Minimum VHF repeater working distance

[yetilicious]

We have a 50w VHF repeater with two antennas set up on a 30' building with a 15' mast. Is there a minimum working distance between the repeater and our employees with VX-231 handhelds? The repeater is situated roughly in the middle of our 80 acre business. If you are standing relatively underneath it, would the repeater still communicate with the VX?

 

[TampaTyron]

depends..

Tell me more about type/age of repeater and your 2 antenna system (type of antenna/feedline/ spacing). You "should" be able to key it up diretly underneath, but sometimes there is a "cone of silence" under high gain vertical antennas. TampaTyron

 

[fineshot1]

We have a 50w VHF repeater with two antennas set up on a 30' building with a 15' mast. Is there a minimum working distance between the repeater and our employees with VX-231 handhelds? The repeater is situated roughly in the middle of our 80 acre business. If you are standing relatively underneath it, would the repeater still communicate with the VX?

Give us more info on the antenna configuration please. i assume two antenna's are one for rx
and one for tx? is that right? what kind of cable are you using on these antenna's? How far apart
are these antenna's? what kind of antenna's are they? seems per your description both antenna's
are about 45 feet above the ground? what is the surrounding terrain like on this 80 acres of land? do
you have hills & valleys or is it all flat?

 

[davidgcet]

with VHF you really need a duplexer. the repeater tx is bad about desensing the RX and completely blanking it out. as the others said we really need to know how far apart the antennas are and if that distance is horizontal or vertical.

the same thing applies to the portables, too close to another unit while txing and it could blank the other handheld, though usually this only happens with mobiles.

 

[yetilicious]

First off, thanks everybody for your input. I really appreciate it.

1)Yes we have two antennas one for RX and TX no duplexer installed. The cable looks like 1/2 or 5/8 coax. The core has 4 or 5 thick strands of copper.

2)I would say the antennas are roughly 50' apart diagonally from each other. The invoices say they are:

NCG Comet CA-F22GF
NCG Comet CA-F22GF [CA-F22GF] - $139.95 : The Antenna Farm :: , Your Two Way Radio Source!

If these are the wrong ones, they can be replaced.

3) The property is flat asphalt with trees, snack bars and some of the sellers spaces are metal buildings about 8' tall made from corrugated metal.

4) it is possible for me to raise the antennas higher if need be. If I have to go 60-70 I can we'll just build a bigger gig.

5) If it makes a difference our freq, are in the 150-160 range.

6) Here's a photo of our place. The parking lots on either side are ours too and a Google Map link
Google Maps

 

[davidgcet]

the exact freqs are needed to verify spacing required, but getting one antenna higher than the other will make up for seperation distance more so than horizontal spacing does.

is there a specific reason you do not have a duplexer? did you design this system yourself or was it configured by paid professionals? i ask because a pro should have made sure that the antennas were setup far enough apart to no interfere with each other.

i personally don't think you have them far enough apart, but adding more seperation is also going to mean more line loss. easier to go with a duplexer and have a properly tuned antenna system.

BTW, if the center conductor is stranded you have something like RG8 or a similar line. if this line is real long, you could also improve performance by replacing it with heliax to lower line loss.

 

[baycomm]

IF IT WORKS, it will never work well. This is certainly not installed to an acceptable professional standard.
You will need at least 450 ft of horizontal separation or 40 ft of vertical separation to get 60 dB of isolation between the antennas. This would only be adequate for a low power repeater. We usually aim for a minimum of 80 dB isolation even with a 40 watt repeater. The frequency separation between transmit and receive is also critical, there is no standard frequency split on VHF. If the channels are too close to each other, you will never be able to get them to work. The Comet antennas are not considered to be adequate for commercial service. I would recommend 5-7 dB fiberglass antennas from Laird or PCTEL. The Cable should be LMR-400 with a solid center conductor. Using Heliax would be of little benefit unless your cable run is over about 100 ft. I suspect that this system was either bought mail order or from a very inexperienced dealer. If you want it to work properly, hire a professional. Let me know where you are located & I will PM you the name of a reputable dealer.

 

[yetilicious]

@davidcget
The freqs are RX 154.5700 / TX 156.1700. I didn't design/build the system. The original guy who put everything together left the company and I was "promoted" into it among my other duties. We can buy a duplexer, there just wasn't one installed at the time for reason unknown.

@baycomm
I'll look into those two antenna companies and start pricing that cable.

 

[rfradioconsult]

The guy that put it togather didn't know much about radio; your repeater is illegal. First your 154.57 is a MURS channel no repeater operation allowed, second your 156.17 is not an assigned channel but falls in the Marine VHF band. If your intent is to upgrade your system start by contacting a radio professional for guidance before you get a visit from the FCC.

You don't stand much of a chance qualifying for a VHF Business Radio Service repeater, the most you could hope for is a UHF low-power repeater given the description of the area you want to cover. My suggestion would be pull the plug on this beast and start fresh. If you can get ahold of the guy responsible ask him where the license is.

 

[davidgcet]

agreed, it sounds like he picked 2 freqs out of thin air and just put them to use. you can be fined several thousand bucks for EACH unit you are operating illegal on EACH channel for EACH day.

 

[fineshot1]

First your 154.57 is a MURS channel no repeater operation allowed, second your 156.17 is not an assigned channel but falls in the Marine VHF band.

You are correct on the 154.570 freq but 156.170 is not in the marine band. The marine band starts
at 156.255 or .275(cant remember which), although 156.170 does fall between two valid channel
centers(156.165 and 156.1725) so it is an invalid frequency. It seems like that fella just made up
his own freq pair or perhaps he through a dart at a dart board to pick them.

 

[rfradioconsult]

You are correct on the 154.570 freq but 156.170 is not in the marine band. The marine band starts
at 156.255 or .275(cant remember which), although 156.170 does fall between two valid channel
centers(156.165 and 156.1725) so it is an invalid frequency. It seems like that fella just made up
his own freq pair or perhaps he through a dart at a dart board to pick them.

Marine channel 01A 156.050 MHz, Marine channel 05A 156.250 MHz;; thus 156.17 falls between Marine 01A and 05A.

 

[fineshot1]

Marine channel 01A 156.050 MHz, Marine channel 05A 156.250 MHz;; thus 156.17 falls between Marine 01A and 05A.

Your right - but they(below) are the only marine freqs in that range and do fall
in between commercial freq boundaries which I never noticed before. I hope the
OP is not near any coastal ports.

01A 156.050 Port Operations and Commercial. VTS in selected areas.
63A 156.175 Port Operations and Commercial. VTS in selected areas.
05A 156.250 Port Operations. VTS in selected areas.

 

[yetilicious]

Thanks everybody for your info and help.

I went a head and took down the system. After finding out everything in the past couple of days, it's not worth it. I did however put in a call to a local dealer to have one of their consultants come out.

 

[texasemt13]

Looking at your facility, I see it's almost a mile across (unless there's more I haven't seen).

With this distance you might be able to use simplex operation, and no repeater may be required. I'd ask the consultant to do a feasbility study. You never know, unless you try. 70cm business band simplex might get it done, on a 5W HT, and might work a little better than 2m simplex in the urban terrain.

If a repeater is necessary it shouldn't have to be too high.

You did the right thing by removing the out of compliance system equipment, and I commend you on that.

 

[rfradioconsult]

I would suggest you post details of what the local dealer is proposing, you don't want to end up with something tha isn't suited for your application or price range. Good luck.

 

[TampaTyron]

Also,
make sure the vertex radios are NOT set up for power save on tx. If the radio rx a strong signal, it will tx a low power signal. PITA........TampaTyron

 

[mjthomas59]

Seems kind of odd to be using a 50watt repeater to cover a square mile?? Like was said Simplex operation would very likely get you that much coverage. Any updates yet from your local dealer on a new legal game plan?

 

[TampaTyron]

vhf portables are not very reliable for more than a couple of hundred yards of range in built up areas. Biggest issue has been the negative gain of the portable antennas. I would question reliability of vhf portable ops in this range/terrain scenario. TT

 

[OpSec]

vhf portables are not very reliable for more than a couple of hundred yards of range in built up areas. Biggest issue has been the negative gain of the portable antennas. I would question reliability of vhf portable ops in this range/terrain scenario. TT

What are you using...Fischer-Price radios?

There may be some noisy spots, but a 5w portable with a decent antenna should cover that property with ease.