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Author Topic: g5rv or ZS6BKW  (Read 1649 times)
VE7SHM
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Posts: 50




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« on: May 09, 2013, 05:55:23 PM »

I have both took the g5rv down and put up the zs6bkw and it match better every were but 80 meter which i use a fair bit over 10.1 ..I put my G5RV back up but changed the ladder line to 300 ohm now i get this i never use 10 meter is it worth put the zs6bkw back up  it match a little better on a few of the other band but not bye much thanks

3.729 --1.69

3.968--3.60

7.055 -- 1.92

7.268-- 1.73

14.200--3.95

14.300--4.65

18.300--4.73
18.100--5.47

28.665--5.59
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W5DXP
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Posts: 3559


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« Reply #1 on: May 10, 2013, 06:27:23 AM »

I have both took the g5rv down and put up the zs6bkw and it match better every were but 80 meter ...

Here's my SWRs for my ZS6BKW. On 80m, I have a 500pf series doorknob capacitor on the coax side of the 1:1 choke. That cap is shorted out on all bands except 80m.

3.85 MHz, 2:1

7.05 MHz, 1.3:1

14.175 MHz, 1.4:1

18.14 MHz, 3.2:1

24.95 MHz, 1.8:1

28.4 MHz, 6:1

29.3 MHz, 1.1:1
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
W8JX
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Posts: 5659




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« Reply #2 on: May 10, 2013, 08:32:04 AM »

Here's my SWRs for my ZS6BKW. On 80m, I have a 500pf series doorknob capacitor on the coax side of the 1:1 choke. That cap is shorted out on all bands except 80m.

Do you have a picture of how you did this?
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W5DXP
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Posts: 3559


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« Reply #3 on: May 10, 2013, 03:21:08 PM »

Do you have a picture of how you did this?

No, but it's easy to describe. For 80m:

XMTR---500pf cap---1:1 choke====ladder-line=====dipole

For all other HF bands:

XMTR----short--------1:1 choke====ladder-line=====dipole

The 500pf doorknob cap is mounted in a metal box with a coax connector for input and a coax connector for output. A SPST knife switch is mounted on the outside of the metal box electrically in parallel with the capacitor. The knife switch is open for 80m operation and closed, thus shorting out the cap, for operation on all other HF bands. With the knife switch closed, shorting out the cap, the antenna is a standard ZS6BKW.

The way the cap works is to find the frequency at which the impedance looking into the tuned feeder is 38.5+j83 ohms which is 3.85 MHz for my ZS6BKW antenna system. Since the 500pf capacitor is -j83 ohms, it resonates the antenna system for an SWR of 1.3:1. (Note: Such is a good reason for carrying around a Smith Chart in one's head.)
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
VE7SHM
Member

Posts: 50




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« Reply #4 on: May 10, 2013, 04:04:44 PM »

I have both took the g5rv down and put up the zs6bkw and it match better every were but 80 meter ...

Here's my SWRs for my ZS6BKW. On 80m, I have a 500pf series doorknob capacitor on the coax side of the 1:1 choke. That cap is shorted out on all bands except 80m.

3.85 MHz, 2:1

7.05 MHz, 1.3:1

14.175 MHz, 1.4:1

18.14 MHz, 3.2:1

24.95 MHz, 1.8:1

28.4 MHz, 6:1

29.3 MHz, 1.1:1

Very interesting my ZS6BKW (w8amz) is far better made than my mfj g5rv and has a better match every were but 80 meter were it's very bad i will give your idea a try cause in the end i think the zs6bkw is a better wire ......thanks
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W5DXP
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Posts: 3559


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« Reply #5 on: May 11, 2013, 05:44:55 AM »

...i will give your idea a try cause in the end i think the zs6bkw is a better wire ......thanks

Note that a 500pf cap is not a perfect SWR=1:1 solution. A variable cap would result in better SWRs across a wider bandwidth. That's what I'm going to try next when I get time. Maybe 300pf fixed in parallel with a 100pf variable would be better.
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
WB6BYU
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Posts: 13152




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« Reply #6 on: May 11, 2013, 08:57:34 AM »

Quote from: VE7SHM

Very interesting my ZS6BKW ... has a better match every were but 80 meter were it's very bad...



That is a feature of the design.

The G5RV design should give a reasonable match on 80, 40, 20 and 12m.

The ZS6BKW was designed to give a better match on more bands, but 80m was not one of them.
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VE7SHM
Member

Posts: 50




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« Reply #7 on: May 11, 2013, 09:34:06 AM »

Quote from: VE7SHM

Very interesting my ZS6BKW ... has a better match every were but 80 meter were it's very bad...



That is a feature of the design.

The G5RV design should give a reasonable match on 80, 40, 20 and 12m.

The ZS6BKW was designed to give a better match on more bands, but 80m was not one of them.

I kind of knew that but was hoping it would have been better on 80 meters its un readable with my lg-100a ......But 40,20,17,10, match up great with the ZS6BKW
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ZL3OF
Member

Posts: 20




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« Reply #8 on: May 12, 2013, 07:42:27 PM »

The radiation pattern of the ZS6BKW (93ft) and G5RV (102ft) are very similar. So use the version that best matches the band(s) that you are most interested in using.
My preference is the ZS6BKW because it matches on more bands than the G5RV and I tune around a lot.
My auto ATU can match it easily on 80m and the coax section is only 4 metres long so losses are no problem there, 15m and 30m are a different story though!
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