Category Archives: Radio Field Craft

Antennas, Field Radio Kits, Homebrew, Portable, POTA, QRP, Radio Field Craft

Eric’s Go-To Low-Cost, Self-Supporting Antenna System for POTA

16 Comments

Recently, @JasonMartinRF left a comment on my YouTube channel mentioning his excitement about getting on the air with CW but also his concern about the high cost of antennas—especially self-supporting options that don’t require trees. His comment resonated with me because many operators face the same challenge when setting up a portable station, particularly for POTA or other field operations.

I immediately thought of my friend Eric McFadden (WD8RIF), who has extensive experience with lightweight, affordable wire antennas that don’t rely on trees for support. Eric has long used a homemade end-fed random wire (EFRW) antenna paired with cost-effective mast solutions, making it a great choice for portable activations. I asked him if he’d be willing to share the details of his setup, and he generously wrote up the following guide.

A Budget-Friendly Self-Supporting Antenna System for POTA

by Eric (WD8RIF)

Because I’ve long used low-cost homemade wire antennas for POTA, and since I usually don’t rely on trees to support these antennas, Thomas asked me to describe an antenna and support systems I often use for my POTA activations.

My “Go-To” antenna for POTA is a 28½’ end-fed random wire (EFRW) antenna with three 17’ counterpoise wires. This antenna covers 40m through 6m (and sometimes 80m) and is constructed from inexpensive speaker wire which can be purchased at big box stores in 50’ and 100’ spools. This two-conductor cable can easily be split into two conductors and the thick insulation helps prevent the finished antenna from tangling.

The idea behind the EFRW antenna is that the length of the antenna is not close to a ½-wavelength on any frequency for which it will be used. The EFRW is not resonant on any band of interest and, thus,  it requires the use of an antenna tuner (ATU).

The benefit of the EFRW is that it can be stealthy and lightweight, it can be relatively short when compared to simple resonant antennas, and it can support operation on multiple bands. It is true that this antenna requires the use of an ATU, but even an inexpensive manual tuner can be used for this purpose.

To construct my version of the EFRW, split the speaker wire into two separate conductors. Cut one conductor to a length between 28½’ and 29’ to create the radiator. Cut three more conductors approximately 17’ long. Strip a ½” or so of insulation off of one end of each of the four wires. If you wish, install banana-plugs on the stripped end; I put a green, red, or orange banana plug on the radiator and “stackable” black banana plugs on the three 17’ counterpoise wires so I can easily attach all three of them to a single “ground” post. Install an insulator of some sort on the far end of the radiator wire, or create a small loop on the far end of the wire using a knot or a nylon wire-tie for hanging the antenna. (I use military buttons as  insulators on my field antennas, and I often use large paper clips to hang the wire to the top of my mast.)

The speaker-wire end-fed random wire antenna
The speaker-wire end-fed random (EFRW) wire antenna. The three 17′ counterpoise wires are on the left; the 28½’ radiator is on the right.

 

You can connect the radiator and counterpoise wires directly to your ATU-equipped transceiver or external ATU using a simple binding-post adapter or, preferably, a 4:1 unun. No coaxial feedline is needed or, in fact, recommended.

LDG 4 to 1 unun and simple binding-post adapter
An LDG 4:1 unun (left) and a simple binding-post adapter (right).

I regularly use a simple binding-post adapter when I’m in the field with my Elecraft KH1 or KX2 field kits. I use a homebrew 4:1 unun when I’m in the field with with my Elecraft KX3 field kit. I use a commercial LDG 4:1 unun (link) when I’m in the field with my Yaesu FT-817ND field kit. (I should note that my KH1, KX2, and KX3 are each equipped with internal ATUs. The FT-817ND doesn’t have an internal ATU but I use a no-longer-available LDG Z-11 ATU with it when I deploy a non-resonant antenna.)

In the field, I suspend the 28½’ radiator as a vertical, as a sloper, or as an inverted-vee, and I lay the three 17’ counterpoise wires directly on the ground, arranged as symmetrically as possible while trying to avoid trip-hazards. (If space is limited, I might lay down only two counterpoise wires or, maybe, even just a single counterpoise wire.)

I usually support the EFRW with a 31’ Jackite telescoping fiberglass mast  (affiliate link) or an inexpensive Goture Red Fox Super Hard 720 carbon-fiber fishing pole (available from multiple sellers on Amazon) from which I’ve removed the top three sections to create a sturdy 18’ pole that collapses to less that 30″. (If you order a Goture 720, be sure to order the “7.2m” version because the top three sections are far too whippy to support a wire.)

I’ve supported the 31’ Jackite mast using a drive-on base (more on this below), bungied to a fence-post or sign-post found on-site, and bungied to my folding camp-chair.

I’ve supported the Goture Red Fox 720 on a custom stake (more on this below) and bungied to my bicycle.

Goture Red Fox 720 bungied to a bicycle and supporting a wire antenna
The Goture Red Fox 720 mast bungied to my bicycle and supporting a wire antenna as a sloper; the KH1 station is on the picnic table.

 

a loop bungie
The sort of bungie I use to strap a mast to a post, my bicycle, or a folding chair.

I often support my 31’ Jackite mast using a homemade drive-on base. This base is constructed from a scrap of 2”x10” pine about 23” long,  a 4″ black plastic toilet flange, a 2’ length of white PVC chosen to provide a friction-fit in the toilet flange, and a PVC reducer at the top. The photos below should provide enough information for you to build your own. I don’t glue any of the plastic items together; I rely on friction to hold the pieces together and I slip the 2’ pipe out of the toilet flange for easier transport in my car. (Disclaimer: I drive a small Honda Fit; I don’t know how well a 2”x10” pine board would survive repeated abuse by a large SUV or pick-up truck.)

Components of the drive-on mast support
The components of the drive-on mast support: a piece of wood, a toilet flange, and some PVC.
drive-on mast base assembled
The drive-on mast base, assembled.
drive-on mast base in use
The drive-on mast base in use at Burr Oak State Park. The 31′ Jackite mast is supporting the 28½’ EFRW as a vertical and three 17′ counterpoise wires extend out from the bottom of the front passenger door. The station is inside the car.

 

 

 

The spike for the Goture Red Fox 720 is simply a 7” length of white PCV just big enough to slip the large end of the mast into, with a matching PVC cap on one end drilled to accept a 3/8” diameter, 8” long spike. Originally, I tried using epoxy to secure the spike in the cap, but this failed, and now I’m using an appropriately-sized push-nut to hold the spike in place. (The PVC and the 8” spike were found at the local big-box store; the push-nut was found at a local well-equipped hardware store.)

Goture Red Fox 720 and custom spike
The Goture Red Fox 720 and the custom spike.
close-up view of the push-on nut securing the metal spike
A close-up view of the push-on nut securing the metal spike to the PVC cap.

 

I hope this article gives you some ideas for your own field operations!

73,
Eric McFadden, WD8RIF
https://wd8rif.com/radio.htm

A huge thanks to Eric (WD8RIF) for taking the time to document his antenna setup in such detail! His approach demonstrates that you don’t have to spend a fortune to get on the air with an effective self-supporting antenna system.

Personally, I believe that using an arborist throw line, a tree, and a simple wire antenna is often the most affordable and effective way to get on the air. However, depending on where you live or where you activate, trees may not always be an option. That’s why having a self-supporting antenna system in your toolkit is always a good idea—it gives you the flexibility to operate anywhere.

If you’ve built an affordable self-supporting antenna system that works well for your field operations, I’d love to hear about it! Feel free to share your experiences, designs, or recommendations in the comments or in a guest post. The more we exchange ideas, the more we can help fellow operators—especially those just getting started—find practical, budget-friendly solutions for getting on the air.

Antennas, Guest Posts, News, Portable, QRP, Radio Field Craft

Comparing Coaxial Loss in RG-58 and RG-316

41 Comments

by Eric, WD8RIF

I recently decided that I would operate portable during the upcoming ARRL 10 Meter Contest and would combine this operation with a pair of Parks on the Air (POTA) activations, one on the Saturday of the contest and one on Sunday. While putting together my field station for this, I realized I wanted to see how lossy my RG-58 and RG-316 feedline cables were on 10m. Yes, I could have resorted to online charts of feedline losses, and I know that the RG-316 is lossier than the RG-58, but I thought it would be fun and more enlightening to make actual measurements, to empirically determine the losses in my particular coaxial cables.

The two coaxial cables in question are both 25′ in length and both are equipped with BNC male connectors on each end. The RG-58 cable is a high-quality cable that was originally manufactured to be a 10Base2 ethernet cable, but it’s probably now over twenty years old. The RG-316 cable was recently purchased from Tufteln (link) and includes an RF choke near one end.

To make my measurements, I used my Elecraft KX2 (link) to generate RF into an Elecraft DL1 dummy load with RF detector (link), using a digital multimeter to measure the voltage at the DL1’s measurement points. I used the formula that came with my DL1 assembly instructions to calculate the measured wattage:
P = (((V x 1.414) + 0.15))^2)/50

I made measurements in the CW portion of the 10, 15, 20, 40, and 80m bands, with the KX2 set at 5 Watts output.

My first set of measurements was made with the DL1 connected directly to the KX2’s antenna jack using a BNC union:

Direct (no feedline)
Band Volts Watts
10 11.62 5.498
15 11.59 5.470
20 11.61 5.489
40 11.63 5.508
80 11.63 5.508

My immediate observation was that the KX2 appears to be generating more than 5w when it is set to be producing 5w but also that the KX2 output is essentially same from 10m through 80m.

My second set of measurements was made with the DL1 connected to the KX2 through the RG-58 cable:

Direct RG-58
Band Watts Watts
10 5.498 4.809
15 5.470 4.844
20 5.489 5.004
40 5.508 5.184
80 5.508 5.276

My third set of measurements was made with the DL1 connected to the KX2 through the RG-316 cable:

Direct RG-316
Band Watts Watts
10 5.498 4.190
15 5.470 4.322
20 5.489 4.507
40 5.508 4.774
80 5.508 4.959

I was pleased to see to see that both the RG-58 and RG-316 behaved as I expected them to: the loss increased with increasing frequency.

Using the magic of MS-Excel, I created a table of Loss in Watts for both cables, relative to direct connection and to each other:

Direct Difference (Loss) (Watts)
Band Watts RG-58 vs
direct		 RG-316 vs
direct		 RG-316 vs
RG-58
10 5.498 0.690 1.309 0.619
15 5.470 0.626 1.148 0.522
20 5.489 0.485 0.982 0.497
40 5.508 0.324 0.734 0.410
80 5.508 0.232 0.549 0.317

In looking at this table, it was immediately obvious that RG-316 is much lossier than the RG-58, particularly on 10m. By looking at the row for 10m, one can see that I am losing nearly 0.7 watts in the RG-58 but I am losing over 1.3 watts in the RG-316.

For completeness, I added columns for Loss in dB to the spreadsheet:

Difference (Loss) (dB)
Band RG-58 vs direct RG-316 vs direct RG-316 vs RG-58
10 0.582 1.180 0.598
15 0.528 1.023 0.495
20 0.402 0.856 0.454
40 0.263 0.621 0.358
80 0.187 0.456 0.269

This exercise showed me that for my upcoming ARRL 10 Meter Contest POTA outings, I would do best by connecting my antenna directly to my transceiver, if possible, without using either coaxial feedline. If conditions at the operating site require me to use feedline, I will chose the RG-58 over the RG-316.

The tables also tell me that RG-316 is pretty lossy regardless of the band; for my regular field operating, unless I’m planning to do bicycle- or pedestrian-portable operations where weight and bulk is a consideration, I’ll carry RG-58 instead of RG-316. (I purchased the RG-316 specifically for bicycle- and pedestrian-portable operations, and I plan to continue to use the RG-316 for those applications.)

At some point, I will repeat this exercise with RG-8X, a feedline that is very close in size to RG-58, is less lossy, but is also heavier and stiffer.

Antennas, Articles, News, Portable, POTA, QRO, QRP, Radio Field Craft, Skills, SOTA

Do I allow antenna wires to touch tree branches during field activations?

16 Comments

Many thanks to Keysrawk on my YouTube channel, who asks:

Do you usually try to use an isolator or do you often let your wires touch branches by just pulling them over? When you deploy 20m EFHWs, for example, do you try to avoid having an end touch a branch and only have the throw line going over the branch? I tried to go through your videos and look but you don’t often mention how far you pull the wire up and possibly over. Thanks!

This is a great question!

Before I answer, I’d like to add a little context:

  1. I am a QRP operator. The maximum amount of power I use in the field is 10 watts, but 99.5% of the time, it’s actually 5 watts or even much less.
  2. I am answering this as a field operator, meaning I’ll be referring to temporary antenna deployments.

That said, the quick answer is no, during park and summit activations, I do not worry about my antenna radiator wire touching tree branches.

I do isolate the end of my wire antennas from tree branches and leaves, but I don’t worry about other parts of the radiator touching.

Also, all of my antenna wire has some sort of jacket–I don’t run bare wire in the field.

More often than not, when I deploy a longer wire antenna–say, a 40M EFHW–I simply use a tree branch to support the apex of the antenna if I deploy it in an inverted vee configuration. Continue reading Do I allow antenna wires to touch tree branches during field activations? →

Guest Posts, How To, Radio Field Craft

Radio Field Craft: Rand explores the handy Prusik Knot

11 Comments

Many thanks to Rand (W7UDT) who shares the following guest post:

The Prusik Knot… strain relief for Wire Antennas and Coax.

By W7UDT, Randall ‘Rand’ Tom

The Prusik knot is a simple, yet effective means to provide needed strain relief to wire antennas and coax, while deployed. It’s comprised of a simple loop or length of suitable cordage (of smaller diameter than the shank, Coax or Wire, it secures).

The link below, is from our friends at Animated Knots…. It’s a brief video tutorial on how best to tie the Prusik knot. Having the Prusik in your ‘bag of tricks,’ will help make your next field deployment be a successful one.

https://www.animatedknots.com/Prusik-knot

As seen in the instructional video, the knot is comprised of a simple loop of cordage, sufficient in length for the task, which is fine, but, I would recommend NOT making a loop. Rather, keeping tag ends for easier anchoring. These tag ends should be at least 12” in length. This is called an open-ended Prusik. Either way, both have utility.

To do this, fold a 24” of cordage in half, to make a ‘bite.’ Lay the bite over the shank of the coax or wire, and feed the tag ends inside the bite loop. This forms a larks-head knot. Wrap two additional turns around and through, then dress and test the knot to form the Prusik. Simple. Anchor (tie) the tag ends at a point where strain relief is best positioned. Then adjust (slide) it to load.

After deployment, I would also recommend leaving the Prusik attached. It comes in handy, when coiling your feed lines or elements later for proper storage.

The Prusik allows it to slide along the wire or coax while free of tension, yet it holds fast under load. Much like a monkey’s fist hanging onto a vine. The tag ends, can then be affixed to suitable anchor where needed. The key here, is using a smaller diameter cordage, than the wire or coax itself.

The Prusik, along with similar ‘Friction Hitches’, can be used in any number of applications in Ham Radio. e.g. Anchoring coax, joining linked antenna elements, power cords, and adjustable guying. The list is long, wherever strain relief is needed.

I would encourage you to tie it, try it, test it, and judge for yourselves. As well, I would encourage you to check out other useful climbing friction hitches… YouTube is a great place to start. I hope you find this useful afield, and to hear you ‘On the Air!’

73! de W7UDT (dit dit)

W7UDT, ‘Rand’, lives and operates near Boise Idaho, with his lovely wife Stacy. Portable QRP operations, along with his Jeep and Harley are his ‘vices.’ Your comments and questions are welcomed. My email is [email protected].