eHam
eHam Forums => Antennas, Towers and more => Topic started by: VK4WTN on March 29, 2023, 09:07:03 PM
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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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Front to rear.
Tom KH0/KC0W
KH0W.com (http://KH0W.com)
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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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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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Front to rear.
Tom KH0/KC0W
KH0W.com (http://KH0W.com)
Providing a correct answer is apparently less appreciated than a vague suggestion promoting a youtube channel.
Nice eh?
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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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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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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).
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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.
(https://i.imgur.com/MJeFt7q.jpg)
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.
(https://i.imgur.com/GUCksuo.jpg)
Clearly for more complex antennas a full plot is advisable....
Grover
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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
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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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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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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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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 (https://www.bhphotovideo.com/c/product/1603982-REG/sharp_8m_b120c_120_class_8k.html)
Tom KH0/KC0W
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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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When you come across a page with too large images, you can use the so-called Bookmarklets (https://en.wikipedia.org/wiki/Bookmarklet).
Current browsers no longer allow inserting javascript directly into the address bar, but it is possible to bypass this by saving the javascript to Favorites, which then looks like this in the Firefox browser:
(https://chromos.cz/_exported/eham/bookmarklet_as_favorite.png)
Then write the desired javascript in the URL field, for example to shrink all images larger than 800px to 800px:
javascript:var%20i,L=document.images.length;for(i=0;i<L;++i){document.images[i].style.maxWidth='800px'};false();
Then, when you come across a page that you wish to reduce the images on, just click on that Favorite.
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Updated plots:
(https://i.imgur.com/6iuWJDs.jpg)
(https://i.imgur.com/6cSFYnp.jpg)
Probably easier to view on your browser.
Grover
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Maybe 10 or even 15 (?) better comparators?
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A good example of the difference between Front/Back and
Front/Rear is this pair of Moxon patterns from DK7ZB (https://www.qsl.net/dk7zb/Moxon/2-m-Moxon.htm).
(https://www.qsl.net/dk7zb/Moxon/2m-hor.gif)
(https://www.qsl.net/dk7zb/Moxon/2m-ver.gif)
The first shows a clean rear pattern, good Front/Rear over
180 degrees. The second has a deep null directly off the
back (good Front/Back), but much stronger pattern
approaching 90 degrees from the rear null, so the
Front/Rear is not as good.