[Repeater-Builder] Re: Repeater Antenna Choice
Dipole phasing is not easy even for the Decibel 420 type antennas. It is common for very sharp nearfield nulls and cancel areas expecially near and underneath a mountain top mounted antenna. I label the effect something similar to what I call unwanted nearfield/local re-entrant energy. Less of a similar antenna in the case of the DB-408 would have less gain but less close-in and below problematic areas. It would also have a different vertical radiation angle. Using at least one of all the Decibel DB-408 and DB-420 type antennas from a mountain top repeater site... I can tell you first hand there is quite a bit of difference in portable and distant in-building coverage using the higher gain Decibel DB-420 antenna. There is also something to be said for what I call the antenna capture area, which is the shear amount of dipole surface area (metal) spaced up and down many wave-lengths on the tower. In most cases there should never be too much antenna but there can be the wrong antenna for an application and location. One sidebar I noticed in your post... you weren't using a Decibel DB-420 Brand Antenna. The Signals Brand Antenna first used in your system is a different animal indeed. cheers, s. 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. 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
[Repeater-Builder] Re: Repeater Antenna Choice
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.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
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]
[Repeater-Builder] Re: Repeater Antenna Choice
Simple... The largest Decibel, Sinclair, Telewave or similar folded dipole style antenna you can manage to put in the air. Antennas are probably the only part of the free lunch rule... when applied to radio system coverage. There are two types... the standard folded dipole Decibel antenna like your DB-408, which tends to cover a 10 to 20 MHz Segment of the entire UHF band. 450-470 is a typical example. The second type of folded dipole is a much more wide band antenna sold by Sinclair and a few other companies. You will see some models of the Sinclair design easily cover 420 to 495 MHz. The two above folded dipole antennas might look similar but are fed by different matching systems and their sizes are different. ... and their vert horz radiation patterns are different. There is a case to be made for using both the narrow band segment Decibel Antenna and the wide band Sinclair full band antenna. cheers, s. Derek [EMAIL PROTECTED] wrote: I'm looking for input on what kind of antenna to use for several 440 MHz amateur repeaters. Background: Suburban area surrounding metropolitan city of about 700,000. HAGL for antennas range from 260' to 320' on 400' and 500' towers. I'm looking to maximize mobile and portable input, even possibly looking to use 1-5/8 heliax as I recently installed this size hardline on my repeater and have been very satisfied with the results. I've used the DB-408 antenna and am happy with it's performance, but am wondering about significant difference in using a DB-420 for future repeaters. Also considering the RFS 1151 (Tessco # 435830) fiberglass antenna. It is tuned for 440-450 MHz and has 8dB gain, but I've heard some say fiberglass is not the way to go for repeaters. Any thoughts are appreciated. Derek
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
[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.
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.
[Repeater-Builder] Re: Repeater Antenna Choice
--- In Repeater-Builder@yahoogroups.com, Nate Duehr [EMAIL PROTECTED] wrote: I don't think the comments about where you want to put your signal apply as much as some folks would have you believe. Even though the 408 pushes more gain to the horizon, it still is rated for something like 7 degrees of vertical beamwidth to the 3 dB down points. Ummm Nate maybe you got the numbers mixed up. The 420 would be the one with more gain to the horizon. And it's the one with the 7 degrees of vertical beamwidth. The 408 has a 14 degree vertical beamwidth. During a local discussion here recently someone also pointed out that the 408 and that other one with 10 dipoles (sheesh!) that they make now, have a lot of really odd-ball types of coax in their harnesses for the phasing, and there's a LOT of it. How much energy is really making it to the dipoles in a 408, and how much is just radiated from all that relatively lossy coax in the phasing harness itself? We'll all never know, I guess. But there *has* to be some loss there. Sure there's loss in that there *sometimes* wierd coax. And a few minutes with a calculator one could take a good stab at the amount of loss in the harness. But we're seeing the published gain figures in the face of these losses, so I feel compelled to not concern myself about that too much. Other's experiences with the 408 and other high-gain antennas not reaching close-in stations very well make me wonder if something else was going on. Multipath and various forms of fading can really be a bear in urban or hilly environments. Again, I think you meant to say 420, no? 7 degrees down with 3 dB of difference in signal, right in close, shouldn't make that much of a difference, since you're closer to the repeater. I'll admit though, again, that the Sinclair 4-bay's numbers for vertical beamwidth sure look a lot nicer for a building-top system than the DB's... it has something like 9 more degrees of vertical beamwidth to it's 3dB points. Yeah, that means some of our signal is going up, where it's not needed... but with gain numbers similar to the DB's and a wider beamwidth, doesn't that say something about the antenna itself? Just my opinion... (That 7 degree number for the 408 is from memory, but you can get the specs and do the triangle math yourself, pretty easily... fire up the old pythagorean theorem and do some engineering... then decide. I ran the numbers for the Sinclair 4-bay at our 11,440' MSL site that's over 5000' HAAT, to see if down-tilt was needed. It had a MUCH larger vertical beamwidth over the DB's, and the answer was, not needed at all. 1 degree of electrical down-tilt would have been nice, perhaps... to push just a tiny bit more signal into Denver... but not really necessary at all.) 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). I'm with you on liking the dipole antennas... Laryn K8TVZ
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]
[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
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
