Yagi antenna for monitoring P25 trunked system

Cowley639

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Hey everyone,

I am setting up a Uniden 996 to monitor the State of Kansas KSICS P25 Trunked system from my office. I live on the "fringe" of the closest tower site to me, and it is the only one I can even remotely pick up from my location.

So my question is; In terms of antennas, would it be in my best interest to put a Yagi antenna up and point it at the (Dexter) tower? I have an antenna mount on the roof (from an old Satellite Dish) which is about 30ft in the air.

If a Yagi it the best way to go, which one would you recommend? Also, what's the best way to know you are pointing it directly at the tower?
 

mmckenna

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If a Yagi it the best way to go, which one would you recommend? Also, what's the best way to know you are pointing it directly at the tower?
If all you want to listen to is that site, then yes, that's your best option.

Which model is 'best'? Well, as always, that depends. Depends on what your definition of best is. That depends on your budget. Get one that covers the 700/800MHz band. That might be a Yagi, or it may be a Log Periodic design.

As for aiming, take your scanner up to the antenna, connect directly to it, aim the antenna until the bar graph signal level shows the highest level.
 

Cowley639

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I would assume it would be to my advantage to get the highest gain yagi I could find as well?
 

bchappuie

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Yagi is best. Need to get the location of the site, to your location. I would use my Commander Compass app on my Iphone to point the antenna. No recomendations on antenna, I Usually build my own, but just find a decent cheap 800MHZ antenna.
 

mmckenna

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I would assume it would be to my advantage to get the highest gain yagi I could find as well?
Maybe. Depends what else is in that general direction. If you have a cellular antenna along that path, pointing a high gain antenna at it can result in overloading the front end of the scanner and wiping things out.

Generally speaking, and purposely not going into deep details, there are ways to work out the link loss budget. You look at the signal source, distance, power levels, transmit antenna gain, and figure in your antenna gain, cable losses, and get the received signal to a point where you scanner can decode 100% of the packets. Anything beyond that is unnecessary.
 

mmckenna

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Does a Yagi need to be tuned to the specific tower site control frequency?
Not really. They are broad banded enough that getting one band specific is fine. The control channel is only one of the frequencies in use, and the traffic channels might be several megahertz away. In certain situations, the control channel can roll to one of the traffic channels.
 

Cowley639

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I run a Yagi 700-800mhz in the attic covering the closest tower 4 miles away and the furthest 30 miles.
The closest tower to me is 24 miles away, so hopefully putting it on the roof (about 30ft high) with no major obstructions (trees, other buildings, ect) I hope I will be okay.
 

Cowley639

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To find the site location go to RR and look up the call sign (from there you can get a map view) or go to the FCC ULS web site and get the actual site coordinates.
Bill
Yes, I am aware of that, and know exactly where the tower site is.
 

mmckenna

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The closest tower to me is 24 miles away, so hopefully putting it on the roof (about 30ft high) with no major obstructions (trees, other buildings, ect) I hope I will be okay.
Can you receive the site now? That will answer most questions. If you can and decoding is poor, a higher gain antenna will improve the signal.

If you cannot pick it up now, then the issue might be what's called "topographical shielding", or in simple terms "too much dirt between you and the transmitter". Over 20 miles, you need to consider antenna height at each end and make sure the curvature of the earth doesn't get in the way. There are online "distance to horizon" calculators that will assist with determining this. It's not a brick wall, though, coverage can extend a bit beyond the curvature of the earth, but not much.
 

Cowley639

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I can sporadically yes. For now I am only using the 996 with the crappy stock antenna Uniden provides. I get 1 (maybe 2 on some occasions) bars on the signal level meter. Now keep in mind that is just me standing at ground level.

Hopefully I the Yagi antenna 30ft in the air helps.

I do know State Troopers have made traffic stops right near my office using the system and see to have no issues with radio coverage.
 

mmckenna

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I can sporadically yes. For now I am only using the 996 with the crappy stock antenna Uniden provides. I get 1 (maybe 2 on some occasions) bars on the signal level meter. Now keep in mind that is just me standing at ground level.

Hopefully I the Yagi antenna 30ft in the air helps.

I do know State Troopers have made traffic stops right near my office using the system and see to have no issues with radio coverage.

OK, that's a good sign. A yagi antenna up 30 feet and with some good coaxial cable should work well. You shouldn't need a high gain Yagi antenna to improve coverage.
Depending on how long the cable run is from the antenna to your scanner, you may need to spend more on the coax than the antenna. RG-6 might be a good option, but if it's a long run, you may need something a bit better.
 

Ubbe

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Can you somehow take your scanner to the roof and power it using extension cords and open the squelch and listen to the control channel frequency of that tower and see if there's any kind of signal? It you can faintly hear a signal then a yagi will help. If you hear nothing compared to when you remove the antenna then it's doubtful if a gain antenna will help.

edit (Ok, I see now that you have some reception from that tower, so a yagi antenn will indeed help)

/Ubbe
 

Cowley639

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Can you somehow take your scanner to the roof and power it using extension cords and open teh squelch and listen to the control channel frequency of that tower and see if there's any kind of signal? It you can faintly hear a signal then a yagi will help. If you hear nothing compared to when you remove the antenna then it's doubtful if a gain antenna will help.

/Ubbe
I will definitely be trying that in the next few days...
 

Cowley639

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OK, that's a good sign. A yagi antenna up 30 feet and with some good coaxial cable should work well. You shouldn't need a high gain Yagi antenna to improve coverage.
Depending on how long the cable run is from the antenna to your scanner, you may need to spend more on the coax than the antenna. RG-6 might be a good option, but if it's a long run, you may need something a bit better.
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?
 

mmckenna

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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?
 

Cowley639

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The building is a Television production facility, so lightning protection, and fire suppression isn't that much of an issue. We have several things in place to stop that. We have cable troughs that route cable throughout the entire building. Moving everything from video and audio to data and now RF.

To top it all off across the alley from the facility is a 60ft tall building (city hall) with a 150ft VHF/UHF repeater tower behind it for the city police and fire dept I live in (not in the direction that the yagi is pointing).

Our building (including the taller City hall building behind us) has lightning rods that are higher than any of the equipment on the roof. So I'm not at all worried about lighting. We've had equipment on the roof here for 30+ years and have never had an issue (and we get a lot of severe weather here in southern Kansas). I don't think the fire rated cable will be an issue, nothing to my knowledge in the building is anyway considering I helped install the vast majority of it...

I found a 100ft chunk of LMR-400 on eBay with an N connector on one end, and a BNC on the other.

I am looking at purchasing this Yagi: https://www.theantennafarm.com/catalog/browning-br-6388-b-3588
 
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