in mobiles would become noisy and portables were tough. It got changed to a Sinclair 4-element folded dipole, and the improvement was substantial. Slight loss out at the extremes of the coverage area. I'm convinced that bigger isn't always better. You need to use the right antenna for the intended coverage. If all of your users are out at the extremes of where your repeater is located, the highest gain antenna might make more sense. I'd dare say that this usually isn't the case. Chuck WB2EDV - Original Message - From: Keith, KB7M To: Repeater-Builder@yahoogroups.com Sent: Monday, November 26, 2007 11:31 AM Subject: Re: [Repeater-Builder] Re: Repeater Antenna Choice The area served by many of our radio sites (we are in Central Utah), sit at approximately a 12 degree downtilt from the sites. Most of these sites are at 3000-4000' AGL. In some cases, we have opted for lower gain antennas to cover close in areas better. We designate repeaters as local or wide area coverage to account for this. Wide area repeaters get high gain antennas to aim for the horizon (about 50-100 miles out), and local area repeaters get lower gain antennas for about 5-20 miles out. In some cases we opt for directional antennas such as corner reflectors or dipole arrays with all elements on one side of the mast when we want to cover the populated areas better at the expense of the back country. -- Keith McQueen [EMAIL PROTECTED] 801-224-9460
Re: [Repeater-Builder] Re: Repeater Antenna Choice
About 275 - 280 feet. Chuck - Original Message - From: Laryn Lohman [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Monday, November 26, 2007 10:39 PM Subject: [Repeater-Builder] Re: Repeater Antenna Choice Chuck, how far vertically above the portables would that 420-style antenna have been, considering the hills in the area, etc. Laryn K8TVZ --- In Repeater-Builder@yahoogroups.com, Chuck Kelsey [EMAIL PROTECTED] wrote: We had a DB-420 style antenna (actually it was made by Signals, but it was folded-dipole design) on our UHF repeater at work. We were constantly having difficulty with portables being able to hit and hold the repeater and they were no more than 1/2 mile out. The local M/A-Com shop kept saying too much antenna. We changed it out to a DB-408 and the problem was corrected. We are in rolling hills and the antenna was about 70' above ground level at a water tank. I plotted the antenna pattern against topographic map data and discovered that the portables were in some deep nulls with the higher-gain antenna. Yahoo! Groups Links
Re: RE: [Repeater-Builder] Re: Repeater Antenna Choice
Here in Florida near a beach we have found exposed dipoles like the DB224 are destroyed by the salt air. They last 6-10 years. This is most often withing a couple miles of a beach although I've seen a number die when mounted at longer distances. I prefer the fiberglass larger ones like the Super Station Master or Celwave 200. They last forever. Understand lightning is a problem due to their construction using soldered connections. Fiberglass enclosed antennas such as the Diamonds and Comets do not last...look at their flimsy construction and one can see why. 73, ron, n9ee/r From: gervais fillion [EMAIL PROTECTED] Date: 2007/11/24 Sat AM 08:06:27 CST To: repeater-builder@yahoogroups.com Subject: RE: [Repeater-Builder] Re: Repeater Antenna Choice Hi all we have been using here Sinclair SRL-210 a4 for many years ,they are well built,4 dipoles . they have been cloned by many telecom compagny as Comprod too we have tested Fiberglass antenna,after a time the coating of the fibreglass dissapear and the fiber of the fiberglass broke due to salted winds,we prefer metal antenna since then to bad i have one in my garage,srl210,which i dont used for many years 73/s all gervais To: Repeater-Builder@yahoogroups.com From: [EMAIL PROTECTED] Date: Sat, 24 Nov 2007 13:13:12 + Subject: [Repeater-Builder] Re: Repeater Antenna Choice Derek, Going to the higher gain antenna may cause shadowing in some areas close in to the repeater site if its up real high. I also like the DB-408 antennas and am using them on my systems. The fiberglass antennas are OK also, But if they take a lightning hit they are gone. I had an ASP copy of a DB813 on a water tower and it took a direct hit and it still worked great. I had a big burn mark on one of the loops. It also had a red plastic cap on the top and it was burned and blackened. To me the loop style antennas are the way to go for antennas in areas the there is a good chance of being hit by lightning. If you are going to sidemount a fiberglass antenna you need to be 3 to 6 feet out from the side of the tower as the fiberglass antennas need room to flex. An arm out to the upper part of the fiberglass antenna is a good idea. With the antenna manufactures going overseas to build antennas the quality is not like the ones we got years ago. You may want to look at COMPROD antennas. There web site is www.comprodcom.com they build great antennas. 73 from Paul W9DWP Yahoo! Groups Links Envoie un sourire, fais rire, amuse-toi! Employez-le maintenant! Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
Re: [Repeater-Builder] Re: Repeater Antenna Choice
On Nov 25, 2007, at 8:19 PM, Laryn Lohman wrote: Hi Larry, yeah... reading back through it I transposed 408 and 420. Nate, perhaps you could clarify that paragraph... Anyway, I was just comparing published vertical beamwidth numbers for various bands/manufacturers/gains. Within a degree or so, it doesn't matter who makes it, you'll find 14-16 degrees beamwidth for antennas rated at 6 dbd, U or V. And for antennas rated at 9 dbd you'll find them at around 7 degrees, U or V. Makes sense, since everyone starts out with the same applied RF, and since no manufacturer has yet to modify the laws of physics to their favor (though many try to convince you differently hehe), there has to be pretty much the same shape/beamwidth of the RF donut for the same gain at the horizon. (Omni antennas). Agreed. I think what I was trying to say was there were a lot of people stating that the narrower vertical beamwidth/higher gain antennas would shoot over the top of users from a low HAAT site. I don't think that's true at all. Even the high-gain antennas have 6-7 degrees of 3dB vertical beamwidth and in close, I doubt losing 3dB (even when multiplied by the ERP) is really going to show up as a bunch of close-in holes... if you're standing directly under the building perhaps, but once you get that close the loss is nothing. Doing a quick calculation here... Assuming 350' HAAT, 0 degrees of downtilt, and a 7 degree vertical beamwidth: Radio Horizon: 26.46 miles Lower 3dB beamwidth horizon: 1.08 miles Upper 3dB beamwidth horizon: Over the radio horizon Same HAAT, 16 degree vertical 3dB beamwidth: Radio Horizon: 26.46 (same, of course) Lower 3dB beamwidth horizon: 0.47 miles Upper 3dB beamwidth horizon: Over the radio horizon (A difference of .61 miles - covers better in the neighborhood right around the structure, maybe... but the signal would be so strong there anyway...?) But -- I'll admit, we don't do much low-level stuff around here. I'm curious why folks think it makes that much of a difference? I'm with you on liking the dipole antennas... Having read Ron's comment about salt water eating them up, I guess there are probably places where a fiberglass stick would be wanted... but definitely not out here in our dry air at altitude. -- Nate Duehr, WY0X [EMAIL PROTECTED]
RE: [Repeater-Builder] Re: Repeater Antenna Choice
Hi all we have been using here Sinclair SRL-210 a4 for many years ,they are well built,4 dipoles . they have been cloned by many telecom compagny as Comprod too we have tested Fiberglass antenna,after a time the coating of the fibreglass dissapear and the fiber of the fiberglass broke due to salted winds,we prefer metal antenna since then to bad i have one in my garage,srl210,which i dont used for many years 73/s all gervais http://www.emoticonesgratuites.ca/?icid=EMFRCA120
