Need Help with 2 Meter J-pole Antenna Placement

Cressida81 · Nov 24, 2014

I am trying to decide where to put a 2m antenna on my house for my 5w handheld base station.
I was given the J-pole for free so that is the antenna I will be using. I'm sure there are better antenna options but this is the one I'm set on because its the one I already have. Along with the antenna I was given about 40 feet of cable (mostly something thicker than rg8, and then the last 13ft segment is rg8u).
See the attached picture. They've all got pluses and minuses. I am inclined to go with option 1 because it can be done now.
Option 1 - Have enough cable to do it now, doesn't require a taller ladder, very short run. Downsides are that its not very high. Better than inside but it is worth the effort?
Option 2 - High location, don't need a taller ladder. Downsides are that I need more cable, needs to be very thick and expensive cable because its running VHF.
Option 2 - Have almost enough cable, shorter run means can buy higher loss cable, High location. Downsides are that I don't have a tall enough ladder to mount something there and will also need to purchase more cable.

Any ideas or suggestions? The mount point will likely be an old Satellite Dish mount (j shaped thing).

prcguy · Nov 24, 2014

Option 3 looks best to me and since it takes the least amount of coax for reaching the roof top. You can lay on the roof and install the satellite mast (its called a J mount) to the rafters at the roof peak. If you have any roof overhang you can usually screw the J mount on the roof in that area since the overhang will not leak into the house.

You should also ground the antenna/coax to code but I see your AC panel is probably on the east side of the house opposite the radio room. You should be able to ground to the air conditioner on that side of the house but its not as good as the AC panel.
prcguy

w2xq · Nov 24, 2014

Option 3. Looks like you'll clear houses around you. But do it right with a single run of good-quality coax since you are running just 5w. A short jumper should help avoid flexing the radio connector. Plenty of discussions here about coax choices vs run lengths; don't forget waterproofing connections and a drip loop. I wouldn't put an antenna on a chimney that vents smoke or gases. HTH.

popnokick · Nov 24, 2014

Definitely Option 3 for all the reasons already cited in other posts. Also:
- How old is the "40 feet of cable (mostly something thicker than rg8)"? Is there ANY chance that coax has seen severe service, e.g. kinking, splits, water ingress, corrosion, etc.? Give serious consideration to replacing it with new, known good 50 ohm low-loss coax and new connectors. It will help your 5W go farther.
- Based on what I've read, j-poles will tend to couple RF back into the coax shield and radiate from the shield/outer conductor. Use a balun at the base of the antenna to prevent that.

K5MPH · Nov 24, 2014

number 3 looks the best the less coax you use the better...............

cmdrwill · Nov 24, 2014

popnokick said:
- Based on what I've read, j-poles will tend to couple RF back into the coax shield and radiate from the shield/outer conductor. Use a balun at the base of the antenna to prevent that.

Correct, better than a balun you may use a ferrite choke on the coax just below the J pole. The ferrite choke needs to be for 146mhz, and they do make clamp on types too.

AK9R · Nov 24, 2014

From an RF standpoint, location 3 is probably the best. Up high with a shorter run of coax than location 2.

However, you also need to consider grounding and lightning protection. The National Electric Code says that any aerial needs to be bonded to a ground rod and that ground rod should be the same as the electric service ground or bonded to it.

I am not going to give any further advice on the topic because hams like to debate proper grounding techniques, but I will toss something out for you to consider. If you put the antenna at location 1, and that still gets the antenna high enough to reach your local repeaters, then your antenna will be less of a lightning rod. Food for thought.

hhrj · Nov 24, 2014

I vote #3 for all the positive reasons stated before....
HHRJ

Cressida81 · Nov 25, 2014

#3 sounds like a winner. Found out my neighbor Ham has an extension ladder. So I'll be able to get up there. He's got some serious lightning protection on his 50 ft tower and hasn't been hit in the several years he's had it. We've got a lake 100 yards away from us so that might be why. He said I didn't need to worry about grounding it... but I think thats not a great idea.
Yes, the AC panel is on the other side of the house so the house's grounding rod is about as far away as it can be. The fence posts are metal, or I could hammer a rod into the ground, not sure I can manage an 8ft rod though, a few feet maybe.

Please give me some suggestions between code and practicality.

Also a suggestion for cable thats less than $1/ft to use for VHF on this run (probably 40-50ft plus possibly an extension going around the room to my desk (the desk is not RIGHT at the window there, its on the other side of the room (making the run an additional 6-7 feet).

w2xq · Nov 25, 2014

I haven't needed to buy coax in many years, but the last was Belden 9913. RR has many discussion threads on coax. Take a read through. Assuming you are an ARRL member, sift through back issues of QST (available on line) for articles and advertisers. Bottom line: don't necessarily go cheap on cable, waterproof your connections, and use quality connectors. It is easier to do an installation properly the first time rather than redo it every few years. YMMV. HTH.

Cressida81 · Nov 25, 2014

I've read many many discussions on cables... Seems like a different answer half the time. Or too many answers all of which are varying degrees of "right".

Cressida81 · Nov 25, 2014

I'm leaning towards rg8/rg213 as it seems like an ok compromise on price, flexibility, and loss for the 40 foot run.

wucherer · Nov 25, 2014

Coaxial Data

RG-8/U db per 100 feet - source from belden
30 MHz - .57
50 MHz - 1.2
100 MHz - 1.8
200 MHz - 2.7
500 MHz - 4.7

RG-213/U db per 100 feet - source from - universal radio
30 MHz - 1.2
50 MHz - 1.6
150 MHz - 2.8
220 MHz - 3.5
450 MHz - 5.2

Do you know when you add in-line any adapters there is a loss of 0.3 db per each too. Also re-thinking option 3 would be the greatest optimal point and remember HEIGHT is your best friend so the higher you go with the antenna within the 100 foot range since your concerned with db loss. 73 de N2OBS

Cressida81 · Nov 25, 2014

2meter fm voice. So around 144-145mhz.
5w handheld for now. Possibly 8w or 50w mobile if Santa is nice to me this year (can't decide if I got a 50w mobile if I would put it in the car replacing the 8w or keep it inside as a base).

Open stub jpole so hopefully a little gain there.
40-50ft run hopefully no longer. I'm a terrible judge of distance so I might be over estimating it.

Cressida81 · Nov 25, 2014

So based on my information and using the http://www.saarsham.net/coax.html page
I've got ( i put in a 1.1 swr because I'm not expecting a perfect 1:1.5)

Online Coax Cable Loss / Antenna Gain Calculator
For Belden 8237 (RG-8)
================================================
Cable Loss per 100 ft at Operating Frequency = .93 dB

Cable Length = 40 Ft.

Calculated Loss = 0.4 dB

Power into Cable = 5 Watts

Power out of Cable = 4.6 Watts

Gain of Antenna = 1 dBd

ERP of Antenna System = 5.8 Watts

Calculated 11/25/114 at 3:10:45 PM

I also put a 1db gain from the j-pole because while some people say its got a 2-3db gain I'm going to knock it down a notch for worse case scenario.

That all being said it looks like Belden 8237 (RG-8) would work out ok, I at least wouldn't be losing power.

prcguy · Nov 25, 2014

If its a store bought J pole and made well it has 0dBd gain at best and if its home made then make it a little negative like -1 or -2dB because you don't really know if its resonant or tuned right. Assume a worse VSWR so make that 1.5 or 2:1. Although this only tweaks the outcome a little I like to input more realistic info over wishful thinking.

All you need now is distance to local repeaters, repeater antenna system info, obstructions, fresnel zone clearance info and you can predict what you can talk to. Well, sort of.....
prcguy

Cressida81 said:
So based on my information and using the Coax Calculator page
I've got ( i put in a 1.1 swr because I'm not expecting a perfect 1:1.5)

Online Coax Cable Loss / Antenna Gain Calculator
For Belden 8237 (RG-8)
================================================
Cable Loss per 100 ft at Operating Frequency = .93 dB

Cable Length = 40 Ft.

Calculated Loss = 0.4 dB

Power into Cable = 5 Watts

Power out of Cable = 4.6 Watts

Gain of Antenna = 1 dBd

ERP of Antenna System = 5.8 Watts

Calculated 11/25/114 at 3:10:45 PM

I also put a 1db gain from the j-pole because while some people say its got a 2-3db gain I'm going to knock it down a notch for worse case scenario.

That all being said it looks like Belden 8237 (RG-8) would work out ok, I at least wouldn't be losing power.

jim202 · Nov 25, 2014

Do not under any circumstances ground the antenna or coax cable to your air conditioner. If you do any research of the NEC (national electrical Code) grounding section 250, you do not daisy chain devices for grounding.

I am not sure where your located, so can't even guess what type of soil you have to try and drive a ground rod into. It is not that hard to drive an 8 foot ground rod in normal soil. If you have hard pan that's a whole different story. You could try making a small hole in the ground and filling it with water for several days to soften the soil.

Locate a good sized sledge hammer and use it to drive the ground rod. It would work better if you had someone holding the ground rod while you try to pound on it.

The use of a # 2 solid wire is the best selection to use for ground wire. Make sure you use a compatible grounding clamp to secure it to the ground rod. Lowe's and Home Depot should have several to select from.

You might also check with your home insurance company on grounding antenna systems. They are the ones with the final decision on paying any claim. They also have some good information for the most part. But, depending on the company, you may or may not find them easy to work with on this subject.

prcguy · Nov 25, 2014

A home run wire to the main electrical panel ground is best and there are maximum distances and wire sizes stated for that. If a short direct path is not available to the main electrical panel, NEC allows antenna ground connections to things like a nearby metallic conduit that has a home run to the main panel. The OPs nearby air conditioner may allow for this and NEC Article 810 covers antenna grounding.

Any additional ground rods must be bonded to the main panel ground with no less than #6 copper wire and possibly larger depending on distance, per NEC.

#2 wire is not the best selection for grounding, it depends on the distance and other factors. My last job required 500MCM stranded for all ground connections and that's about 3/4" diameter without insulation.

Checking with a VP friend at one of the largest insurance companies, they have never denied a home claim due to any grounding or wiring issues.

BTW, even though I was certified by SCBA as an instructor for antenna installations, I will not tell anyone on a public forum how to ground anything beyond the NEC.
prcguy

jim202 said:
Do not under any circumstances ground the antenna or coax cable to your air conditioner. If you do any research of the NEC (national electrical Code) grounding section 250, you do not daisy chain devices for grounding.

I am not sure where your located, so can't even guess what type of soil you have to try and drive a ground rod into. It is not that hard to drive an 8 foot ground rod in normal soil. If you have hard pan that's a whole different story. You could try making a small hole in the ground and filling it with water for several days to soften the soil.

Locate a good sized sledge hammer and use it to drive the ground rod. It would work better if you had someone holding the ground rod while you try to pound on it.

The use of a # 2 solid wire is the best selection to use for ground wire. Make sure you use a compatible grounding clamp to secure it to the ground rod. Lowe's and Home Depot should have several to select from.

You might also check with your home insurance company on grounding antenna systems. They are the ones with the final decision on paying any claim. They also have some good information for the most part. But, depending on the company, you may or may not find them easy to work with on this subject.

prcguy · Nov 25, 2014

And another thing, use a slide hammer to install a ground rod most of the way then maybe a sledge hammer for the final foot or so. It's nearly impossible to hit the end of an 8ft ground rod when first pounding it in.

You can make a ground rod slide hammer from 1 to 2ft of 1/2" steel water pipe threaded on both ends, a screw on pipe cap, a large pipe flange and some weights from an old barbell set.

Place 10 to 30lbs of barbell weights on the pipe and screw on the pipe cap and flange. Its best to also put some metal washers up inside the pipe cap so the ground rod doesn't blow out the top of the cap.

Place the pipe flange side over the ground rod and slide the weights up and down to pound the rod in.
prcguy

jim202 said:
Do not under any circumstances ground the antenna or coax cable to your air conditioner. If you do any research of the NEC (national electrical Code) grounding section 250, you do not daisy chain devices for grounding.

I am not sure where your located, so can't even guess what type of soil you have to try and drive a ground rod into. It is not that hard to drive an 8 foot ground rod in normal soil. If you have hard pan that's a whole different story. You could try making a small hole in the ground and filling it with water for several days to soften the soil.

Locate a good sized sledge hammer and use it to drive the ground rod. It would work better if you had someone holding the ground rod while you try to pound on it.

The use of a # 2 solid wire is the best selection to use for ground wire. Make sure you use a compatible grounding clamp to secure it to the ground rod. Lowe's and Home Depot should have several to select from.

You might also check with your home insurance company on grounding antenna systems. They are the ones with the final decision on paying any claim. They also have some good information for the most part. But, depending on the company, you may or may not find them easy to work with on this subject.

Thayne · Nov 25, 2014

The NEC says 6 AWG copper is the largest needed for a manufactured grounding electrode, (unless you have something free laying around)

Need Help with 2 Meter J-pole Antenna Placement

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