Ripples in the Ether

Clackamas Schematic

Since FDIM 2010 is in the history books, it is my pleasure to finally publicly release my entry into the FDIM 2010 QRP Challenge: The Clackamas 40 Meter Transceiver.

The rig is a VXO-tuned superhet that operates around 7.030 MHz. The heart of the design is the BF998 dual-gate MOSFET (which was popularized by W7ZOI on his website and in EMRFD). The BF998 is used as the front-end mixer and as a combination product detector/BFO. My new favorite AF amp, the TDA7052, is my choice for the single allowed IC. The VXO signal is mixed with a carrier oscillator in a JFET mixer, which is then bandpass filtered and fed to a BS170 power amplifier.

Please download my contest writeup for full details of the design. I’ll dissect the design in further detail in future posts.

I recently received a couple of excellent photos of completed Willamette transceivers, and I just can’t help but brag on these wonderful creations.

W8BH Willamette with Digital Dial

W8BH completed his rig quite a while ago but recently upgraded it by adding a KD1JV digital dial. Looks very sharp, Bruce!

K3PG Willamette in Sonic Tray Chassis

I’m really getting a kick out of this one. K3PG, appropriated an old Sonic drive-in tray to create a chassis for his Willamette. I really enjoy seeing the more mechanically inclined hams build cool enclosures out of interesting scraps. He did a great job with the shielding between the VFO and mainboard. FB work Paul!

Clackamas in TPC-41 Enclosure

Yesterday I got the Clackamas all dressed up nicely in its new Ten-Tec TPC-41 enclosure. I have such a stack of bare, half-finished circuit boards laying in the shack that it’s always a real pleasure to get a project to the point where it’s well enough developed to put it in a case. It’s also much nicer to operate the rig when you don’t have to fumble around with holding a pot or switch in one hand while trying to work the control with the other. One valuable lesson that I’ve recently learned about the mechanical side of things is that a step drill bit set is an indispensable time saver, especially when you have many different sizes of holes to drill in the same enclosure.

The rig is all ready to make the trip the Dayton for show and tell. In the meantime, I’m going to try to make a few more QSOs with it when I get a few spare moments. Hope to catch you around 7.030 MHz.

Over the last week or so, I’ve been coming home from work nearly every morning thinking about ways to tweak the Clackamas (FDIM 2010 QRP Challenge) rig. I’m sure that Jennifer is wondering if I have OCD at this point. This morning I was able to stamp out the last few bugs in project and get the parts count to 72. There was a nasty PA oscillation that I had to tame and I was having trouble pulling my carrier oscillator low enough to get the transmitted signal on the right sideband. Somewhat satisfied that the thing might actually work, I went to sleep with the hope that I could try a QSO this evening when 40 meters would give me a better chance of making a QSO.

After dinner I managed to slip into the shack after Jennifer laid down to rest and I bribed Baxter to leave me alone with a Kong full of treats. I thought about trying to self-spot in order to scare up a QSO, but that didn’t seem right. I wanted the first QSO to stand on the rig’s own merits, not because I asked someone to listen for me. So I parked somewhere near 7030 kHz and started banging out a straight key CQ with 1 watt output. After about 5 rounds of CQ, I started getting the sneaking suspicion that I had screwed something up, but I trusted that my pre-QSO checks on the rig were correct. So I kept at it.

After a few more CQs, I finally got my reward. A huge signal about blasted the phones off of my ears! And it was saying my callsign! I got a reply from W7MDK in Peck, ID. I was so excited that the QSO didn’t go so great, but we got all of the pertinent information across. He was going a bit faster than I normally copy, and I think my speed was impaired even further because of my extreme excitement. Dick gave my 1 watt a 579, while he was easily 40 dB over S9 here. I cut the QSO short to stop me from embarrassing myself further, but I got the first one in the log!

It’s said that there isn’t much better for the homebrewer than to turn on that newly created receiver and hearing signals off the air for the first time. It’s hard to argue with that, but I think that making a complete first QSO with a rig you designed and built yourself has to top even that experience. Sorry to toot my own horn so shamelessly, but I’m just thrilled with the love of radio right now.

The next steps are to get going on the documentation for the judges, get the prototype into an enclosure, and start working on a second copy of the rig to make sure I can duplicate it from the schematic. I can’t wait to share the design details with everyone, but that’s going to have to wait for another month or so. In order to get the rig within the required parts count, I had to trim the receiver down to 34 parts. The transmitter ended up being 30 parts and the VXO came in at 8 parts. However, I was able to make the Clackamas a true transceiver, not just a trans-receiver.

Stay tuned for additional details as I can release them!

Update: Just worked JF2QNM in the JIDX contest. 1 watt spans the Pacific! Of course, all of the credit goes to the op on the other end, but it’s still really gratifying to have your HB 1 watt signal make a nice hop like that.

I’m up to my elbows in the design work for the 2010 FDIM QRP Challenge, and I think I’ve come far enough along to give the rig a name. I’m happy to announce that I’ve dubbed this project Clackamas, in keeping with my tradition of naming my creations after Oregon rivers.

The receiver is pretty close to its final configuration (I hope), so I took it in to work so I could measure the performance using the very nice calibrated test equipment at my bench. This is my first time making this entire range of receiver measurements, and I have to say that it was quite interesting. I wish it was something that I had started taking more seriously a while ago. I have a wish list for test equipment a mile long, but I’ve realized that I really need to get my hands on a pair of good signal generators, hopefully ones that can give me an output down to -140 dBm.

I followed the procedures in the ARRL Test Procedures manual as closely as I could (do yourself a favor and save a copy of this highly useful document). The numbers came out pretty close to what I would expect, so I’m reasonably sure they are legitimate. I’m just hoping that I can win the challenge so that my rig gets taken to HQ for the real battery of tests! Below is the results of my testing, followed by a very brief commentary on the numbers:

IF Bandwidth: 462 Hz
MDS: -126 dBm
3rd Order DR (20 kHz): 80.5 dB (S5 signal level per ARRL Lab Procedures)
IIP3 (20 kHz): -5.2 dBm
Blocking DR (20 kHz): 102.6 dB
IF Rejection: 23 dB
Image Rejection: 48 dB

Clackamas IF Response

I believe that the MDS, dynamic range, and IIP3 measurements are all acceptable for a receiver using 40 parts and a 7-part VFO. I know why the IF and image rejection is so horrible (it’s because of a design trade-off), but I can’t get into the details of that yet. The filter response is a bit funky, but I’m sure that my impedance matching isn’t the greatest. On the air, it’s my opinion that the rig sounds decent. Maybe I can record some audio this weekend and post it. Let me know what you think; does this sound reasonable to you for a compromise superhet? I’d love to hear your comments on this.

KC2UHB with EFHW Tuner

Our favorite fashion hacker/ham, Diana Eng, KC2UHB, has posted a new article on the Make Magazine blog with instructions on how to build an End-Fed Half Wave antenna tuner and deploy it with an antenna. (BTW, did you see that she was recently named to the ARRL Public Relations Committee? An excellent choice the League.)

Her BOM calls out an air variable cap from MFJ and a T94-2 ‘roid, so I suspect that her tuner could handle a bit more than QRP power. In typical ham fashion, it appears that she was too eager to get it on the air to worry about little things like putting it in an enclosure. FB with that Diana, I think most of us can relate.

It sounds like she had great success using this setup with her FT-817 for some SSB QRP fun:

Setting up my antenna for 20m the first time took about half an hour, and I was able to get very close to 1:1 SWR using the 9:1 input with a vertical wire supported by a tree. Over the next hour or so, operating from a park bench in Brooklyn, using 5 watts on sideband, I made contact with stations in the US, Europe, South America, the Caribbean, and Hawaii. The furthest station was about 5000 miles away, which means I was getting 1000 miles per watt out of this setup. I’m sure it was a big contest station and not another QRP operator sitting on a park bench with a wire antenna, but it was still fun.

I’ll take this opportunity to shamelessly promote my own EFHW tuner, which I’ve managed to get back up on my new website. Don’t forget to compare to AA5TB’s design, which features probably the best page on this subject matter which I’ve seen.

I’ve noted with quite a bit of interest the recent surge of comments on QRP-L favoring a QRP exodus up from 7030/7040 kHz to [part of] the old Novice watering hole of 7100 to 7125 kHz. The esteemed Arnie Coro, CO2KK seems to have ignited the fire with this post to the reflector:

Dear amigos :
The 40 meters band changed last year … when the worldwide assignment for ITU Regions I, II and III was finally made totally compatible for the first 200 kiloHertz. According to what we have learned here, this was a difficult to work out agreement, but at the end
thanks to the presence of radio amateurs sitting as members of many of
the nation’s delegations attending the ITU WARC… it became a reality…
So, now we have the 7100 to 7200 segment for radio amateurs exclusive use. My understanding is that the US FCC decided to expand the 40 meter phone band down to 7125 kiloHertz…
That leaves the segment from 7100 to 7125 kiloHertz quite useable for CW…
My suggestion is to start using 7105 or 7110 kiloHertz as the QRP
meeting frequency, replacing 7030 and 7040 kiloHertz that are under so much QRM, especially from digital modes. I agree that many stations have already equipment with crystals for either 7030 or
7040 kHz… but for those of us with VFO capability, enjoying the much
more clear channels between 7105 and 7110 kHz opens up the possibility of many more QRM free QSO’s…
My observations carried on during the past several days confirm that
that segment of 40 meters right next to 7100 is clear much of the time  !
Let’s give it a try !!!

73 and DX
Arnie Coro
CO2KK

The positive response to Arnie’s call to action was immensely gratifying to me. In addition to all of the reflector replies, there have also been some ham bloggers taking up the topic. I’ve long been a fan of this little slice of bandwidth, but at times it has been hard to scare up contacts there. In the last couple of years, SKCC has probably been making the most extensive use of the sub-band, which has increased the traffic there a fair amount and has brought more attention to the frequencies as a place to have a nice, relaxed CW QSO.

Not to long ago, I dreamed about ways to help increase the use of these frequencies, and even started chatting with a few other hams about ways to spark some interest. However, like a whole lot of my ideas, they never get off the launchpad since I just don’t have the time to invest in all of them. After having a few unpleasant encounters with RTTY contesters running me off 40 meter frequencies last weekend, I’m even more determined to help promote 7100-7125 as a QRP (and general CW) safe spot.

I’ve become inspired enough that I’ve decided to take a new design for a minimalistic superhet rig that I’m working on and adapt it to operate on these frequencies. If there’s any interest in it, I might even take a crack at offering it as a kit for purchase. Long live 40 meter QRP!

This weekend, I’ve been participating in the SKCC Weekend Sprint when I get the opportunity in between other obligations. At about 0900 local, I heard F6HKA on 20 meters coming in pretty well with a very fluttery signal. As you can see on the azimuth map for my QTH, the path to France goes right over Greenland, so it’s not a huge stretch to assume that the unique signal quality is due to auroral effects from the increasingly active Sun.

After about an hour of trying, I finally managed to snag a QSO with Bert using 5 watts! A great day for QRP!

F6HKA-1811-14-Feb-2010-14046.mp3

Take a listen to this QSO which was recorded a bit before I made my contact with F6HKA. You can definitely hear the watery, fluttery sound of his signal.

I’m very pleased to report the first (to my knowledge) completed Willamette transceiver which was born in Europe. Vincenzo, IZ5GVP sent along to me a couple of photos of his very nicely constructed Willamette. He reports that it works well and that he’s considering modifying it to operate on the 30 meter band. Three cheers for Vincenzo!

Thanks to some prompting from a Willamette builder who inquired about some performance issues with his rig, I was able to identify an error in the bill of materials which causes a significant degradation in receiver sensitivity.

Fortunately the fix for this problem is very simple. Audio preamplifier collector resistor R49 was incorrectly called out as 10 k, when it should have been listed as 4.7 k. If you have a 4.7 k resistor in your junkbox, just swap it in at the R49 position. A 5.6 k resistor will also work fine here. Alternately, you could just parallel another 10 k resistor across the existing one. I will be happy to supply the correct resistor to any builders who purchased a kit from me and need one.

I’ve determined that this wasn’t a design flaw, but a transcription error. My original hand-written notes have the correct value and my prototype does work correctly (I’m sure NA5N would have caught this problem in the prototype he evaluated). Somewhere in the process of creating the schematics in my schematic capture program, I entered the wrong value. I did build a beta rig with all of the same schematics/BOM that everyone else did, but I didn’t catch the error at the time. I will update the schematics and BOM posted on my website in short order to prevent any further problems.

Please accept a most humble apology from me for not realizing this significant error for a very long time. I do believe that you’ll be pleased with the difference in sensitivity once you install the correct resistor. The receiver should sound like you would expect a proper direct conversion receiver to sound. After the modification, you should be able to run the AF gain at ~75% or less during most operating conditions.

I’d like to thank W0EP, N1RX, WB8ICN, and WB9VTB for their assistance in resolving this matter!