How close is too close?

BlueDevil · Feb 11, 2016

We are looking at installing a second repeater for our business operations. Our site is very limited on space available for mounting of antenna hardware and equipment. I know it is best to have as much separation as possible between repeater antennas, especially when operating within the same band (VHF). More horizontal spacing is usually required than vertical spacing depending on the type of antennas you are using.

Take a look at this picture and give me your thoughts on how close is too close. We are considering putting a 2 bay folded dipole antenna on the empty post/mast to the right of our current repeater antenna. We would run this in a directional pattern in the same direction as the picture's point of view. In your mind/opinion would this just be way to close? We don't have a whole lot of other options. One option would be to use an antenna combiner and run the two repeaters off the one antenna but that is going to decrease our coverage area fairly significantly I believe.

I would love to be able to put some equipment on this Verizon tower but so far I haven't had any success with that.

Voyager · Feb 11, 2016

You want it as far away as possible (as you said) - at least a full wavelength if possible - so as to avoid antenna pattern corruption.

Minimum spacing for technical reasons will depend on the filtering in use on the systems.

BlueDevil · Feb 11, 2016

I could check and see if it would be possible to raise the current in place antenna to help provide some additional vertical separation.

mass-man · Feb 11, 2016

Not terribly technical answer, but you might reconsider the combiner idea!!!

mass-man · Feb 11, 2016

You could move that empty mast to the other side of the building...that would be better than where it is...

Antenna Systems Information - Combiners

good luck

Voyager · Feb 11, 2016

mass-man said:
Not terribly technical answer, but you might reconsider the combiner idea!!!

That would only work of both are only transmitting. For T/R you are back to the same issue (need a second antenna plus a multicoupler now). And combiners are not cheap.

cmjonesinc · Feb 11, 2016

Could you not put it on the lift and run some coax across? And my, what a tiny Verizon tower hahaha.

Outerbanks4wd · Feb 11, 2016

What about mounting 2nd repeater in/on Ski Patrol building?

16b · Feb 11, 2016

Outerbanks4wd said:
What about mounting 2nd repeater in/on Ski Patrol building?

I second that idea; you could move the empty mast over to the other building. It's hard to tell from your picture what the height difference is, but I'm guessing the real world difference won't be much given that you're on the top of a hill/mountain.

cmdrwill · Feb 11, 2016

Are you using that Station Master for the ski patrol operations?

BlueDevil · Feb 11, 2016

cmdrwill said:
Are you using that Station Master for the ski patrol operations?

Yes we are.

SCPD · Feb 11, 2016

Similar thinking?

cmdrwill said:
Are you using that Station Master for the ski patrol operations?

I wonder if you're thinking what I'm pondering. Do you need all the gain at the top of a mountain?
Seems like part of the solution would be to reduce the gain by going to quarter wave verticals, and possibly mount them on the same mast, one directly under the other, which would go far towards attenuating intermod, yet still give great coverage because of the height.

Voyager · Feb 11, 2016

The quarter wave would get into the valleys better, too.

kayn1n32008 · Feb 11, 2016

BlueDevil said:
We are looking at installing a second repeater for our business operations. Our site is very limited on space available for mounting of antenna hardware and equipment. I know it is best to have as much separation as possible between repeater antennas, especially when operating within the same band (VHF). More horizontal spacing is usually required than vertical spacing depending on the type of antennas you are using.

It will be easier to mitigate PIM/active mixing by combining the two repeaters onto the same antenna.

BlueDevil said:
Take a look at this picture and give me your thoughts on how close is too close. We are considering putting a 2 bay folded dipole antenna on the empty post/mast to the right of our current repeater antenna. We would run this in a directional pattern in the same direction as the picture's point of view. In your mind/opinion would this just be way to close? We don't have a whole lot of other options. One option would be to use an antenna combiner and run the two repeaters off the one antenna but that is going to decrease our coverage area fairly significantly I believe.

It is too close to add a folded dipole array. I would suggest ditching the station master and just go to a four dipole array. Combine the two repeaters together and call it good. You may want to look at antennas with a bit of down tilt if that is the highest elevation where you operate though.

BlueDevil said:
I would love to be able to put some equipment on this Verizon tower but so far I haven't had any success with that.

Do not waste your time, or money. You already are likely at the high point where your antenna is already mounted. The 3 to 6m extra height will not make an inch of difference in your coverage footprint.

Even going up 100m above where you currently are will not net you much additional coverage, just fill in some dead spots with in the current coverage... Extend coverage MAYBE a few additional kilometres, MAYBE.

Rather than waste the money to get on Verizon's tower, spend it on a decent combiner/Rx multi coupler and a 210-C4. It will be money well spent. Spending money getting on that puny tower, well you might as well just buy crack and smoke it. At least that way it will actually do something for you. More importantly, the feeling afterwards, realizing it was a waste of time, will be the same.

kayn1n32008 · Feb 11, 2016

Voyager said:
That would only work of both are only transmitting. For T/R you are back to the same issue (need a second antenna plus a multicoupler now). And combiners are not cheap.

Actually no. IF the pairs are close he may be able to combine the Transmitters, multi couple the receivers, and run both into a Duplexer.

Combiners can be made for as little as 0KHz transmitter separation.

BlueDevil · Feb 12, 2016

At this point I am not exactly sure what our repeater pairs will be as they are going through the coordination process. I like the idea of putting the repeater on another building but the small building where the current repeater is located has a much better location for storage and security purposes.

Voyager · Feb 12, 2016

kayn1n32008 said:
Actually no. IF the pairs are close he may be able to combine the Transmitters, multi couple the receivers, and run both into a Duplexer.

That's one heck of an assumption. I know you said IF, but what are the chances?

kayn1n32008 said:
Combiners can be made for as little as 0KHz transmitter separation.

Now that I would like to see; A filter that passes frequency X but rejects frequency X...

kayn1n32008 · Feb 12, 2016

Voyager said:
That's one heck of an assumption. I know you said IF, but what are the chances?

Dunno. I have no clue what the VHF band looks like where the OP is.

Where I live there are three VHF repeaters sharing the same single antenna:

The transmit frequencies are:

Rpt 1: 157.005
Rpt 2:171.360
Rpt 3:169.080

The receive frequencies are

Rpt 1:163.450
Rpt 2:172.095
Rpt 3:169.515

All three use the same antenna for both transmit and receive.

Voyager said:
Now that I would like to see; A filter that passes frequency X but rejects frequency X...

http://www.sinclairtechnologies.com/catalog/resources/pdf/TCC2234-DI.pdf

Minimum separation 0MHz maximum separation 3MHz. They exist.

Sent from my iPad using Tapatalk

Voyager · Feb 12, 2016

Wow. That's all I can say.

I didn't know it was possible to have rejection of a given frequency and pass that same frequency at the same time. That has GOT to be a typo.

Maybe that full duplex simplex repeater project isn't as far away as I thought.

freddaniel · Feb 12, 2016

Without actual frequencies, this is just an exercise in generalizations. Placing two VHF repeater antennas within 10 feet of each other is a guarantee only one will work at a time. Isolation would be about 14 dB.
For a design to accommodate another single VHF repeater, or many more, I would suggest either placing your new dual-dipole antenna on the top of the Verizon tower, or on the tall pine tree seen to the left of the tower. Use Heliax cable down the tree and underground to your building. For just one more repeater, connect to this antenna. This spacing will provide at least 35 dB isolation, so the repeaters may not interfere with one another. If you end up with interference, then add at least a single junction isolator to each transmitter.
If you wanted to install more repeaters, then use one antenna for common receive and the other antenna for common transmit, using standard combining methods, of dual junction isolators, etc.
Placing more than one repeater on a single antenna can be done, but depending upon the frequencies, it could cost anywhere from $2,000 to $10,000, for all the isolators, hybrids, and cavities. And what about the added rack space for all those cavities?

How close is too close?

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