I'm currently working on putting up a new VHF repeater for one of my agencies. Two questions (for now):
1) I have a great antenna site on top of a 100' monopole on top of some of the highest terrain around. I'm guessing that due to the location I'm going to get coordinated / licensed for a fairly low ERP. Given this, is there any point in putting up a gain antenna? I may have to go with some downtilt anyhow, so I suspect that a little more downward radiation wouldn't hurt in order to avoid having a "shadow" along the main road that runs under the site. Wind survivability is also an issue. I asked what kind of wind speeds they had at the site. They said the last anenometer come off the roof at 115mph!
2) I was going to explore the site's coverage potential by connecting a CDM1550 to the existing antenna and bouncing MDC radio checks off of it. When I got there I was happy to find four runs of hardine available for our use, with connectors on the end. Check the link below and see if you can tell me what these are. They look like some seriously overlength "N" connectors, but of course I didn't have any "N" adapters on me when I went up the hill. Are these "N", DIN, or what? For scale, I believe that's 7/8" hardline. Also, these have sat unused for around 8 years now. They look like solid brass with a bit of oxidation. Is there a good prep or cleaner I should use before putting them into service?
Here's the link: http://www.cyberonic.net/~jherming/
Thanks!!
Connector ID and repeater antenna gain
Moderator: Queue Moderator
I would get licensed for the larger ERP, as it will allow for possible future expansion of a power amp or different transmitter. As for the gain antenna...do it! Every bit of antenna is better. If your going to do it, use the best for a commercial installation. Don't overlook the best of what's available to ground it too, since you're on top of a monopole. If radiation angle permits, a folded dipole may be the ticket, as these are quite resistant to lightning and from the sound of it, your site is a good candidate for a strike. Is there other equipment at this site? You may have intermod problems if there are, so anticipate that, too. Persoanlly, I would use little downtilt if I were doing this setup, although I may just be wrong since I don't know the terrain or haven't seen the site.
Thanks Jim!
The site is a cell phone site. Other than the cell panels at the top of the monopole, there are currently no other radiating antennas. The cables in the picture go to 1) a VHF omni on top of the pole 2) A low band folded dipole aprox. 40' AGL, and 3) 2 UHF Yagis 20' AGL, one pointed towards one of the county's radio sites, and the other one pointed at the next hill over in the opposite direction. Obviously one of my predecessors (no one knows how to reach him) had a real plan here, but I'm not party to it, so I'm pretty mich starting over.
The lease for the site specifies that they must install and maintain antennas for the local emergency services organizations, none of which have been used up until now. There is currently an omnidirectional fiberglass VHF whip on the very top of the pole, above the cell panels, of unknown model or specification, that has been whipping around in the wind for 8 years now. Accordingly, I'm just planning to replace it with the best I can find for our application.
The whole install was done by one of the largest cellular carriers, and I can't begin to find fault with anything in the install or shelter. The grounding and lightning protection seem absolutely top notch. After 8 years there's not even any dust to be found.
<font size=-1>[ This Message was edited by: HumHead on 2002-03-31 00:54 ]</font>
The site is a cell phone site. Other than the cell panels at the top of the monopole, there are currently no other radiating antennas. The cables in the picture go to 1) a VHF omni on top of the pole 2) A low band folded dipole aprox. 40' AGL, and 3) 2 UHF Yagis 20' AGL, one pointed towards one of the county's radio sites, and the other one pointed at the next hill over in the opposite direction. Obviously one of my predecessors (no one knows how to reach him) had a real plan here, but I'm not party to it, so I'm pretty mich starting over.
The lease for the site specifies that they must install and maintain antennas for the local emergency services organizations, none of which have been used up until now. There is currently an omnidirectional fiberglass VHF whip on the very top of the pole, above the cell panels, of unknown model or specification, that has been whipping around in the wind for 8 years now. Accordingly, I'm just planning to replace it with the best I can find for our application.
The whole install was done by one of the largest cellular carriers, and I can't begin to find fault with anything in the install or shelter. The grounding and lightning protection seem absolutely top notch. After 8 years there's not even any dust to be found.
<font size=-1>[ This Message was edited by: HumHead on 2002-03-31 00:54 ]</font>
Dont go overboard on the antenna gain. There is the problem of too much gain which translates into too small of a vertical beamwidth, which will shift badly in any wind that bends the antenna beyond six to ten degrees, and that can kill a signal.
On VHF about three to four db gain transllates to 40 degrees down to 20 degrees at the higher gain. The five to six db gain fiberglass antennas bend too much in the wind. If you have to go beyond 4 db, use a heavy duty four element folded dipole like the Sinclar.
My personal choice would be(from thirty + years exp.) would be a three db gain, 4.5 DBi, ComTelco BS150XL3 and it is 96" long. And go with the 7/8 hard line and typ N connectors, and premimum jumpers, no less than LMR400Flex with the Times connectors.
On VHF about three to four db gain transllates to 40 degrees down to 20 degrees at the higher gain. The five to six db gain fiberglass antennas bend too much in the wind. If you have to go beyond 4 db, use a heavy duty four element folded dipole like the Sinclar.
My personal choice would be(from thirty + years exp.) would be a three db gain, 4.5 DBi, ComTelco BS150XL3 and it is 96" long. And go with the 7/8 hard line and typ N connectors, and premimum jumpers, no less than LMR400Flex with the Times connectors.
My sincere thanks to all for the valuable input!
It looks like I'm currently looking at a 3dB gain antenna with 3 degrees of downtilt as a happy comprimise between gain, stability of coverage, and minimizing "shadows". Happily I already have runs of 7/8" hardline at my disposal.
My goal is to have this project done right the first time, particularly with regard to IM protection and grounding. I'm actually also in the process of cleaning up a couple of "professional" installations that were put in with ZERO grounding on anything at a couple of other sites.
I firmly believe that cutting corners at the outset inevitably costs you in the long run.
Thanks again to all!
It looks like I'm currently looking at a 3dB gain antenna with 3 degrees of downtilt as a happy comprimise between gain, stability of coverage, and minimizing "shadows". Happily I already have runs of 7/8" hardline at my disposal.
My goal is to have this project done right the first time, particularly with regard to IM protection and grounding. I'm actually also in the process of cleaning up a couple of "professional" installations that were put in with ZERO grounding on anything at a couple of other sites.
I firmly believe that cutting corners at the outset inevitably costs you in the long run.
Thanks again to all!
Good choice on the three db gain, and the proper grounding. If you do use a circulator, dont forget the harmonic filter after the circulator unless you are using a pass+notch duplexer. Trans output--circulator--duplexer. Or trans--circulator--harmonic filter--antenna (using seperate antennas)
Now all you need is one of Will's repeater modules.
Now all you need is one of Will's repeater modules.