Base antenna height

[scan18]

I have probably a dumb question for the antenna experts out there as it relates to base antenna height above ground level.

I live an a mountainous area where elevation changes quickly over short distances. My house is at roughly 1,000 ft. ASL and down the street from me it gets down to about 800ft. ASL or so and even lower.

Theoretically, if my antenna is mounted only 10ft. above the ground (obviously not ideal), and someone down the street from me has the exact same equipment but with the antenna mounted on a 50 ft tower, who would get the better range? Again, considering exact same radio, antenna, coax, etc.

Would I get the better range because my antenna is still at a higher elevation? Or would the person down the street get better range because their antenna is mounted at a more ideal height above ground level?

This is mostly just for my own curiosity.

Thanks!

 

[doctordialtone]

Would I get the better range because my antenna is still at a higher elevation? Or would the person down the street get better range because their antenna is mounted at a more ideal height above ground level?

As always, it depends, but generally the antenna that is the greatest height ASL has the advantage.

It depends on surrounding terrain and foliage and structures.

Generally, whichever antenna has the best (and shortest) "view" of the receiving antenna has the advantage.

The exception would be in the case of DX. Please refer to this website for more:
Propagation

 

[scan18]

Thank you Dr. , makes sense.

 

[doctordialtone]

Thank you Dr. , makes sense.

You got it!

 

[KC5AKB]

Great Question

 

[k7ng]

Very interesting question.
The answers you get will probably be more or less 'the higher the better'... but that rule of thumb works best when talking about AGL, not ASL.
In general, 'height above ground' matters more than 'height above average terrain' assuming your interest is within a few miles' radius.
Type of antenna matters somewhat...
But 'down the street'... is that 100 yards or 2 miles?

Beyond a few miles, there are many more factors in the mix that might affect results.

Sorry, but that question can be answered only in generalities and approximations without a lot more information and Sentence 2 will still be most germane, regardless.

 

[scan18]

Very interesting question.
The answers you get will probably be more or less 'the higher the better'... but that rule of thumb works best when talking about AGL, not ASL.
In general, 'height above ground' matters more than 'height above average terrain' assuming your interest is within a few miles' radius.
Type of antenna matters somewhat...
But 'down the street'... is that 100 yards or 2 miles?

Beyond a few miles, there are many more factors in the mix that might affect results.

Sorry, but that question can be answered only in generalities and approximations without a lot more information and Sentence 2 will still be most germane, regardless.

Yes, all good points. The street I am on is fairly steep, so I’m thinking in the couple hundred yards range maybe less. So the general topography would be the same, other than the difference in altitude.

 

[spongella]

Not a dumb question at all, a very basic and excellent one. Replies were excellent too. Not sure if the CB regs still limit antenna height, may want to check that just in case, but at your elevation you are at a definite advantage.

 

[jim202]

Let me go into more detail on some of the issues. Let me start with the house. The type of contsruction comes into play here. If it is a total wood frame house, then your doing good and it won't have that much of an effect. But it will depend on the siding on the house and they type of insulation in the walls. Metal siding on the house will kill or hinder good reception. if you have aluminum backed foil insulation in the walls, that will be a problem. if you have a metal roof, that will be a major problem.

Going into the issues of trees, the worst type to have around is pine trees. This really comes into play as you go south and get into the long needle pine trees. They just kill reception at the 700 and 800 bands.The needles are just about resonant at those frequencies and they kill being able to have good reception through them.

So much of the issue of height depends on the structure construction materials and what frequency your looking to receive. But the higher you can get your antenna, the better reception you will get. This is a good rule to thing about when planning any antenna.

So the questions to work with is to think about what is frequency first. Second, what type of building construction do you have to work with. Third is what type of trees do you need to take int account. Third is how will the antenna location will be effected by what is around it.

Remember that HF antennas don't like to have any other metal around the. This also goes for tree branches sand leaves. So keep them away from these objects. It will effect the SWR on transmitting. Receive is not that much of a problem. but you can get some signal attenuation. The higher in frequency you go, the more important this will be.

I am going to stop here as I need to leave for work.

Jim

 

[dlwtrunked]

I have probably a dumb question for the antenna experts out there as it relates to base antenna height above ground level.

I live an a mountainous area where elevation changes quickly over short distances. My house is at roughly 1,000 ft. ASL and down the street from me it gets down to about 800ft. ASL or so and even lower.

Theoretically, if my antenna is mounted only 10ft. above the ground (obviously not ideal), and someone down the street from me has the exact same equipment but with the antenna mounted on a 50 ft tower, who would get the better range? Again, considering exact same radio, antenna, coax, etc.

Would I get the better range because my antenna is still at a higher elevation? Or would the person down the street get better range because their antenna is mounted at a more ideal height above ground level?

This is mostly just for my own curiosity.

Thanks!

If the earth were perfectly round (with no local or other obstructions), the line-of-site range (to the earth surface) would be proportional to the square-root of the antenna height in feet. That would be added to that of the transmitting antenna. But in your case, other posters are correct, you have too many local things going on (round earth not a good model) to come to any statement about which would get better range and it will depend equally a lot upon the circumstances of the transmitting antenna. I do recommend that you see (and create a free account)
Radio Mobile Online

 

[prcguy]

There is more to consider. All antennas at all frequencies are influenced by proximity to ground, which can push the radiation pattern up off the horizon making your signal weaker at a distance. Some of the worst effects from this are when the antenna is at 1/4 wavelength or lower above ground where the pattern will be really skewed upward. At CB frequencies a 1/4 wavelength is about 9ft.

At heights of 1/2 wavelength and multiples of 1/2 wavelength above ground this effect is minimized with the first 1/2 wave (18ft for CB) will have a pattern lower to the ground than something lower and a little higher and with each successive 1/2 wave increment the pattern gets closer to the antennas advertised (free space) radiation pattern of a main lobe at the horizon. If you can get the antenna up one wavelength or 36ft you would be in ok shape with more signal at the horizon than the same antenna mounted at 10ft or 22ft or something other than a 1/2 wave increment.

Another thing that happens that's probably in your favor is when you mount an antenna on the side of a sloping hill, the radiation pattern will be pulled down in the direction of the downward slope. So if your main direction of communication is in the direction of downhill you might get two wavelength height performance on the pattern at just 1/2 wavelength above ground.

Height is king on VHF/UHF and CB antennas so get it as high as possible and try to keep the base near 18ft, 36ft, 54ft, etc.

 

[scan18]

Yes, even though I am at 1000ft ASL, I’m at the base of a 14,000ft volcano so my range is certainly skewed in one direction, mostly towards the ocean unfortunately.

Thanks for all the replies so far, learning a lot.

Obviously I can’t control my elevation, so need to get the antenna as high above ground as possible. Weekend project

 

[KB4MSZ]

On antenna height restrictions for the CB radio service, here is what the FCC site states:

"There are several additional things to consider when using a CB device, including:

• You may not raise the power output of a CB transmitter.
• You may not attach a "linear," "linear amplifier" or any other type of power amplifier to your CB transmitter.
• There are no height restrictions for antennas mounted on vehicles or for hand-held devices.
• For structures, the highest point of your antenna must not be more than 20 feet above the highest point of the building or tree on which it is mounted, or 60 feet above the ground. There are lower height limits if your antenna structure is located within two miles of an airport.
• You may use an on-the-air pseudonym ("handle") of your choosing.
• You must at all times and on all channels, give priority to emergency communications."

Also attached are the revisions to the CB radio service which came out last year, as well as the complete set of rules. Of special note is the removal of restrictions on long distance communications within the US and Canada. Communications outside of these areas is still prohibited.

 

[iMONITOR]

Going into the issues of trees, the worst type to have around is pine trees. This really comes into play as you go south and get into the long needle pine trees. They just kill reception at the 700 and 800 bands.The needles are just about resonant at those frequencies and they kill being able to have good reception through them.

Jim

That's surprising and I always wonder about that. However I have row of long needle pines on the East side of my house, about 120' long, as tall as my two story house, and maybe 18' wide at the base with needled branches all the way down to the ground. The row of trees if only about 30' from my house. My office/shack it on that side of my home on the first floor. Worst situation ever right? Nope!

Using only a Remtronics rubber ducky antenna on the back of a BCD996P2 I used to get a full-bars signal from 12 Miles South of me from Warren, MI on their old 800MHz system, prior to them joining MPSCS/Macomb Counties simulcast system, loud and clear! It's interesting to note I also have no problem with simulcast on 700/800MHz regardless of the scanner I use. I've used Radio Shack/GRE/Uniden! I also have a BCD325P2 with a Comet Miracle Baby antenna that's about 1-1/4" long. It also receives everything loud and clear!

The pine trees are also between my house and Selfridge Air Base that's about 10 miles as the crow flies, and I hear their departures/arrivals and aircraft loud and clear on VHF/UHF AM using a Diamond D220R and a DPD Production's MilTenna Omni, both of which are temporarily sitting inside my office until the weather improves, not on the roof, not even outside the house! Go figure? Sometimes I think people over think antenna requirements unless you have an unusual situation. With regards to antenna height, I think you can get to a point of diminishing returns when you factor in the loss of long runs of coax. Some have coax of 125'+. Maybe that fact that I don't use hardly any coax is what's helping, that and maybe my pine trees?

Note: I'm 604' above sea level

 

[W5lz]

As to the original question;
It isn't ASL that determines antenna radiation paterns (where stuff goes or comes from), but AGL. Height above ground level (If the antenna is above dirt) it's what shapes that antenna's pattern.

 

[scan18]

I just realized, based on those height restrictions for antennas mounted on a building or structure, if the highest point of the antenna can’t be more than 20 ft. above the highest point of the building, then technically you can’t mount an imax2000 or something like that on a building at all? I believe an imax2000 is 24 ft. long.

Or am I reading that wrong?

 

[doctordialtone]

Or am I reading that wrong?

Here's a review. I would call the supplier and ask about the height regulation.

Imax2000

Antenna Regulation

 

[KB4MSZ]

I think what this refers to is in the case a tall building, such as say an 8 story condominium, the antenna top can't be more than 20 feet above the building. In that case a 24 foot antenna would technically be illegal, and a shorter antenna such as a 1/4 wave or 5/8 wave would have to be used. Note that the regulation states "whichever is higher". This would place the base of the antenna some 80 feet or more above the ground, but the obstruction of the building requires it. That's my take on it.

 

[KB4MSZ]

There are no height restrictions for antennas mounted on vehicles or for hand-held devices.

This regulation brings to mind some really amusing mental pictures.

 

[JayMojave]

The higher the better from my experiences. While raising a 5/8 wave length ground plane antenna and several yagi beam antennas on crank up towers, we watched the received signal strength on a radio as the antennas were raised to in some cases 90 feet above the ground, the higher the antenna the more stronger the signals got.

Jay in the Great Mojave Desert