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Author Topic: Coax length for 5w HT use to roof mount antenna?  (Read 19884 times)

Posts: 17479

« Reply #15 on: January 29, 2013, 02:47:18 PM »

And there are even more types than that, they just aren't as common in ham use.

The most likely types are RG-8X, which is about 1/4" in diameter, and the
RG-213 / RG-8 / LMR-400 types which are about 0.4" in diameter.  The larger
types have lower losses:  VK1OD's transmission line loss calculator includes
all of them, so you can make your own comparisons:

You'll find RG-8X listed as "Belden 9258":  it is more flexible and will fit through a
smaller hole.

Roof would probably be better than attic if you have a place to mount it, because
the signal doesn't have to pass through the roofing material.  (In some directions,
at any rate.)  You also may be able to go higher, while you don't have to worry
as much about weatherproofing an antenna in the attic.  But if the coax is going
to run outside anyway, putting it on the roof saves having to bring it back inside
the building.

A 36' telescoping mast with an antenna on top attached to the side of the house
might be a good starting point if you don't have other convenient roof access
and/or mounting points.

Posts: 12621

« Reply #16 on: January 29, 2013, 04:07:38 PM »

And wow... there are so many types.......

I got a chance to measure... at bare minimum if I go stright outside then stright up to the corner of the roof at the highest peak would be 66 feet, given a few feet to account for droop, angling, hiding the cable inside I guess I'd be grabbing a 70 foot or 75 foot roll and having the ends installed or giving it a go myself. Recommendations for the minimum recommended, suggested, and best scenerios off of that list so I can get a price estimate at what I'm looking at? Thanks all!

The shorter that run the less line loss with any coax. I would still suggest RG8x here and install your own connector on at least one end and this will simplify routing and you could even terminate one end with a connector native to HT if you want. I would also suggest drilling a hole through wall if path is shorter. It is not really a big deal and will not effect home value. If you use RG8x you can even drill through mortar between blocks to pass coax through. 

Ham since 1969....  Old School 20wpm REAL Extra Class..

Posts: 6252

« Reply #17 on: January 30, 2013, 09:34:48 AM »

AA4PB---The suggestion to stick a pipe in the ground outside with an antenna on it was to see what kind of an improvement it would be against a simple rubber duck antenna.  That suggestion was not meant for use as anything permanent.

Posts: 48

« Reply #18 on: January 30, 2013, 12:24:54 PM »

Here is what I would do if I were you. See if you can find a ham in the area who could loan you 75 ft of known good coax. Decide which antenna you want and buy it. Hook the antenna and HT to the borrowed coax. Take your antenna and HT to various locations where you might install it. Try it and see how it works. You don't need to be in the basement to try this out as long as the HT is connected to the coax. Try some different spots, including the basement. Since you aren't using the rubber dummy load now (HT Ducky) what you get by moving everything around will be pretty close to what you get when you finally route the cable and go through the process of snaking it to your antenna. The antenna may be affected by nearby objects, metal and otherwise, but with 5 Watts that won't be a problem while you are testing locations.  Have access to an extension ladder or extendable painter pole? Temporarily mount your antenna to the pole or ladder and run it up. You should be able to experience the improvement that higher elevation brings if your initial received signal is iffy at the ground level. If you get a location that works, note what kind of coax you have borrowed. If it works, and it probably will, it's good enough.  Buy that type or better when you are ready to do your installation. If you do something like this I guarantee that you will learn something about antenna placement. I love learning by doing.

Have fun, but make sure you have a cover story when your neighbors ask what you are doing waving that stick around.


Posts: 23

« Reply #19 on: January 31, 2013, 08:53:31 AM »

I like the idea of at least trying to simply get the signal outside via the basement.  You may be surprised that just getting it outside of the walls is all you need.  Obviously you can test this with an HT.  If you stand where the antenna might be right off the ground but outside , how is your signal strength? 
« Last Edit: January 31, 2013, 08:59:23 AM by WQCC256 » Logged

Posts: 70

« Reply #20 on: February 03, 2013, 09:27:50 PM »

I was in the same situation, kind of.  My house is a bi-level.  The lower floor is half underground in the front but walks out to ground level in the rear.  In my lower level shack my dual-bander HT was lacking.  On a whim, I bought a Radio Shack dual band antenna and a cheapo 20' piece of 50 ohm coax from the same place.  This was enough for me to get the (cheapo) antenna clamped to my deck rail (on the upper level) and into my shack to the HT. 

It was like night and day.  I could hear repeaters I didn't even know were there.  The idea is; do you need the Cadillac setup or something to improve on what you have?  I opted for the later, which has since been replaced, but provided a means to have some fun. 

That said buy decent coax, consider building and antenna, and get the antenna as high as you can. 

Posts: 2567

« Reply #21 on: February 04, 2013, 06:14:28 AM »

This can be made out to be so complicated and that just scares people off.

The references the original poster made was regarding reception (scratchy signals, ergo poor receiver signal levels). It does not matter if he has an HT, mobile or base station radio. If he is non-line-of-sight and working off of reflected/refracted signals to his antenna then the only things that will help him out are height and system gain.

Poor receive signal levels are never corrected with more transmitter power on your part.

Losses due to feedline are negative gain factors. A good antenna is a positive gain factor.

Any HT on a "duckie" is going to be with a negative gain. Most duckies are on the order of -3 to -6 dBi and with their operating position (next to your head, not vertical, etc...) this is even worse.

If an extra 10' of coax will get you another 10' in the air then whatever feedline losses you encounter are more than offset by an increase in your line-of-sight distances to the radio horizon. There is a practical limit to this; assuming there is no terrain your radio horizon is;

10' height        4 miles
20' height        6 miles
30' height        8 miles
40' height        9 miles
50' height      10 miles
60' height      11 miles
70' height      12 miles

This assumes that the receiving site at the other end is at ground level (0 feet) if they have height then the two radio horizons are added to give a much longer path distance (example, you at 30', the repeater at 50', (8+10=18) 18 miles point to point line-of-sight).

Usually someone is higher up, a repeater mounted on a tower on a hill. All of that needs to be taken into consideration, also any terrain that may be blocking you in the middle (path profiles at VHF/UHF) and other weird things like Fresnel zones, knife edge refraction (do not worry about that now).

Any sort of outdoor antenna at height is better than an HT duckie. Get in the air and get "on" the air.

Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
Free space loss (dB) = 32.4 + 20 × log10d + 20 × log10 f
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