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Author Topic: What is the difference between F/B and F/R of a yagi  (Read 519 times)

VK4WTN

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What is the difference between F/B and F/R of a yagi
« on: March 29, 2023, 09:07:03 PM »

This might be a dumb question. I often see the reference to F/R for a yagi antenna. We know that F/B is the front to back ratio of the yagi but what is F/R? I can't seem to find the answer on google.
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KC0W

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Re: What is the difference between F/B and F/R of a yagi
« Reply #1 on: March 29, 2023, 11:49:39 PM »

 Front to rear.

 Tom KH0/KC0W
    KH0W.com
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K6SDW

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Re: What is the difference between F/B and F/R of a yagi
« Reply #2 on: March 29, 2023, 11:52:31 PM »

ARRL/QST's new technical editor, KE0OG, has an excellent YouTube video on this subject you might find interesting.

GL/73
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VK4WTN

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Re: What is the difference between F/B and F/R of a yagi
« Reply #3 on: March 30, 2023, 12:54:22 AM »

Thanks guys. I had thought it would be front to rear. But I see some companies publishing F/B and F/R figures. I assume both are the same meaning. I will have a look at that video. thanks Wayne
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KF6QEX

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Re: What is the difference between F/B and F/R of a yagi
« Reply #4 on: March 30, 2023, 01:35:39 AM »

Front to rear.

 Tom KH0/KC0W
    KH0W.com
Providing a correct answer is apparently less appreciated than a vague suggestion promoting a youtube channel.
Nice eh?

 
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sdrawkcab daer tseb si txet sihT

N4MU

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Re: What is the difference between F/B and F/R of a yagi
« Reply #5 on: March 30, 2023, 04:48:03 AM »

ARRL/QST's new technical editor, KE0OG, has an excellent YouTube video on this subject you might find interesting.

He's their Technical Editor now? Agrhhhh...jusst another reason...

GL/73
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W3FLH

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Re: What is the difference between F/B and F/R of a yagi
« Reply #6 on: March 30, 2023, 05:24:17 AM »

ARRL/QST's new technical editor, KE0OG, has an excellent YouTube video on this subject you might find interesting.

He's their Technical Editor now? Agrhhhh...jusst another reason...

GL/73


He's actually a Contributing Editor, per QST credits (pg.4).  I understand where you're coming from, though.

Tony W3FLH
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WB6BYU

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    • Practical Antennas
Re: What is the difference between F/B and F/R of a yagi
« Reply #7 on: March 30, 2023, 09:19:42 AM »

Front / back compares the forward signal strength
to one directly off the back of the antennas.  You
can have a deep rear null, and still have large
rear lobes in other directions.

Front / rear compares the forward signal strength
to the strongest lobe over the rear 180 degrees of
the antenna.  If you are interest in reducing
interference, that is a better measure (unless
the interference is coming from only a single
direction directly opposite the desired signal).

N0GV

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Re: What is the difference between F/B and F/R of a yagi
« Reply #8 on: March 30, 2023, 12:02:13 PM »

Front / back compares the forward signal strength
to one directly off the back of the antennas.  You
can have a deep rear null, and still have large
rear lobes in other directions.

Front / rear compares the forward signal strength
to the strongest lobe over the rear 180 degrees of
the antenna.  If you are interest in reducing
interference, that is a better measure (unless
the interference is coming from only a single
direction directly opposite the desired signal).

Exactly correct.

There are other and better characterizations as well as Main/Largest Secondary  Lobe ratio that can be specified as well  Below are some examples of, first, a 5 element Yagi for the 20m band one wavelength above an average ground. Note the rear lobe isn't the largest secondary lobe, the forward lobe at 45 degrees of elevation is the largest secondary lobe.



In the second image I have used the same basic antenna, again 20m above an average ground, as the basic element of a horizontal array with 1 lambda horizontal spacing. Note the additional lobes. This basic antenna is what we call "well behaved" as it has no off angle horizontal lobes that are very large.



Clearly for more complex antennas a full plot is advisable....

Grover
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N8NK

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    • N8NK QRP
Re: What is the difference between F/B and F/R of a yagi
« Reply #9 on: March 30, 2023, 12:13:42 PM »

Can't you guys be normal people? Must every thread be responded to with hostility? Many here should probably find a more suitable hobby.
Regarding YouTube references: is this a bad thing? I have a channel. So it's wrong of me to proudly mention my story of working S. Argentina with 2.5 milliwatts with a true S7 signal level?
So it's wrong of me in an end-fed thread to suggest winding your own multi-tap UNUN or building a 'DX Commander' for free?
I'll never stop doing so.. and therefore, have given the trolls and haters and stuck-on-themselves snobs a new guy to hate on. Bring it.
Chuck, N8NK
YouTube channel: N8NK QRP
(NO it's not monetized. I get nothing from it but the satisfaction of encouraging others to build antennas, learning CW, etc)
dit dit
« Last Edit: March 30, 2023, 12:16:16 PM by N8NK »
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VE7RF

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Re: What is the difference between F/B and F/R of a yagi
« Reply #10 on: March 30, 2023, 12:21:43 PM »

Front / back compares the forward signal strength
to one directly off the back of the antennas.  You
can have a deep rear null, and still have large
rear lobes in other directions.

Front / rear compares the forward signal strength
to the strongest lobe over the rear 180 degrees of
the antenna.  If you are interest in reducing
interference, that is a better measure (unless
the interference is coming from only a single
direction directly opposite the desired signal).

If doing yagi's in software, like long boom 144 mhz arrays etc, typ the FR is set for greater than 180 degs, like 200-270 degs.  That's done to kill  sidelobes, that can easily form on each side
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AE0Q

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    • AE0Q Amateur Radio
Re: What is the difference between F/B and F/R of a yagi
« Reply #11 on: March 30, 2023, 02:43:09 PM »


Clearly for more complex antennas a full plot is advisable....

Between trying to figure out how to see the whole images, I missed your comments entirely since I could only see the plot images by opening on the Imgur site.

This other image hosting site seems to give more viewer-friendly format, since it has the option to RESIZE the images !!!

https://postimages.org/

Select the 800 x 600 option or smaller so they show up on here without being 4 times the screen width.

Glenn AE0Q
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N2SR

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Re: What is the difference between F/B and F/R of a yagi
« Reply #12 on: March 30, 2023, 04:57:34 PM »

Clearly for more complex antennas a full plot is advisable....

Grover

Could you make those graphs larger?  I couldn't see them on my 120 inch monitor.

Thanks.


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KC0W

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Re: What is the difference between F/B and F/R of a yagi
« Reply #13 on: March 30, 2023, 05:52:04 PM »


I couldn't see them on my 120 inch monitor.
 


 Thanks much!!!

I've been searching for how to spend that measly $126,295 I have buried in coffee cans in my backyard.  https://www.bhphotovideo.com/c/product/1603982-REG/sharp_8m_b120c_120_class_8k.html


                                                                                Tom KH0/KC0W
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N0GV

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Re: What is the difference between F/B and F/R of a yagi
« Reply #14 on: March 30, 2023, 07:34:50 PM »

Sorry guys, I did it on my work (word processing) machine and did not see the scaling - just change your browser magnification to 25% to view the plots or wait till I get back in to the office to re-scale and send new plots... :(

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