Chris Warren at Off Grid Ham has a nice, longish article on Portable Antennas For The Off Grid Ham. Please see Chris’s article on his site for the helpful antenna diagrams.
We’re not special.
Off grid amateurs spend a lot of time focusing on the power source for their equipment. While that’s understandable, we musn’t be distracted from the rest of the amateur radio chain. This time we’re going to look at the other end of the system: portable antennas.
To be clear, off grid radio does not require a “special” antenna. Any antenna that can be used for conventionally-powered operating can be used for off grid. Since most off grid radio is done in a portable/temporary/outdoor setting, or for survival/prepper/EMCOMM purposes, some antennas are more suitable than others. Operators who live in apartments, have HOA restrictions, spouse objections, or otherwise cannot have a permanently mounted antenna are in this mix too. Portable Antennas
It’s not practical to go over every possible option as there are dozens of them; we’ll cover the pros and cons of a few of the most popular. If you’re a newcomer to amateur radio, you’ll gain some focus about different antenna choices. At the end of this article I will include links to more detailed information.
A word about portability. Portable Antennas
The definition of “portable” varies considerably depending on who you ask. “Portable” can mean anything from a large trailer full of equipment to a handheld radio in a shirt pocket. It’s up to each individual operator to decide what works for them. Most of the antennas described in this article are not “portable” in the sense that one could back pack all day with it (along with all their other gear). They will all fit in an average car and can be hand carried short distances.
The classic random wire.
There is hardly anything simpler, less expensive, and easier to understand than the random long wire. This antenna has been around since the beginning of radio and is still used today. They can be made from any conductive wire and erected in any fashion…
If you’re going with a random long wire antenna, you’ll need a separate antenna tuner. The integrated antenna tuners on modern radios will not likely be enough. You can try it and you might get lucky, but very few internal antenna tuners have enough range of correction to get a random wire down to the 50 ohm load the radio requires. I have an external tuner that feeds an unun with a ground plane wire for my random wire antenna; that modified setup works well plugged into my FT-817. Portable Antennas
The tradeoff for ease & simplicity is inefficiency. The antenna tuner does not “fix” this problem. Whatever losses are inherent to your random wire will still be there.
Other random wire considerations.
You’ll also have to consider that random wires are not self-supporting. How do you plan on getting your antenna off the ground? You can bring a PVC pipe or telescoping mast but lugging it along that may not fit with your definition of “portability”. Another option is to run your random wire up to a tree. That too may be problematic. Is there a suitable tree at your operating site? Be aware that many public parks in the United States prohibit attaching anything to the trees, even temporarily.
Some hams advise cutting the wire to be a certain length, or to avoid a certain length. This is done to make the antenna work better across all the bands. That’s fine, but then it’s not really a “random” wire. This may seem like semantic nitpicking but if you are going to cut a wire to a specific length you may as well take it all the way and make a proper end fed or dipole antenna. My wire antenna truly is random; I have no idea exactly how long it is. For all its faults, random wires really do work, and there’s no beating the low cost and simplicity.
The magnetic loop. Portable Antennas
The magnetic loop is one of the most beloved and hated antennas in all of hamdom. I’m not sure why, but every time it comes up in conversation, strong opinions fly back and forth.
Magnetic loop antennas are a conductive loop, a variable capacitor, and a smaller coupling loop. The loop can vary in size, with some versions having less than a three foot diameter. In spite of their small size and odd appearance, mag loops are quite effective. Magnetic loops do not require a tuner and are excellent for restricted space applications, such as apartments, motorhomes, etc. One of the big benefits of magnetic loops is they do not need to be mounted high off the ground. Any elevation greater than one loop diameter is just as good as mounting it on a 100 foot tower.
Magnetic loop disadvantages.
Mag loop antennas have narrow bandwidth. This has a lot to do with the “Q” value of the antenna, which in turn is related to the antenna’s small size, but that’s more than we’ll get into this time around. If you change your transmit frequency, even a little, the antenna will need to be re-tuned. Therefore, you will need easy physical access to the loop. There are commercially made mag loops such as the MFJ-1788 with a remote tuning head. It’s an expensive option, so consider your needs and wants carefully. Also, mag loops will have very high exposed voltages, even at low transmit power levels. Although it’s not necessarily dangerous, if you touch a mag loop while it’s energized, you’ll likely get a very memorable jolt! Keep it away from children, pets, and untrained bystanders.
If you prefer to build you own, the internet is full of plans and tips for DIY versions. By the way, the loop does not have to be a perfect circle, or even be a circle at all. Octagons and other shapes are acceptable. Portable Antennas
In my opinion, magnetic loop antennas are highly underrated. Once you learn its quirky ways it will provide excellent results.
Commercially made portable vertical antennas might be the most popular antenna for off gridders. There are many choices: Buddistick, Alpha Antenna, Chameleon, and others. They generally do not require a tuner and will operate over numerous bands. Unlike mag loops, verticals maintain good bandwidth without constant adjustments. And unlike random wires, they do not take up much linear space when deployed. They’re easy to set up and take down and self supporting. There’s a lot to love here. I personally use an Alpha Antenna FMJ and I must say it delivers on its promises.
The main disadvantage is the cost. Commercially made portable antennas are pretty dang expensive for what you are getting. I realize a lot of the price tag is related to research & development expenses, plus the relatively low production runs of these products. Because portable antennas can be a serious financial commitment for the average operator, it’s important to do your homework and make sure you’re getting an antenna that is appropriate for your operating goals. Portable Antennas
There are so many other antennas that we can’t realistically go through them all here. Some of these antennas are quite effective, others not so much. Still others are just more complicated versions of well established designs. Experimenting is a big part of the fun, so don’t be afraid to take a chance. Home brew antennas are typically inexpensive and can be recycled into something else if they don’t work out.
Here is an Off Grid Ham article from 2016 that goes into detail about random wire antennas, including notes on how to build your own.
This awesome database gives DIY plans for over four hundred antennas. It’s one of my favorite antenna resources and I highly recommend you bookmark this one.
This lengthy (33 page) PDF goes into deep detail about magnetic loop antennas, including operating theory. If you are or want to be a mag loop geek, this one’s for you!
Here’s another very well written and illustrated article about mag loops.
Here is a handy on line mag loop calculator if you want to take a stab at building your own.
The Villages Amateur Radio Club published this very well done guide to stealth antennas for those living in HOAs, apartments, etc.