I'm planning basicly the same thing only on UHF. But the mountain is 7200' and valley is 3000 feet. I decided on using 4 Bay folded dipole array. Offset off the tower for the 9 dB lobe pattern. This will still give a thick enough pancake and the antenna looks like it will survive the weather.
Remember that the more bays you have on an antenna the narrower your pancake is so you might end up throwing all your power over the service area and not get any in it. A TV station in Las Vegas tried making up all of their 200kW ERP by using antenna gain and only 10kW of transmitter. They got reports that the signal looked better when they were switched to their emergency antenna with low gain than the main one. If you need the high gain, You can choose to use electrical down-tilt, 2 degrees would be ideal for the elevations you said. 4 bays would be decent on VHF but you may not have the tower space for it so it may be easier to get or build 2 bay folded dipoles or even a single folded dipole for your application. That will give a decent vertical pattern and 3dB or 0dB of gain respectively. If you need the 1/4 or 5/8 antenna, Try building a ground plane out of brass welding rod. Seal the whole coax connection with a big clump of RTV. ---------- Original Message ---------------------------------- From: "Hellewell, Byron (Mission Systems)" <[EMAIL PROTECTED]> Reply-To: [email protected] Date: Tue, 23 Mar 2004 13:48:45 -0700 >Hi > I am doing some planning for an VHF repeater on the top of a >9000 foot high mountain top. >The coverage is to the valley floor about 4000 feet below the repeater site. > >To get good valley coverage I have been contemplating using a >1/4 or 5/8 wave antenna mounted upside down. > >I am looking for suggestions from those who have had experience with upside >down antennas. > >I know about the radome sealing problems and lightning protection. > >The antenna will also be subject to high winds and ice loading. > >Wondered about shadowing of the mounting structure in the pattern. > >Thanks for the help >Byron > > > > > > >Yahoo! Groups Links > > > > > > Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
