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Commercial Radio Antennas - Please keep discussion related to professional, commercially used antennas and antenna systems for the two-way radio industry. Topics for the use of these antennas on amateur bands are accepted here.

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Old 09-07-2017, 8:54 AM
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Default Help with antenna selection

Ok, we are putting our new system online in a few weeks and are ordering the antennas. Currently, we are slated to use 2 Commscope AVA5-50FX one for the Sheriffs department and one for the fire department. Both systems will be VHF 110watt running sinclair duplexers through 7/8 Heliax total run of 330f, thats from duplexer to antenna for each system. Concerns are being raised about the antennas being sufficient and if there is something better out there. What are your suggestions?
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Old 09-07-2017, 9:14 AM
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What ERP does the license allow?

The FCC license will show a maximum ERP. That needs to be considered in your design.

As for "best" antenna, that can mean a lot of things depending on exact location, terrain, what the license allows, etc.
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Old 09-07-2017, 9:24 AM
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we are replacing ours right now until the other site is completed. and it calls for 110 ERP for both.. The new systems are 150 ERP. We are in a vary mountainous region and the tower and 2 antennas are at 1410 elevation, the new site will be 3.5 miles further away and at antenna 1551 ft.
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Old 09-07-2017, 9:38 AM
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The elevation that I mentioned are elevation at antenna.
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Old 09-07-2017, 9:55 AM
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Default Help with antenna selection

If top mounting on a tower, I generally stick with the folded dipole designs. Quick and easy, a DB-222 but I will use engineered arrays from Telewave and Sinclair if needed.

Your looking at about 2.6 dB of loss through the filters and feedline so if choosing higher gain solutions you will have to back the power down on the repeater.

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Old 09-07-2017, 10:24 AM
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Another major point here that hasn't been mentioned is what the average elevation is where you expect the radio system coverage to be?

I ask this question because if your antenna is mounted up on a high mountain and your use is down on the level ground below the mountain, then a normal antenna will be a poor choice. It will put all the transmit and receive ability out on the horizon. You might be better off with an antenna with some down tilt.

You really haven't given enough information to even make a guess here as to what antenna would be the better choice. This is an area where many agencies fall off the technical curve and use the wrong antenna.

Some homework is in order here to make sure your installing the antenna that fits your tower location and provides the coverage you expect. Walk into this with an open mind and get some engineering help if needed.
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Old 09-07-2017, 10:54 AM
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Quote:
Originally Posted by jim202 View Post
Some homework is in order here to make sure your installing the antenna that fits your tower location and provides the coverage you expect. Walk into this with an open mind and get some engineering help if needed.
I agree.

There are software packages that will allow you to figure estimated coverage based on exact antenna location, ERP, HAAT and a bunch of other factors. Knowing which antennas will provide the coverage down in the low spots, canyons, valleys, etc. is really important. It takes more than just picking an antenna design or gain number. There's a lot involved.

Considering a decent antenna is going to cost $1500 or more, spending a bit of money on getting a coverage study done might be a good investment. At least it will give you something to look at, and especially point at when/if the coverage complaints start coming in.
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Old 09-07-2017, 1:21 PM
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I don't want to use the wrong antenna... That's what I'm getting at. We have virtually no help with decisions on the system or what we can and cannot use. Our county has no regulations on that other than they have to be able to communicate with us. Our current is WQEZ310.. AMSL 372.0m HAAT 128.0 HGT to Tip 60.3m. The new site is located on KNKN848 site number 6 AMSL 377.0m HGT to our antenna 96m. The new license hasn't been update on the database yet. Even though I have received confirmation. I hope this helps.

Also, what software is available?
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Old 09-07-2017, 3:45 PM
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You could try this site: https://www.towercoverage.com//

However, it's only as good as the data you put in.
I'm a bit confused, are these two systems for the Sheriff and Fire department? If this is, then it's a "life safety" type thing, and you'd need to be very careful about this. Not saying you should't try, but be aware of the liability if things don't work.

While it is a big expense, hiring a consultant to figure out the myriad of details can be very valuable. That can save a LOT of headaches and a lot of money.
Putting antennas at 330 feet is going to take some work. If you don't get this right, you'll spend more money on new antennas and install. That can add up quickly. There's a lot involved in getting this right, and having an experienced person assist is a real good idea. While I can appreciate your desire to save the county money, this really isn't something to design using input from bunch of strangers on an internet hobby radio site. I'd strongly recommend hiring a professional 2 way radio consultant to assist you. They'll have the tools and experience to start this off on the right track. Trying to do this on the cheap using the internet as a source of information might turn into a bigger issue. Especially if the radio coverage puts officers/fire fighters lives at risk. That can quickly turn into a nightmare with unions, lawyers, etc. Just don't want to see you get hoisted for this.
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Old 09-07-2017, 4:38 PM
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The above is very good advice.
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