Can you stack Yagi antennas?

YagiDoo

DTVUSA Rookie
#1
I've got 1 Winegard Yagi up on the roof and it has worked pretty well for me without a rotor for the stations we like to watch but there are a couple located on a separate tower in the other direction that I'd like to pick up. Would it be possible to add another Yagi about a foot higher and point it in the other direction?

YD in ND
 

Piggie

Super Moderator
#2
yes. but we need more information. I have antennas joined all over the place on my roof and others here do also.

First what type of Winegard yagi do you own? Model number is best.

Second go to TVFool.com TV Fool

it will show a map and if the address locator is off then drag the red icon to your house.

Make sure you put in how high your antenna is above the ground.

Then click make a radar plot.

then copy and paste the bold link here. That way we can see the stations possible and the levels hence type of antenna and how you could join them.
 

Don_M

DTVUSA Member
#3
:welcome:

"Stacking" refers to pointing identical antennas in the same direction for added gain. What you wish to do is called combining, and while it is possible, you'll probably need quite a bit more spacing between the antennas for any chance at success. Sufficient distance between antennas prevents them from interacting with one another. These interactions are usually to the detriment of reception.

Spacing is a function of the lowest receivable channel at your location. The channels stations use for DTV broadcasts are often different from the channel numbers they display. You'll need to look up your market at Rabbit Ears, or generate a reception report for your location at TVFool, to find out the lowest "RF channel" available to you. Please let us know what this channel number is, and we can tell you what the minimum spacing requirement would be. BTW, the bare minimum distance when dealing with any VHF signals is three feet, and it's frequently quite a bit more than that; an all-UHF environment requires less than three feet, but even then, more than a foot remains advisable.

Even after taking these precautions, the antennas may still act to cancel each other out and worsen reception. If they do, the best solution is to have two discrete antenna systems, each sending a coax cable down to an A/B video switch at the TV tuner that would be used to select the antenna bringing in the desired station. Remote-controlled and manual A/B switches are available.
 

Piggie

Super Moderator
#4
"Stacking" refers to pointing identical antennas in the same direction for added gain. What you wish to do is called combining, and while it is possible, you'll probably need quite a bit more spacing between the antennas for any chance at success. Sufficient distance between antennas prevents them from interacting with one another. These interactions are usually to the detriment of reception.
Good point and when I read the title before clicking on it the image I had in my mind were two identical antennas in the same direction. But then I forgot to comment that is really combining. Good catch.

Spacing is a function of the lowest receivable channel at your location.
While in theory your statement here is spot on. But in the practical sense I use the lower channel or frequency of the higher frequency or channel antenna to set the spacing, in particular if the frequency difference between the two antenna is in the order of 2 to 3 times the other, which is true in spacing VHF and an UHF antenna in combining.

The smaller size of the higher frequency antenna does very little damage to the aperture or capture area of the larger lower frequency antenna. Yes it does interfere but not to a great degree if you need to stack closer.

For example, if you stack a high band yagi with a UHF yagi. The rule of thumb aperture area of the high band antenna is about 5 feet above and below the antenna. This by theory and your statement would be the closest one should combine these two antennas. And in fact it's the best.

However if vertical mast room is at a premium you can "cheat" and put the UHF within about 3 to 4 feet of the VHF without affecting the VHF antenna much. Of course it won't affect the UHF that has an aperture about 1/3 of the VHF or about 20 inches.

Mine are stacked 3.5 feet apart, even with the UHF orthogonal to lower of my stacked VHF yagis. I tested the VHF without the UHF there, then with it there (only on a quality meter on my TV) and found no difference in the VHF.

Why did I stack that close when the bottom VHF yagi is 26.5 ft up? Because one of my weakest UHF's is LOS at 18 ft. I like to get 5 feet above breaking into LOS to lessen the Fresnel and other ground effects.

I did try the UHF lower and it was weaker. I found the UHF came alive at 22 ft, so I added another foot, and then not seeing any degradation on VHF, I left well enough alone.

However, like you say, 5 feet is the best distance, but given a tight situation or one like mine, one can even cheat down to 3 ft if the VHF signals are strong, and at 4 feet I have yet to see a problem.

===========

Now an aside that happens a lot. I have my VHF on top, because of the height needed to reach Jacksonville FL (61 miles) compared to the UHF in Gainesville ( 27 miles to 35 miles).

But given about the same distance and in most situations the UHF needed more height. Thus is normally put on top of the mast.

Now imagine a short pole. Typical 20 feet, side mounted to a house with a metal roof. This means the UHF is up 20 feet and about 8 feet above the metal roof. But the VHF at 5 feet is then only 3 feet above the metal roof. This will cause more problems then putting the VHF only 3 feet below the UHF thus getting the VHF 5 feet above the roof.

Actually in the case, I would suggest if the person has VHF problems to put the VHF on top if it can be mechanically secure.

Winegard suggests on their VHF yagis be at least 3 wave lengths or about 15 feet for VHF above a metal roof.
 

NewGuy

DTVUSA Jr. Member
#5
Now an aside that happens a lot. I have my VHF on top, because of the height needed to reach Jacksonville FL (61 miles) compared to the UHF in Gainesville ( 27 miles to 35 miles).

But given about the same distance and in most situations the UHF needed more height. Thus is normally put on top of the mast.
Just a question for my general knoweldge but why would a UHF antenna need more height?
 

Don_M

DTVUSA Member
#6
Just a question for my general knoweldge but why would a UHF antenna need more height?
The higher the radio frequency, the more the receiver needs line of sight for error-free signals. Higher antenna mount points usually make for better line of sight (but not always). UHF signals are those above 300 MHz; VHF signals are between 30 and 300 MHz (MHz being the same scale used in the FM band). The lower the frequency, the better a signal will propagate -- or travel long distances and remain receivable -- near the ground despite obstacles such as vegetation, ridges, and even the curvature of the earth itself.

I've seen claims that each additional foot off the ground yields as much as an additional dB of signal strength... but I've also never heard of anyone verifying the claim in the field with test instruments, either.
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#7
clarification

Don_M wrote:
The higher the radio frequency, the more the receiver needs line of sight for error-free signals. Higher antenna mount points usually make for better line of sight (but not always). UHF signals are those above 300 MHz; VHF signals are between 30 and 300 MHz (MHz being the same scale used in the FM band). The lower the frequency, the better a signal will propagate -- or travel long distances and remain receivable -- near the ground despite obstacles such as vegetation, ridges, and even the curvature of the earth itself.

I've seen claims that each additional foot off the ground yields as much as an additional dB of signal strength... but I've also never heard of anyone verifying the claim in the field with test instruments, either.
----------------------------------------------------------------
For clarification to novice readers here, Channel 14 is the lowest UHF television channel and it operates between 470 and 476 mHz.
Jim
 
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IDRick

DTVUSA Member
#8
The higher the radio frequency, the more the receiver needs line of sight for error-free signals. Higher antenna mount points usually make for better line of sight (but not always). UHF signals are those above 300 MHz; VHF signals are between 30 and 300 MHz (MHz being the same scale used in the FM band). The lower the frequency, the better a signal will propagate -- or travel long distances and remain receivable -- near the ground despite obstacles such as vegetation, ridges, and even the curvature of the earth itself.

I've seen claims that each additional foot off the ground yields as much as an additional dB of signal strength... but I've also never heard of anyone verifying the claim in the field with test instruments, either.
Hi Don,

I usually see a 4 to 6 dB increase in margin to dropout when moving my antenna from 6 ft AGL on the patio to 15 ft AGL on the roof. This is very repeatable at my test location.

Best,

Rick
 

Don_M

DTVUSA Member
#9
I usually see a 4 to 6 dB increase in margin to dropout when moving my antenna from 6 ft AGL on the patio to 15 ft AGL on the roof. This is very repeatable at my test location.
Ah, yes... but unless the patio mount is directly underneath the roof mount, or very close to it, this represents a change in two variables -- height, plus horizontal location. A couple of feet laterally is no biggie in VHF work, but a couple of inches can be huge for UHF signals.
 

Piggie

Super Moderator
#10
On HF and VHF the old very very loose rule of thumb was double the height, gain 6 db. Which is close to what you see Rick.

UHF tends to be more determined as do you have gain and LOS, since gain is so easy at UHF.

Like I say, it's a very very loose rule of thumb.

=========

There is another important contributor to gain increasing with height. It's the number of wavelengths above your ground plane with a directional antenna, in particular horizontal.

Anything above 4 wavelengths that part of the improvement ends for most practical purposes.

Take the HF bands where this affects your reception even more than on VHF.

An example would be a 40 meter dipole. Most hams have trouble getting them more than 30 feet off the ground and even that takes some rigging. That puts the dipole 1/4 off the ground. You can think of it like a 2 element beam with the ground being the reflector. It tends to emit radiation a very high angle with the horizon being zero degrees. The pattern is also very omni in the azimuth.

Now just put that antenna 60 ft up which is only 1/2 a wavelength. Oh man alive do the signals come alive out over 1000 miles. It's because the angle of radiation is closer to the horizon. Get one up 100 to 120 ft and you really hear stuff out several thousand miles if the band is open you would never hear on one only 30 feet up.

The other factor you find is your dipole up that high becomes bidirectional as shown in pictures of it's pattern with weak reception off the ends.


====

While this isn't the same exactly how it works on VHF with a yagi, being to close to the ground does raise the angle of radiation.

This goes back to why my stacked yagis work into Jacksonville so much better than a single. It's not about 2.5 db gain, but lowering my angle of radiation toward the horizon where over the horizon signals are generally the strongest.

Anyway yes being higher helps for more reasons than just getting LOS in most cases.
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#11
re: VHF

Piggie wrote:

Anyway yes being higher helps for more reasons than just getting LOS in most cases.
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Yep, being higher (in the 70s) certainly helped me in some ways too :hippie:- umm - and your explaination agrees with my personal frustrations on 40 meters VS 15 meters at the time. (yes, there was plenty of sunspot activity then)

Until now, I did not understand why none of my 40 meter dipole variations were nearly as 'hot' as my simple 15 meter dipole!

Piggy, THANK YOU for your (so it seems) continual edumacation of me! :applause: This is interesting.
Jim
 
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