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Stacking Antennas

Jphila20

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Southern Lorain County, Ohio
#1
I have two Yagi antennas and want to see if I can stack them one above another to increase the signal on a distance tower. The antenna has a freq range of 698 - 780 with 14dBi gain. The vertical beam width is 30 degree. It's just over 50 inches long.
I have looked on line for some type of calculator and they are over my head. :{) Changing Dopt to wave length and dividing by beam width?????
I got the antenna from DMS wireless, YA70014F and a single antenna works great for the local towers. I'm looking to pull in better the Cleveland Police system, GCRCN which operates off the Justice Center in downtown Cleveland. I know that the antenna is not an 800mhz antenna. With just single YagiI I get some radio traffic now depending on weather condition. It's approximately 30 air miles.
Thanks!
 

KB4MSZ

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Tampa, Florida
#2
If the antennas are identical and are phased and spaced together ideally, it will produce at best 3db gain over what you have with one Yagi. On a typical Ham radio this would show 1/2 S unit more signal strength. I guess this could make a notable difference if your current signal level is borderline.
 
Last edited:
Joined
Jun 16, 2013
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3,227
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Texas
#3
You'll need to build a co-phasing harness which will require the following:

  • [li] 2 antennas space 1 wave apart[/li]
    [li] 2 pieces of an odd quarter of 75 ohm coax (3/4 works if going with 1 wave of spacing)[/li]
    [li] a simple T connector[/li]

Hook it all up, I'd use the lowest frequency you wish to use to figure your spacing out. Simply T the two odd quarter pieces of 75 ohm coax together (this creates a power divider matched to 50 ohms on either end). Regular 50 ohm coax goes to the unused end of the T.

I've done this before with UHF for a foxhunt antenna. We actually tested it and found a true 3 dB gain over a single antenna but what was really improved was the front to side and front to back ratios (6 to 9 dB) making the array much more directional. Note, I've not done vertical spacing, only horizontal phasing. In theory you could also use a simple two-way divider like you would see from Mini-Circuits which is already matched to 50 ohm.
 

Frankhappyg

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#4
You’ll get 14dB between 698-780mhz.
But for monitoring the Greater Cleveland Radio @ 850mhz your dB is significantly less.
My suggestion is get the right antenna for the right frequency before you stack two antennas that aren’t tuned for the frequency desired.
I run the Wilson 301111 with excellent results 55+ miles


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Joined
Sep 8, 2006
Messages
2,773
Location
Stockholm, Sweden
#5
Yagi antennas often drop in gain a lot when you go higher than it's designed frequency and not so much when you go lower. Theoreticly it is a 3dB gain when stacking but it is also losses in the cabling as you need them to be of an exact lenght and the two antennas need to see the exact same signal, difficult with reflections and such from terrain or buildings, and the impedance match stub have to be done precise and those will works as a bandpass filter attenuating all other frequencies.

You probably will gain some just be raising the single antenna 3 feet. In your situitation I would had dropped the stacking with all its hassle and got a $30 preamp and a $10 variable attenuator as non of your scanners have the same sensitivity and noise figure as a low noise preamp and you'll gain at least 3-4dB just from that, and then the additional gain that the coax loss are at 800MHz when installing the preamp at the antenna or with the coax as short as possible to the amplifier.

/Ubbe
 

Jphila20

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#6
If I bought the Wilson 301111 antenna what kind of loss would I expect using RG-6 instead of 50 ohm cable for a 25 foot run?
The DMS wireless YA70014F is already setup with RG-6 and a F connector.

What pre-amp and variable attenuator would you guys suggest?

Thanks for the quick response and info!
 
Joined
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Stockholm, Sweden
#7
That Wilson have very few elements that gives a lower gain. Another $40 antenna will give twice the gain and are a better alternativ to stacking but will also give a more directional beam, compared to a lower gain antenna that picks up from a wider angle that might be neccesary for you.
Altelix 800 MHz 900 MHz 15dBi Stainless Steel Outdoor Yagi Antenna WiFi 2G SCADA | eBay

25 foot of RG6 only attenuats 1.5dB at 900MHz so probably not worth the trouble of using a mast mount amplifier. But an amplifier have less noise than a scanner and will improve reception just by connecting it betwen coax and scanner.

Ultra Linear LNA 0.01-2 GHz Gain>20dB PGA-103 ESD Protection+ Gain Stabilization | eBay
The company has a lot of different filters if you should need any, but with a 800MHz antenna you probably won't need them.

Antennas Direct ATT-1 Variable Attenuator 0-20dB - NEW | eBay
It's this kind of attenuator with F connectors but they are usually $10-15 so it must be possible to find others.

You'll also need adaptors, or pigtails are better, to connect everything together. Remember that you only need something like 6dB gain from an amplifier and the rest of the gain needs to be attenuated and the sweet spot are easily found with the variable attenuator betwen amp and scanner. I'm not sure about that amplifier but others can also be powered from the coax using a bias-T power inserter if you at some point want it mast mounted.

/Ubbe
 

Frankhappyg

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#8
If I bought the Wilson 301111 antenna what kind of loss would I expect using RG-6 instead of 50 ohm cable for a 25 foot run?
The DMS wireless YA70014F is already setup with RG-6 and a F connector.

What pre-amp and variable attenuator would you guys suggest?

Thanks for the quick response and info!
Was just given you what I run antenna wise.
Personally even at 50 feet I would switch coax.
Altelix Low Loss 400 is what use around $40 for 50 feet.
Always think if you’re going to try to get the most range out a antenna out of the higher frequencies use the right coax even on a 50 foot run.
I don’t know how far you are from Cleveland but I’m about 60 miles and can’t get them probably do to the terrain and buildings.
But on the other hand I can get Cuyahoga on MARCS.
It’s to bad Cleveland isn’t on MARCS-IP. It wouldn’t be that hard to pick it up from a neighboring county site.


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Frankhappyg

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Northeast,Ohio
#10
25 foot of Altilex 400 attenuats 1.2dB at 900MHz compared to 1.5dB for RG6. Not much different except for the huge cost difference.

/Ubbe
Lol,huge ?
$25 feet is $20.
If I spend $650 on a scanner $120 to put up a mast & antenna I’m not worried about $50 for the correct coax.
400 @ 900 MHz @ 50feet is 1.95
RG6 @ 900 MHz @ 50feet is 3.0
Take all the dB you can get.


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Last edited:
Joined
Jun 30, 2006
Messages
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Location
So Cal - Richardson, TX - Tewksbury, MA
#11
Instead of a critical length 75 ohm phasing harness to combine the antennas you can use a good 2-way 50 ohm power divider and two coax jumpers of any length as long as they are exactly the same length. A power divider or splitter used this way will not incur a 3dB loss because you are combining two identical antennas in phase.
 

mm

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Dec 19, 2002
Messages
596
#12
At 750MHz with a 30degree E beamwidth the proper stacking distance is 2.535 feet.

You'll need a phasing harness/2 port power divider and most important is to make sure that the feed point connection of both antennas are facing up in the same configuration.

By this I mean if the antennas are stacked vertically with a center to center/boom to boom spacing of 2.535 feet make sure that the element side that is connected to the coax center on each phasing line is facing up on both antennas otherwise the antennas will be out of phase.

Phasing line/2 port power divider construction:
https://directivesystems.com/wp-content/uploads/sites/2/2015/05/What-are-PDs-and-PLs.pdf
 
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