Posted: 8/13/2017 5:52:09 PM EST
So, I'm kind of diving in head first to this whole ham thing. Passed my general back in July and have already got my 2m/70cm up and going on a mobile. I've got an HF radio on the way (Icon 7300) along with a G5RV Junior wire antenna, power supply etc.
I've got friends that live right in the middle of the path of totality for the upcoming eclipse outside of St. Louis and have been reading that there will be a lot of ham activity that day so I wanted to try and participate. Here's my question as it relates to this antenna. I'm going to configure in an inverted V and have the capability to get the center mast up to about 23' with items I have laying around (aluminum light stand and carbon fiber boom pole). I've read conflicting comments about whether or not I will need a balun for the feed line.
Manufacturer says no because of of the ladder line but others have indicated that a balun is necessary. Any advice?
Here is the mast, put it up just to make sure it would be stable. May move the guy lines higher, have plenty of extra rope in them.
The 17th Edition of the ARRL Antenna Book has little to say about the G5RV. However, this document http://www.hamuniverse.com/n4jaantennabook.html states that a balun is used, contrary to the original design of the antenna. Section 14 covers the G5RV (it's about halfway down the link).
Incidentally, the linked document is well worth downloading and printing out (it's a long .pdf file) as it not only covers the more popular antennas used, but also info on propagations and feedlines
It would be a good thing to put a good RF choke at the point where the ladder line transitions to coax. Is it required? No, baluns are rarely "required", but you get better performance with them.
Never used a G5RV myself but many do with good results. I concur with Gamma762, a choke would be a good idea at the transition of window line to coax. May not be needed at all, you will just have to see. The certain length 450 ohm window line is part of the matching network or matching stub if you will on that antenna. I would recommend a ferrite-based choke instead of an air wound coax type. Most wound coax over PVC type chokes for instance don't not work well over the entire HF spectrum. You can wind one for 10m frequencies & it will not offer enough impedance on lower frequencies.
I don't know the tuning range of the 7300's internal tuner, (I assume it has one?) but some bands will present large or low impedance's to the tuner. Yes, you will need a tuner to work multiple bands on this antenna. Just hang it the best you can & you will be able to work enough bands to keep you busy a long time.
** Updated: I looked up the Icom 7300 tuner specs: Matching impedance range: 16.7 ohm–150 ohm unbalanced (VSWR better than 1: 3). This is about typical of most internal tuners. Once antenna is up at operating position, you can check impedance values with analyzer on the bands you wish to use. **
Good tech and advice above
Take manufacturer's statements with a grain of salt in this case - unfortunately there's sometimes a informational "race to the bottom" that goes on with small profit margin items like this.
So you end up with the "no balun required, and be sure to use 100 ft of coax for our ALL band G5RV" type stuff.
As above, the balun isn't actually "required", but is needed for optimum performance.
But G5RV's are MULTI band antennas, not ALL band antennas, and the phony "100 ft of coax" stuff simply uses coax loss to mask high SWR. IOW you end up with and ALL band antenna that only puts out decent power into the air on a few bands - the other bands waste the power in heating the coax.
If you like modeling these things, IMAXGRAF works well to show what's going on with G5RV type antennas, either in the old DOS program or newer xcl version ===> http://www.w5dxp.com/goodbad/goodbad.htm
If you need to get a quick antenna up, you might just go with a horizontal dipole, single band, Its what I do for portable ops.
I don't use a choke, balun or anything else. 1.0 swr and 49 for impedance.
I get the whole antenna up around 20' with each leg suspended in a tree, and the feed point on a pole or tree as well.
I have had a few people that have tried to give me a g5rv antenna, and when I ask why, they noted it didn't work as well as their dipoles they had up, and would rather have a resonant dipole than that antenna.
OP, the balun thing can be confusing. There is a lot of information (often more confusing) available on this subject. An "RF Choke" type of balun (a.k.a. as 1:1 Current Balun) can be beneficial if installed at the end of coax cable, as close to the antenna feed-point as possible. In your case, the antenna feed-point will be where the coax cable connects to the ladder line.
Yes, your antenna should work without a balun. A balun will keep RF energy from flowing on the outside of the coax's shield thus making it a part of the radiating antenna.
BTW, I also have a G5RV JR antenna in my "Radio Go Bag". It works ok on 40-10m bands. Obviously it requires a tuner. It's not a high performance nor high efficiency antenna but it's an acceptable compromise. I simply put 3 "snap-on" type RF chokes at the end of the coax cable. It's not a very efficient RF choke but it's better than no choke at all. A better balun would have been a proper choice but I hardly ever use that antenna to justify it.
Also it's advised to run the ladder line perpendicular to the antenna and perpendicular to the ground (for as long as possible. Keep the ladder line away from any conductive objects and the mast (if conductive).
1) Use a 1:1 Current Balun
2) Use the shortest length of coax needed to go from the transceiver to the antenna
3) Try and keep your Dipole legs as flat as possible. For the G5RV Junior, if your center is at 20', keep your legs elevated to at least 10'. This will keep the interior angle on the inverted V greater than the 120-degree minimum. At 10' on the dipole ends with a G5RV Jr, you should have around 140 degrees if the center is at 20'.
Thanks all for the advice. Looks like I need to cook up a balun to get the best out of the antenna, seems easy enough to do.
@OutlanderSystems thanks for the advice for the ends, was planning on using a couple other smaller stands for the ends but may not have run them all the way up to 10', will be easy enough to do.
@Jester_MP I thought about just stringing in a couple trees but it has been a while since I've been to my fiend's place and I don't remember how many trees he has and where they are located on his property. I figured having the masts available I'll have the most options for set up.
Think I am going to whip up a simple 2m dipole as well, figure that there may be a good deal of traffic on those frequencies and having an antenna (not attached to my truck) will be of benefit too...off to the hardware store after work.
The really unfortunate thing is that I'm headed out of town for work for several days and all of this will just be sitting in boxes until I get home...
With all the info above, i.e. no excessively long coax run, and a 1:1 Current balun / Choke, the antenna will perform great - efficiency is easily better than 70 % on the bands the G5RV version is intended for.
If you like rolling your own, avoid the "ugly balun" stuff - coax air-wound chokes are narrow-band devices and can cause as many problems as they can solve. Steve G3TXQ has a great article on the details of wideband ferrite chokes "Classic G3TXQ Balun / Choke Article" ===> http://vtenn.com/Blog/?p=28
And, as always, HEIGHT is your friend - get that unit up as high as is practical, and it in general will reward you with lower angle radiation and stronger DX signals.
If you're looking for a quick, cheap and decent performing antenna for 2m/70cm, check out the dual band N9TAX slim Jim. Dead simple to deploy and take down, and works reasonably well.
My son and I use a MFJ G5RV that is 30 feet above ground. MFJ's instructions required a coil of coax, but I used an ugly balun instead.
It works fine and we don't have any problems with it. He's used it to make contacts around the world, so its working fine for us.
I'm using a home-brew ZS6BKW antenna. I took a el-cheapo MFJ-1778 G5RV and took 3.7ft. off each end of wire and added 11ft. of ladder line. It is supposed to perform better on some bands. A comparison can be found here.
It seems to work OK, I've had contacts on the west coast and a couple of Russian ones. If I had it up higher, it would probably do better. Right now, it's strung up at the center bit at the top of a Harbor Freight flagpole that is 20ft. tall. Some of the ladder line is sitting on the ground at 20ft. but should be OK at 30ft. I put a short bit of coax from the ladder line to the house and put a lightning arrestor and an RF choke on the line before the coax that runs in the house.
If using true ladder line, that is, two wires spaced 4"-6" apart, like a rope ladder, use a 4:1 balun near the transmitter, with
coax coming in to your tuner/power meter/transceiver. True ladder line is 600 ohms.
If using window line (often mistakenly called ladder line) which is like giant TV twinlead, use a 4:1 balun. Window line is
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