G5RV versus a Fan Dipole
Hello to all -
I currently have a G5RV up at 35-feet in an inverted V configuration, and a 20m dipole up at 30-feet on the same fiberglass mast.
I know the G5RV isn't the greatest, and I'm considering a change in antennas.
Would a Fan dipole be more efficient than the G5RV? since I do have two spots available on the fiberglass mast (35-feet and 30-feet), I am considering two different fan dipoles to gain a little more efficiency.....the top one being 80, 40, 20 or something, and then 17, 15, 10.
I don't use 80 or 40 much, I usually use 20, 17 and recently 15.
Thanks in advance for the advice!
Put the Fan dipoles up. Better antennas than the G5RV.
I have a Fan for 80/30. I had it configured for 80/40. I just changed it over to 30 meters yesterday because I put up a trap 20/40 dipole yesterday.
With the Fan dipoles you can tune them so you do not need to run a tuner on the main frequencies you use. If you do not run an amp then the rig's auto tuner will handle the SWR if you move off your favorite spots of the band.
Take your time trimming them.
Make goal here is to try to avoid using the external tuner and I am almost there.
Good Luck.........Rick VE3FMC
Is this a classic G5RV with the 34 foot matching section plus coax on the end to the shack? Are you using a tuner? Those are things you need to tell us.
A G5RV (classic style, with the twinlead/ladder line matching section and coax) is a very good antenna on 20 meters and 12 meters with no tuning. It will have some gain over a 1/2 wave dipole cut for 20 meters. It will also show gain on 12. Keep in mind that above 1/2 wavelength a dipole starts to show distinct patterns and nulls in different directions.
A G5RV is a good antenna. It is more versatile than a 20m 1/2 wave dipole - however, you have to use a tuner to operate it multi band.
Now, if you are tuning it, you have to consider that the impedance mismatch on 30m is very, very high. This makes the choice of feed line quite critical. Google coax calculator and check different lengths of feed lines (your coax) and see what they have for loss at different SWR.
There is nothing more efficient about a 20m dipole over a G5RV. With a good tuner and coax section that is not too small a grade, and not too long, the G5RV will perform as well as the 20m dipole or better.
The resonant frequency of the antenna (or system) doesn't have anything to do with its *efficiency*
As long as the system is matched to the transceiver, the only losses come in how the line performs nominally and how the line handles the high SWR on the line.
If you only have 30' of height to work with, its going to be tough to squeeze a fan dipole in. They are also a real pain to hang and tune.
See if you can get up higher than 30'. That will help you more than almost anything els you do - provided all the other variables are in place.
Last edited by AE2CS; 11-23-2010 at 01:57 PM.
This really depends more on what you hope to accomplish, and expect from an antenna than anything else. I would certainly say that a "fan dipole" is an excellent antenna. You just have to expect that the elements will have a certain amount of "coupling" to one another and this will skew the performance a bit from a single band dipole. You also have to consider the mechanical construction of a fan dipole, which can be quite "difficult" to maintain, especially when the first windy day comes along.
It is hard to know for sure precisely how your proposed fan dipole will radiate...it all depends on the bands, number of elements, spacing, flat-top or vee arrangement, etc. But somehwere close to a skewed or distorted figure-8 pattern on each band would be likely. This is as opposed to the G5RV, which ranges from roughly figure-8 to clover-leaf to an almost end-fire beam pattern with lots of lobes and nulls, depending on the band. Your performance might seemingly improve on some bands, but suffer on others, particularly if you are used to "good DX" on a certain band (hypothetically, an advantageous lobe to Europe on 20 meters, for instance, on your G5RV, whereas the Fan Dipole may suffer in that direction).
There really is nothing WRONG with a G5RV, in any way, when compared to any other antenna. You just have to understand the difference in how it behaves vs. other antenna options. The biggest gripe that many of us have with the G5RV ISN'T that its a bad antenna (it certainly is not), its that manufacturers and vendors package it and sell it as a miracle antenna, and new hams have high expectaions with very little by which to compare it to, thinking they have the BEST antenna in the world without ever learning the truth, which is that it is no better or worse than many other antenna designs.
My favorite mode? Morse, of course.
Currently I am using about 30-feet of RG-213 to feed the G5RV, terminated at the 35-foot feeder with an open coil choke. The coax runs into the house to the internal tuner on my Kenwood TS-570sg.
The 20m dipole is fed with about 65-feet of RG-8x (its what I had on hand). I can see some difference in receive on the two sometimes, the 20m dipole always winning an S unit or two over the G5RV, even though the 20m dipole is slightly lower (by 5-feet) than the G5RV.
Using my MFJ259b I can see the G5RV isn't overly resonant anywhere (closest on 20m natuarlly)....the best SWR is around 2:1. It is my understanding that the closer to resonant the antenna is, the greater efficiency (less mismatch loss) it has in radiating a signal.
Originally Posted by AE2CS
I beg to differ with that statement. I have a 80 meter dipole up and the apex is right at 30 feet. My lot is 60'X110' and the dipole fits in. One leg is not straight but it fits.
They are not a pain to tune either. If you can access the ends of the dipole then they are easy to tune. I never solder the insulator on until the antenna is tuned. And I tune mine the old fashioned way, without an analyzer.
I use 4 tie off points for my 80/30 meter fan.
No problems with my Fan, setting it up was easy. At one point I had 4 bands on the same feed point.
If you are only using 30 feet of RG 213, it is very doubtful that you are seeing much by way of noticeable mismatch loss on all but perhaps the most overly mismatched bands. And being that 20 meters is a "natural" match for the G5RV and your resonant dipole, even with a slighly higher SWR perhaps on the G5RV, I would doubt SWR having anything to do with the S meter difference you are seeing.
Originally Posted by AK4BM
Rather, on 20 meters the G5RV is a clover-leaf pattern, and your dipole is a figure-8 if properly installed. This means that you have 4 nulls in the G5RV and only 2 with the dipole. Also, having 4 nulls and a clover-leaf means you also have 4 LOBES. This has the benefit of offering more "diverse" geographical coverage, but it is my understanding that gain in 2 of 4 directions is sacrificed vs. the dipole with two lobes and two nulls. This would account for MANY times where the s-meter would be showing a better signal on the dipole. HOWEVER, theoretically there would also be times where the G5RV SHOULD beat the dipole, when the extra lobes come into play. This may not, however, become evident if the antennas are oriented in such a way that the extra lobes are not pointed toward areas of high activity.
My favorite mode? Morse, of course.
Since you don't care about 80m operation, here's what I would do. Convert the G5RV to a ZS6BKW, i.e. change the dipole length from 102' to 90' and change the parallel matching section from 30' to 40'. That will give you 40m, 20m, 17m, 12m, and 10m operation. Then convert your 20m dipole into a 15m dipole for operation on that single band. Seems that might satisfy your needs with minimum effort.
Originally Posted by AK4BM
I personally use a 1/2WL 20m dipole fed with ~64 feet of ladder-line for operation on all HF frequencies above 14 MHz.
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.
That's an excellent idea. Thanks for figuring out the lengths.
Originally Posted by W5DXP
Would someone more knowledgeable than me please explain what antenna efficiency is and is not?
A non-resonant antenna (e.g. a G5RV operating on 20m) is NOT less efficient than a "resonant" 20m dipole.
Impedance mismatch does not mean the antenna is inefficient.
This is a common myth - that "resonant" antennas are "more efficient" than non-resonant antennas.
It gets repeated over and over and over again.
An antenna is NOT a tuning fork. We like to think of it that way - but it doesn't work that way.