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Author Topic: Coax length for 5w HT use to roof mount antenna?  (Read 19873 times)

Posts: 37

« on: January 28, 2013, 06:50:39 PM »

I'm contemplating putting an antenna in the attic/roof to run down to my HT in the basement where I stay to use at max 5w... since I get scratchy signal depending on where I stand. I can't afford a dedicated basestation rig just yet, but I'm not sure about coax length limitations and antenna tuning etc. My mobile yaesu was plug and play kit with antenna and coax (dont even remember the length) and never did any adjustments on it but has worked fine. The only experience "tuning" was for my cb, which had a built in swr meter and tuning knob...along with a scew up/down tip on the antenna. basically you went to the center frequency, adjusted the knob until swr was minimum, then ran to the edge channels and repeated. if the swr was to high, you would just screw the tip in or out and try again and bring the levels down. there are no such features on my ht obviously, do i need a tuner to be able to hook up my ht to a line and external antenna? and does the radio have enough power to use it? I'm guessing I'd need about 75-100 feet of coax to get from the attic down, or maybe a little more if i have to put it on the roof because i would have to snake it out to a corner, up out and over to get there (not willing to drill holes on the roof at this point)

Posts: 3331

« Reply #1 on: January 28, 2013, 07:16:34 PM »

If you buy a commercially available amateur dual band vertical antenna, to 'match' the handheld you have, you won't need to adjust it nor use a 'tuner' in line.  Indeed, most of these antennas offer no means to make any adjustments, anyway.

However, the type of feedline you use, and its length, are of great importance.

At the frequencies you are using, typical coaxial cable is VERY lossy, and adding even a 50 foot section of certain types of it is just like eliminating the antenna.  

You should do an internet search for "coax loss" to learn more about this phenomenon.

Cables that exhibit low enough loss to run 75-100 feet at VHF and UHF frequencies will be relatively costly, indeed they can cost more than your radio.
You may find that running the antenna on the roof is not economically feasible.

Fortunately, you have other options, such as a small end-mount beam mounted on a short mast just outside the basement.  I would seek the the help of a knowledgeable ham in your immediate area, who can visit you and offer guidance and suggestions.  I used to live in NJ but not near where you are, however, there are certainly a lot of hams in the country's most densely populated state, and especially in a tech-rich area like where you are, you'll find plenty of local help.  For example ... try these guys, they are truly top-tier:
« Last Edit: January 28, 2013, 07:23:41 PM by KZ1X » Logged

Posts: 12619

« Reply #2 on: January 28, 2013, 08:21:40 PM »

Why do some "scare" the guy about coax loss here? No need to worry about it.  When dealing with a HT and its duck antenna, even a lossy cable with external antenna will well out perform a HT with duck in basement.  The guy is not doing EME moon bounce or weak signal DX. Even RG-8X will work fine here and be easier to route and place less strain on HT connector than a bigger coax.
« Last Edit: January 28, 2013, 09:11:49 PM by W8JX » Logged

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

Posts: 2409

« Reply #3 on: January 28, 2013, 10:12:32 PM »

You'll find the data of the suggested RG8X under
This specifies the loss as about 7 dB for 400 MHz at about 100 feet and about 3 dB on 2m.
Try to make the cable as short as possible and you should be fine.

Posts: 6252

« Reply #4 on: January 29, 2013, 05:24:25 AM »

Don't pay much attention to the gloom and doomers that try to discourage you from trying your thoughts.  The antenna on a hand held isn't a very good one to begin with, so if you do put a good antenna up and connect to it, any losses you would experience would more than be made up for by the antenna itself.  The only thing I would avoid is the use of RG58 cable for that long a run.  The use of a better quality coax would be much better for what you're attempting.  

If you want to, simply stick a short piece of pipe into the ground outside a cellar window and put the antenna on that.  Then you could use a piece of RG58--not longer than about twenty feet--and see what kind of signal you can get.  Even that would be much superior to a rubber duck antenna in the basement.

One last thought.  If you do put an antenna up on the roof and run a good quality coax to it (RG 8X or even RG 213) you could simply use that antenna when you do get your 'basestation' rig.  If you do use a heavier cable, using a short jumper of RG 58 would be advisable to prevent undue stress on the antenna connection of the handheld.  In that regard, putting up the roof antenna and a good coax would be investing in the future--something well worth doing.  73!
« Last Edit: January 29, 2013, 05:37:23 AM by K1CJS » Logged

Posts: 14491

« Reply #5 on: January 29, 2013, 05:46:09 AM »

There is effectively no loss in coax that is run vertical  Grin  Running it vertical means that you are getting the antenna up higher in the air and the signal you gain by the added height more than makes up for the loss in the coax to reach that height.

I'd put the antenna outside on the roof even if it meant an additional 20 feet of coax run. Use the lowest loss coax that you can afford, but even RG8X will be worthwhile.

Bob  AA4PB
Garrisonville, VA

Posts: 225

« Reply #6 on: January 29, 2013, 06:09:53 AM »

just like W2BCD I generally operate my HT from the basement for 2 meter FM which is the location of my shack.  I have a 50ft tower with a Cushcraft 5/8 wave 2 meter antenna on top fed with RG8.  Total length of coax is around 75 ft down the tower over to my pass thru panel and then into the basement.  Before the 5/8 wave went up, I used a home build J-pole encased in PVC tubing feed with LM400.  The LM400 was swapped out because of the installation of a rotor and I need something that would flex, which the LM400 does not do very well.


Posts: 510

« Reply #7 on: January 29, 2013, 07:38:10 AM »

For the best performance uou should put the antenna outside and as high as possible. With VHF/UHF you want to have an unobstructed line of sight to the other station/repeater and putting it higher means your radio horizon is farther out. With the longish coax you will want to invest in something that will have a relatively low loss and is very durable. I'd recommend LMR-400 or equivalent.  It's about $1/foot. You can buy pre-made cables with the connectors attached usually in increments of 25' or you can save money by buying the bare coax and soldering on your own connectors.

If cost is a problem, you can also save buy making your own antenna. A simple homemade 1/4 wave ground plane or j-pole with LMR-400 will perform better than a typical Diamond or Comet 2 meter antenna with RG8X with the length of coax you are suggesting.

Posts: 12619

« Reply #8 on: January 29, 2013, 08:35:16 AM »

If cost is a problem, you can also save buy making your own antenna. A simple homemade 1/4 wave ground plane or j-pole with LMR-400 will perform better than a typical Diamond or Comet 2 meter antenna with RG8X with the length of coax you are suggesting.

This is not true at all. A larger Diamond or Comet not only has higher gain but larger capture area as well and gain will exceed line losses too. They will far out perform a Jpole or 1/4 wave on LMR 400 even when using RG8x. Some get pretty anal about line loss but it is greatly over rated.  On a 100 foot run on 2m, RG213 has about 1 db more loss than LMR400 and RG8x about 1.5 db more than 213. Moral is get a decent antenna and do not worry about expensive LMR400 for FM repeater work.

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

Posts: 17477

« Reply #9 on: January 29, 2013, 09:11:06 AM »

That's either a very tall building, or a very indirect coax run, if it takes 75 - 100'
to get from the basement to the roof.  I'd suggest seeing if you can run it down
through a closet, where you can drill unobtrusive holes top and bottom and pass
the coax through out of sight.  If the roof really is up at least 50', then even a
simple antenna will work quite well.  (In fact, it may work too well, because
you may find that signals are so strong it causes intermod in your receiver.)

There is no "magic length" of coax.  Use the minimum necessary to reach from the
antenna to the radio, but don't worry about an extra 5 or 10 feet (which may come
in useful if you rearrange the shack.)  Many commercial antennas don't have any
provision for tuning, but some do, and you may find that the resonant frequency
shifts somewhat when mounted in the attic.  In that case, check with the local
radio club and borrow an SWR meter to check it.

Choice of coax is a matter of your personal trade-off between cost and signal
strength.  For weak signal work (typically SSB or CW) an extra 3dB of loss may
mean a number of stations you can't work, but FM is not a weak signal mode.
Once you have enough signal to hit the desired repeaters reliably, there isn't
much benefit in spending more money to upgrade your coax.

Just raising a 2m antenna from 5' to 20' provided 11dB of improvement in some
tests that I ran.  You'll probably get at least as much raising it from the basement
to the 5' mark, and at least a few dB due to the difference between a simple
ground plane and a rubber duck.  You can use RG-58, or even tiny RG-174, and
still come out ahead with a 100' length, and that is for only a 20' height.  If
the roof is higher, and/or if you can shorten the coax length, you'll see even more

That's not to say that RG-58 (or RG-174) is necessarily the best choice:  if you
have to go buy something, then RG-8X or RG-213 would be better.  But if you
are on a tight budget and all you have is RG-58, or 75 ohm TV coax, go ahead
and use it:  it will still be an improvement over your current situation.


Posts: 37

« Reply #10 on: January 29, 2013, 12:58:46 PM »

Alot of great info in there thanks all.

Well I'm only getting sketchy signal strength because I'm in the basement... so I don't think I'd need all that great of a location, I just figured the roof would be the highest line of sight. my house is strange. the front faces east, and i'm less then a half mile from the ocean so there wouldnt be anything of interest comming from that direction. I'm sure from the roof thered be a nearly clear line of sight to ny/long island area... during the summer on ht's i can pick up fire/police/ems some days ground level.

anywho, from street level the driveway goes up about 10 feet verticle until it reaches the basement level, but other then the driveway wall and 4 ground level coal windows, the entire basement level of the house is under ground. the main level of the house i get decent signals from, depending on where you are, you might get a hiss of static say if the walls and the kitchen refridge or whatever is in the way...BUT the back yard then goes up another 15 feet or so until its ground level again, so signals from the west in the basement are almost nill from the basement, somewhat staticy on the first floor. the roof goes up another 8 feet or so from the top of the first floor, so probably from the very top of the roof, is really only a few feet above ground level from the west.

Looking due south from the north side at a crossection of the house, (roughly accurate, x's are dirt):

                                      /         attic                   \                                ___________
                                     |---------------------------|                                 /xxxxxxxxxxxx  20'
                                   _|____________ first floor|             _________/xxxxxxxxxxxxx  15'
                                 /X|____basement level____|deck|    /xxxxxxxxxxxxxxxxxxxxxxx  10'
                   ______//XX <-stairsXXXXXXXXXXXXXXXXXXXxxxxxxxxxxxxxxxxxxxxxxxxx 5' up from street level
---street----/xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx street level maybe 25' above sealevel?

Where my computer and couch are pretty much in the middle of the basement, so I'd have to run the coax up to the ceiling then over to the outside wall on the south side and run it outside (existing tv cables come in there anyway so no new hole through cinderblock necessary) then either up to the roof, or up and into the outside vent window into the attic. To run direct to the attic would be challenging to do, it would go up to the ceiling, then back and around into a closet, then up into the kitchen behind a refridge, then down to the other closet, then up along ac ducting into the attic. the line length to the roof from outside would probably be shorter by a few feet then snaking it up... but not by too much, but then it would also be running near some electrical lines and the refridge motor if that is an issue. thats why i was considering the roof more then the attic, but wasnt sure how much signal loss works over coax.
« Last Edit: January 29, 2013, 01:01:40 PM by W2BCD » Logged

Posts: 37

« Reply #11 on: January 29, 2013, 01:04:21 PM »

hmm diagram looks fine on my end but from the forum view it comes out screwy. the right side is the back yard. the ground level in the back is about eye level if you are standing in teh basement, goes out about 10 feet where we have a deck, then goes up another 5 feet, is level for a bit, then goes up another 5 feet is level for abit, then goes up about 5-10 more feet until it levels off with my neighbors yard at roughly the 20 foot mark above street level. so an antenna on the first floor level would still be below ground level west, with nothing but trees and houses north and south for about a block then would still be over most homes in line of sight all the way to NY and no idea how far south... and a clear shot over the ocean to the horizon. on the roof it would be clear sailing east, north and south, but it would only be a few feet above ground level looking west. if it were in the attic, same storey but maybe only a foot or so above ground level west.
« Last Edit: January 29, 2013, 01:07:46 PM by W2BCD » Logged

Posts: 815

« Reply #12 on: January 29, 2013, 01:24:16 PM »

If you had a choice, you should have obtained a mobile radio and power supply.
This would have all but eliminated the coax issue with the power the radio would have at up to 50 watts.
No battery upkeep etc.
A good dual band antenna will allow you to get into more area repeaters and coax length would no longer be an issue.
Good luck.

Posts: 37

« Reply #13 on: January 29, 2013, 01:53:29 PM »

Don't get me wrong, I have a mobile in my truck and I love it, but I'd also like a base station at home, but I don't have the $1200ish to do it with just yet. And I figured since I'd need to put an vhf/uhf up there for the base station then I might as well make that my first purchase and reap the benefits of being able to use it with my ht in the meantime.

ps. I completely forgot while making my nice little diagram lol to mention that the 2 repeater system's I use most often, and most of the public emergency stations I listen too all "almost make it" into the basement... so if there would be any gain from a good antenna in the attic/roof with that long a line to the ht it would still accomplish my short term goal. i just wasn't sure if it were possible at all with an ht and that long a line.

since i'll eventually be using the same antenna/coax for the base station in a few months when i can afford one (I have a lot of hobbies pulling my wallet at once right now lol) I think I could pony up for a coax that will be good quality if someone could recommend a type for that length? i've never soldered so making my own is out, I'm not a fan of that side of the hobby anyway so I wouldn't even really be interested... hence also no interested in strining up my own antenna Smiley


Posts: 37

« Reply #14 on: January 29, 2013, 02:24:30 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!
« Last Edit: January 29, 2013, 02:40:07 PM by W2BCD » Logged
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