Tag Archives: QRPp

Guest Post: Lake Thunderbird (K-2792) with a homebrew transmitter!

Activating (sort of) Lake Thunderbird (K-2792) with a homebrew transmitter

Sam Duwe WN5C

When I dove into radio a couple years ago a few sub-hobbies caught my attention: QRP, portable ops, CW, and homebrew. Of course, these all fit nicely together, but in my mind there was a huge leap between soldering an unun and a building a radio. But why not try? What’s the worst that could happen by melting solder and then sitting at a picnic table? This is how I built a simple transmitter and kind of activated a park.

The Michigan Mighty Mite

Nearly everyone has heard about the Michigan Mighty Mite (MMM), a QRPp transmitter popularized by the Solder Smoke blog. There are countless YouTube videos and posts across the internet. It’s very simple: a single transistor, a variable cap, a coil, a crystal and some resistors and a cap. Supposedly one can get up to half a watt of output (I couldn’t). But with a small purchase from Mouser one can oscillate. That seemed pretty cool.

I hadn’t touched an iron until I started playing radio. But I’ve been drawn to homebrew projects. I built a regenerative receiver last year which was very rewarding. I’ve also put together kits (a QCX mini and a TR-35). But my dream has always been to construct a transmitter/receiver combo, or a transceiver. I thought a good place to start was the MMM.

I built the transmitter based on the common schematic for the 40-meter band. The MMM is crystal controlled but I opted to solder in a socket and buy a handful of crystals, so I have the luxury of operating on 7056, 7040, and 7030 kHz. I made a few other improvements, too. The first was to build a low pass filter to attenuate harmonics. Second, although I haven’t finished it yet, the switch on the right will be to choose between multiple crystals. And third, I added a BNC jack to connect a receiver, with a transmit switch. When not in use the transmitter will dump into a dummy load. This receiver switching idea was lifted from the design of the MMM that QRP Guys produces.

When I tested the transmitter at home the best I could get with my charged Bioenno 3 Ah battery was about 300 mW output. The filter is reducing things somewhat, but maybe I need to look into a different transistor or rewind the coil. But I was able to get a 339 signal report from Illinois (no sked) in the midst of distance lightning crashes, so I had a little confidence going forwards. School is out for me this summer, so I decided to head to the park. Continue reading Guest Post: Lake Thunderbird (K-2792) with a homebrew transmitter!

QRPp POTA: How many hunters can I possibly log with only 100 milliwatts–?

As I walked out the door on the morning of Tuesday, March 21, 2023, I grabbed my Elecraft KX2, MM0OPX 40 meter end-fed half-wave, and a key I hadn’t yet taken to the field: my Bamakey TP-III!

I had a full day of errands, appointments, and carting my daughters to/from school, but I also had a good 90 minute window to play radio!

As I’ve mentioned previously, the Vance Birthplace (K-6856) is incredibly convenient this particular school term. I pass by it twice a week, and I feel incredibly fortunate because it’s a wonderful POTA site with POTA-friendly staff. They all know me quite well there at this point.

The Vance site is a small park and the only negative (from the point of view of a POTA activator) is if you have poor timing, you might arrive only to find that a large school group has taken over the site. This is especially a concern on weekdays during school hours–in other words, the time I usually activate Vance.

I pulled into the Vance site that morning and there were no vehicles there other than park staff. A good sign so far!

The only appropriate spot to activate at Vance (if you operate a portable HF station) is in or near the picnic shelter. The rest of the site is where visitors wonder through the old homestead and take guided tours.

I never set up my station in the middle of park activities or in a viewshed.

At the end of the day, we represent all Parks On The Air activators and the amateur radio community at large when we’re in public spaces. The last thing we want to do is detract from others’ park experience.

Before pulling any gear out of the car, I walked into the visitor center and asked the park staff for permission to set up in the picnic shelter. I always do this because if a school or tour group is scheduled to visit the site that day, they almost always need the picnic shelter and have it reserved.

Fortunately, no one had scheduled the picnic shelter, so the park ranger told me, “It’s all yours! Have fun!

Proper POTA Flea Power!

I like shaking up each new activation in some small way so that it’s not a carbon copy of any previous activation.

Since, like most POTA activators, I visit the same local parks the bulk of the time, it adds a little extra challenge and fun to try different gear combinations, experiment with new antennas, or even (as in this case) try different power settings–! Continue reading QRPp POTA: How many hunters can I possibly log with only 100 milliwatts–?

Guest Post: Extreme QRP–Testing the AX1 with WSPR and 20mW

Many thanks to Keith (KY4KK) who shares the following report:

Extreme QRP – Testing the AX1 with WSPR and 20mW

by Keith (KY4KK)

Thomas, thanks for all of your activation videos related to the Elecraft AX1 antenna.  I ordered one the day you announced the package deal, and it arrived in less than a week.  I’ve activated a few parks with it already (20m SSB).  Like you and many others, I’m impressed.

I was very interested in Thomas Barris’ (DM1TBE) March 12 QRPer post using WSPR to test his POTA antennas in Germany.  Then I saw Bob’s (K7ZB) post about his ZachTek Flea with 300 milliwatts in CW mode.  To me, extreme QRP represents some of the magic of HAM radio.  I’d like to share one of my most recent WSPR experiments related to the AX1.

About a year ago, a friend (NG4S) loaned me his pair of WSPR transmitters and suggested that I explore building and comparing antennas. I’ve been hooked on antennas of all kinds and WSPR since then.

I began doing WSPR tests on the AX1 the day after it arrived.  With two transmitters set to the same frequency and power output, you can do direct comparisons between two antennas under identical propagation conditions.

I’ve already done a couple of comparisons between the AX1 and other commercial antennas.  But I think the test I just completed might be of particular interest because it pits the AX1 against an antenna I’ve seen you use many times – a 28.5’ end fed with a 28.5’ counterpoise.  I used 24 AWG silicone insulated wire. The end of the radiator was placed on a 19’5” telescoping fishing pole.  This is my preferred POTA mast when I can’t use a tall tree.

I spent some time trying to control other variables so that the only significant difference during the test would be the antennas themselves.

For example, the SOTA Beam WSPRLite Classic transmitters don’t have an ATU.  So, I had to make the antennas resonant on the 20-meter WSPR frequency of 14.097 MHz.  For the AX1, Thomas’ videos helped a lot.  I used a clip-on capacitance hat and adjusted the counterpoise to 15’ 2”.  This gave me an SWR of 1.17:1.  For the end fed, I tried the two UNUN’s I had available and settled on the 49:1, which got me the closest (2.2:1).  I then used a manual tuner to achieve an SWR of 1.29:1.

I also wanted to deal with the difference in power output between the two transmitters.  Although they’re identical, and both set to 20 milliwatts, there is no way to ensure both are actually producing that output level.  Based on tests by NG4S, one of the transmitters runs at 19 milliwatts.  The other actually outputs 27 milliwatts.  So, my plan was to run the test for 48 hours. At the end of 24 hours, I would switch the transmitters (and callsigns) so that both antennas would benefit (relatively equally) from one of the transmitters being stronger.

At the end of Day 1, I reviewed the data from the two transmitters on dxplorer.net/wspr.  The end fed averaged a 5.7 dB gain over the AX1 based on reports from receiving stations that spotted both transmitters in the same 10-minute block (simultaneous spots).

On Day 1, the stronger transmitter was on the end fed.  The maps below are from WSPR.rocks.

AX1 – Day 1

End Fed – Day 1

I was pretty impressed that the AX1 got into Europe and Africa on only .019 Watt!  I always have good luck with end feds, so was not too surprised to see this one perform well. Continue reading Guest Post: Extreme QRP–Testing the AX1 with WSPR and 20mW

QRPp: Activate a park with ⅒ of a watt–? I had to at least try!

In my last published field report, you might recall that I successfully activated a park using 500 milliwatts or ½ of a watt. I was so surprised by the results of using this QRPp power level I immediately made plans to push the power level even lower during my next activation.

Let’s face it, I was drunk with a lack of power!


After my last field report, there were quite a few questions about the term QRPp and what it means. To be honest, I’m not sure if there’s an “official” definition, but here’s what is widely accepted as QRP power categories:

  • QRP: 5 watts to 1 watt (for some contest 10 watts = SSB QRP)
  • QRPp: Less than 1 watt to 100 mw
  • QRPpp: Less than 100mw

I don’t own a field radio that allows me to lower the output power to QRPpp levels. In fact, few of my radios actually allow me to lower power below one watt.


My Elecraft radios, however, do allow me to lower power output to as low as 0.1 watts or 100 milliwatts.

The plan

On Wednesday, December 7, 2022, my travel schedule shifted and it opened up the entire afternoon to play radio.

A rarity indeed!

It was very rainy and foggy that day and I didn’t have my ENO rain fly with me, so I decided to visit a park with a good picnic shelter to keep me, an my gear, nice and dry.

Fort Dobbs State Historic Site (K-6839)

I had four park options with covered picnic shelters within a 45 minute drive. I decided that I would try to activate Fort Dobbs State Historic (since it had been a couple months since I’d visited) and Lake Norman State Park would be my back-up plan.

Fort Dobbs is a small park, so I called in advanced and asked for permission to do the activation and also asked if their picnic shelter was reserved.

The rangers there know me, so the phone call was pretty quick–no need to explain POTA nor my motivations. They told me that on rainy/foggy December days they have so few guests that I was welcome to use the picnic shelter or even the entire park if I wished (perhaps an ideal time to erect a Rhombic antenna–okay, just kidding!).

The Dobbs park rangers an volunteers are the best!

Setting up

On the way to the site, I decided that I would deploy my MM0OPX end-fed half-wave I’d cut for 40 meters.

I needed to make the most of my 100 milliwatts, so I figured the MM0OPX EFHW would be the best antenna for the job. Continue reading QRPp: Activate a park with ⅒ of a watt–? I had to at least try!

POTA with 500 milliwatts CW and 10 watts SSB using the Elecraft KX2 and PackTenna Random Wire combo

I’d like to start this field report with a side story. I’ll keep this reader anonymous since I haven’t asked for permission to post his story (although I’m certain he wouldn’t mind!):

A QRP Christmas Gift

Yesterday, I was contacted by a reader who had just received an amazing gift.

On Christmas morning, his wife presented him with a tiny wrapped box and inside there was a small note:

“Get yourself a great field radio. You have Carte Blanche!” 

What an amazing gift…right–?! She literally said Carte Blanche!

Evidently, she is familiar with my YouTube channel  (poor thing) because he often watches my activation videos on their living room TV. [Between us, I’m a bit surprised she still loves him after subjecting her to my videos.]

She told him, “Run your choice by Thomas before ordering.”

The funny bit? He approached me with this very question in November as he plotted a 2023 radio purchase. He couldn’t decide between the Icom IC-705 and the Elecraft KX2.

He wrote yesterday to tell me that he placed an order for a new Elecraft KX2 with all the trimmings; Elecraft’s KX2 “Shack-In-A-Box” package plus a set of KXPD2 paddles.

The KX2 is back-ordered due to parts availability, so he won’t receive his unit for several months, most likely.

Based on his operating style, I think he chose wisely. The IC-705 is a benchmark field radio, but he was looking for something that he could pair with a random wire antenna (the ‘705 lacks an internal ATU) and that would be easy to use on SOTA activations. He’s new to CW as well and loved the fact that the KXPD2 paddles attach to the front of the KX2.

Why do I mention this story? Because it’s not only fresh on my mind, but it’s the same radio and antenna I used during an activation on Thursday, December 1, 2022.

Tuttle Educational State Forest (K-4861)

As I pulled into Tuttle’s parking area that day I had a tried-and-true field radio kit pairing in my pack: my Elecraft KX2 and PackTenna 9:1 Random Wire antenna.

As I mention at the start of my activation video (see below), with the Elecraft KX2 and a random wire, I could easily activate all of the summits, parks, and islands I desire. It’s such an effective, flexible, and portable combo.


To shake things up, I decided to knock the output power of the KX2 down to one half of one watt–500 milliwatts–at least for the CW portion of my activation.

Why not?

Plus, I don’t think I’ve ever validated a POTA activation with 1/2 of a watt, so it might make for a fun challenge! Continue reading POTA with 500 milliwatts CW and 10 watts SSB using the Elecraft KX2 and PackTenna Random Wire combo

1993-2004 NorCal QRP Club Journals now available online

(Source: KI6DS via QRP-L)

I would like to announce that the complete collection of QRPp, the NorCal QRP Club Journal that I did from 1993 to 2004 is now on line.  Chuck Adams has scanned in every page of every issue and has it on line at http://www.k7qo.net/NorCal_QRPp.html.  This is a temporary site, as we want to make sure that all of the bugs are out of it before we place it on the NorCal page where it will have a permanent home in about 3 weeks.  This material is for the education of QRPers, and it will always be free.  No one will ever have to pay anything to access it.  We ask that no one makes it available on CD for distribution in any way.  Everyone is granted permission to make an archival copy, but no one is granted permission to post any part or portion online.  We want there to be one site where it is available.  Some of the schematics will be redrawn and Chuck is coordinating that effort.  I have struggled for years on how to make the information available and decided that this is the way to do it.  Every article was donated, no one was paid anything for writing any article.  So, I wanted to make it available for free.  Enjoy.  Thank you to Chuck Adams for doing the work to make the pdf’s, to Dean Davis for his future work in putting it on the NorCal web page, and especially to all of the contributors over the years.  72, Doug, KI6DS