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Author Topic: Compare G5RV to ZS6BKW  (Read 8554 times)
KV9U
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Posts: 166




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« on: January 08, 2009, 04:55:55 PM »

Have any of you ever built both a G5RV and a ZS6BKW antenna and done an A/B comparison?

What kind of real world differences did you measure, if any?

The main benefit of the ZS6BKW appears to be the improved impedances for ease in matching at more frequencies without as much loss in the coax portion of the feedline.
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G3TXQ
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Posts: 1464




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« Reply #1 on: January 09, 2009, 07:08:06 AM »

I wouldn't expect the difference in the antenna lengths - 102ft vs 93.5ft - to have any significant effect on the radiation patterns. Even on 10m the azimuthal patterns are very similar.

As you know the ZS6BKW provides a good 50 Ohm match on 40/20/17/12/10 - more bands than the G5RV. But a lot of folk like the fact that the G5RV is a reasonable match on 80m. I guess a decision largely depends on which are your favourite bands.

The ZS6BKW probably makes for longer QSOs, explaining what the antenna is Smiley

73,
Steve
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WA7NCL
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Posts: 625




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« Reply #2 on: January 09, 2009, 08:14:32 AM »

ZS6BKW appears to be a balanced antenna.  Seems like it would benefit from a 1:1 choke balun on the coax to ladder line connection.  If you added the balun, I would expect that it does not have the common mode problems of G5RV on bands where SWR is low.

You could get the same performance as ZS6BKW by extending the ladder line all the way to the shack and using a tuner.  It would probably tune on all bands.

The G5RV is offset fed so depending on how well you decouple the feed line, you get common mode on the feed line.  This means the feed line is part of the antenna.  Which means how the feed line runs to the shack affects the performance.  That's why a lot of guys have "RF in the shack" or some guys get good results with g5rv and some don't.

I would always try to avoid antennas that have a lot of feed line radiation for the simple fact that a feedline runs down from the antenna and quite often is near the ground or grounded structures.  Who know's what the radiation pattern and efficiency will be in that case.
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G3TXQ
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Posts: 1464




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« Reply #3 on: January 09, 2009, 08:27:17 AM »

>> WA7NCL wrote: The G5RV is offset fed so depending on how well you decouple the feed line, you get common mode on the feed line.<<

Nope! The G5RV is a balanced antenna just like the ZS6BKW. Both antennas benefit from a 1:1 current balun at the ladderline/coax transition.

Steve
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W7MJM
Member

Posts: 109




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« Reply #4 on: January 09, 2009, 08:46:42 AM »

You might want to check out the discussion of this family of antennas in Bill Orr's (W6SAI) HF Antenna Handbook http://www.amazon.com/W6Sai-Hf-Antenna-Handbook/dp/0943016150

By varying the antenna and balanced line feeder lengths, you can optimize performance on your desired bands of operation.

Also take a look at www.cebik.com for his articles of the G5RV/ZS6BKW family of antennas.

Finally, there was an article in QST, which also appears in one of the ARRL Wire Antenna books, entitled "Five Bands, No Tuner" http://www.arrl.org/members-only/tis/info/pdf/9506059.pdf  
which describes yet another G5RV variant. I've used that design in a sloping configuration, achieving excellent results on 40, 20, 17, 12 and 10 meters. It worked exceptionally well on 20, where it is close to the length of an extended double zepp on that band. I used a W2DU-style 1:1 current balun to make the transition from balanced line feeder to coax.

73,
Martin
W7MJM

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G3TXQ
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Posts: 1464




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« Reply #5 on: January 09, 2009, 09:02:09 AM »

Martin,

As far as I can see the ARRL Wire Antenna book 5 band design IS the ZS6BKW. The antenna and feedline dimensions are almost identical, and the band coverage is the same, even though it's by a different author. ZS6BKW published his design at least 10 years earlier than the ARRL version!

Steve
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W7MJM
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Posts: 109




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« Reply #6 on: January 09, 2009, 10:20:30 AM »

I guess the laws of physics hadn't changed in those 10 years! Hi, hi.  -73, Martin W7MJM
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N3OX
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Posts: 8853


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« Reply #7 on: January 09, 2009, 11:27:50 AM »

"The ZS6BKW probably makes for longer QSOs, explaining what the antenna is Smiley "

Another important consideration is that the ZS6BKW, the likely lesser known antenna, does not suffer from 10dB antenna prejudice loss as the G5RV does.

W8JI's G5RV page says this:

"Announced Tests

I also did tests that called the antennas by name. I would say "This is the the G5RV,G5RV, G5RV. This is the dipole, dipole, dipole". The results were rather revealing.

   1. When I would call each antenna by the correct name, the G5RV was reported "weaker" or with "poorer audio" or some other negative comment more than 80% of the time. The remaining stations reported no difference!
   2. When I would call each antenna by the opposite name, the antenna I was calling the G5RV was still reported in some negative context about 80% of the time. The remaining percentage again reported no real difference.
"

73
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
G3TXQ
Member

Posts: 1464




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« Reply #8 on: January 09, 2009, 11:36:31 AM »

Dan,

Yes, I enjoyed reading about Tom's "experiment".

Of course you could generate even more intrigue about the new antenna by explaining that it is shorter than a G5RV ......  without saying by how much Wink

Steve
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N3OX
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Posts: 8853


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« Reply #9 on: January 09, 2009, 01:52:47 PM »

Steve,

I think it's one of the best examples of emotionally measured antennas on the 'net.

I'm working on another one.

When I get bored with what's on the radio at night, I'm going to continue trying to work European stations on 80m CW with the ERP equivalent of an 80m hamstick: about 2.5W to a full size 1/4 wave ;-)

Got 3 EU DXCC in the bag already in one night...

73
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W1YB
Member

Posts: 93




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« Reply #10 on: January 11, 2009, 07:14:15 AM »

I have built and used both recently (Unfortunately not at MY QTH.) I prefer the 'Z' because you don't need a 'match' of any sort on 6 bands. You can also do 6M at 1.3:1. We also have a resonant dipole on 80 M (which works 30 with a bent wire cap). An EFHW is used for 15M.

For what the place (and the $$$) currently allow I think it is by far the best compromise for us. They are all 'Vs' at about 60' so the 80M dipole is too low for any long haul work.

I doubt you can beat it for the $100 or so we have in the whole shootin' match.

There are folks who swear by the 'G', though.

Try both and see what is best at your QTH.

73  
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K9AUB
Member

Posts: 8




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« Reply #11 on: August 15, 2009, 03:47:09 PM »

While I don't have a G5RV up to simultaneously compare it with the ZS6BKW, I DO have a 40 meter Carolina Windom that I have compared both the G5RV and ZS6BKW against.  My ZS6BKW is up 46 feet high at the center, and the Carolina Windom is approximately the same height, or a little higher.  The ZS6BKW is most definitely a contender, and then some!  It outperforms the Windom on 40 meters by about 1 S-Unit.  30 meters not tested due to high SWR on the ZS6BKW.  20 meters was the surprise band.  The ZS6BKW isn't a LITTLE better; it's a LOT better, around 1 to 1.5 S-units.  The Carolina Windom outperforms the G5RV on 20, so this came as a surprise, and speaks volumes for the ZS.  17 meters, the ZS is about 1 S-unit better than the Carolina Windom, which in turn beat the G5RV.  15 meters... wasn't impressed with the ZS on this band, but it doesn't claim to perform well there, either.  12 meters... no signals to compare.  10 meters... the ZS is at least as good as the Windom, and that's DARN good.  The SURPRISE was on 80/75, where the Carolina Windom simply does not perform well, and neither does the G5RV.  BUT... I DO have a nice 75 meter Inverted L up with 7 radials underneath, and it's been a very good 75 meter antenna in the past.  The ZS6BKW matches it at the least.  So, we have a very serious all-band performer, probably one of the best simple wire antennas out there.  On looking at the ZS6BKW, I was struck by how very similar it is to a 20 meter Extended Double Zepp.  Except for the feedline, the two antennas are virtually identical.  And performance is also about identical on 20.  Since the EDZ has 3 dB of gain on its native band, that makes the ZS6BKW a quite competent DX contender and overall performer.  Of course, since it's an all-band antenna, it all comes together to make the ZS6BKW a wonderful all-band performer, giving at or near maximum performance on every advertised band.  If you have 90+ feet of space available to string one up, give it a try.  I guarantee you won't be disappointed.  And if you're running a G5RV, you might want to retire it.  The ZS6BKW definitely outperforms it on every band.  By the way, I did put a 1:1 voltage balun at the bottom of the 450 ohm twinlead.  A current balun would probably be better, but I didn't have one on hand.  And the voltage balun seems to do the trick.  Oh, also, twist the 450 ohm line a few turns as it descends and you'll greatly reduce noise pickup from power poles, etc.
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K4SAV
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Posts: 1831




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« Reply #12 on: August 15, 2009, 06:26:47 PM »

Here is an EZNEC comparison of a G5RV and a ZS6BKW.  Both antennas are flat-top at 50 ft and over average ground.  The attenuation of the matching sections are included plus the attenuation of 100 ft of RG8X.  These numbers represent the maximum gain at whatever elevation angle that occurs.  Chokes were assumed to have zero loss and chokes were used on both antennas. The azimuth and elevation patterns of these two are very similar.  Gain differences result mostly from mismatches in impedance.  Gain numbers are in dBi.

Freq _ G5RV ___ ZS6BKW
3.6 ___ 5.08 ____ 3.15
7.1 ___ 6.39 ____ 5.39
10.1 __ 3.78 ___ -1.88
14.1 __ 7.64 ____ 7.31
18.1 __ 7.01 ____ 6.77
21.1 __ 5.09 ___ -1.57
24.9 __ 8.67 ____ 6.75
28.5 __ 5.32 ____ 5.65

Note that neither of these antennas claim to operate all these bands.
The ZS6BKW antenna was constructed from the information in this pdf document:
http://tinyurl.com/plmexh
The G5RV used a 34.8 ft length of Wireman 551 ladder line.

Jerry, K4SAV
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K4SAV
Member

Posts: 1831




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« Reply #13 on: August 15, 2009, 06:51:32 PM »

One other point.  Since the gain differences result mostly from impedance mismatches, and that mismatch can change a lot over a band, then the gain can also change with frequency.  For example compare gains on 10 meters:

 Freq __ G5RV __ ZS6BKW
28 ____ 4.72 ____ 3.94
28.5 ___ 5.32 ____5.65
29 _____6.32 ___ 7.36
29.5 ___ 7.62 ___ 7.55
30 ____  9.0 ____ 5.86

That means a little difference in physical configuration, or a little error in lengths, or the operating frequency, can make a significant difference.  Also the azimuth patterns of these antennas on the high bands have many lobes and nulls, so the gain in a particular direction can vary by a very large number of dBs compared to another direction.  If you think about what it would take to compare these two antennas (which might not be aligned parallel)  in A/B tests, and how you would analyze the resulting data to arrive at a conclusion, the amount of testing and analysis required will boggle your mind.

Jerry, K4SAV
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G3TXQ
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Posts: 1464




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« Reply #14 on: August 25, 2009, 11:46:29 AM »

Jerry,

I see very different figures to yours when I model the two antennas. For example, on 17m I see a 5dB advantage to the ZS6BKW - that's what I would expect given that the VSWR on the 100ft of RG8X is over 30:1 with the G5RV and about 1.5:1 on the ZS6BKW.

I don't see how you have the ZS6BKW at a disadvantage on that band? I pretty much disagree with the figures for all the other bands too! I wonder what we are doing different?

Steve G3TXQ
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