The Truth About the G5RV Antenna

And Two Other Improved Alternatives To This Basic Design

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G5RV antenna1. The G5RV Antenna
Although the popular G5RV antenna is often promoted as an antenna that works well on all bands from 80 through 10 meters, that is absolutely NOT the case.

This is not to say that the G5RV doesn't work well on SOME bands. But it does NOT work well on ALL HF bands. That's my point.

There are some bands where the SWR on the coax is out of sight and the feedline losses are astronomical.



2. The ZS6BKW Antenna
Depending on which bands you want to operate, there is a better design which involves shortening the antenna and lengthening the section of ladder line. G0GSF (ex-ZS6BKW) came up with a similar design that is a significant improvement over the G5RV.  Even that design still doesn't cover all the HF bands

The ZS6BKW's top section is 93' (instead of 102'),
 and the 400 ohm ladder line matching section is 39.8', (instead of 30.6').

Before you buy or build that G5RV, do yourself a favor and Google g5rv ZS6BKW|G0GSF.
To summarize:



3. The W0BTU Antenna
Our modification to the G5RV and ZS6BKW antennas, while also somewhat of a compromise of frequency ranges and VSWR, lets us use all HF bands between 80 and 10 except 30 and 60* meters.

EZNEC file for the W0BTU version, which uses a 97' straight top section, a 39.5" length of "450 ohm" (usually, the actual Z is 420 ohms) window line, and 75 ohm coax feedline.

You can tweak the lengths slightly to suit your height, operating preferences, etc. The design height of these SWR plots is 40' above ground.

Frequency vs. SWR plot (3.5-29.7 MHz.)
The above bands can be used without switching the feedline, just like the ZS6BKW antenna.
However, removing 8.5' so that the length of the open wire line is 31' lets this new design also work well on:

The W0BTU antenna covers more bands than either the G5RV or the ZS6BKW.
A simple DPDT knife switch (or banana plugs and jacks) near ground level lets us use 75/80 and 15 meters, if desired. Even though the VSWR is relatively high on 75 and 80 meters, lower coax loss on that band at least lets us operate there using just one multiband antenna.


NOTE: The remaining 8.5' section is not connected in any way on 75, 80, or 15 meters. It must be totally removed from the feedline. If one end of it is left connected, the antenna doesn't work right.


* Well, it will work on 60 meters, if you use a 76' length of the 420 ohm window line; SWR is below 1.5:1.


Note that the SWR values in the above charts are
at the antenna. Some commercial G5RV antenna designs rely on the loss in a long coax feedline to bring their claimed SWR down in lieu of—or in addition to—an antenna tuner.





The G5RV vs. the ZS6BKW
Per http://www.karinya.net/g3txq/g5rv:


G5RV
Band   Best    Worst
       VSWR    VSWR

80m     3.2    12.6
40m     4.9     5.9
30m    48.     49.5
20m     2.5     3.7
17m    32.1    33.6
15m     6.1    12.9
12m     3.6     4.6
10m    51.     59.6

ZS6BKW
Band    Best   Worst
        VSWR   VSWR

80m     8.3    18.8
40m     1.1     1.4
30m    87.     89.
20m     1.2     3.2
17m     1.4     1.6
15m    80.     90.
12m     1.2     1.4
10m     1.5     9.7



Balun
You should use a ferrite-core broadband 1:1 current balun (choke) right at the junction of the window line and coax to keep RF off the outside of the coax shield. We used one of K9YC's (Jim Brown) designs using about 6 turns of the 75 ohm coax feedline wound through 4 or 5 stacked Fair-Rite 2.4" diameter #31 ferrite cores. A "ugly" balun made from coax wound on an air core is not recommended, as it does not span near as wide a frequency range (see http://www.karinya.net/g3txq/chokes/).


A much better alternative to any of these three antenna designs is running the open-wire line from the center of a dipole all the way to a balanced antenna tuner, which was recommended by Louis Varney, G5RV himself. That antenna will work on ANY band from 80 through 10 meters. (And that's what I eventually did with this improved antenna design here at my QTH.)




References:



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http://www.w0btu.com/g5rv_antenna.html - Last Edited December 18, 2013

 

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