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Author Topic: G5RV Antenna Feedline  (Read 625 times)
KC2PHJ
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Posts: 21




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« on: July 08, 2007, 07:10:41 PM »

I have recently installed a G5RV antenna. Its designed for 40-6M. Its 51 ft. with a 16 ft 300 ohm line turning tail. From the tail the coax line is attached to my LDG Z-100 tuner then my radio. It tunes in great on 40, 20 & 6m (< 2.0:1). The other bands 18, 15 & 12M has a high SWR (higher than 3.0:1 SWR). 10M the SWR is 2.5:1. I have 50 ft of coax from the tuning tail to the tuner. Should I shorten the coax to get a better SWR on the other bands?
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SSB
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Posts: 1




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« Reply #1 on: July 08, 2007, 07:30:48 PM »

If you want a multiband antenna, then buy a multiband antenna.  I cannot figure out why so many of these G5RV antennas are bought.  Trap and multiwire dipoles are true multiband antennas.  Try one.

Alex....
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K0ZN
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Posts: 1548




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« Reply #2 on: July 08, 2007, 07:36:33 PM »


Hi.

That type of antenna will NEVER have a "low" SWR on all bands. That is just the nature of the beast. A G5RV is a compromise by nature; it CAN'T be optimized on all bands simultaneously (and the original design never intended that). I would say the SWR numbers you are quoting are very good for that type of multi band antenna. You NEED a tuner for that type of antenna. Keep in mind, SWR does NOT mean it won't radiate quite efficiently. Some antennas, such as a Center Fed Zepp can have very high SWR (10+:1) on some bands and radiate very efficiently due to low loss transmission line. The "problem" is NOT the SWR....the problem is the additional loss high SWR can cause in coaxial cables if they are very long. That is why 450 ohm "ladder line" and open wire lines exist...they have very low losses at high SWR compared to coax...but they have their own set of "issues" too and cannot be directly substituted for coax.

Only more complex and expensive "wide band" antenna systems have a low SWR across a very wide frequency range. Typically these antennas are out of the budget (and physical size) of most hams and are used mainly in commercial and military stations.

Respectfully, pick up a copy of the ARRL Antenna Book....even an older copy on Ebay is fine.... and put in a little book time on antenna basics. The knowledge you gain will be VERY helpful and allow you to have more fun with the hobby. Antenna theory as a whole, is way too extensive a subject to be addressed here on eHam.

Sounds like you have a good antenna set up... get on the air and have some fun!

73,  K0ZN
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KB9CRY
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Posts: 4283


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« Reply #3 on: July 08, 2007, 08:01:03 PM »

The original G5RV was designed for 20M and an occasional use on 40 and 15.  All other bands were not in the original design plans as you are finding out.  It will work but marginally as your tuner is telling you.
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KA8YLY
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Posts: 18


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« Reply #4 on: July 08, 2007, 08:22:21 PM »

the G5RV I grew up with was 102 (51 feet per side) feet of wire with about 30 feet of 300 ohm line to feed it, the 300 ohm line was directly soldered to the coax in the attic.

I used that antenna (with a tuner) for a LONG time and got great results from it. it wasn't great on 160 and there was a lot of rf in the shack (made the keyer go crazy) on 40, but it worked ok on other bands. Pitcairn Island on 15cw with it. all sorts of 40 and 80 dx.

now I have a bigger lot and basically run an 80 meter dipole (longer than a G5RV) and feed it with 50 feet of 450 ohm line. I find this config works really well. particularly on 30 for whatever reason. work tons of dx with that antenna.
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KE3WD
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Posts: 5689




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« Reply #5 on: July 08, 2007, 10:42:53 PM »

You could likely get a better tune with a different matchbox.  

Not to knock the one you've got, but it sounds like the short G5RV is simply outside its limitations.  

Maybe look into a good manual matchbox.  


.
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N6AJR
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Posts: 9908




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« Reply #6 on: July 08, 2007, 11:47:20 PM »

Bye the way, none of this is mine, Its just stuff I pulled from here and there. thanks to all the folks with the great sites. this is My take on the multi-band, single feed wire dipole ( but fan dipole is easier to type.  a true fan dipole is also called similar to a cage dipole and has 3 or 4 wires of different lengths on the same band , like a 64 foot , 66 foot and 68 foot  double leg wires on the same feed to give wider bandwidth, but bottom line, they are cheap, easy to build, and they work..
 
 
http://www.ku4ay.net/dipole.html
http://www.qsl.net/kd7rem/antdipole.htm
http://www.hamuniverse.com/multidipole.html
http://www.angelfire.com/nb/ni4l/ni4ldipole.html
http://www.arrl.org/tis/info/pdf/9611073.pdf
http://www.geocities.com/n2uhc/2banddipole.html
http://www.qsl.net/na4it/fandipole.html

 
 
 
by N3JBH on October 12, 2006    
FAN DIPOLE OR MULTIPLE BAND DIPOLE SPECS:
(Each leg is shown in length so you will need two legs.)

10 METERS = 8'4"
12 METERS = 9'5"
15 METERS = 11'1"
17 METERS = 12'10"
20 METERS = 16'8"
30 METERS = 23'2"
40 METERS = 32'9"
60 METERS = 43'7"
75 METERS = 60'9"
80 METERS = 65'6"
160 METERS = 123'5"
137 KHZ = 1708'1"  
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WW5AA
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Posts: 2086




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« Reply #7 on: July 09, 2007, 08:02:18 AM »

Poor Varney would be crying over his beer at seeing what is now being called a G5RV. Varney's original antenna calls for around 102' of flat top (not inverted "V"), 28' of 600 ohm ladder line and at least 75' of 72 ohm coax. You will find that changing the length of the coax will have a profound effect on the SWR. Of course low SWR is not an indication of the effectiveness of an antenna.

73, de Lindy
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WT0A
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Posts: 922




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« Reply #8 on: July 09, 2007, 02:39:52 PM »

Lindy
I was thinking it was 300 ohm line and "at least" 65 feet of coax (and no Balun), Of course the variations probably started the moment it was first published.
73, look for you on central states
Glen WT0A
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WW5AA
Member

Posts: 2086




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« Reply #9 on: July 10, 2007, 09:37:03 AM »

Hi Glen,

Here is Cebik's info on the G5RV. Seems the World Radio artical was a little different. I used 600 ohm feeders on my first G5RV as I thought that was in the original artical. Cebik showes it as 525 ohm. Anyway, after building half a dozen G5RV's I was convinced that a plain jane doublet is better anyway. Catch you on 40.

http://www.cebik.com/wire/g5rv.html

73, de Lindy
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KC2PHJ
Member

Posts: 21




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« Reply #10 on: August 27, 2007, 11:57:12 PM »

What model tuner do you suggest?
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