Tripod vs Gable and Maximum mast size

[oguruma]

I want to put an antenna on my roof/eve. The feedline will run along the exterior of the wall, inside some schedule 40.

I am trying to decide between an eve/gable mount, or a tripod. I live at the bottom of a hill, so as high as I can get it, the better.

I live on the Oregon coast, and we get some pretty gnarly wind. Not hurricane strength, but quite a bit of sustained wind and fast gusts.

I want to try a 1/4 wave antenna, since it seems like this would give me the best chance at getting "up and out" over the hill. From what I have read, since I don't have horizon (due to the hill) a 1/4wave ground plane antenna might be my best bet.

What is the tallest mast that is recommended for a roof-mounted tripod? What about for a gable mount?

 

[N4GIX]

I have three tripod mounts on my roof, two of which have been up for almost 25 years now. All three use 2 x 5' mast sections. Any higher would require guying, which I didn't want to do.

I live in Hammond, IN and we have had sustained winds up to 60 mph over the years and I've had no troubles at all.

My GMRS antenna is ~8' long, so total height for that is 18' to the tip of the antenna.

 

[oguruma]

Thanks for the input. Is the requirement for guylines a code issue? Or just based on a reasonable understanding of how they perform?

Adding guylines is not going to be feasible (unless I want a divorce).

10' from the top of my roof would get me up and over my neighbors roof, which I think would be beneficial.

 

[N4GIX]

Not a "code issue" so much as good sense. The 5' mast sections are heavy-duty, but the where they connect together is the weakest point.

These mast sections are designed to carry TV antennas which are horizontal in cross-section and typically have far less wind loading than a tall vertical antenna. Since the wind loading would be higher near the top of the antenna, more force would be placed on the single joint of two mast sections.

My background includes roughly 45 years of experience installing antenna systems and towers.

 

[WA8ZTZ]

You don't mention how high of a tripod, what frequency range for the ground plane antenna, or your type of roof construction.

However, generally speaking... a properly installed tripod will be more substantial than a gable mount and will get your antenna higher. A 1/4 wave ground plane for, say, 2 meters and above will present a very small wind area. Check the manufacturers specs for wind area and wind loading for the antenna of your choice. You may be able to safely use a 10' mast... all depends upon how high of a tripod, how well it is mounted, size of antenna, and manufacturer specs. My suggestion would be to use 1 1/4" electrical EMT rather than TV mast. It is far more substantial than residential TV mast and comes in 10' lengths so no weak joints.

You also need to consider proper grounding for lightning protection. Consult National Electrical Code Article 810. And. of course, stay well away from any electrical lines for both safety and noise reasons.

Good luck with your antenna project.

 

[oguruma]

No overhead power lines nearby, so we are good there.

This would be 1/4 wave on 2M antenna.

Thanks for the input on the conduit vs tv mast.

As far as grounding, is some 4 gauge wire run to my existing electrical grounding rod sufficient? The ground rod is about 22 feet from the proposed antenna location.

The tripod was I thinking about using has 3' legs. I am just spitballing, as I have never set anything up like this before.

I know that I have marginal signal to the main repeater in our county with an HT, and I am assuming that an antenna outside my house would give me sufficient signal.

 

[SCPD]

Hi Ogur....
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I'll echo the recommendation about the tripod- a quarter wave antenna for 2 presents a minimal wind load. How high above the tripod and the roof?...I don't think you will notice any difference between 5 feet and 10-- though at 5 feet you will worry less during storms. I say put it high enuff, but not so high that it looks unstable, and draws snarky comments (I'd highly favor the choice of no more than 5 feet.)
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Reminds me of an old ham saying
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"If by spring, the winter storms didn't bring down your antenna, then you didn't put it high enuff"
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I, BTW, do NOT endorse that.... at all !
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One thing you might want to consider is a small beam instead of a quarter wave vertical. A 4 element beam is nothing when it comes to wind load. It will give you ~7 db's over a quarter wave, if that is important to get over your blocking hill. Its easier and cheaper than taking the chance of trying to go higher....

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..............................CF
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[oguruma]

I'm not sure what would be best. What I understand about about the 1/4 wave radiation pattern is that it's less flat. Anything that travels towards the horizon is going to hit the ocean to the (3/4 mile) west, and a hill to the east. It was explained to me that a bunch of gain might not do much, since it's going to hit a hill, anyway.

Would a beam antenna let me diffract over the hill?

 

[WA8ZTZ]

The 4 AWG grounding conductor should be copper and run as directly as possible to your grounding location which should be bonded to the building grounding electrode system. Use proper listed ground clamps. Again, let NEC Article 810 be your guide, Mike Holt has excellent info on this... do a search.

Given your windy location on the coast, a 10' mast on a 3' tripod maybe be pushing things a bit even with just a simple 2 meter ground plane antenna. You have to consider the affects of ice loading on the mast and antenna if you get freezing rain and sleet storms there. You have to make a judgement call on this as you are familiar with the WX conditions in your area.

Also, use good feedline coax (for example, RG-8, not RG-58) to keep losses to a minimum. Otherwise all your effort getting the antenna up in the air will be wasted... eaten up in feedline loss.

Lots of things for you to think about here with even a simple antenna installation.

btw... what is your roof construction... you need to figure how to attach the tripod securely to your roof material.

 

[SCPD]

If I am reading you correct, Ogur, you want to put your 2 metre signal into an area that might be blocked by a hill, Simply elevating your antenna, even one as simple as a quarter wave, may be sufficient. As far as gain is concerned, a 3, or 4 element beam will give you 6-8 dbs of gain, the equivalent of ~3 to 4 times increase in your transmitter's power. There are times when a higher angle of radiation is desirable- like radiating an HF signal out of a mountain valley (believe me, this I know... ) - but in your case, you want to put as much energy in the direction of your intend'd target as you can. A quarter wave antenna for its higher angles of radiation will not to be to your advantage.
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An analogy- go out at night and shine a flashlight at a tall fence, and on the opposite side, from a distance, see how much scatter'd light is seen coming over it. That's your quarter wave-- Now direct a car's headlight at the same spot-- this is a beam antenna; A big difference, noticed, I'm sure. Its the increase in scattered, incidence rays that will be your ability to get a 2 metre signal over your hill. Your VHF signal will behave much like like that light beam.
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But I mention this as something to try, should the quarter wave itself prove insufficient. By all means, try that first, but keep in mind, that throwing a 7 db increased signal at that hill WILL make a difference.
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_____________________________________________________________
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You ask'd about how to ground your antenna. You'll get a tonne of advice from hams on this subject. As both a ham and one who works in stuff, I'll caution you to be chary. To that end, I've attached a copy of my recommendations -- peruse it with the same proviso....
.
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http://lightningsafety.com/nlsi_lhm/IEEE_Guide.pdf
.
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This publication is by the IEEE, an organization I am a member of. Remember too, that there is a big difference between grounding equipment for AC shock hazards, and grounding for lightning protection. That guide is written in a manner that makes this clear- and how you can effect a proper system for both.
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I think you'll do just fine- keep in mind that if something doesn't work out as expected, try out something else. Ham radio is a good percentage experimentation....
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.
.........................CF
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[oguruma]

I'm actually the one (my house, anyway) that is blocked by the hill. I live 100 feet up a 250 ft hill, so there's 150 feet (of elevation) of hill between me and, well.... the rest of the county.

The main repeater I have marginal signal to with an HT (outside). With my trucks 1/4 wave mag-mount antenna (located in my driveway) I have sufficient signal, but without full quieting. I don't have a base station rig, so if I want to work that repeater I have to do with X-Band via my mobile rig.

My goal is to 1) gain sufficient signal to work that repeater with full quieting. 2) increase my simplex range.

With respect to the height of the antenna, there is a house very close to mine, about 7 feet, and above mine in elevation. I would assume that getting it high enough to clear his roof would be advantageous.

I will have to think about issue of securing the ground wire.... I wanted to run it along to soffit to hide it, but I suppose that wouldn't be "as direct as possible".

If I am reading you correct, Ogur, you want to put your 2 metre signal into an area that might be blocked by a hill, Simply elevating your antenna, even one as simple as a quarter wave, may be sufficient. As far as gain is concerned, a 3, or 4 element beam will give you 6-8 dbs of gain, the equivalent of ~3 to 4 times increase in your transmitter's power. There are times when a higher angle of radiation is desirable- like radiating an HF signal out of a mountain valley (believe me, this I know... ) - but in your case, you want to put as much energy in the direction of your intend'd target as you can. A quarter wave antenna for its higher angles of radiation will not to be to your advantage.
.
An analogy- go out at night and shine a flashlight at a tall fence, and on the opposite side, from a distance, see how much scatter'd light is seen coming over it. That's your quarter wave-- Now direct a car's headlight at the same spot-- this is a beam antenna; A big difference, noticed, I'm sure. Its the increase in scattered, incidence rays that will be your ability to get a 2 metre signal over your hill. Your VHF signal will behave much like like that light beam.
.
But I mention this as something to try, should the quarter wave itself prove insufficient. By all means, try that first, but keep in mind, that throwing a 7 db increased signal at that hill WILL make a difference.
.
.
_____________________________________________________________
.

You ask'd about how to ground your antenna. You'll get a tonne of advice from hams on this subject. As both a ham and one who works in stuff, I'll caution you to be chary. To that end, I've attached a copy of my recommendations -- peruse it with the same proviso....
.
.

http://lightningsafety.com/nlsi_lhm/IEEE_Guide.pdf
.
.
This publication is by the IEEE, an organization I am a member of. Remember too, that there is a big difference between grounding equipment for AC shock hazards, and grounding for lightning protection. That guide is written in a manner that makes this clear- and how you can effect a proper system for both.
.
I think you'll do just fine- keep in mind that if something doesn't work out as expected, try out something else. Ham radio is a good percentage experimentation....
.
.
.........................CF
.
.
.

 

[lmrtek]

You can easily use a 10 ft section of 1.5 inch EMT conduit with a 5 ft tripod and it will be rock stable

gain omni antennas would likely be a poor choice and beam antennas also would be a poor choice unless tilted up in the air at a high angle

 

[oguruma]

You can easily use a 10 ft section of 1.5 inch EMT conduit with a 5 ft tripod and it will be rock stable

gain omni antennas would likely be a poor choice and beam antennas also would be a poor choice unless tilted up in the air at a high angle

So what would be a good choice? My original idea of the 1/4 wave omni?

Also, does anybody have any recommendations for a make/model of a rooftop tripod?

 

[SCPD]

I'd try the simplist first-- the quarter wave, --and go from there, depending on the results. Since you can get a usable signal now into the repeater you desire, but not as strong as you wish,- have you consider'd getting a 'brick?',,, an amplifier? (ie; Mirage brand)... If you're using only a HT, increasing the power 30-80, or more, watts-- plus they often have receiver pre-amps, may make the difference. If you are looking for omni direction coverage, at this stage stay with the quarter wave.
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.......................CF

 

[majoco]

All the theorising is good but - make yourself a 1/4 wave ground plane out of an SO239 connector, attach a feedline, tape it to the longest bit of plastic pipe you can, or even just garden canes, fix it to a fencepost or similar and connect your handheld - see what you get!

That's what I did with my Slim Jim, wandered around with the ground plane on a long bamboo pole until I found the "sweet spot" - now I get over 60 miles along the coast on 5 watts - bit scratchy though!