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Author Topic: G5RV  (Read 412 times)
W8ZIP
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« on: September 07, 2003, 08:11:19 AM »

I plan on installing a G5RV mini. Due to limited space I would need to cut off about 2 feet from the antenna.
I was wondering how much would this effect the antennas performance and should I trim equal ends off the span or just take the 2 feet from one end.

Thanks in advance

Tom    
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K0BG
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« Reply #1 on: September 07, 2003, 09:35:27 AM »

Removing length will only add to the losses of an already lossy antenna. You'd be better off with as long a doublet as you can string up, feed it with ladder line, and match it with a tuner.

Alan, KØBG
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EI2IV
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« Reply #2 on: September 07, 2003, 09:39:27 AM »

Don't cut it off any end!

"Dog leg" it.
Just let 1 or 2 feet of each end hang down vertically this should have little or no effect on antenna performance. Cutting the antenna will de tune it.

73
James
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K1ZC
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« Reply #3 on: September 07, 2003, 09:49:30 AM »

I don't think either approach is particularly good.  The legs of a G5RV, like a dipole, are cut to a specific length for a reason.  If you adjust the length you will have a fine antenna, but it will be optimized for a freqency outside the ham bands.

The G5RV design is actually 1.5 X lambda which makes it longer than a dipole.  If you don't have the space for a G5RV why not just build (or buy) a dipole that is cut properly for the band(s) you want to work?

Finally, you might want to play around with some of the free antenna software.  I like MMANA which is freeware from this link:

http://www.qsl.net/mmhamsoft/

The software comes with a big library of antennas, so you can probably find a model for the antenna you are interested in.  Then look at the radiation patterns from the standard antenna model, and compare it with the modifications you suggest to see what effects those will have.  It is quite instructive as a learning exercise.

73,
Jim  
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EI2IV
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« Reply #4 on: September 07, 2003, 01:23:16 PM »

RE: K1ZC

"Dog Leging" a dipole or g5rv does not ajust the electrical length in any way so therefore the antenna will NOT be "optimized for a freqency outside the ham bands."

"The G5RV design is actually 1.5 X lambda which makes it longer than a dipole."

This may-be so if comparing it with a 20 meter dipole
468/14.150 = 33.07 feet for a 20 meter dipole!
468/7.050 = 66.38 feet for a 40 meter dipole!
The G5RV half size is 51 feet!

Tom's problem is that the 51' antenna will not fit in his space, it is 2 feet too long so by just letting a foot each leg hang down from the ends it will fit with very little if any effect on the antenna.

"why not just build (or buy) a dipole that is cut properly for the band(s) you want to work?"

The 1/2 size g5rv will work fine on 40 meters, dog leged to fit into his 49' space  A dipole cut properly for 40 meters is over 66'long and will create a bigger problem for Tom to fit in his space (unless he uses some sort of loading and that is still a compromise).

Another very simple solution to your problem Tom would be to slope the G5RV.

73
James
   
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AF0H
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« Reply #5 on: September 08, 2003, 12:57:30 PM »

The G5RV is not a resonant antenna anywhere, but it easily tuned to the amateur bands and performs fairly well.  I do agree with dropping the ends instead of cutting them off.   The last 1/6 of the antenna (dropping the ends down) has very little effect on radiation patters, so this won't hurt or help you either way.

73 de
AF0H - Rob
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