That might be somewhat of an issue, I will need about 100ft of coax. My office is basically right in the middle of the building, and the only access inside the building from the roof makes it about 100ft from my desk including running from the mounting location to the hole through the wall, through the attic and down into my office.
We have point to point WiFi dish on our roof to send internet to one of our other buildings across the alley (the dishes are pointed away from the direction I will pointing the Yagi) and the closet where all our network gear is right next to my office. We ran about 100 ft of Cat5 cable to the dish from that room. Which is how I am coming up with the 100ft of coax number.
Maybe RG8 or LMR400?
Ah, commercial install...
So, that raises some challenges. Those challenges exist on the residential side, but it's a bit more pronounced on the commercial side.
Trick is lightning protection. You don't want your antenna to be the one that lets the lightning into the building. Ideally the point to point network link should have protectors on both the network cables as they enter the building. That helps protect the equipment inside the building if the lightning decides it really is fond of your network antennas. Giving a lightning strike an easy path into your IT closet or any other part of the building is a big deal. National Electric Code specifically addresses this, the building owner will want it, so will your fire department, and anyone else that is paying attention.
But it's not hard to solve, just costs a bit more.
Like I said, the network radios should be mounted on properly grounded masts, the Ethernet cables should have lightning suppressors where they enter the building. It's not uncommon/unheard of for your average IT guy to not do this, and I'd not be surprised if that's the case with this install. But, like I said, you don't want to be "that guy". Even if lightning doesn't hit your antenna, even a nearby strike can cause damage. Doesn't matter if your antenna is the culprit, if the right people see that it's not properly protected, there'll be some explaining to do.
So, yeah, you could mount the 800MHz Yagi antenna on the same mast as long as it's not in the path to the other site.
If the support mast was properly installed, it'll be grounded/bonded to building steel and the building ground. The lightning suppressors on the Ethernet cables should be mounted where the cable enters the building and those will be grounded to a building ground. You can use the same setup. Mount your antenna on the grounded mast. Run your coaxial cable to the point where the Ethernet cable protectors are mounted. Mount your lightning protector there and ground to the same point they are. Then extend your coaxial cable down through the building to the radio.
You'd want something like a Polyphaser:
https://www.theantennafarm.com/catalog/polyphaser-is-50nx-c2-1913
As for coaxial cable, that's a challenge. 100 feet is a lot of cable at 800MHz. Also, routing it through a building that far comes with some additional requirements.
Losses in coaxial cable go up with the length of the cable, and go up with the frequency. 100 feet at 800MHz will require something decent. That rules out RG-8. LMR-400 would be about the minimum I'd use. LMR-400 will lose about half your signal before it even makes it to your scanner. Thats acceptable and you'll overcome some of those losses by using a higher gain antenna.
If your Yagi has, say 9dB of gain (realistic at 800MHz) and you have a 3dB of loss in your cable, your effective gain is now 6dB through the system, not counting connectors and a bit of loss in the Polyphaser. 6dB isn't bad and it sounds like you have a decent signal to work with.
On the other hand, RG-6 will probably lose about 90% of your signal before it makes it to your scanner. That's bad.
RG-8 is a bit better than RG-6 in this application, and you'll only lose about 80% of your signal.
So, LMR400 would be my choice.
Now, here's the other challenge….
When you run cable through a building, you have to pay attention to the material the cable is made from. In a fire, the cable will burn. If it's an outdoor only rated cable, it can burn quickly and carry fire through the building. The jacket will also outgas all kinds of nasty chemicals as it burns. This is pretty serious and a fire marshal that is paying attention will bust you for it.
But, there's a solution! It just costs money….
Depending on exactly where the cable is run, you will either need a "Riser Rated" cable or a "Plenum Rated" cable. Riser rated is used for vertical runs through a building (Risers) and for passing through non-air handling spaces. If you route your cable through a drop ceiling and that space above the drop ceiling is used as an air return for the HVAC system, then you must run a Plenum rated cable.
Anywhere the cable passes through a wall, conduit, or any other type of fire protection, you must also seal the hole around the cable with a fire stop putty.
So, LMR-400 is the right cable, but you'll either need LMR-400FR at $1.69 per foot:
https://www.theantennafarm.com/cata...g213-cable-515/fire-retardant-rg-8-cable-545/
Or, you'll need Plenum rated LMR-400 at $2.00 to $5.00 per foot:
https://www.theantennafarm.com/cata...213-cable-515/plenum-low-loss-rg-8-cable-547/
So, it gets expensive. Question is, who pays for it? Is it your employer, or is this coming out of your own pocket? If they are going to pay, then no issue, maybe. If you are going to pay, then this could get expensive really quickly, especially if you need the Plenum rated cable. At some point it may make more sense to mount a remote control scanner up where the cable enters the building to avoid the long run of coax and just link down to a PC to listen.
Probably not what you were expecting, right?
