A couple of observations: Same gain - same coverage. Fiberglass encased or exposed dipole - 5.8 dBd = 5.8 dBd - this is about the max you can expect from a 2M antenna before the law of diminishing returns kicks in. More Gain for $$$$BUCKS - look at a DB228 - 40 some odd ft long exposed dipole array and an offset pattern. Some of the numbers I have seen published for antennas are pure bull. Let the buyer be ware.
My 30 years in LMR and lots of trips up the tower. Fiberglass encased antennas get blown to kingdom come more often than exposed dipole arrays. Exposed dipole arrays suffer loose hardware and noise when you run in duplex - learn about isolated TEEs and effective sensitivity before you go any further. Ron, N9EE makes a lot of sense on this one - easy to get to and change - use the diamond or comet job - also hustler. Nate hit the nail on the head about Height...Why have a 100 plus watt repeater in a non-voted system with 2 to 4 watt talkies trying to talk in....Don't make much sense and won't buy you any coverage - now one way paging, or tall tower with split send and rec antennas and TTA - makes a whole new game plan. Best option - birds nest on the ground - find a tall building WITHOUT radio tenants - A congested site that cannot receive is close to useless unless you have a separate receive site, or voting receivers. You can also reach a point of diminishing returns on antenna height - remember 96.6 plus 20 times the common log of the distance in miles plus 20 times the common log of the frequency in Ghz will yield path loss. Start with a 4 watt talkie in the clear (deduct 20 dB for wearing the talkie on your belt in a car), and calculate to space loss, antenna gain, line and duplexer loss, and see how much over say -120 dBm actually gets to the receiver. Most receivers get 12 dB sinad at around 118 to 122 dBm at the antenna. Don't forget effective sensitivity - just because the receive can hear -119 from a generator don't mean the noise from a paging or fm broadcast station won't stifle the receiver. Also cavity filters don't necessarily block out of band signals. Anyhow, the point is that when the subscriber unit lacks enough RF to get to the receiver due to path loss, antenna height won't help. 50 ft - I would probably use 1/2" heliax, and first use whatever antenna I have laying around. If I have to reach in my pocket and buy the thing, then the $200 job looks pretty good (because at 50 ft it is easy to change out when it craps out) - Don't forget proper grounding, grounding kits on the transmission line, polyphasers, etc. Another thing - is the site in the middle of the desired coverage area ? If not, an offset pattern antenna may be in order (no need to pump signal into an area where there are no users. If the 50 ft tower is on a big mountain overlooking the town, then both an offset pattern AND depressed pattern may be in order. Anyhow that is how I would handle the question for my own use. As always I may be wrong, your mileage may vary, etc. Best 73, Steve NU5D skipp025 wrote: >> after our test here we found also that Fiberglass seems to >> catch static much more then metal antenna. >> > > Static is not exclusive to one type of antenna... I've had > >
