Wideband Transmission #1

This is the first in a series of blog posts covering a wide variety of topics. In the past, I have used Twitter for my microblogging needs. For a variety of reasons, I'm on a Twitter hiatus right now, so I'll be using this series to convey some of the disconnected (and possibly connected) random thoughts that I feel I need to get out there. I don't think I'll be abandoning Twitter completely, but I will be reworking the ways in which I use it once I come back.

I'm also in the process of disconnecting completely from Google, so I wanted to give fair warning to those who correspond with me via my Gmail account that I will be abandoning that service very soon. I've already deleted my Google+ profile, and will be deactivating the rest shortly. I'll probably describe my rationale for this later, but keep in mind that I've been a Google customer data mine for nearly a decade, so this is not something that I undertake lightly. I'll try to get alternate contact information to those of you who regularly correspond with me.

It is an age of new beginnings.

Clackamas 2 Prototype

With the introduction out of the way, let's get down to the good stuff. Above, you can see the latest project on the Etherkit bench. It's a re-work of the receiver from the Clackamas transceiver (the rig that I submitted to the 2010 FDIM 72-part challenge). I've decided to make this receiver into a cheap & cheerful little kit to get people warmed up for building the CC1. It's currently for 40 meters only, is a superhet, and is VXO tuned (covers 7.030 MHz plus a bit more). It is 100% discrete component (you can see a TDA7052 IC above, but I've abandoned it for a different AF amp) and will be SMT construction. The receiver itself is pretty simple, but you can see there's a fair bit of other circuitry on there. That stuff is mute and sidetone circuits. It's easy enough to design a standalone receiver, but most of them will probably just gather dust after being built unless they can interface to a transmitter easily. With this extra circuitry, you can just split off your transmitter's key line and connect it to this receiver to have built-in muting and sidetone. My goal is to make this project cheap and fun to build. I'll be fast-tracking this one so I can get back to the CC1 soon.

Oddly enough, another project from the FDIM Class of 2010 is also coming out soon. As spotted on The QRPer, the Cyclone 40 transceiver is based on the rig that Dave Cripe, NM0S submitted as his 2010 FDIM 72-part challenge entry. I recall that the rig had a very unique design and that the specs were impressive. Dave's a great designer, so be sure to buy one to get a rig unlike anything else you've seen before and to support 4SQRP.

Choking off the Internet firehose that I had previously directed at me has allowed me to devote a bit more time to enjoyable activities that I've neglected, one of those being reading. I'm currently enjoying a book I've had on my shelf for a while now called Seeing in the Dark by Timothy Ferris. It's billed about being about amateur astronomers, but it does get into the professional side quite a bit as well. It's a good read and very entertaining, and I can't help but see a lot of parallels between amateur radio and amateur astronomy.

That's a great segue to the final item, which is a bit of fun from our favorite Canuck astronaut, Cmdr Hadfield. He's leaving ISS in a few days and just released a surprisingly touching (although obviously light-hearted) rendition of Space Oddity by David Bowie (one of my guilty favorites). Cmdr Hadfield may not be on the level of Neil Armstrong or Yuri Gagarin, but he's definitely making a play for Coolest Astronaut Ever.

The Clackamas QRP Transceiver

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.

All Buttoned Up

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.

Sweet Success!

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.

A Sneak Peek at Project Clackamas

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.