POTA Fun: Pairing Mike’s “Oreo” Balun/EFHW with the Venus SW-3B

A few months ago, Mike (KE8PTX), contacted me with info regarding his latest 3D-printed creation: a compact housing for an end-fed half-wave balun.

Mike’s 3D drawing

He called it the “Oreo Balun.”

Once printed, and after he wound the coil and installed the BNC, he sent this photo:

It’s cute, isn’t it?

He then surprised me by putting it in a padded envelope and sending it to me as a gift. Wow–thanks, Mike!

Oreo plans

End-Fed Half-Wave antennas are popular portable antennas for a reason: they’re effective!

They’re compact, easy to deploy, and resonant.

I only needed to attach some wire to the Oreo Balun, trim it, and hit the field!

Earlier this year, my buddy Vlado and I built two doublets with some scrap wire I had in my antenna parts box.  I measured the amount of wire I had left from that same spool. I knew it wasn’t enough length for a 40 meter EFHW, but I did think there was enough for 30 meters.

After giving it a bit of thought, I liked the idea of having a dedicated 30 meter EFHW. For one thing, 30 meters is a great band for field deployments and in the past this band has saved my bacon when either 40 meters or 20 meters was wiped out. Thirty meters is also a refuge WARC band during contest weekends.  In addition, a 30 meter EFHW is short enough that it could be deployed on most SOTA summits (which often have shorter trees).

Fortunately, I had just enough wire for 30 meters. IN fact, after trimming the antenna, I only had about two feet of wire to spare. It’s as if I had planned it! I would have never guessed that spool of scrap wire would have made two doublets and one 30 meter EFHW.

The next logical thing to do was take the Oreo to the field and play radio!

South Mountains State Park (K-2753)

On Friday, February 11, 2022, I had just enough time to fit in a quick trip to South Mountains State Park for an impromptu activation and hike as I traveled back to the QTH.

The previous day, I took my Venus SW-3B on its maiden SOTA voyage and had a blast!  It was the only radio kit I’d packed on this overnight trip and, frankly, I was eager to get even more on-the-air time with it. Here’s my full gear list:

SW-3B Ultra-Compact Field Kit

Other Gear:

Setup was quick and easy!

I’ll admit that I was a bit skeptical about completing a full activation on 30 meters that afternoon. Propagation that day was in the dumps; earlier, my buddy Eric (WD8RIF) had completed two activations in Ohio and noted that it took much longer to snag the ten needed for a valid activation. In this case, I was limiting myself to one band.

Audio recording

Of course, I made a real-time, real-life activation video at the park that day and since the SW-3B has no internal speaker, I paired it with my thrift store Sony ICD-PX-312 digital recorder for the second time.

I should note here that the SW-3B’s sidetone does pump a bit and you might hear this in the recording. I wish there was an easy way to lower the sidetone in the SW-3B just a touch. It’s not uncomfortable to me, I just like control of my sidetone volume. In the audio, you can hear a bit of lite popping as the recorder copes with the audio gain. Otherwise, I’m super pleased with the audio quality using the in-line recorder.

On The Air

I planned on this being a short activation mainly because I was eager to fit in a hike afterwards.

I hopped on 30 meters not knowing exactly what to expect. I started calling “CQ POTA” and after being spotted, I started working stations in rapid succession.

 

In the end, I worked a total of thirteen stations in 11-12 minutes before calling QRT. I’m certain had I taken an additional ten minutes, I would have picked up an additional 5 or so stations.

QSO Map

Here’s what about 5 watts into the Oreo EFHW can yield in short order:

Activation video

Here’s my real-time, real-life activation video–as always, without any YouTube ads:

Click here to view this video on YouTube.

 

Post activation, I did have a very enjoyable hike on the Clear Creek Trail.

No matter what time of year, the lake at Clear Creek is always beautiful.

Thank you

Thanks for joining me on this most rewarding activation!

Once again, I found that the SW-3B’s performance was admirable and tailored very nicely for the CW field op. The filter is the right width, the audio is pleasant (save the somewhat thumpy sidetone), and having that one CW message memory really helps with the workflow.

Again, if you missed out on on ordering a Mountain Topper MTR-3B from LnR Precision, then the SW-3B is a good alternative.

Of course, LnR Precision still produces the MTR-4B and I will soon have that little radio in the field thanks to a kind reader who sent it to me on loan. Interestingly, it has the 8o meter band which I don’t typically use in POTA, thus a good excuse to build something.

I’d like to send a special thanks to those of you who have been supporting the site and channel through Patreon and the Coffee Fund. While certainly not a requirement as my content will always be free, I really appreciate the support.

I hope you get a chance to play radio in the coming days. Here in North Carolina, spring is definitely on the way and it’s always beautiful to the point of being completely distracting. It’s difficult to stay indoors in front of a computer. I’ve got so many field plans.

Have a wonderful week, friends!

72,

Thomas (K4SWL)

10 thoughts on “POTA Fun: Pairing Mike’s “Oreo” Balun/EFHW with the Venus SW-3B”

  1. Great post Thomas.

    What happened to February’s antenna build project?

    I have an EFHW and. Trapped dipole that I need to get busy on building as well as add wire to my doublet and tune my Spark Plug EFHW.

    1. It’s next! I’m running about 1 month behind on getting videos and field reports published at the moment.

      1. i know the feeling. I was just curious.

        I just created a website for QRPGuy.com/QRPGuy.net. It is live and I am slowly adding content. I have to get some images for it and work on some of the features but it is slow going. I can write the content as I am good at that. But the images and getting out to do activations takes time to get right.

  2. The mtn topper 4b is in route right now. Ordered Jan 23. Looking forward to trying that.

    Thx for the post pics.

    Now on to the vid.

    AD8EV

  3. For the connection between the SW-3B and the recorder: pick up an attenuating patch cord. That should bring the audio output level down enough for the recorder to handle. You could buy a cable or make one from spare parts. Should help with the pumping coming from the recorder’s ALC circuit…

  4. ‘Nother great post, Thomas! Obligatory Pedantic Moment: that-there thing’s an autotransformer, not a balun or unun. (For some reason, this distinction hasn’t yet landed in the ham radio mainstream.) They’re easy to make and really work.

    I’ve been using band-tuned EFHWAs for a few years now, and they’re brilliant when you don’t want to be schlepping a tuner. They can throw some weird curves (the thing about being too close to the ground [?!], lurid common mode drama…) but those are easily managed when you know about them and you just can’t beat the simplicity and speed of set-up and take down.

    Basically, the whole thing is black magic.

    I also totally concur about 30m, especially it being a refuge from man-made band closures. Never understood why brasspounders haven’t flocked to that band. In addition to the points you made here, it also offers manageable antenna lengths. Not quite as manageable as 20m, but better than 40m, for sure.

    I understand that 17m is also sheltered from contests, but have never had an opportunity to work it.

    Thanks again, Thomas!

    Rob
    KB7PWJ

  5. Thomas, I appreciate your posts. You’ve provided me with ideas for how I would like to handle my own mini-expeditions, park activations, and vacation operating. The photos and videos make your writing come alive. You have, by far, he best site for QRPers to follow and learn from. I look forward to your most recent posts each week. The detailed listings of equipment used is particularly helpful.

  6. I would only comment that the Oreo Balun is most likely a transformer and not a Balun.. A Balun, by definition is designed to attenuate common mode currents on the outside of a coaxial feeder when feeding a balanced antenna. So 1st off, nothing is balanced in the instance of an EFHW- the antenna is unbalanced and the feedline is unbalanced. So, is it an UNUN- again no, as it is unlikely it has any effect on EFHW common mode. The common mode impedance at the end of an EFHW is very high, putting unrealizable restraints on an UNUN choking Z at that location. A quarter wave from the matchbox, a 1:1 choke could be used to reduce common mode.
    Finally, it is simply not possible to build an N:1 (where N is an integer >1) BALUN or UNUN on a single core. One can build an N:1 unun or balun by following up the Transformer with an effective 1:1 choke.

    Regards,.
    Dale W4OP

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