Repeater Antenna Location

rescuer · Post by **rescuer** » Sat Dec 30, 2006 11:46 am

Hello,

I have a question and someone may be able to help me on. We have access to 2 repeater antenna sites, both for free. Of these two which do you think will be better for a VHF (155MHz) repeater.

Site 1: Approx. 1100FT AMSL with antenna approximately 100FT on tower.

Site 2: Approx. 1400FT AMSL with antenna approximately 40FT on top of tank.

With all things being equal, which site do you think would be best?

Thanks for the help!

EPC_1111 · Post by **EPC_1111** » Sat Dec 30, 2006 11:57 am

What kind of coverage are you looking for? What kind of antenna are you using? Best is a relative term.

HLA · Post by **HLA** » Sat Dec 30, 2006 12:18 pm

i've always concidered higher to be better if both have the same antennae and output. do you have any more info on the sites?

440roadrunner · Post by **440roadrunner** » Sat Dec 30, 2006 12:30 pm

There are many, many variables, here,

I assume by your statement that the antennas are already onsite?

How good quality are the antennas? Are they known reputable brands, that belong in this type of service, and are they in good condition? Is the site owner willing to let you do the work if antenna work needs to be done? Just hiring a crew, if required, can break a project.

What are their gain and patterns?

If feedline is onsite, what is it, and how good condition?

As to the site locations, height isn't everythng. If one site is shaded by other hills sometimes the higher site can give worse coverage, and.....

Sometimes the location makes a huge difference. If one is more centrally located to the area you are interested in covering, that might be better. On the other hand, if the "more central" site has shading problems, sometimes a site that is off in a corner of the county, yet has a good, fan shaped coverage down into the desired area is better.

The only SURE way is to do some sort of coverage map, to estimate coverage. If there are areas that you KNOW are going to be good, because of lack of hills, etc, then concentrate on the question areas, and makes sure you have a good path in those areas.

phrawg · Post by **phrawg** » Sat Dec 30, 2006 12:32 pm

Important factors are your placement on the tank. On a rail
around the side can be a disaster as far as pattern is concerned
regardless of the 400 foot height difference. On the top
near center is ok. How much feed line is involved at each location ?
are they basicaly in the same area or is there a really different
geographical location for each in relation to the coverage area
desired ? would the 400' height difference put the repeater in
a place to recieve more distant signals that could actually
be considered interference. Fill us in and let's see what we can
do to help out here. Phrawg

Jim2121 · Post by **Jim2121** » Sat Dec 30, 2006 1:06 pm

output wattage also? 110 watts? 15 watts? and as 440roadrunner said: " hardline?" is it 3/4" andrews? thinner? thicker?
500 feet, or 100 feet long? ect........

N4DES · Post by **N4DES** » Sat Dec 30, 2006 2:08 pm

And what is the surrounding area AMSL. If your at 1000' AMSL this is a no brainer vs if you were say 50' AMSL then it really wouldn't make a big difference.

Also who else is at the site and who is going to perform the intermodulation study. Would be a good idea to look at the FCC website and do a search by Lat/Long for each.

There is a lot more that needs to be answered before you can attempt to make a decision as others have pointed out.

rescuer · Post by **rescuer** » Sat Dec 30, 2006 9:53 pm

OK, I'll try to answer a few of the questions.

Neither site has an antenna, we are going to place it. We have the space available for free at either site. The antenna will most likely be a run of the mill antenna, something like a 10' monopole or similiar. Both will use the same type of feedline, With the lengths being almost twice as long on the 100' tower.

Site # 1, has about 6 other repeaters within a 50' radius. 4-VHF, 1-UHF, & 1-800MHz. This site is located on the borderline of our coverage area. 1/2 hardline approx 150' run. There is a higher mountain ridge (~2000') about 6 miles away blocking our mutual aid district.

Site # 2, is about 100' away from a cellular tower. There is also a 171MHz low power repeater at the site (something with the water flow). This site is likewise on the border of our coverage area, although on the other end. The location will be on top of the water tank. The tank sits on the ground, i.e. not elevated like most. 1/2" hardline approximately 75' run. There is some higher (~2000') mountains about 1 mile away, that would block our mutual aid district.

The repeater is 50 Watt. Input of 159.175, output of 155.120.

Power and shelter is free at both sites.

I don't now the average terrain around either site except that site # 1 appears to be a more isolated peak than site # 2. By this I mean, Site # 2 is closer to the 2000' mountains.

I know, ideally the best site would be on top of the 2000' mountain ridge. I would love to go there but we would have to lease land, pay for power etc. We have contacted some land owners about this, and one day it may workout, although I don't see it happening for a few years.

I hope this will help you, help us answer our question.

Thanks,

440roadrunner · Post by **440roadrunner** » Sun Dec 31, 2006 11:32 am

It sounds to me from what you are saying ...."blocking our mutual aid district." This implys that neither of these sites is going to give you adequate coverage. Really the only correct thing to do, is get some folks out there on site, even with simple mobiles, and try to do some rough and dirty site coverage testing. If you have no measuring equipment, try to experiment with different power levels and even some handhelds, to test range and coverage.

My first impulse would be to go with site no2, simply because it is RF clean compared to no.1. If any of the 4 VHF transmitters are close to your RX freq, you may have troubles. You'll need a much better duplexer in that situation, and if any of the other 4 have inexpensive notch type duplexers, you'll have fun arguing with them, too.

911-EMT · Post by **911-EMT** » Thu Jan 18, 2007 11:21 am

1) Site #1 and site #2 is shaded by a hill of 2000’
2) Site #1 and site #2 is on the border of the coverage area
3) Site #1 and site #2 Neither site has an antenna yet
4) Site #1 and site #2 is Power and shelter is free
I would look at site #1 since it is 240’ higher then site #2 and of course with a good duplexer like “440roadrunner” explained.

firetech792 · Post by **firetech792** » Fri Jan 19, 2007 6:48 am

155.12 mhz isn't a valid frequency. Closest would be 155.13 mhz.

rescuer · Post by **rescuer** » Sun Jan 21, 2007 12:26 pm

Oops, got the frequencies crossed a bit.

The input to the repeater is 159.120. The output of the repeater is 155.175.

Sorry about that.