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Author Topic: Ridiculously High SWR for G5RV Jr.  (Read 347 times)

Offline bandarr3000

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Ridiculously High SWR for G5RV Jr.
« on: November 17, 2018, 0028 UTC »
I have a RadioWavz G5RV Jr. in a quasi-inverted V (145 degrees), with the peak at 24 feet.  The matching segment hangs freely.  I have 80 ft of RG-213 running to the balun.  I'm getting these SWR readings at the end of the feedline with my MFJ-259c:

40m   7.0000      3.8
40m   7.3000      5
30m   10.1000      20.2
20m   14.2000      5.4
17m   18.1000      7.6
15m   21.3000      22.1
12m   24.9000      > 25
10m   28.5000      1.7
6m   50.8000      > 25

What is bothersome is the ridiculously high SWR on 30/15/12/6.  It's advertised for 40-6. The feedline checks out OK.  Anyone have this kind of experience with the G5RV-type antennas?
« Last Edit: November 17, 2018, 0102 UTC by bandarr3000 »
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Offline KaySeeks

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Re: Ridiculously High SWR for G5RV Jr.
« Reply #1 on: November 17, 2018, 0228 UTC »
No, I don't. However that won't stop me from asking questions.  :D

1) From memory, the SWR of a G5RV varies wildly over 3-30 MHz so it may just be that the frequency points you mention happen to have high SWR.
You do have 1.7 at 28.5 MHz so that gives me hope that the antenna isn't totally FUBAR. I seem to remember that many G5RVs are sort of resonant around 11-16 MHz so how about just plotting that range in 0.25 MHz steps while using the coax and seeing if you hit any sort of reasonable (VSWR < 2.0) nulls in that range?

2) How easy is it for you to connect your antenna analyzer to the feed point of the antenna without using the coax at all? (Yeah, I know it's getting cold outside.) Even if you have to physically lower the feedpoint temporarily for this exercise, it would be worth it to see to see the antenna alone like this, given that the SWR is so high using the coax. I don't know what to expect but I 'm trying to see if the antenna by itself actually has (more) reasonable SWR at some frequency, any frequency, this way.



« Last Edit: November 17, 2018, 0237 UTC by KaySeeks »
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Offline Brian

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Re: Ridiculously High SWR for G5RV Jr.
« Reply #2 on: November 17, 2018, 1730 UTC »
I have one here somewhere but haven't used it in years but I'm pretty certain that you need to use an ATU.

Offline bandarr3000

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Re: Ridiculously High SWR for G5RV Jr.
« Reply #3 on: November 17, 2018, 1752 UTC »
...so how about just plotting that range in 0.25 MHz steps while using the coax and seeing if you hit any sort of reasonable (VSWR < 2.0) nulls in that range?

How easy is it for you to connect your antenna analyzer to the feed point of the antenna without using the coax at all?

This summer I did go through the HF band slowly with my analyzer, but I didn't plot anything.  i found the antenna's resonant frequency (well, 1.1: 1) at just over 15 MHz.  I did this with and without the feed line in order to rule out feed line issues.  The results were very similar.  I will have to plot my findings at much smaller increments, as you suggest.  I'm using the MFJ-259C, so it will all have to be documented by hand.
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Offline Traveling Wave

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Re: Ridiculously High SWR for G5RV Jr.
« Reply #4 on: November 17, 2018, 1754 UTC »
 Louis Varney designer of the G5RV said a good ATU was needed to make it work as a multiband antenna. Plenty of info on the internet about making G5RV's work.
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Offline Josh

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Re: Ridiculously High SWR for G5RV Jr.
« Reply #5 on: November 18, 2018, 2007 UTC »
Tried swapping the wires at the feed?
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Offline ThaDood

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Re: Ridiculously High SWR for G5RV Jr.
« Reply #6 on: November 19, 2018, 1627 UTC »
The question that I have is, what is within close vicinity of that G5RV? Is it close to a sheet metal barn? Are powerlines / utility lines close by? Is it right over a wire / metal fence? Is it right over a solid sheet of bedrock under very shallow soil? (I had that up in WNY.) What I'm getting at here is possible close reflections can throw off your VSWR's on some bands, but look fine on others. Passing thoughts, again...
From DC to light, I take a huge spectrum bite!

Offline bandarr3000

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Re: Ridiculously High SWR for G5RV Jr.
« Reply #7 on: November 20, 2018, 1844 UTC »
The closest metal thing would be hardware on the tree house just below, but nothing significant.  The next would be the gutters on the house about 20 feet away.  It's clay and topsoil pretty far down (thank you, ice age glaciers). 
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Offline Ray Lalleu

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Re: Ridiculously High SWR for G5RV Jr.
« Reply #8 on: December 05, 2018, 1057 UTC »
From the Radiowavz site :
-the "G5RV jr" is only 51ft long, so this is the half size version of the G5RV, designed for 28 MHz, not the full size version designed for 14 MHz
- "An antenna tuner is required to make this antenna work on multiple bands"

From John D Heys G3BDQ in "Practical wire antennas" (first edition):
-"unfortunately the coaxial cable feed of a G5RV antenna must never be buried"
and he concludes by :
"An examination of the G5RV antenna reveals that there is little advantage in using this design, and the author would always instead  advise the use of tuned feeders all the way from the antenna centre down to an ATU."
(this last sentence has been deleted in the second edition edited by Ian Poole G3YWX).

From Steve Nichols G0KYA in "Stealth Antennas" :
he found that a G5RV antenna  used as an inverted V loses even its last advantage, the low angle lobes on the design frequency (both in real use and with modeling software)

I could not find quickly more bad advices, but I remember something like "a grossly exaggerated legend" about the G5RV. De profundis.

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Ray, western France.

Offline Stretchyman

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Re: Ridiculously High SWR for G5RV Jr.
« Reply #9 on: December 05, 2018, 1229 UTC »
Ray is right it's for 10m ONLY and why you'd use a horiz on 10m, god only knows.

There's no antenna that covers all those bands without tuning or lots of traps etc.

Please realise it's not that simple and most antennas are sold with a load of BS.

If you want an antenna, stick up a half wave dipole trimmed for the band you want.

Will work on x1 & x3 so a 7MHZ dipole will be fine on 21MHz with a clover leaf pattern.

Take (send) your antenna back and tell them they are liars, coz they are...

Str.



'It's better to give than receive' so why RX when you can TX!

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Offline Josh

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Re: Ridiculously High SWR for G5RV Jr.
« Reply #10 on: December 05, 2018, 2256 UTC »
Further reading on the antenna in question;
https://www.w8ji.com/g5rv_facts.htm
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Offline Looking-Glass

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Re: Ridiculously High SWR for G5RV Jr.
« Reply #11 on: December 06, 2018, 0746 UTC »
I operated a G5RV when I was living in the Central Pacific and found a huge variant in SWR across the bands, always been told and read that an ATU is a basic requirement of getting the best out of the G5RV.

Feedline types also play a role in various SWR levels with this antenna, primarily for the 10m band the introduction of a half decent ATU enhances coverage to some of the other HF bands with varied results and of course, loss of sensitivity etc.
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Offline Stretchyman

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Re: Ridiculously High SWR for G5RV Jr.
« Reply #12 on: December 06, 2018, 1259 UTC »
Please forget the G5RV, it only works well on 20m and a half size one as stated in this post  only works on 10m and a horizontal antenna on 10m is fairly useless anyway.

Get rid, move on...

People ALWAYS ask, what antenna to use, VERY simple answer DIPOLE

Please don't bother with anything else unless you really know what you're doing, have loads of space and time to piddle about.

The very fact the antenna has been advertised to work as stated is a blatent lie.

Str.
'It's better to give than receive' so why RX when you can TX!

                            Buy one from me, NOW!

Great discounts on ALL my transmitters if purchased via HFUnderground


                                              ;)