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VHF Antenna recommendation for tower

AUGOLD

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Feb 21, 2018
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Notasulga
Our company has filed an application for a VHF repeater system and we have tower space on a new tower offered to us at 300', 275', 250' and at 225'. Our TX freq is 152.885 RX is 158.885 Our pending license is at 110 watts power and 175 watts ERP. What antenna recommendations for the best coverage? We do not want to break the bank but we don't want the cheapest antenna either, what would be recommended? We may upgrade to a MOTOTRBO system later, what antenna would be best suited if we want to upgrade to MOTOTRBO later?
 

prcguy

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Jun 30, 2006
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So Cal - Richardson, TX - Tewksbury, MA
Before recommending an antenna, have you looked at the cost of 300ft of good quality feedline like 7/8" Heliax at minimum? That will probably cost way more than the antenna.

Our company has filed an application for a VHF repeater system and we have tower space on a new tower offered to us at 300', 275', 250' and at 225'. Our TX freq is 152.885 RX is 158.885 Our pending license is at 110 watts power and 175 watts ERP. What antenna recommendations for the best coverage? We do not want to break the bank but we don't want the cheapest antenna either, what would be recommended? We may upgrade to a MOTOTRBO system later, what antenna would be best suited if we want to upgrade to MOTOTRBO later?
 

mmckenna

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What does your license say?

When they coordinated the license, they should have filled out what the antenna height was. You'll need to stay inside what the license allows.

There's some work that needs to go into the design. The power output is determined by the repeater, but the ERP will take into account all the gains/losses in the system. That means you need to work out what the duplexer losses are, anything additional like IM suppression panel, feed line losses, lightning protectors, antenna gain, etc.

It's not hard to do, but it takes some time to work out. Your maximum ERP can be 175 watts, but you can be under that. Don't get hung up on wattage numbers as your only method of determining distance.

For your antenna, you need to consider at what height it'll be (that'll be on the license/license application), then you need to take a look at what area you are trying to cover. Your license will permit your mobile stations to transmit within a certain kilometer radius around your repeater. Choosing the antenna necessary to do that is a bit of an art, gain, down tilt, radiation pattern all play in to the decision. It can be done with some expensive software (EDX, etc) and your frequency coordinator or radio shop can assist. Antennas and feedline can be very expensive, (easy to spend $2K on just one antenna, and figure suitable feedline being in the dollars per foot). It can really pay off to have a pro design that stuff. If you make a mistake and it doesn't work as expected, it's a costly mistake, not only to replace the antenna, but to send the tower monkeys up there to do it.

I've been a fan of Telewave, but I know you'll get some other great input from a few of the others on this site.
Also, knowing your budget helps. You don't want to put a $300 Chinese crap antenna 300 feet up on a tower with a bunch of other tenants. That'll make you unpopular really quick. Also, the tower owner may have some requirements regarding wind loading. Wind loading needs to include the area of the antenna, mounting hardware, and all that coaxial cable running down the tower.

Probably not going to get the level of help you need on a scanner/amateur radio hobbyist website. There are some things that are worth paying for, an experienced engineer to design your system is one of them.

As for the future, it doesn't matter if it's analog or Trbo, the antenna doesn't care. But it will matter when it comes to designing the coverage of the system. Digital can work a bit better, and that may mean you can get by with a different antenna than you'd need for analog.
 

K4EET

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Feb 18, 2015
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Severn, Maryland, USA
@EastAlabamaNews, please take what @mmckenna said to heart. Very wise statements there, obviously from first-hand experience. And to emphasize two points...

<snip> Probably not going to get the level of help you need on a scanner/amateur radio hobbyist website. There are some things that are worth paying for, an experienced engineer to design your system is one of them. <snip>
Being a tower that your antenna(s) is/are being placed on, you will probably need your own PE's (Professional Engineer's) "blessing" that your hardware does not exceed the tower's design for wind loading. For example, at those heights, if the tower was designed for half-inch LDF on your run(s) and due to signal loss you decide to use 7/8 inch LDF, you would be setting the stage for a tower collapse. This is but a single criteria of many that needs to be considered by an engineer as @mmckenna eluded to.

<snip> As for the future, it doesn't matter if it's analog or Trbo, the antenna doesn't care. But it will matter when it comes to designing the coverage of the system. Digital can work a bit better, and that may mean you can get by with a different antenna than you'd need for analog.
OTOH, digital can also require more sites than analog, again depending on system design and system coverage requirements. That paid RF engineer can keep you out of the quagmire of coverage issues now and later if you do a switchover. Don't guess!
 

WB9YBM

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May 6, 2019
Messages
1,221
Location
Niles, IL
Our company has filed an application for a VHF repeater system and we have tower space on a new tower offered to us at 300', 275', 250' and at 225'. Our TX freq is 152.885 RX is 158.885 Our pending license is at 110 watts power and 175 watts ERP. What antenna recommendations for the best coverage? We do not want to break the bank but we don't want the cheapest antenna either, what would be recommended? We may upgrade to a MOTOTRBO system later, what antenna would be best suited if we want to upgrade to MOTOTRBO later?
At those antenna heights, I'd also recommend looking at mechanical integrity/quality because of strong winds...
 
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