Help with base antenna for NYC rooftop

[BK87]

Hello,

I’m newly licensed and setting up my GMRS base radio. I’ll be using a Kenwood TK880H from my apartment on 6th floor in Brooklyn NY.
I’m stuck trying to figure out what antenna I should get and what’s the proper way to install and ground it on a residential building rooftop?
Goal of the antenna is to hit 6-10 miles away from me to reach family. Any helpful tips will be appreciated!
I was thinking a base antenna that I can mount on a PVC pipe and tether it to a wall mount already on the roof. But major concern is proper grounding and lightning protection. Do I need a lightening arrestor and is a wall ground sufficient on a rooftop?

 

[mmckenna]

A lot depends on your budget. Antennas can run anywhere from cheap Chinese junk to several thousand dollars.
Take a look here, but skip the Tram and Browning brand unless your budget and/or your minister of war and finance dictates otherwise.

https://www.theantennafarm.com/catalog/antennas-191/base-antennas-193/commercial-base-antennas-258/omni-directional-antennas-976/380-525-mhz-uhf-antennas-250/uhf-omni-directional-ant-1096/

Grounding is required by the National Electric Code and for good reasons. Especially if you are in a rented apartment. Making sure your install is done right and doesn't become a path for high amounts of unwanted energy entering the building should be first and foremost. That means you need to ground the mount and have an entrance protector where the coaxial cable enters the building. Finding a proper ground may be a challenge on a rooftop. I suspect you may find that none of the other antennas are properly grounded up there, but don't let that convince you not to do yours correctly.

As for mounting, get a 10 foot length of 1 1/2" rigid conduit or water pipe. Mount the antenna to the top of that. Mount the other end to the bracket on the roof with something like this: https://www.theantennafarm.com/catalog/pctel-mmk4-7671
Keep the bottom of the mast off the roof, it will move around a bit and if it's sitting on the roof membrane, it'll slowly wear a hole through it. That'll let water in, and the landlord will get grumpy.

Higher gain antennas will put more of your transmitted power towards the horizon, which will give you more coverage out away from your building, but may create issues near in around it. Don't go overboard with gain, though. A good 3-6dB gain base antenna will be a good compromise.

 

[prcguy]

I would recommend using a 2" DirecTV antenna mount, the same as the satellite dish in your first pic, then something like a Laird FG4605 antenna on top. This antenna is 76" long and 5dBd gain, which is reasonable without getting too large. The reason I would recommend the DirecTV "J" mount is someone already set a precedence mounting one to the roof facade, so just do what they did.

To meed code for grounding on a commercial building you can run a 10ga copper wire and clamp that to any metallic conduit on the roof that has a main line run to the buildings main AC power entry point. Something like a conduit to a roof top air conditioner should suffice and keep the wire run under 30ft.

Here is info on an ok Laird base antenna for GMRS and there are probably cheaper places to get them: Laird 5dB Fiberglass Omnidirectional Antenna (FG4605) from Solid Signal
It looks like you only have to get a signal in one direction and if so a small Yagi would do just fine. You can get 10dBd gain Yagi's on Ebay cheap like under $50 new, something like this: COMTELCO, Y3347-C, ANTENNA, 450-470MHZ, NEW IN BOX | eBay

If you were local in So Cal I have a few of the Laird FG4605s in my garage cheap.

 

[n5ims]

A couple of comments that hopefully will help. First off, make sure that you get written permission from the building owner (it may help to get it from the landlord or building manager, but at best that may push some blame down on them and you still might get most of it) and follow their guidelines on what, where, and how to put up your antenna (but still follow all codes). Now that your butt is covered on to the main point of your question.

First off, where you propose installing it may be a good place to install it, but since it'll be directly in front of the DirectTV dishes, you can expect any and all blame for problems with signal problems by folks using them. Sure, it's unlikely that you'll actually be the cause, they'll see that 1) things worked prior to your install, 2) you installed "directly in front of the dishes", and 3) the problem happened after your install. The first thing they'll say is "take that *&#$%@ antenna down NOW!" and you may even get to find a new place to live. A better choice may be further down and away from the dishes. That said, the dishes are most likely grounded and may help solve that part of the problem.

I do like the idea of a small yagi for several reasons. First, it's small and less visible. Second, you may be able to pass it off as a TV antenna to others. Finally it will concentrate the signal where you want it and away from areas you don't. This will improve the signal where it counts and may help eliminate (or at least reduce) interference from other signals that may swamp the ones you want (either because they're nearby, have very high power, or even both).

 

[BK87]

I do like the Yagi idea but my concern is that if I’ll want to hit repeaters or link with others in different areas, the yagi will become useless with its uni directional beam. And yes I will ask for permission before installing it.
I don’t think there is a textbook way to really ground this on an old residential building, but I will get a good lightening arrestor. A lot of buildings have crowded rooftops with TV antennas and cellular antennas. I don’t think they interfere with each-other.

 

[mmckenna]

I do like the Yagi idea but my concern is that if I’ll want to hit repeaters or link with others in different areas, the yagi will become useless with its uni directional beam. And yes I will ask for permission before installing it.

A folded dipole, or a couple stacked would be an option. You can skew them a bit to make them slightly directional.

I don’t think there is a textbook way to really ground this on an old residential building, but I will get a good lightening arrestor. A lot of buildings have crowded rooftops with TV antennas and cellular antennas. I don’t think they interfere with each-other.

The lightning arrestor will still need to be grounded if you want it to be effective.