Best Antenna for repeater for large town in PA

[AlexM]

Hello,

I hope all is well!

I recently was given the opportunity to setup a legal GMRS repeater on top of a 152-155 foot high rise building that is in my town. My town consists of many high rise buildings around the same height with the tallest being 158 feet tall at the current moment, but they are currently building several more so who knows how tall those will be. The repeater will be 50 watts and needs to be able to serve my collogues who are inside these high rise buildings with there HT's scattered 10 miles max in each direction, also each collogue has their own GMRS licenses so its legal to use. My questions are what is the best antenna to use for this that will not be crazy expensive also is 50 watts enough? I was going to use a Vertex Standard VX-7000U Desktop Repeater, or is there a better repeater I should be looking at that is around the same used price. Also what type of gain antenna should I be looking at for this application. I would also like to get more then 10 miles in each direction but am trying to be realistic.

Thank you!

Alex

[Sshannon]

26 minutes ago, AlexM said:

Hello,

I hope all is well!

I recently was given the opportunity to setup a legal GMRS repeater on top of a 152-155 foot high rise building that is in my town. My town consists of many high rise buildings around the same height with the tallest being 158 feet tall at the current moment, but they are currently building several more so who knows how tall those will be. The repeater will be 50 watts and needs to be able to serve my collogues who are inside these high rise buildings with there HT's scattered 10 miles max in each direction, also each collogue has their own GMRS licenses so its legal to use. My questions are what is the best antenna to use for this that will not be crazy expensive also is 50 watts enough? I was going to use a Vertex Standard VX-7000U Desktop Repeater, or is there a better repeater I should be looking at that is around the same used price. Also what type of gain antenna should I be looking at for this application. I would also like to get more then 10 miles in each direction but am trying to be realistic.

Thank you!

Alex

Regulations limit you to 50 watts, so it’ll have to do, but terrain and antenna height will determine range more than power. If you have the height 10 miles is well within reason.  After all, those 5 watt handhelds have to reach you. 
I don’t own a repeater but I have seen a lot of posts recommending a Laird DB404 antenna. You will also want to minimize feed line losses by choosing the best feed line you can. 
 

Edited to add:

Good reference post-

 

[AlexM]

27 minutes ago, Sshannon said:

Regulations limit you to 50 watts, so it’ll have to do, but terrain and antenna height will determine range more than power. If you have the height 10 miles is well within reason.  After all, those 5 watt handhelds have to reach you. 
I don’t own a repeater but I have seen a lot of posts recommending a Laird DB404 antenna. You will also want to minimize feed line losses by choosing the best feed line you can. 
 

Edited to add:

Good reference post-

 

Okay, thank you so much for the response. The repeater will be in central PA so a lot of valleys and ridges. Also I've setup small antennas on my home but never on a high rise building like this. What should I know about grounding, what type of grounding is needed? I really don't want the building to get struck by lighting and burn down  

[Sshannon]

8 minutes ago, AlexM said:

Okay, thank you so much for the response. The repeater will be in central PA so a lot of valleys and ridges. Also I've setup small antennas on my home but never on a high rise building like this. What should I know about grounding, what type of grounding is needed? I really don't want the building to get struck by lighting and burn down  

There are literally books written about tower and antenna grounding. I’ll see if I can find you some links. The Bible is a document by Motorola named R56 something or other and there are lots of links to it on this forum. Be right back. 

[Sshannon]

See this thread:

 

[AlexM]

3 minutes ago, Sshannon said:

See this thread:

 

Wow this is great information. Thank you for taking your time to retrieve this info for me.

[Sshannon]

3 minutes ago, AlexM said:

Wow this is great information. Thank you for taking your time to retrieve this info for me.

It can be overwhelming; I don’t think anyone would dispute that. A high rise building like that should have a grounding system that you should tie into. Talk to the maintenance engineer if there is one. 

[Sshannon]

Here’s an article about grounding and high rise buildings:

https://comm-omni.com/polyweb/rooftop.htm
 

[KAF6045]

1 hour ago, AlexM said:

The repeater will be 50 watts and needs to be able to serve my collogues who are inside these high rise buildings with there HT's scattered 10 miles max in each direction, also each collogue has their own GMRS licenses so its legal to use. My questions are what is the best antenna to use for this that will not be crazy expensive also is 50 watts enough

The repeater will still need its own ID circuit/system (the only repeaters that don't need an ID system are private repeaters where the ONLY users are immediate family members using the call sign of the repeater owner).

50W is the maximum output (at the antenna connector on the transmitter) permitted by regulations.

The highest gain antenna you can find -- so long as it provides a signal at the desired user locations (the higher the gain, the narrower the beamwidth in elevation -- so someone at ground level may not be heard-by/hear the repeater, but someone 15 miles off may be fine [that's the ~ horizon distance for a 160 height]).

Assuming 3dB loss in coax, you'd have 25W AT the antenna. A 10dB gain antenna will give the impression of a 250W signal, but as mentioned, that will be focused toward the horizon. A simple half-wave dipole will only have a peak equivalent of the 25W, but will have a beamwidth that will cover ground to sky from a short distance away from the repeater. If you've looked at cell-phone towers, you've no doubt noticed that the antennas are mounted in sets of three AND are tilted downwards to improve local ground level coverage.

[Wrvq441]

[Wrvq441]

I’m currently reading this book. It sticks with code, but refers to many other things/ concerns as well.

It stresses that you also need to comply with your local building code. Especially since you’re mounting this on someone else’s building. For insurance purposes along with public and fire safety, you need to do everything possible to protect yourself from liability.