G5RV - use with or without balun?
I am making a 10-40 meter G5RV (the lite version) and am using 450 ohm ladder line. Would it be appropriate to use a 4:1 balun at the bottom to connect 50 feet of RG8x coax?
You would be better off to make the total length of the antenna itself 20 meters long (half wave at 40 meters) then use the parallel line feeder all the way to the radio, couple it with a simple tuner to match the feedline/antenna combination to the 50 ohm antenna port on the transceiver.
Then you could use it on any band you want with better efficiency than the "compromise" G5RV type antenna which uses a parallel line section between a coax feedline and the antenna proper to try to provide a match to the transmitter over a wide frequency range without a tuner.
If you have an unbalanced tuner, then take the ladder line str to it. Your results will be multitudes better. That is what he is trying to say. If you dont have a tuner however, the balan will be needed. BUT consider picking up a tuner instead. Its night and day with performance.
The "origional" design of the G5RV does NOT use a balun. Coax and ladder line are directly connected. It will work just fine without it. Just be sure to adhere to the proper lengths of the ladder line & coax. I cant remember what those were right now but I presume you have the plans etc. In fact, it should tune up real nice with the internal (3:1) tuner on 40-meters, of whatever radio your using.
Last edited by N9XV; 06-09-2008 at 10:54 AM.
It's all about the antenna! Build the antenna. Put up a bigger antenna, put up a better antenna, you can never over achieve when it comes to antennas!
The G5RV is one of the most maligned antenas today, with most of the negative comments being wrong.
Originally Posted by kb9wwv
You can see how a G5RV really works at a few links:
You can and should use a balun at the transition of the coax to the balanced line, but it should be a 1:1 choke or current balun, You absolutely do NOt want a 4:1 balun.
Thank you for all the advice so far, I really appreciate it. I happen to have a Kenwood TS-450 with internal antenna tuner and, at this time, do not have plans to purchase an external tuner. So it seems i need to get a "1:1 choke or current balun". Thanks! I'm heading out camping this week and am going to give this G5RV a try.
The G5RV is maligned for a number of reasons but the primary reason is: If you have a tuner that will accept balanced feedlines (has a built in balun) and you have space for a fourty meter dipole, you will have a better result just feeding the antenna with balanced line all the way to the tuner.
A G5RV designed for 20 meters will have more loss on any band (other than 20 meters) when compared to a dipole of the same size fed directly with balance feeders into a tuner. That's a fact. Also, the G5RV will not provide a flat SWR on any band and requires a tuner to work. The dipole fed with ladder line can be tuned to nearly 1:1 SWR with less loss than the G5RV. The choice is yours.
i'm sorry you don't have the experience or understanding to realize that others possess a skill set that you seem to dismiss as fantastical.
G5rv For 10-40 Meters
I have homebrewed a 40/20 fan dipole antenna with a 1:1 choke balun that directly connects to my feedline which is RG8X. See the building plans at hamuniverse.com in the antenna design section. The plans call for more wires but I only built the 40/20 meter portion. The balun is called the "Ugly Balun" which is also described very well and easy to build. I use a Kenwood TS-450SAT and the built-in tuner will work well for 80-10 meters. I built the choke balun because it was recommended to eliminate RF in the feedline coax. The antenna is installed in my attic in a north/south alignment. I am sure if it was installed at 40 feet outdoors it would no doubt work much better. Good luck with your project!
73's de Bob
Unfortunately, that "fact" is more of a myth than anything else. Let's get real. For 80m, 40m, 20m, and 12m, the loss difference in ladder-line fed 102' dipoles and G5RVs is virtually unmeasurable in the ballpark of 1/10 of one S-unit. What you say is measurably true for the G5RV only on 30m, 17m, 15m, and 10m.
Originally Posted by KA4DPO
Here's a case where the G5RV is proven to have less loss on 3.6 MHz.
Assume a 102 foot dipole feed with 100 feet of 450 ohm ladder-line on 3.6 MHz. The feedpoint impedance is 30-j408 ohms according to EZNEC. The feedline loss calculator at http://www.vk1od.net/tl/tllc.php says the losses in the ladder-line will be 0.731 dB.
For the G5RV, the losses in the series matching section will be the same as the first 30 feet of the ladder-line fed dipole and equal to 0.343 dB. The SWR on the remaining 70 feet of RG-213 will be 3:1 according to EZNEC making the coax losses equal to 0.340 dB and the total G5RV feedline losses = 0.683 dB.
At 3.6 MHz, the G5RV actually has less loss than the ladder-line fed dipole because the ladder-line is sporting an SWR of almost ten times greater than that of the coax. Of course, on the four HF bands where the G5RV performs well, the difference is virtually undetectable. Who can detect 1/10 of one S-unit difference?
73, Cecil, www.w5dxp.com
The maximum power transfer theorem works just as well for a non-resonant antenna as it does for a resonant antenna.
Half Size G5RV with Balun
I've installed today an LDG 4:1 balun. this was just a test and within few hours i've been on air i can say that i prefer this antenna with the balun.
with this set up most bands (especially the 20m) are less noisy with an improved S/N ratio. That said the SWR has increased on 20m as if the antenna has lost it's original property of being a 20m antenna design.
The balun however has made possible to get a better match on 40m and also on 80m which i was not able to do before. Obviously performance on 80m is poor and i've not made any QSO yet.
All other reports (mainly European Sations) are more or less similar to the previous unbalanced set up.
The coax feeder has about 9 turns RF chocke
hope this can help
73 de Rod / 2E0RPS