Existing Tower Evaluation

[WBA]

I have an existing 30 ft antenna tower that came with my property. I'm looking to mount a Comet CA 712-EFC on it for UHF (GMRS) base station.
Here are my questions:

Once I remove all of the existing leftover antennas and components, I will have a top to the tower that looks similar to this.
-How would I go about mounting the antenna? Do I just strap it to the side of one of the upright pipes (supports)?
-Do I need a mast? If so, other than matching the size to the diameter of the top mast hole, what other considerations?
-Is there a limit to the mast height?

In evaluating the tower, it is anchored into the ground and bracketed to the house a good way up.
-Is there a decent way to determine if the grounding of the tower is sufficient (being anchored into the ground) through excavation or testing, etc?
_ Are there any other grounding/bonding points between the antenna, mast, coax, that need to be considered?

I am looking to get pre-made lengths of TM Lmr-400 coax for the run from the antenna down the tower. I'm trying to understand lengths of coax needed and terminations needed prior to hookup to the radio.
-From the antenna, with the coax running down the tower, do i have to terminate the run for grounding prior to entering the house? If, so what do i need for that?
-Are there any decent resources with diagrams explaining this process?

If I am planning to possibly mount additional antenna on the tower should I be considering different options for the current UHF install?

Are there any other antenna options I should be considering?

Thanks in advance for your time.

 

[mmckenna]

I have an existing 30 ft antenna tower that came with my property. I'm looking to mount a Comet CA 712-EFC on it for UHF (GMRS) base station.
Here are my questions:

Once I remove all of the existing leftover antennas and components, I will have a top to the tower that looks similar to this.
-How would I go about mounting the antenna? Do I just strap it to the side of one of the upright pipes (supports)?
-Do I need a mast? If so, other than matching the size to the diameter of the top mast hole, what other considerations?
-Is there a limit to the mast height?

You want to mount the antenna per the manufacturers recommendations.
A mast would be the right way to do it.
Strapping the antenna against a leg directly will cause issues with tuning the antenna if you don't have it spaced out correctly.

Limit on mast height depends on the spec for the mast. Usually when doing this stuff on towers, the mast is a specifically designed item, not a piece of conduit or fence top rail. It's something that gets engineered into the overall design.
The "right" way to do it is to contact the tower manufacturer and check with them. They'll sell the correct parts needed to add the mast, and that will include specs on the antenna loading.

But a small antenna like that isn't going to much of an issue. Keep the mast as short as necessary.

In evaluating the tower, it is anchored into the ground and bracketed to the house a good way up.
-Is there a decent way to determine if the grounding of the tower is sufficient (being anchored into the ground) through excavation or testing, etc?
_ Are there any other grounding/bonding points between the antenna, mast, coax, that need to be considered?

I would not trust someone else's work if you don't know how it was done. Assume that it's not grounded and install a new ground rod at the base.
Yes, it may technically be grounded through the mounting bolts/rebar, but since you can't see if that was done correctly, it's not a good idea.
There are ground testers, but they are expensive. Much easier to just drive a new ground rod and know it has been done right.

That ground rod must be bonded to your homes existing ground rod. The tower needs to be bonded to that ground rod.

Industry standard is usually to ground the coax at the antenna end. This may be accomplished through mounting. On really tall towers, coax grounding is often done periodically as it runs down the tower.
You do want the coax shield grounded where the cable exits off the tower face.

I am looking to get pre-made lengths of TM Lmr-400 coax for the run from the antenna down the tower. I'm trying to understand lengths of coax needed and terminations needed prior to hookup to the radio.
-From the antenna, with the coax running down the tower, do i have to terminate the run for grounding prior to entering the house? If, so what do i need for that?

As I said above, grounding at the antenna and at the transition off the tower.
You also need a lightning protection device where the coax enters the home, and that gets grounded.

To ground the coax where it transitions off the tower, you would use a cable specific grounding strap to do that.

GK-S400TT Standard Tinned Ground Kit for LMR400 2-Hole Lug 3Ft Lead - Talley Inc.

Standard Tinned Ground Kit for LMR400 2-Hole Lug 3Ft Lead

www.talleycom.com

LMR-400 is fine for connecting directly to the antenna. If you were running larger coax, it's common to use a transition cable to make the connection between the stiffer cable and the antenna.

So, length of cable coming down the tower to the lightning protection device. Then length of cable to reach where your radio is. Then a short, flexible jumper to make the final connection to your radio.

LMR-400 is fine if this is a short run and you have no plans to ever run a repeater on this antenna. If you ever plan on running a repeater on this tower/antenna, you need something like Heliax cable.

-Are there any decent resources with diagrams explaining this process?

There are. Some of them get really deep and may overwhelm you. The Motorola R56 document is pretty much considered the grounding "bible" in the industry. A lot of it is overkill for hobby use, but it will give you some good ideas.

A simple guide is here:

https://www.mikeholt.com/instructor2/img/product/pdf/17LED-1498-sample.pdf

If I am planning to possibly mount additional antenna on the tower should I be considering different options for the current UHF install?

Tower specific cross arms are a good way to do this. That will allow you to mount antennas spaced off the side of the tower.

You could mount your GMRS antenna on one of those down the tower face, but you will want one antenna at the top to make best use of the height.

Are there any other antenna options I should be considering?

Comet makes hobby grade antennas. That's fine for many and having a limited budget is a reality. Nothing wrong with that.

If you have a good budget for this, consider an LMR grade antenna made by one of the commercial manufacturers. Most of the real costs in your setup have to do with all the little details and the your labor. You don't want to put up a cheap antenna and have to replace it in a few years. The antenna system is the most important part of your station, don't go cheap.

 

[WBA]

Thanks for the detailed response. The Mike Holt article was very helpful.

So, unless I'm reading that incorrectly, the requirements for grounding/bonding of the system are to ground the "mast" (which the code defines as the metal support structure for the antenna - ie: the tower-) and the lead-in conductor (the coax) at the antenna discharge unit. Both of these are to be run to (terminated at) the Electrical service grounding electrode(s). While it's permissible to add an additional grounding electrode (ground rod) for the tower, it is NOT required.

Assume that it's not grounded and install a new ground rod at the base.

Based on the code as explained in the Holt article, I thought tying to the Electrical service electrode (ground rod) is sufficient. Did I miss something?

Industry standard is usually to ground the coax at the antenna end. This may be accomplished through mounting.

Can you explain what you mean by the mounting as means of grounding (bonding) the coax?

You do want the coax shield grounded where the cable exits off the tower face.

Ah, so the GK-S400TT (link you sent) is for this specific purpose? Does it work by simply slipping over the coax (no termination) or does it require the coax be terminated like at the discharge unit?

So, length of cable coming down the tower to the lightning protection device

lightning protection device = antenna discharge unit (term used in the article?)


Any Idea how to determine the manufacturer and model of the tower? It's rather well "patina"-ed.

consider an LMR grade antenna made by one of the commercial manufacturers.

Just looking at Antenna Farm and browsing their category "commercial base antenna" brings up the comet, browning, tram, etc... which I'm guessing don't qualify. How can I determine if it's LMR grade?

Thank you.

 

[mmckenna]

Thanks for the detailed response. The Mike Holt article was very helpful.

So, unless I'm reading that incorrectly, the requirements for grounding/bonding of the system are to ground the "mast" (which the code defines as the metal support structure for the antenna - ie: the tower-) and the lead-in conductor (the coax) at the antenna discharge unit. Both of these are to be run to (terminated at) the Electrical service grounding electrode(s). While it's permissible to add an additional grounding electrode (ground rod) for the tower, it is NOT required.



Based on the code as explained in the Holt article, I thought tying to the Electrical service electrode (ground rod) is sufficient. Did I miss something?

The thing you are trying to accomplish with all this is to give the energy of a lightning strike (either direct, or nearby) an easy path to ground. Lightning has been shown to take the shortest path. That shortest path may not be following a long wire to find your home ground rod. Preferred method is to put at least one rod directly under the tower so the majority of energy will take that route.

Two things you need to consider:
National Electric Code is for safety. It's to help reduce the chance of the people in the house getting killed/injured. It is not the final answer on everything. At minimum, you need to met the NEC requirements. However, it's OK to do more. And it's a good idea. Adding that additional ground rod at the tower base will give that direct path to ground. Bonding it to the existing house ground rod keeps everything at the same potential (important).

Can you explain what you mean by the mounting as means of grounding (bonding) the coax?

The antenna mount, where it actually attaches to the mast, it usually connected to the outer shield of the coax connector. So, mounting the antenna to the mast is usually what happens. If you want to go full professional on this, they often use the coax grounding kit near the top of the tower. Ideal is that the tower structure is a much larger conductor than the coax, and can handle a lot more energy. Goes back to that "easy path to ground" thing.

Ah, so the GK-S400TT (link you sent) is for this specific purpose? Does it work by simply slipping over the coax (no termination) or does it require the coax be terminated like at the discharge unit?

Yes. The coax outer jacket gets stripped off. The clamp goes around the outer shield of the coax and it all gets grounded through the pigtail wire. Very important to use the kit that includes the sealing compound and cover that with tape.

lightning protection device = antenna discharge unit (term used in the article?)

Yeah, there's a bunch of different names for them.

Polyphaser is a good brand that is well respected.

https://www.polyphaser.com/type-n-surge-protector-700mhz-blocking-cap-gas-tube-is-50nx-c0

You can get cheaper protectors, but there are places to save money, safety devices isn't that place.

Any Idea how to determine the manufacturer and model of the tower?

Look for any part numbers that you can google.
You can try sharing a photo here (details are good) and see if anyone recognizes it.

It's rather well "patina"-ed.

Beware.
Normal for them to look like that. But if you are going to climb it, make sure you look very, very closely at the point where it's mounted to the ground. Look for any rust. Rust may be internal and not visible from the outside. Tower climbing is dangerous. Renting a bucket truck is cheaper than a funeral or a very long hospital stay.

Just looking at Antenna Farm and browsing their category "commercial base antenna" brings up the comet, browning, tram, etc... which I'm guessing don't qualify. How can I determine if it's LMR grade?

Thank you.

Yeah, Comet, Browning, Tram make antennas that will work on the commercial part of the bands, but they are not what I'd consider commercial grade.

Laird
Pulse/Larsen
Telewave
DBSpectra
RFS
CommScope

Some of those get really expensive and would not be appropriate for hobby type use, unless you won the lottery and wanted sick bragging rights. Laird base antennas have worked well for me in the past when budget was a concern and I needed a reliable base antenna. The Laird FG-460# series are pretty decent for the price. I've installed quite a few Telewave antennas at work and they are durable, but you'll pay for that.

A good antenna is important and worth the investment.

 

[JustinWHT]

1. How would I go about mounting the antenna? Do I just strap it to the side of one of the upright pipes (supports)?
2. Do I need a mast?
3. Is there a limit to the mast height?
4. Is there a decent way to determine if the grounding of the tower is sufficient (being anchored into the ground) through excavation or testing, etc?
5. Are there any other grounding/bonding points between the antenna, mast, coax, that need to be considered?
6. From the antenna, with the coax running down the tower, do i have to terminate the run for grounding prior to entering the house? If, so what do i need for that?
7. Are there any decent resources with diagrams explaining this process?

1. Antenna mounting clamps . Amazon $25. Attached pic.
2. Another ten feet of mast pipe isn't going to add any significant range
3. 200 ft, including tip of antenna.
4. Drive a ground rod and connect to utility master ground with #8 ga copper wire.
5. As I posted Hole in Brick where Coax Passes through......Best Way to Seal Around the Coax? on suggestion for grounding coax.
6. See 6. above.
7. The Motorola R56 manual. Motorola r56 2005_manual