Dayton 2010

Dayton/FDIM 2010 – Days 2 and 3

Hans Summers Presenting at FDIM 2010

Please accept my apologies for the long delay in posting my impressions of Hamvention and FDIM. I was literally on the move every waking hour of my time in Dayton on Thursday, Friday, Saturday, and Sunday. Up about 6 AM to shower, at Hamvention all day, then FDIM at night. Back to N8ZM’s house around 11 PM to crash in the easy chair. I’ve never worked so hard to have fun. My writeup is going to focus mostly on FDIM, since that was the main reason that I was in Dayton. I probably can’t give you much information about Hamvention that you haven’t already heard thousands of times from other hams. Besides, the muse has taken leave from me again, so I don’t want to butcher this recap any more than is necessary.

My adventure in Dayton got off to a proper start on Thursday, which was seminar day at FDIM in Fairborn. I arrived around 7 AM, which was a bit early, but I got a chance to get a seat pretty close to the front of the room. By the start of festivities at 8 AM, the room was pretty much full. There had to be more than 200 attendees (I unofficially heard that this was the best attendance at FDIM in a few years).

There were a total of six presentations for the day. I’ll give you a brief rundown of my impressions of each one.

  • K8ZT – The morning started off with a presentation by Anthony Luscre, K8ZT about strategies for being successfull in QRP contesting. The PowerPoint deck for this talk came in a over 140 slides, which meant that Anthony had to rip though the slides at a lightning pace. He gave some good inspiration to those of us who have not yet taken the QRP contesting plunge.
  • G0UPL – Next up was world-class homebrewer Hans Summers, G0UPL. His presentation was about his QRSS efforts. About half of his talk covered information that is already on his website, but he did get into some areas that I haven’t seen him cover before. I especially enjoyed seeing his natural power battery experiments. At the end of his talk he announced the sale of a kit version of his latest QRSS transmitter, which I’ll cover later on. He came with the stereotypical dry British humour (LOL), which I enjoyed immensely.
  • G3RJV – My favorite talk of the day was given by the legendary Rev. George Dobbs, G3RJV. He did a masterful job of combining a grand tour of simple receiver designs with more philosophical aspects of our hobby. You can tell that Rev. Dobbs has honed his public speaking skills quite well from his years in church.
  • NE1RD – After lunch break we were treated to a great talk by B. Scott Andersen, NE1RD on the topic of his 100 Pound DXpedition. While the 100 Pound DXpedition is not a QRP-specific topic, NE1RD put a QRP spin on the talk by focusing on his recent CQ WPX QRP efforts on St. Thomas.
  • K8IKE & K4ZLE – Jim Everly, K8IKE, and Jay Slough, K4ZLE brought a power-packed presentation about  acquiring a set of “good enough” test gear for the homebrewer and how to use this gear to perform a useful subset of the ARRL lab procedures for RX and TX performance. We also had a bit of good-natured sarcastic side commentary from Ed Hare, W1RFI from the League’s lab. This was extremely useful stuff and I wish that they had a little more time to delve into this topic.
  • K9AY – The final talk of the day was from prolific FDIM speaker Gary Breed, K9AY. He covered low band QRP operating; mostly focusing on the challenges of deploying a useful DX antenna on these bands. Gary brought some good information, but unfortunately he had to compress the end of his speech quite a bit because he ran long in the first half. Fortunately, the proceedings had all of the information that was skimmed over.
FDIM 2010 Thursday Vendor Night
FDIM 2010 Thursday Vendor Night

After a long day of sitting and listening to speakers all day long, we had a few hours to get up, grab some dinner, and stretch our legs. By 8:00, the main ballroom was reconfigured for QRP vendor night. The room was not 100% filled with vendors (as you can see in the photo to the right, most of the tables in the middle of the room were empty), but there was still quite a bit to see. Hendricks QRP Kits had the largest display, but Diz from was probably a close second with his huge stock of ‘roids, components, and RF Toolkits. As I mentioned earlier, Hans Summers announced the sale of his latest QRSS transmitter as a kit with a PCB and a microcontroller that he would custom program with your callsign. This was the most popular item of the night. For nearly the entire two hours of Vendor Night, there was a large line of people waiting to purchase a kit and have it customized by G0UPL. I hope this sparks a lot more QRSS activity here in the States.

K3PG Sonic Tray Chassis Willamette
K3PG Sonic Tray Chassis Willamette

One very neat aspect of the night was getting to meet a bunch of the QRPers that I’ve known for years via the mailing lists but have never seen in person. Some of the highlights that stand out for me were my introductions to WA0ITP, K3PG, K8IQY, NM0S, KC2UHB, W8DIZ, and WB8ICN (sorry if I missed anyone!). It was a pleasure to finally be able to shake hands with my peers and mentors. I’d like to give a special shout-out to Diz for his salty greeting! That’s the way to make a guy feel like a part of the gang from the first minute! I loved it! It was also a treat to have a good, long conversation with K3PG, whose enthusiasm for the Willamette was truly humbling, as well as infectious. Chatting with WA0ITP seemed like two old friends talking. I’ve collaborated with him so much via e-mail that it seemed perfectly natural to pick up where the electronic communications left off.

I hate playing favorites, but I think the true highlight of the night was meeting Mikey, WB8ICN. I was sitting in the lobby of the Holiday Inn, working on my laptop and waiting for the Vendor Night festivities to start. I wasn’t paying much attention when a couple set down in the chairs opposite from me. They were having a lively conversation for quite a while, but I was engrossed in reading the FDIM Proceedings CD that I purchased earlier in the day. After a while, the gentleman sitting there was getting more and more animated in his conversation. At that point, my curiosity got the best of me so I had to check out what was going on. Something seemed vaguely familiar, but it took me a few moments before I saw the shirt with “WB8ICN” embroidered on the chest. Of course, I got up and introduced myself to Mikey and his wife Marybeth, which seemed to take him by surprise a bit! We had an awesome conversation and were probably getting a bit louder than we should have been. That was the only time we got to talk at Dayton and I wish I had more time to BS.

I’m only going to skim over Friday, since it was a bust regarding FDIM. Hamvention was as large and as crazy as everyone had said it would be, especially the flea market. Sometimes I get a bit overwhelmed in such huge venues, so I wasn’t really acclimated to what was going on until Saturday. I imagine that I looked like a lost puppy dog wandering around. Hara is pretty old and decrepit, but that certainly didn’t slow down any of the activity. The only thing that was really “offensive” to me about the place was the bathrooms. I never used them at Hara, but just walking within 30 feet of the entrance was enough to make me want to gag. I think I still have nightmares about the smell alone. God help anyone who actually had to use them

Due to a bit of a communication error on my part, I didn’t make it to Friday’s FDIM activities until the event was almost over for the night. So I’ll just skip right on past that and get to the good stuff about the Saturday night banquet in my next post.

Homebrewing, QRP

W8DIZ 5 Watt CW Amplifier Analysis

I finally got the proper binocular ferrite cores that I needed to build the W8DIZ 5 watt amp correctly. You can see my previous post on this amplifier here. In my last post, I noted that I was seeing some strangeness in the drive level circuitry. I found that I had a very bad connection through my ammeter to the DC power supply, and once it was corrected the drive circuitry worked as it should.

For this basic analysis of the amplifier, I took measurements of the RMS voltage of the amplifier output into a 50 Ω dummy load with a constant input amplitude of 0 dBm. I also measured the total current draw of the circuit, which allowed me to calculate the amplifier efficiency. Note that no low-pass filtering was used at the output of the amplifier. The output waveform was not sinusoidal, but my DSO is able to do a good job measuring RMS voltage.

Test Equipment

  • Tektronix TDS 1012 Digital Storage Oscilloscope (100 MHz bandwidth)
  • Tektronix SG 503 Leveled Sine Wave Generator
  • Tektronix DM 502A Digital Multimeter
  • Tektronix PS 503A Power Supply
  • M3 Electronix FPM-1 Frequency Counter/Power Meter

Test Conditions

The DC power supply to the amplifier was set to a loaded voltage of 13.5 VDC. The signal generator for the input signal was set to 0 dBm power output into 50 Ω, which was verified with the FPM-1 each time the frequency was changed. Two sets of measurements were taken, one with R6 set to minimum and the other with R6 set to maximum.


Min Max
MHz VRMS (V) PO (W) IDC (mA) VRMS (V) PO (W) IDC (mA) Eff.
1.8 13.7 3.75 440 22.4 10.03 957 0.776
3.5 20.2 8.16 768 23.9 11.42 992 0.852
7.0 13.8 3.81 470 21.7 9.42 844 0.826
10.1 9.3 1.73 300 19.8 7.84 732 0.793
14.0 5.24 0.55 174 17.6 6.20 635 0.723
18.7 3.12 0.19 103 14.4 4.15 514 0.598
21.0 2.07 0.09 78 12.6 3.18 452 0.521
24.9 1.53 0.05 65 9.05 1.64 326 0.372
28.0 1.19 0.03 60 6.56 0.86 232 0.274


As Diz states in his original post, the efficiency of the amplifier is quite good. However, both the power output and the efficiency starts to droop a bit above 20 meters. It’s my belief that this is a function of the gain-bandwidth product of the two PA transistors. According to the datasheet, the FT of a 2SC5739 is 180 MHz. Given the rule of thumb of having a FT at least 10 times the output frequency, it makes sense that the output starts to get a bit weak around 18 MHz. I do have some similar devices (2SC5954) with a slightly higher FT of 200 MHz that I will probably substitute in the circuit to see if I can improve the upper HF response a bit. There seems to be some kind of strangeness at 3.5 MHz, which doesn’t allow me to get much power output range. I’ll have to check with Diz about this. Regardless, this would still make a very fine QRP amplifier up to the 15 meter band. The amplifier is extremely stable and the PA transistors don’t get very hot during long periods of use. I currently have the transistors floating freely, but a modest heat sink would probably be a good thing if running the amp at full power output. This kit will be a great addition to the RF Toolkits line.