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Construction Notes: VO1DR Monopod Antenna Mount

July 3, 2024 Thomas Witherspoon 8 Comments

Many thanks to Scott (VO1DR) who shares the following guest post:

Construction Notes – VO1DR Antenna Mount for Camera Monopod

by Scott Schillereff, VO1DR

Further to my article about radio during trip to Portugal, a number of readers asked for details on how I mounted my whip antenna system to my camera monopod for /P use. Here are some photos and notes on this.

General notes:

This is a “straight-through” design. Just direct connections from the BNC center pin to whip (via brass nut), and BNC housing to radial connector.
This is not a cook-book construction article, rather just a show-and-tell of how I built mine. You can use what you have on hand to build something similar.
I suggest you start with your telescoping whip, so you know the size and threads for mounting bolt.
You could use any type of connector for the radial (wingnut, knurled nut, spade lug, alligator clip, whatever you like). I prefer banana jacks since a) I can push in the radial banana plug fast, b) the plug is a weak release point (pulls apart if someone walks into the radial), and c) I can easily attach additional radial wires, if desired.
Use a strong case (metal clamshell or cast aluminum work well). With the whip extended, there can be substantial forces (bending moment) from wind or handling. A tiny plastic case would be fractionally lighter but might fail.
For size, the one I used (25 x 25 x 50 mm; 1” x 1” x 2”) is about as small as I would go. It needs to have a big enough footprint to sit firmly on a camera mount fitting.
Use high heat (e.g., Weller 100-140 W solder gun) when soldering the center pin wire to the brass whip mounting nut. Solder the wire to the brass nut before you epoxy the nut.
I custom made the white plastic insulating bushing (where whip screws in). This was from a nearly-right bit from my junk box. You can be creative here. You could also epoxy on short piece of close-fitting, thick-walled PVC pipe around the outside of the whip mounting hole as a supporting sleeve to give some lateral support to whip when it is screwed in.
Dry-fit everything (before epoxying) to make sure nothing touches that shouldn’t and you can screw in the camera nut and whip fine. Test proper continuity of center pin and radial connections to BNC fitting. Once glued, there’s no going back!
For surfaces to be epoxied (metal nut sides and bottom, insides of mounting case), slightly roughen with sandpaper or jewellers file, then clean with isopropyl alcohol and Q-tip. This will increase adhesion and strength.
Use good-quality, high-strength, long-cure epoxy (e.g., JB Weld), not el-cheapo 5-minute epoxy from the Dollar Store. LET THE EPOXY COMPLETELY CURE BEFORE MESSING WITH IT! Just walk away from it for a day… (your patience will be rewarded).

Figure 1 – VO1DR Antenna Mount, clamped onto top of monopod. Coax goes to BNC on left; whip screws into top; raised radial connects by banana plug on right

Figure 2 – Antenna mount unclamped from top of monopod. The black plastic fitting (at right, with wedge-shape) fits into slot on platform at top of monopod (at left) and clamps in with cam arm. Large steel screw attaches wedge fitting to antenna mount case. Ruler shows scale of things.

Figure 3 – Antenna mount case (right) unscrewed from camera mount fitting. Steel screw is standard camera mount size (1/4-20 thread size). Black silicone cap keeps dust out of BNC connector. If your camera mount does not have a detachable wedge fitting (like the one on the left), you would simply screw the camera mount screw directly into the bottom of the antenna mount case.

Figure 4 – Top of monopod dissembled to show (clockwise from top): black monopod tube with telescoping whip stored inside (stainless steel with 10 mm brass mounting bolt), antenna mount case, detachable camera mount fitting, and round top plate of monopod. For my monopod, I had to remove one tiny screw and apply gentle torque to break a weak glue joint of this round piece on top of the monopod leg. It remains a snug hand fit (no screw needed).

Figure 5 – Fully assembled whip antenna mount with wiring. Radial (blue wire) with tie-off cord (yellow) at left; RG174 coax (5 m) at right. Whip is only ever screwed in hand-tight. Deploying in the field, I first tie off the monopod to something (park bench, picnic table, fence, tree), then screw the collapsed whip into the antenna mount and clamp mount on top of monopod, then plug in radial and tie the yellow cord off to something (straight out at 2 m height or slope down to ground anchor), and finally connect the coax to the rig. When all in place, I carefully raise the whip (slowly, with two hands to reduce bending forces). Take-down is all in reverse.

Figure 6 – Detail of antenna mount case. Case is 50 mm x 25 mm x 25 mm aluminum clam shell box with square metal end plates. These end plates are screwed in to hold the two halves together. White plastic bushing provides additional lateral support for the whip when it is screwed in. The bushing is glued to outside of case with CA (Krazy) glue.

Figure 7 – Inside of antenna mount case. On left, a ¼-20 steel nut is epoxied to inside of case with strong JB Weld epoxy. In main case, a 10 mm brass nut is epoxied to inside of case with an insulating washer beneath. This brass nut connects to the whip and is “hot”, so must be insulated from the black aluminum case. Yellow wire connects center of BNC to brass nut (soldered). Black wire connects ground side of BNC to radial banana jack. Use plenty of epoxy; there is a lot of force exerted on the steel and brass nuts.

Figure 8 – Detail of inside of case. Note separation of banana jack solder post and edge of 10 mm brass nut. Solder yellow wire to nut before epoxying in nut.

Hope you find this useful. Just use what you have on hand and some ingenuity to make yours!

Best 72, Scott VO1DR

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Sam builds a tiny tabletop HF antenna

October 30, 2022 Thomas Witherspoon 18 Comments

Many thanks to Sam Duwe (WN5C) who shares the following guest post:

A (surprisingly good) tabletop HF antenna

by Sam Duwe, WN5C

I recently built a tabletop QRP HF antenna for 17 and 20 meters, in the spirit of the Elecraft AX-1, so I could operate at lunchtime on the campus where I teach. My wants were something small, that would fit in my work bag, that didn’t require a tuner, and could work on a couple of different bands. But on a lark I decided to attempt a POTA activation at Lake Thunderbird State Park (K-2792) pairing this antenna with my Penntek TR-35 QRP CW transceiver. I figured I’d maybe get one or two QSOs and then switch to a long wire in a tree. But what happened amazed me.

I talked to seemingly everyone. Beginning at 9:00 AM September 26th I worked both 17 and 20 meters for an hour and a half and made 37 contacts from across the country. I even had a Swiss guy call me back on 17 but he faded before we could finish. This antenna, at least as a CW POTA activator, works. Granted conditions were very good, but I’ve replicated this multiple times in the past few weeks, just recently at a picnic table in the parking lot of the Route 66 Museum (K-8644) in Clinton, OK (there is quite a thrill in urban activations).

It has also reasonably low profile and very quick to setup and take down. It is also quite a conversation piece when I set it up at school. I elevated the counterpoise by attaching it to a nearby oak and an interested undergrad sheepishly asked if I was listening to the tree!

The build is pretty simple. Physically the antenna consists of a small painters pole from Walmart and an old tabletop camera tripod. I found a nut that fit the screw portion of the tripod and hot glued it into the orange connecting section of the pole. That way the tripod can then be screwed onto the pole. The RF parts of the antenna consist of a 38” telescoping whip that I scavenged from the rabbit ears antenna that came with my RTL-SDR. It connects using the original connector which was hot-glued into a hole I drilled into the top of the painters pole. I found similar small 3 or 4-foot whips from AliExpress for cheap and these would probably work fine.

I then soldered a long length of speaker wire that was wound into two coils: the top for 17 meters (24 turns) and the bottom for 20 meters (25 turns plus the former 24-turn coil). The speaker wire was the soldered to the center of a BNC connector which I hot glued and taped to the pole. I soldered a short piece of wire from the shield of the BNC for the counterpoise and added an automotive spade connector to attach to a 17-foot length of wire. I also included a switch between the coils and the BNC connector to select either just the top coil (17 meters) or both coils (20 meters) using solder, hot glue, and tape. I then covered my shame in silicone tape.

The most time-consuming aspect of the project was tuning the antenna. It required trial and error to first tune the number of turns on the 17-meter coil and then the 20-meters coil. I extended the counterpoise (for me it’s best when slightly elevated) and the telescoping whip. I performed the tuning with the whip not fully extended to give room to tune in the field. Using a nanoVNA was useful here, as was soldering a pin to the wire to poke through the wire at various parts of the coil to find the best SWR.

In use, the antenna can be affected by both body capacitance and how the counterpoise is situated, so I found that an in-line SWR meter was helpful in making sure all was well. Once set up it is easy to fine tune by just adjusting the whip length. 1.5:1 SWR is about how well I can tune on average. Obviously if you have a tuner you would just have to get it close.

There are a million variation on a small base-loaded vertical antenna, and you can definitely improve upon this design. And, besides the super well-built and elegant AX-1, QRP Guys sells an interesting looking kit, and there are some good 3D printed designs I might want to try out. But regardless how you go about it, it might be worth giving a tiny antenna a shot.

72, Sam WN5C

Antennas, Articles, Guest Posts, How To, News

Steve’s Homebrew Vertical Antenna for POTA

July 26, 2022 Thomas Witherspoon 15 Comments

Many thanks to Steve (KM4FLF/VA3FLF) for sharing the following guest post:

A Great Homebrew Vertical Antenna

by Steve (KM4FLF/VA3FLF)

Last spring, I was going through my many boxes of ham “stuff” looking for items to sell at our club tail gate sale. I came across a couple of Hustler SM Series Resonators (20 /40 Meters) that I had acquired. I am not sure where I obtained them, but I decided they were keepers. That decision turned out to be the first step in a year long process that has given me an awesome homebrew vertical antenna.

After doing a little research I found the resonators and accessories at most of the online ham dealers. They are used primarily as mobile and marine antennas. I had seen where a ham had used these on a ground stake as a portable antenna as well. I ordered a Hustler MO1 mast which is 54 inches tall and thought I would attempt to make a portable POTA antenna.

I had a couple of small aluminum plates that I drilled out a few holes. I cut out a notch to put a SO-239 Stud Mount on the plate as my antenna base. I now had a ground plate, connector, and antenna with resonator. By putting a stake in the bottom of the plate, I was able to get the antenna to stand up. The Hustler resonators have a hex screw for tuning that can be loosened. The antenna can be adjusted for resonance by lengthening or shortening the radiator length. After adjusting the radiator my SWR was still horrible on the two bands.

I had some 14-gauge wire laying around and attached it to the plate using carriage bolts and nuts for my ground radials. I didn’t think about the length of the wires at this point but went with three or four lines around 20 to 30 ft. I was able to use my vertical a few times with moderate success. My SWR on 20 and 40 Meters was around 2:0 to 1 at best. It was bulky and very delicate. Sometimes screwing in or unscrewing the MO1 the SO239 would slide off the edge of the aluminum plate. I put away my contraption for the winter and decided to move on to something else.

In April of this year, I wanted to revisit my project. Continue reading Steve’s Homebrew Vertical Antenna for POTA →

Antennas, Hams, Homebrew, Portable, QRP

Dan’s clever chalk line homebrew EFHW antenna

July 30, 2021 Thomas Witherspoon 2 Comments

Many thanks to Dan (KQ8Q) who writes:

Hi Tom,

I discovered something you might have an interest in for your wire antenna deployment. Years ago when I was a building contractor, we used chalk line for floor layout. It has a very high tensile strength and is very light weight. After reflecting on this, I recently bought a 100’ spool of braided 1 millimeter chalk line and used it for a field deployment. I attached my “throw weight” to it and easily launched it about 60’ into a tree. You can see it in the attached photo holding my homebrew EFHW to my Jeep.

This link is what I used: Tajima PL-ITOL 100 ft .04″ Bold Braided Replacement Chalk Line New | eBay

Click here for full parts list (PDF)

The magnet wire was scavenged from a HUGE transformer from a neighbor’s discarded light fixture.

Lug Nut Throw Weight: left hand threaded from a 1966 Plymouth Fury

I did the new installation for him and he gave me the old one. I promptly disassembled it and collected miles of 14 and 20 gauge magnet wire ?!

I haven’t added the capacitor to this antenna yet because it is sufficiently resonant and broadbanded on 40, 20, 15, and 10 Meters. I did some testing with the capacitors though on my previous build which was the PVC tube EFHW transformer. I believe I may have sent you a photo of that in a previous message. It too was resonant in the same places, but adding the capacitor smoothed and widened the acceptable SWR range.

The attached photos are my complete antenna assembly: matching transformer (49:1), 65.5’ speaker wire, 100’ braided 1MM chalk line, and throw weight (epoxy filled lug nut with short paracord pigtail).

Compact and lightweight.

Dan/ KQ8Q

I love this, Dan! I also like how self-contained and compact it is. What a professional job, too, with heat shrink, proper connection points and tie-offs.

Brilliant work!

Do you have an antenna or radio project you’d like to share on QRPer.com? Contact me!

Antennas, Field Reports, How To, News, Portable, POTA, QRP, Videos

Field Report: Let’s build a super simple antenna on-site and activate this park!

June 29, 2021 Thomas Witherspoon 23 Comments

Until 2016, I had never purchased a commercial field antenna; I built all the ones I had ever used.

These days, I take a number of commercial antennas to the field and use them in my real-time videos and I really enjoy deploying and using them. My buddy Eric (WD8RIF) reminded me, though, that I hadn’t actually used a homebrew antenna in ages. He was right!

You see, while I believe commercial field antennas can be incredibly durable and compact, it’s important to note that antennas are one of the easiest components of an amateur radio system to build yourself. They require only the most simple of tools and are very affordable. And the best part? They can perform as well as those that are available commercially.

I also get a great deal of pleasure out of building things.

A simple goal

I’ve mentioned in previous posts that I often set a little goal that runs in the back of my mind for each park or summit activation I make.

On Monday, June 14, 2021, I made a simple goal: buy my antenna wire en route to Lake James State Park, build the antenna on site, and complete a valid Parks On The Air (POTA) activation.

A very simple antenna

I also decided to employ my Xiegu X5105 since 1.) it’s one of the most affordable general coverage QRP transceivers I own and 2.) it has a built-in antenna tuner (ATU).

One of the cool things about having an ATU is that, if it has the matching range, you can allow it to do the “heavy lifting” in terms of matching impedance.

Although I’d never put the X5105 to the test, I suspected its internal ATU would have the matching range to forgo building a 4:1 or 9:1 transformer and simply pair it directly with a random wire.

All I would need was a 28.5 foot length of wire for a radiator, at least a 17 foot length for a counterpoise, and a BNC to binding post adapter.

The antenna would benefit from multiple 17′ counterpoises, but I really wanted to keep this setup dead simple to prove that anyone can build an effective field antenna with a very minimum amount of components.

Even though I have plenty of wire lying around the house to build this simple antenna, I wanted to pretend I had none to prove that any wire would work.

And to add just a wee bit more challenge, I also limited myself to shopping for antenna wire between my home and the park without making a serious detour from my route. That really limited my options because there isn’t much in terms of commercial areas between me and Lake James State Park.

The wire

As I left the QTH, I decided that the best spot to shop was a Walmart in Marion, NC. It would only be a four minute round-trip detour at most. I had a hunch that Walmart would even have speaker wire which would be ideal for this application.

In my head, I imagined I would have at least three or four choices in speaker wire (various gauges and lengths), but turns out I had a difficult time finding some at Walmart. We live in such a Bluetooth world, I suppose there isn’t much demand for it these days. A store associate helped me find the only speaker wire they had which was basically a 100 foot roll of the “premium” stuff for $17 US.

While I would like to have paid a fraction of that, in the end it’s not a bad price because once you separate the two conductors, you have double the amount of wire: 200 feet.

Although the frugal guy in me cringed, I bit the bullet and purchased their speaker wire. To be clear, though, I could have found another source of wire in that Walmart, but I preferred speaker wire for this application. And $17 to (hopefully!) prove a point? That’s a deal! 🙂

Lake James State Park (K-2739)

Once I arrived on site, I found a picnic site I’d used before with some tall trees around it.

Here’s how I prepared the antenna:

First, I cut 28.5 feet of the speaker wire from the roll and split the paired wires so that I’d have two full 28.5 foot lengths.

Next, I stripped the ends of the wire and attached banana jacks I found in my junk drawer. Although these aren’t necessary as the binding post adapter can pair directly with the wire, I though it might make for a cleaner install. In the end, though, I wasn’t pleased with the connection to the radiator, so dispensed with one of the banana jacks on site, and later dispensed with the other one as well. The connection is actually stronger without the banana jacks.

I then deployed the 28.5 radiator with my arborist throw line, and laid the other 28.5 half on the ground (the ground of this antenna would pair with the black binding post, the radiator with the red post). I only needed 17 feet of counterpoise, but once it couples with the ground, I don’t think any extra length makes a difference (although less than 17 feet likely would).

The antenna was essentially set up as a vertical random wire with one counterpoise.

I then plugged the BNC binding post adapter into the rig, hit the ATU button, and was on the air.

It’s that simple!

My new speaker wire antenna in all its glory.

Gear:

Xiegu X5105
CW Morse “Pocket Paddle”
Arborist throw line
Weaver arborist throw line/weight and storage bag (affiliate links)
Tom Bihn Large Travel Tray
Rite In The Rain Weatherproof Cover/Pouch (affiliate link)
Jovitec 2.0 mm Mechanical Pencil (affiliate link)
Muji A6 Notepad (affiliate link)
Monster Standard Speaker Cable 100ft (Walmart)
BNC to Binding Post adapter
Tools: Wire cutters/strippers, Tape Measure, Banana Jacks

On The Air

I’ll admit: I was a bit nervous putting this antenna on the air. Although I felt the X5105 ATU *should* match this antenna, I had no idea if it actually would.

Fortunately? It did.

At this point, if you don’t want any spoilers, I suggest you watch my real-time, real-life, no-edit, no-ad, video of the entire activation (including buying and building the antenna!).

Click here to watch the video.

Otherwise, scroll for my activation summary…

I was very pleased that the X5105 found a match on the 40 meter band.

I started calling CQ in CW and validated my activation by logging 10 stations in 13 minutes.

Honestly: it doesn’t get much better than this.

I logged three more stations on 40 meters CW, then moved up to the 30 meter band where the X5105 easily found a match.

I worked one station on 30 meters before heading back down to the 40 meter band to do a little SSB. I logged three SSB stations in five minutes.

Mission accomplished!

In the end, I logged a total of 17 stations including a P2P with K4NYM.

Not bad at all for speaker wire!

After the activation, I tested the X5105 ATU by trying to find matches on other bands–I was able to find great matches from 60 meters to 6 meters. Most impressive!

X5105 battery

You might recall that I attempted to deplete my X5105 internal battery at my last (rather long) activation of Lake Norman State Park. I wasn’t able to deplete the battery at that activation, but I finally did at this one.

All I can say is that I’m incredibly impressed with the X5105 internal battery. This was my fourth activation from one initial charge on May 16. The battery lasted for 20 minutes, taking me well beyond the 10 contacts needed to validate this park. I’ll now consider taking the X5105 on a multiple SOTA summit run!

Short Hike

Even thought the heat was intense and the humidity even more intense, I decided to take in a 2 mile hike post-activation. I snapped a few shots along the way.