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Author Topic: Antenna Gain & Site Rental  (Read 15557 times)

AF6D

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Antenna Gain & Site Rental
« on: July 21, 2015, 11:12:22 PM »

This is a difficult topic for me because I am struggling with how to word things for the internet. I tend to speak rather directly and, well...

I just got an email from our new site vendor that is concerned that our LARGE 20 foot commercial antenna is too big and needs to be mounted at ground level making room for commercial customers paying double. This saddened me very much to see once again how it is. Our antenna is a DB224e and side-mounted offers 9dBd of gain. We have one at our back-up site at 85 feet coming down. Our main site has a an omni-directional Commander Tech 5.25dBd gain Station Master clone made "by RFS" that is worlds apart from the DB224. It does not compare favorably. I mentioned that we have a DB222 2-element dipole and I was urged to use it instead, that we not not see the difference between 6dB and 9dB at a repeater site? Really? That has not been our experience already. But what is the truth? It actually won't work - wrong frequency range. It really troubles me to be told directly that a guy is losing money by renting to me when he has 10 towers. Sure, they have value no doubt. I remain grateful still and I suppose I am more confused by being told that I wouldn't see a difference in performance between an 8 foot DB222 and a 23 foot DB224. It has always been my understanding that gain is derived from length. A 6dB gain mobile antenna certainly doesn't compare to a full sized base station antenna. It's all relative to something. Right?
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WB2WIK

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RE: Antenna Gain & Site Rental
« Reply #1 on: July 22, 2015, 08:27:30 AM »

This is unfortunate and happens pretty often when the site/tower owner isn't a ham (some really good sites/towers are owned by hams, and they're more flexible about amateur installations on them).

I'd think if the site is a mountaintop, the biggest difference between  DB224 near the ground and same antenna up high on a tower is the coverage into nearby valleys.  Sometimes a VHF antenna has to be quite high above ground to not suffer a huge "shadow" down below from the very mountain it's located on.

Getting it way high above ground makes that shadow much smaller.  Note the FM-TV BC antennas on Mt. Wilson are mostly on very tall towers, many over 200' high.  That's not to cover Long Beach better, which is line of sight from ground level -- it's to cover the deep valleys that are fairly close by better.

A DB224 is a great antenna and one nice thing about it is you can "see" the entire structure so it's very obvious if anything goes wrong.  A Stationmaster has everything sealed inside, and can suffer damage that isn't the slightest bit obvious.

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AF6D

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RE: Antenna Gain & Site Rental
« Reply #2 on: July 22, 2015, 09:42:20 AM »

The site owner IS a ham. Out of respect  am not mentioning his name or location.

The question remains whether or not I would see a difference between a side-mounted 9dB and a side-mounted 6dB gain antenna. My experience says that the 23 foot tall 9dBd gain antenna WILL excel over a similarly designed 8 foot tall 6dBd gain antenna.

Does anyone agree?
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WB2WIK

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RE: Antenna Gain & Site Rental
« Reply #3 on: July 22, 2015, 09:49:18 AM »

Of course I'd agree.

But remember "gain" isn't at all elevation angles, that's impossible.  The reason the antenna with more bays has more gain is it has a more compressed vertical radiation angle, which can work for you, or against you, or maybe exhibit very little difference depending on the installation and where the users are.

From a mountaintop if I wanted to cover nearby valleys, I'd go for a "downtilt" antenna with most of its radiation below rather than at the horizon.  Doing that can greatly improve local coverage, but can limit DX coverage.  Can't get it all! :D
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W1VT

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RE: Antenna Gain & Site Rental
« Reply #4 on: July 22, 2015, 10:51:31 AM »

According to the data sheet, the vertical beamwidth of the DB 224 is just 16 degrees, which means that if you want to cover angles more than 8 degrees below the horizon, you should consider downtilt or the smaller DB 222, which has a 36 degree beamwidth.  

http://www.repeater-builder.com/antenna/db-224-to-2m.html
This page shows how to move public service versions of these antennas down to the 2M band--you want to make them longer.  He first drilled holes and added bolts--then realized it made more sense to attach aluminum straps to the dipole elements.  But, he never got around to publishing pictures of the revised versions.

Zack W1VT
« Last Edit: July 22, 2015, 12:00:59 PM by W1VT »
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AF6D

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RE: Antenna Gain & Site Rental
« Reply #5 on: July 22, 2015, 02:47:00 PM »

Thanks Zack and Steve. Yes, angle of radiation is achieved by narrowing the aperture. The site is low-level -- 3,800 feet -- and that's why I feel the 9dBd 23 foot tall antenna is the better choice. Here's the HAAT. The color scale is -107dBm to -67dBm. Red is rockin' !

------------------------------------------------------------
Antenna elevation above sea level       : 1171.49m
Average ground elevation above sea level: 476.64m
------------------------------------------------------------
HAAT: 694.849990234375m

That's 2277 feet above the average terrain.

Here are the coverage maps and they do show some differences, like out at the beach to the west. But is there going to a real life difference between a 23 foot tall andtanna mounted 10 feet above ground and a 8foot antenna 10 feet above ground?



« Last Edit: July 23, 2015, 03:35:30 AM by AF6D »
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WB2WIK

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RE: Antenna Gain & Site Rental
« Reply #6 on: July 22, 2015, 03:05:17 PM »

I think it's impossible to know until you try it.
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K1DA

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RE: Antenna Gain & Site Rental
« Reply #7 on: September 20, 2015, 03:19:20 PM »

The "cone of silence" awaits.  Commercial antennas can be ordered with downtilt in the pattern, but gain theat means a drop elsewhere.  As others have said, you can't have it all.
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AF6D

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RE: Antenna Gain & Site Rental
« Reply #8 on: September 20, 2015, 07:16:02 PM »

Thank you Chuck. The site vendor was really unyielding in his demand that we use an 8 foot 3dBd omni or 6dBd side-mounted DB222 instead of the DB224e's that . As a result we took our business elsewhere. The new location is 3,000 feet higher and provides a substantial improvement in performance. The first vendor insisted that we would have to trade off performance for the spectacularly low price of $125/mo. I know of hams that pay $50/mo. I pay that on another site at 6,400 feet. Some hams know someone and, well... Sadly, I am direct to a fault and come across as abrasive when in truth it isn't intended. I don't get the sweetheart deals. :-(
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W2NAP

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RE: Antenna Gain & Site Rental
« Reply #9 on: September 21, 2015, 03:40:31 PM »

Thank you Chuck. The site vendor was really unyielding in his demand that we use an 8 foot 3dBd omni or 6dBd side-mounted DB222 instead of the DB224e's that . As a result we took our business elsewhere. The new location is 3,000 feet higher and provides a substantial improvement in performance. The first vendor insisted that we would have to trade off performance for the spectacularly low price of $125/mo. I know of hams that pay $50/mo. I pay that on another site at 6,400 feet. Some hams know someone and, well... Sadly, I am direct to a fault and come across as abrasive when in truth it isn't intended. I don't get the sweetheart deals. :-(
wish I could find a damn site for just $125/mo, hell lowest I have come across here has been $600/mo. thanks to the vulture companies like American Tower and Crown Castle. and it sure as hell ain't no 3,000ft!
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N8EKT

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RE: Antenna Gain & Site Rental
« Reply #10 on: February 07, 2016, 04:33:37 PM »

In MY part of the country, those massive gain antennas are fairly useless because they simply hill top

So they cause plenty of interference to other systems a hundred miles away yet have poor LOCAL coverage due to their gain

In the hills and valleys of Ohio and West Virginia I've found that 6Db gain is the max for this terrain and many commercial dealers are using 3db repeater antennas to fill the valleys better

Without down tilt, most of that antenna's gain is being wasted at the horizon

I have replaced MANY 9db antennas with 6db antennas and LOCAL coverage was better every time
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AF6D

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RE: Antenna Gain & Site Rental
« Reply #11 on: February 08, 2016, 12:22:59 AM »

In MY part of the country, those massive gain antennas are fairly useless because they simply hill top

So they cause plenty of interference to other systems a hundred miles away yet have poor LOCAL coverage due to their gain

In the hills and valleys of Ohio and West Virginia I've found that 6Db gain is the max for this terrain and many commercial dealers are using 3db repeater antennas to fill the valleys better

Without down tilt, most of that antenna's gain is being wasted at the horizon

I have replaced MANY 9db antennas with 6db antennas and LOCAL coverage was better every time

I absolutely agree with both of your points, Ralph. My home is at 6,250 feet 2 hours east of Los Angeles. Our primary repeater is at 6,450 feet just up the hill from me. We are top-of-tower mounted. The back-up repeater at my home is side-mounted on an 85 foot tower and kicks butt. Better than the primary often times but it doesn't get both the metro area and the high desert. It puts 9dBd into the local areas but has a doughnut hole :( Out at the beach 100 miles away its solid! A 5 watt HT does just fine.

The roads and hiking trails in my immediate vicinity would benefit from a 3dBd gain antenna. In fact, the purpose of our repeater system is that of a REACT-like service for the traveling and recreational ham. We want them to be able to hit one of several machines from damn near anywhere whether or not at the bottom of a canyon or a highway out at the edge of our coverage. I travel 200 miles nearly every weekend and our repeater using a 6dBd Station Commander 620N and 50 watts out to the antenna is loud and clear - usually full quieting - at the outer edge leading into the Tehachapi Mountains. It even makes it into Tehachapi that is covered by four 440 machines. Our 120 mile coverage remains < -70dBm! (30 over-ish on RX.) We would benefit in our mountains more from voting.

But to my point about the low-level site we have mobiles and HT's (we are designed for HT's) that hit us from the flat metropolitan area of Southern California. For this reason as part 1 the side-mounted 9dBd DB224 blankets our coverage area to the outer edges. Modeling with Radio Mobile Deluxe clearly shows, and is supported by actual testing, that the 6dBd antenna does not cover the beach communities nearly as well from the low-level site. Part 2 is that this particular site that I am not naming as a courtesy to a discourteous site owner sits in the middle of several mountain areas that benefit from a signal generated right into its heart. The site is far enough away so that the pattern can spread vertically and on the DB224e the vertical beamwidth is only 16 degrees to begin with whereas the Station Commander is 70degrees. I agree that 9dBd without down tilt would be wasted RF. The 1st design goal that we not out-talk our receive has been met. Our 2nd goal of primary access via HT has not. Using Allstar we can affordably vote equipment but not sites.

On a parting note, I ran an experiment from my home. When we were putting up the 85 foot tower and DB224 we started on 146.520 and moved to another simplex channel. We had users calling "the guys putting up the repeater on the hill" from over 120 miles away. We were using 1 watt HT's to talk during construction/antenna installation!!! The later experiment was while on .52 where my 50 watt base dominates. We were talking about beamwidth and I started on a 6dBd omni and then switched to a discone. I then switched to a 9dBd omni and talked all the way up north to a ski resort (Mammoth Lakes) several hundreds miles away. People began asking who I was talking to and assumed I was faking it until I was humbled by Elmering on the topic of how gain affects our beamwidth. My distance to the horizon plus the other station up north at its elevation and the zone in the middle that was created. One ham firmly declared that it was impossible! for me to talk simplex to a station hundreds of miles away. He would be wrong as most know. The geometric range is the square root of the antenna height x 2. In my case 112 miles. My actual service range factors in refraction. As some know many hams don't understand how we get gain by narrowing the aperture of an antenna. It is further complicated by introducing Pythagoras Theorem. Here's a calculator to which you add 20% for average refraction. http://www.boatsafe.com/tools/horizon.htm It does not factor in topography or obstructions. Maybe this will help someone.
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