Lower Antenna height or Longer Antenna Coax?

[Kugellager]

I am planning a basic base station for my home and am trying to determine the best location for my antenna on my roof.

 

My house is is a standard suburban neighborhood with rolling hills for terrain. It is located in a lower spot in the terrain. I will be using a simple 1/4-wave ground plane antenna fed by LMR-400 for now. I have two locations where I could put my antenna. One location would put the antenna at about 22 ft AGL fed by about 20 ft of coax. The other location would be at about 26 ft AGL with about 55 ft of coax.

 

Which would be better as far as signal range?

 

Or maybe more basically, will the roughly 1 dB of signal loss, due to the 35 more ft of antenna cable, negatively affect the signal range more than getting the getting the antenna 4-5 ft higher above the ground?

 

Thanks,

John

];')

[Radioguy7268]

If you plan to use your "base station" to hit a repeater, there is little benefit to be gained by placing it higher. As long as you can clearly and consistently reach the repeater, your height matters little.

 

If you truly intend to use the radio as a stand-alone base station, speaking directly to portables (or mobile radios in a vehicle) on the same frequency, then height is might. In reality, 4 foot of height is not going to greatly increase your range. You'll be lucky to see 1 extra mile of coverage radius in rolling hills terrain.

[Lscott]

 

Or maybe more basically, will the roughly 1 dB of signal loss, due to the 35 more ft of antenna cable, negatively affect the signal range more than getting the getting the antenna 4-5 ft higher above the ground?

Plugging in the height numbers into this online calculator:

 

http://www.hamuniverse.com/lineofsightcalculator.html

 

shows the difference in range is around 0.5 miles, distance to the horizon, more at the higher elevation. If you were located in an area that was flat its not much of a change. However you're in a bit of a depression so anything you can do to get the antenna higher will be beneficial and a reasonable trade off for a bit more coax loss. At some point you'll likely go for an antenna with some gain which will make up for the extra 1db of coax loss.  

[WRAK968]

The only issue I see with the lower elevation is, what parts of your house are going to block the antenna in which direction. By installing it in the lower part of the roof you affect the RF radiation pattern. This could mean less range in the direction blocked by bits of the house. Your best bet in my opinion, would be to make it the best of both worlds.

Purchase a 5-6' length of metal pipe. It should be at least 1" round and rated for outdoor use or painted once installed. Mount the pipe where you planned to mount the antenna, then mount the antenna to the pipe. The entire project, including clamps and hardware shouldn't be more than $50. This would give you the extra 5-6 feet in height without needing to add 25' of coax.

Also if you wish, you could likely increase to a 10' long pipe, but, I wouldnt go much higher due to the risk of it being blown down and damaging the house.

[axorlov]

For 5' mast the TV mast section can be used. Can be found in Home Depot or Lowes in electrical section next to TV coax. They are 3/4" and quite robust.

[WRAK968]

For 5' mast the TV mast section can be used. Can be found in Home Depot or Lowes in electrical section next to TV coax. They are 3/4" and quite robust.

Not all base antennas can be secured to a 3/4" pipe though. And depending on the antenna they use, the 3/4" could bend in higher winds which is why my go-to is 1-1.5" 1/8" thick galvanized pipe. Its heavy, but it works and lasts.

[Kugellager]

Thanks everyone for the comments and info. I am primarily a dx'er of various bands and have done a lot of diy to satisfy my antennas needs. I have used and experimented with all sorts of materials for masts and antenna construction, tilt-over masts etc.

 

I will either be attaching this to a well secured/supported, but abandoned, 2" copper plumbing vent  (house remodeled but vent left) adjacent to the peak of the roof for the potential low position, or for the high spot, on the 2 ft mast pipe for a 4-bay TV antenna secured to my chimney.

 

@ Radioguy7268 ...I Actually do want to use it as a base station. I'm not into  using them on repeaters - at least for now.  I get about 1.5 miles max usable distance from handhelds now, which barely makes it to my daughters school. My goal is to get another 1/2 mile to mile of range (more would be icing on the cake) as it would cover both of the kids' schools and a lot more of the daily back and forth we use them for now.

 

@Lscott ...That calculator is great...I'm surprised I never stumbled over it before.

 

@ WRAK968 ...Either location will not be blocked by my house but will, at a minimum, get it to even with the top of the roofs of most of my neighbors. I already have lots of materials for masts etc. Just need to place it in the best spot. I plan on going about 5 ft above the roof line even with the lower spot - I don't want it to stick out too much. No home owners association but want to not make too much of a spectacle. Also, the antenna weighs only about 6 ounces...even with the winds we get here there should not be much load.

 

Thanks for all the good information. I'll post back with what I finally do and maybe post a video of it on my YouTube.  Also, I won't be replying to everyone with every post I do...just did this time because I am new to this group etc.

 

John

];')

[Kugellager]

I just realized I never posted the final configuration of my base station antenna.

 

I ended up building a tilt-over mast with a simple 1/4-wave ground plain up at 27ft AGL fed with about 55ft of DRF-400 coax running to the radio. I have tested the base to HT range with my Midland GXT 1050's and can get at least 5 miles to the HT if I am not in a low spot. I have also been able to hit a repeater over 50 miles away that was LOS. I also am able to hit my local repeaters in my local Front Range GMRS group.

 

So basically I did my research online, took excellent advice from this group, did my calculations and that, with a little bit of luck, managed to exceeded my original requirements.

 

EDIT: Added a photo I neglected to the other day.

 

John

];')

[axorlov]

Awesome!

[mpoole]

Nice!  I'm in a mountainous area at 2150 ft running a 50 watt radio.  Because of a ridge interference that is 40 ft higher than my antenna I can't reach 1/4 mile in that direction.  As such I'm moving my repeater to a neighbor's work shop that is 120 higher than I am.   So yes, the higher the better.

[AdmiralCochrane]

Nice!  I'm in a mountainous area at 2150 ft running a 50 watt radio.  Because of a ridge interference that is 40 ft higher than my antenna I can't reach 1/4 mile in that direction.  As such I'm moving my repeater to a neighbor's work shop that is 120 higher than I am.   So yes, the higher the better.

 

Gotta get more people to understand this concept. This is the reason I am not putting up a repeater, my location is weak - and with UHF, its all about height over all terrain within sight.

[Kugellager]

Gotta get more people to understand this concept. This is the reason I am not putting up a repeater, my location is weak - and with UHF, its all about height over all terrain within sight.

I get that myself...which is why I can get that repeater I mentioned over 50 miles away with my base station @25W. It's located at almost 7100 feet and I am at just under 5100 feet with no obstructions in-between - classic LOS UHF radio wave propagation example.

 

Another less understandable (to me) question about of radio propagation is If mpoole can't get 1/4 with only a 40 ft ridge running interference with his 50 watt rig; how come I can get nearly a mile with two HT (HT to HT @ 2w) with a 60 ft+ ridge in  between? See elevation profile below. Situation is from my house in a suburban neighborhood with trees etc. to a park on the other side of the ridge. Signal reception to park is decent to excellent. House is at 5473 ft and reception is at 5506 ft on other side of ridge in park.

 

John

];')

[mbrun]

If you watch the following YouTube video you start to get a clearer picture of what line of sight without obstructions can do for your UHF range. Here the users are demonstrating 27km range using a handheld .5 watt radio over in Europe. Their elevation comes from being high on two opposing hillsides.

 

 

One thing I have come to realize much better is that it is not just sufficient to get the antenna above nearby obstructions but you must also get it above a good percentage of all obstructions between the transmitting and receiving antennas. While the signal might be fully blocked by a hill abruptly, it does pass through and around foliage and many other obstacles but indeed it is attenuated by them. Place a good stand of trees between those same set of radios used in the video demo above and you suddenly you find yourself at .5 miles while the radio horizon might actually be 6 miles.

 

In some recent modeling that I did (and already shared) using an online coverage calculator I was able to see first hand that modest increases in height can be met with insignificant range improvements, even over mostly level terrain. Whereas when I modeled a doubling or quadrupling of antenna height I observed more appreciable increase in coverage.

 

When there are no obstructions, radio range is mostly affected by the radio (antenna) horizon. When you are above the horizon, the rest of the real-world’s obstacles placed in your way are your enemy.

 

Michael

WRHS965

KE8PLM

 

 

Sent from my iPad using Tapatalk

[gman1971]

+1 to mbrun.

 

Also, remember that radio is a SNR game, or a Signal to Noise Ratio game.... sometimes the Signal might still be there, faint, but masked by the overwhelming Noise... much like light pollution under the night skies hides the fainter nebulae, stars, etc... you throw an H-Alpha filter, and all of the sudden the faint wonders of the night appear much clearer...  same with radio.

 

A few feet higher might not make the range noticeable better, but it seems to make the current link quality a bit better... and sometimes every bit counts.

 

Also, remember that not all antennas radiate perfectly towards the horizon, there are nulls on the radiation pattern, both vertical and horizontal... and problems with grounding, problems with feedline, etc... they all introduce nulls on the pattern. So if a subscriber is in one of the antenna nulls will have the same effect as being behind difficult terrain.

 

Wish I lived in a place with no obstructions... with no angry RF firebreathing broadcast 1400 foot towers... 

 

G.