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Antenna repeater upgrade help

rep254

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Jun 1, 2021
Messages
24
Greetings,

I'm working on a project that requires large radio coverage via VHF LMR and we are about to start ordering equipment. I'm are looking at a radius coverage area of about 15 KM (9.5 miles) with a repeater capable of 110 watts of output. Currently there's a 50 watt repeater with an omnidirectional fiberglass antenna which sometimes covers that area but some areas cannot transmit to the repeater. Handhelds can receive perfectly fine.

Im wondering what is better for this new deployment, an omnidirectional fiber glass antenna (3-6 meters in length) or an omnidirectional dipole antenna with 4 x90 degree angles 2-4 meters in length?

I understand that terrain is a key factor but we are doing ok with the current setup despite an urban terrane. I'm just trying to understand what would work better from the same transmission location
 

tweiss3

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If your ground units can hear the repeater at all times, increasing repeater power won't help. It appears your problem is the repeater hearing your ground unit handhelds. The fix for that is get the equipment a tune up, make sure the antenna, feedline, duplexer and receiver are working top notch (why leave performance on the table), then if you are replacing you need to get the antenna higher or add additional receive sites.
 

rep254

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Jun 1, 2021
Messages
24
If your ground units can hear the repeater at all times, increasing repeater power won't help. It appears your problem is the repeater hearing your ground unit handhelds. The fix for that is get the equipment a tune up, make sure the antenna, feedline, duplexer and receiver are working top notch (why leave performance on the table), then if you are replacing you need to get the antenna higher or add additional receive sites.
This site has been operational for the past 18 years. Back then reception and transmission wasn't a problem. There has been a lot of development which is contributing to part of the problem. The reason we are increasing output is to get further as it's necessary without setting up a simulcast system. One observation I've made is the cable form antenna to repeater is over 50m which could be contributing to part of the problem.

Either way there is a new mast being setup with the equipment closer to it but one dilemma I keep coming back to is what antenna to chose and what are the advantages of one vs the other. Omnidirectional or Dipole omnidirectional. Should I just stick with whats there?
 

jeepsandradios

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As said increasing power only lets the repeater talk further. Does not help a portable at all. Normally a portable based system will have receive only sites to help the signal get to the repeater. Your 5watt VHF portable wont talk any better with a 110 watt repeater than a 50 watt repeater.

We use VHF for SAR and have multiple systems, both voted, simulcast and standalone. On the standalone duplexers, hardline and tuning is critical. Sometimes a pre-amp will help on RX but can also increase noise and still not help portables. If its been on site for 18 years with no PM checks thats where I would start first.

As for antenna's I run a mix of DB224 (or whatever the newest model is) and DB fiberglass sticks. I like the dipole as they seem to hold up better in my area. Really depends on tower and what you really need.

10 miles is not far for VHF at all on a decent tower in average terrain. Our SAR sites cover way more than that but have decent sites.
 

rep254

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Jun 1, 2021
Messages
24
As said increasing power only lets the repeater talk further. Does not help a portable at all. Normally a portable based system will have receive only sites to help the signal get to the repeater. Your 5watt VHF portable wont talk any better with a 110 watt repeater than a 50 watt repeater.

We use VHF for SAR and have multiple systems, both voted, simulcast and standalone. On the standalone duplexers, hardline and tuning is critical. Sometimes a pre-amp will help on RX but can also increase noise and still not help portables. If its been on site for 18 years with no PM checks thats where I would start first.

As for antenna's I run a mix of DB224 (or whatever the newest model is) and DB fiberglass sticks. I like the dipole as they seem to hold up better in my area. Really depends on tower and what you really need.

10 miles is not far for VHF at all on a decent tower in average terrain. Our SAR sites cover way more than that but have decent sites.
Right. We are looking to have someone receive at longer distances. thats one of the objectives. I understand transmitting from a far distance with a handheld in an urban area without simulcast will require a higher output handled transmitter but within the 10 mile radius, everything should work. Mobile radios work perfectly within this area.

In this instance, there is a lot of Motorola equipment already in the field and that unfortunately is what we're updating with. If we had the budget to license all the existing portable and mobiles I would suggest we do IPSC or Cap+ conv in a simulcast setup. Unfortunately I to replicate the same setup with updated equipment.

The location in which the repeater is located is already higher than most locations within the given area where a portable would be transmitting form. the problem is there has been a lot of high rise building come up as well as trees growing over the 18 years. We are adding a mast to further increase hight but I still dont know if I want to go with an omni directional fiberglass antenna or an omni directional dipole given their radiation patterns. Is one truly better than the other in terms of reception/transmission (holding all things constant) or should I just go with a fiberglass antenna and updated equipment to replicate what is there?
 

tweiss3

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It sounds like you need to get someone to model the terrain and your antenna options, and spend some time with the catalog reviewing gain numbers with beam width and downtilt until you get the coverage you are looking for.
 

ecps92

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Jul 8, 2002
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Taxachusetts
Two things immediately pop into my head.
18 yrs of Operation - when was it last PM'd (the Repeater and the Duplexer/Cavities)

2nd item is in two parts
a. What Service Part 90 or 97
b. If Part 90, the FCC imposed Narrowbanding to be in use in 2013 (only 9 yrs ago)
so are your radios talking to the repeater Narrow Band and the Repeater is Not ??

Capt'n we can't give you more power as you want is not going to help the repeater Hear better

This site has been operational for the past 18 years. Back then reception and transmission wasn't a problem. There has been a lot of development which is contributing to part of the problem. The reason we are increasing output is to get further as it's necessary without setting up a simulcast system. One observation I've made is the cable form antenna to repeater is over 50m which could be contributing to part of the problem.

Either way there is a new mast being setup with the equipment closer to it but one dilemma I keep coming back to is what antenna to chose and what are the advantages of one vs the other. Omnidirectional or Dipole omnidirectional. Should I just stick with whats there?
 

rep254

Member
Joined
Jun 1, 2021
Messages
24
Two things immediately pop into my head.
18 yrs of Operation - when was it last PM'd (the Repeater and the Duplexer/Cavities)

2nd item is in two parts
a. What Service Part 90 or 97
b. If Part 90, the FCC imposed Narrowbanding to be in use in 2013 (only 9 yrs ago)
so are your radios talking to the repeater Narrow Band and the Repeater is Not ??

Capt'n we can't give you more power as you want is not going to help the repeater Hear better
I've been given the project despite being new because I'm the 'most' technical individual they've had in a while. 18 years is the figure I've been given. Part 90. We are replacing everything with brand new equipment including duplexers etc... and keeping the most recent portables/mobiles that have been purchased.

It sounds like you need to get someone to model the terrain and your antenna options, and spend some time with the catalog reviewing gain numbers with beam width and downtilt until you get the coverage you are looking for.
I suggested someone that is able to survey but no one wants to spend the money on top of backend equipment. I'm trying to make the best of this situation and what I've been given.
 

ecps92

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Without delving more into this. Good info, but need to say
18 yr old Repeater is not Narrowband, your recent portable/mobiles would be Narrowbanded

I would replace the repeater first before anything else. to rule out the hearing issues (Reception)
What is the make/model and maybe serial # of that repeater, others here might be able to provide more info

I've been given the project despite being new because I'm the 'most' technical individual they've had in a while. 18 years is the figure I've been given. Part 90. We are replacing everything with brand new equipment including duplexers etc... and keeping the most recent portables/mobiles that have been purchased.


I suggested someone that is able to survey but no one wants to spend the money on top of backend equipment. I'm trying to make the best of this situation and what I've been given.
 

tweiss3

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You could try this site: Radio Mobile Online

The models are not bad, but its not perfect. The price is right for you though.

You are going to have to spend some time inputting your antenna options and balance the current height and new potential heights.
 

rep254

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Joined
Jun 1, 2021
Messages
24
I would replace the repeater first before anything else. to rule out the hearing issues (Reception)
What is the make/model and maybe serial # of that repeater, others here might be able to provide more info
It's old motorola gear and its all going. The whole purpose of the project is to get the back end squared away first. Currently have SLR 8000's specified with all the necessary components which should be compatible with the most recent purchased of portables/mobiles.

You could try this site: Radio Mobile Online
Ill check it out! thanks for the suggestion.

Thanks for the input thus far. ill dig into which repeater antenna to go with as thats the last component.
 

mmckenna

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I'm trying to make the best of this situation and what I've been given.
Not sure what your experience level is, or what kind of budget you have.

This can get expensive really quickly. There's a lot more to setting up a repeater than buying parts online and asking for input on what is essentially a hobby radio site. It's really easy to make mistakes that can cost a lot of money.

I'd recommend covering your rear on this. It's easy for someone to tell you to do all this as inexpensively as possible, but inexpensive usually results in poor outcomes, and fixing that just increases the cost. In most cases, you'll save a ton of money by either hiring a consultant who has the knowledge and tools to do this correctly the first time, or finding a reputable radio shop that has the experience and test equipment to do it for you.
Yes, that'll cost money up front, but a proper consultant will help you do things right the first time. A good consultant will have something better than free software to model coverage. A good consultant will have modeling software that will have ground clutter files that will give you real coverage plots down to the square meter that will take into account new buildings, foliage, etc. A good consultant will be able to look at your existing equipment and tell you if you need to replace hardware, or just have proper adjustments made.

There's a ton of posts on this site where someone comes in with the exact same questions you have, and often they've spent a ton of money randomly buying new hardware and still are not getting the results they want. If any part of your plan involves buying hardware online and setting it up yourself without the right test equipment, you're on the wrong track.
 

mmckenna

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Currently there's a 50 watt repeater with an omnidirectional fiberglass antenna which sometimes covers that area but some areas cannot transmit to the repeater. Handhelds can receive perfectly fine.
I agree with the others, throwing more RF output power from the repeater isn't going to solve this. You also need to look at what your FCC license allows. It should list a maximum transmitter power and Effective Radiated Power. Unless your license already covers a 110 watt repeater and the added ERP that a new antenna will give you, you'll need to start working with a frequency coordinator.

This issue sounds like your duplexer may not be up to the task. If the repeater can talk out to the handhelds, but the handhelds can't get back in, it may be desense. A technician with a service monitor should come out to your sight, and do a full PM on your system. Buying new hardware without that is just pissing in the wind.
 

rep254

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Messages
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Not sure what your experience level is, or what kind of budget you have.

This can get expensive really quickly. There's a lot more to setting up a repeater than buying parts online and asking for input on what is essentially a hobby radio site. It's really easy to make mistakes that can cost a lot of money.

I'd recommend covering your rear on this. It's easy for someone to tell you to do all this as inexpensively as possible, but inexpensive usually results in poor outcomes, and fixing that just increases the cost. In most cases, you'll save a ton of money by either hiring a consultant who has the knowledge and tools to do this correctly the first time, or finding a reputable radio shop that has the experience and test equipment to do it for you.
Yes, that'll cost money up front, but a proper consultant will help you do things right the first time. A good consultant will have something better than free software to model coverage. A good consultant will have modeling software that will have ground clutter files that will give you real coverage plots down to the square meter that will take into account new buildings, foliage, etc. A good consultant will be able to look at your existing equipment and tell you if you need to replace hardware, or just have proper adjustments made.

There's a ton of posts on this site where someone comes in with the exact same questions you have, and often they've spent a ton of money randomly buying new hardware and still are not getting the results they want. If any part of your plan involves buying hardware online and setting it up yourself without the right test equipment, you're on the wrong track.
I appreciate the advice and word of caution. I'm not by any means a profession in this field but do understand enough to know not to go down the rabbit hole. I was providing as much background information as I could in hopes that I'd gain more insight into what would be a good antenna choice. My overall goal is to try and understand which antenna would prove 'better' than the other ( I know this is a broad question and there are many factors) and why some people prefer omnidirectional dipole over omnidirectional fiberglass antennas.

as far as cost etc. I generally am a do it right or don't do it at all type of person. Unfortunately I'm dealing with people that are stuck in their ways and 'know' whats best. Luckily no money has been spent and im trying to follow through given the constraints and get as much info as I can before money is spent.

Either way I hear you completely. thank you again.
 

mmckenna

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and why some people prefer omnidirectional dipole over omnidirectional fiberglass antennas.
You'll get a lot of different input on this.
Depends on the location and what you are trying to cover. I 'like' dipoles and have used them in a couple of places.
I have other sites where a fiberglass omni has worked well.

Again, this is a place where someone with the -right- modeling software and knowledge of the area can save you a lot of time, money and trial/error testing. If this antenna is on someone else's tower, you also need to consider what your tower lease allows, tower climber costs, etc.
 

mastr

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May 7, 2005
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...I generally am a do it right or don't do it at all type of person. Unfortunately I'm dealing with people that are stuck in their ways and 'know' whats best...
...I suggested someone that is able to survey but no one wants to spend the money on top of backend equipment. I'm trying to make the best of this situation...
This could bite you in the you-know-where pretty easily. If you must go forward without a prior run of a coverage/performance survey program, ask the "no one" who won't pay for it to give you the refusal in writing. That will either get the survey approved or give you a person to point at when/if your efforts are not seen as good enough.
 

mmckenna

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Yeah, this can turn into a trap really quickly.

And before replacing antennas, you should have someone sweep your existing setup. If it worked before, but isn't now, don't rule out a damaged antenna, damaged coax, etc. Blindly replacing parts without knowing which part failed isn't the way to do this.
 

prcguy

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Yes on this comment. It would be nice of someone knowledgeable ran a few basic tests and there could be something fairly simple that has degraded over time causing weak receive or loss of coverage. Even a simple test of a temporary antenna and basic radio at the repeater site to see if it will hear handhelds out to the distance you expect. Then run the repeater off the same temporary antenna to see if that has the same range and so on. At least you will know the potential range you can achieve and if the repeater system or current antenna is the problem.

Yeah, this can turn into a trap really quickly.

And before replacing antennas, you should have someone sweep your existing setup. If it worked before, but isn't now, don't rule out a damaged antenna, damaged coax, etc. Blindly replacing parts without knowing which part failed isn't the way to do this.
 

rep254

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Noted. Ill look into getting the right people involved. Thanks for all your feedback. I appreciate it.
 

wgbecks

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Above all, a site noise level test needs to be performed that is especially important for VHF systems whereby numerous emitters now pollute
the spectrum that wasn't the case years ago! Take the advice of @mmckenna and hire a competent shop or consultant to evaluate your
entire system and to measure the site noise floor.
 
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