Ripples in the Ether

So I’ve taken the plunge into the strange and magnificent world of Twitter. I resisted it for a while because I didn’t see much value in it, but I’m starting to get what the hype is all about. One area where I will freely admit that I have a weakness is in keeping up with my e-mail. I subscribe to tons of e-mail lists, which is bad enough. But it’s easy enough to mass delete posts from mailing lists. However, having a big web presence (at least for a ham) means that a lot of people e-mail you personally. Don’t get me wrong, I love getting e-mails from people who stumble upon my writings on the web. The problem that I have is that I feel obligated to put as much time into replies as senders put into their e-mails. So when someone sends me a great e-mail that is 10 paragraphs, I feel like I have to reciprocate in kind if I’m able to. The problem is that it gets me into a rut where I feel like procrastinating because I can’t sit down for 20 minutes in one stretch to craft a worthy reply. Not very cool, and not very fair to those who are expecting a response.

On the other hand, Twitter molds your messages into a forced austerity. I feel quite a bit more liberated in my ability to shoot off quick replies to Tweets from my ham buddies, knowing that I’ve taken care of business and have moved on. The back-and-forth dynamic is also very invigorating compared to e-mail. It’s almost like a live chat, but just a tad bit slower.

Twitter is also quite good as a place to get raw information about breaking events. The recent Mumbai terror attacks proved that, much to my surprise. You have to filter this kind of raw data (well any kind of Internet data) through a skeptical eye, but it was amazing how much of the live Tweets from incident turned out to be essentially accurate.

Of course, there’s always a downside to any trendy new technology, and Twitter is no exception. As you may have noticed throughout the ham blogosphere, folks are finding that it’s hard to filter the good stuff out of the cruft once you start following large numbers of people on Twitter. Really, no one cares that I’m currently trimming my nose hair or that I’m in the 5th hour of my Top Chef viewing marathon. The challenge for me is to fight the information overload. Much like a raven with ADHD, I find information on the Internet to be like one shiny bauble after another. It’s extremely easy for me to lose myself in the irresistable ebb and flow of the information currents. Seeing those Tweets pop up is quite destracting and hard to ignore. There’s no doubt that you have to have self-discipline to be an effective Twitter user.

Now that I’ve taken my turn beating this quite-dead horse that 20 people in line in front of me have already taken their whacks at, I have my catharsis. Isn’t that what the blogosphere echo chamber is all about? I’ll do my best to actually publish some real content here on the blog, instead of more navel-gazing introspection. But what do you expect from an introvert anyway?

Blizzak's Snow Dog Minion

This is where I get to blow off some steam about this ungodly weather we have been having. Warning: cabin fever is setting in.

The weather forecasters have not been doing a very good job with this one. We got socked with a good bit of snow on Saturday but they assured us that the arctic air would be out of here no later than Monday and everything would melt. Instead, we only picked up another 5 inches of snow last night, bringing our total to about 1 foot. Now they are hinting that this thing could last all week. I don’t have any chains for our little Nissan Versa, because we never freaking need chains around here. I always thought that any valley dwellers like us who get studded tires and chains for driving around here were overreacting. Turns out I was wrong. By the time I figured out I was wrong, all of the tire stores sold out of chains. TriMet isn’t running any bus lines near our house either. So Jennifer and I are stuck.

Cabin Fever

And I have to get back to work. Tek isn’t closing down, so any time that I can’t get to work is eating into my non-existant vacation time. Not to mention that we are making our big year-end push to get products completed. So I’m well and truly screwed. I’m sure my poor manager is freaking out right about now.

Who Needs Fake Icicles?

Just to make sure I wasn’t just fooling myself about the severity of the road conditions, I took Baxter for a walk down to the main arterial a few blocks from my house. Our road is a sheet of packed snow and ice, but I thought that maybe there was a chance I could make it once I got out to the main road. No such luck. Once we got out there, it was hell. There was still a good couple of inches of ice even in the well-worn tracks in the road. No vehicle without chains was making it out there. So Baxter and I trudged back home, tails between our legs.

You’re probably wondering what the hell the Bilzzak stuff is about? Some tire manufacturer has been running TV commercials for a tire they called Blizzak. It cracks me up, because it sounds like the name of some warlord out of a fantasy movie or some mythical snow god than it does a tire. So, in my delusional state, I’ve appropriated the name for the angry god who has visited snowmaggedon on our humble city. Cue By-tor and the Snow Dog.

Oh, and all I have to say about this is:

No, seriously, that stinks. What bad luck. I hope that you get home soon and safely.

As I mentioned in a previous post, I did the calculations to change the AF filter in the Willamette from a low-pass filter with a 3.3 kHz cutoff to a peaked low-pass filter with a cutoff frequency nearer to 1 kHz. I finally got around to implementing the mod last night and got a chance to listen to it on the air today and take some measurements of the filter response.

First off, let’s take a look at the filter response:

If you compare this to the old response, it probably won’t look drastically different, but it does cut off a bit eariler than the original filter. There is a bit of a peak as predicted, although it’s a bit wider and shallower than expected.

However, the real proof is in the listening. I found (purely qualitatively) that the response of this filter was much tighter sounding than the original. Much of the high frequency interference is gone, and you can tell by tuning through a signal that it drops off much more quickly at the higher AF frequencies. You do lose some of the “crisp” direct conversion sound, but I feel like this is made up for in the utility of having greater filtering.

Here are the steps that you need to take in order to modify your own rig:

• Replace R50, R51, R54, and R55 with 24 kΩ
• Replace C55, C59 with 100 nF
• Remove C56, C57 then place a 1 nF capacitor from Q12 base to ground (in the place where C56 was located)
• Remove C60, C61 then place a 1 nF capacitor from Q13 base to ground (in the place where C60 was located)

One other small thing that you might want to do is replace C65 with a 1 uF capacitor. I noticed that when the AF gain control was set to maximum, that there would be an annoying popping during keying. This change helps to eliminate this problem.

I hope that you enjoy this modification to the rig. In hindsight, I’m not really sure why I designed such a wide open AF filter, although I suspect it was because I wanted to preserve the “DC” sound of the rig. However, I think that utility trumps a nicer sound in this case and will make the rig more usable overall.

Sorry about the dearth of posting on the blog lately, been busy with two things: work and another web project. That other web project is a reincarnation of QRPedia, a failed QRP wiki. This time, I’ve reconfigured the site using a CMS. Accounts are open to anyone, and being a member will give you the ability to post to a personal blog, write stories about QRP and homebrewing which appear on the front page of the site, edit “books” of QRP information with others, and post the details of useful circuits to a repository. It seems to be taking off pretty well after its introduction on qrp-l.org earlier this week. I would appreciate it if you would stop on over for a look and sign up for an account if you like what you see. I’m always open for ways to improve the site, so don’t hesitate to contact me with your questions, concerns, improvements, or corrections. Thank you!

QRPedia 2.0

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.

Measurements

Conclusion

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 F_T of a 2SC5739 is 180 MHz. Given the rule of thumb of having a F_T 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 F_T 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.

I concur with Bill at SolderSmoke: MAKE Magazine was skirting way too much over into the “knitting needle” side of things. Thankfully, they have redeemed themselves with their recent videos on the LED, and now the lowly resistor. This video probably won’t teach any of you something new about resistors, but it’s great to see them get back to this type of content.

MAKE presents: The Resistor from make magazine on Vimeo.

W8DIZ 5 Watt CW Amp

A few days ago, W8DIZ made a post on qrp-l.org announcing a new addition to his RF Toolkits line. This one is a 5 watt CW amplifier using a push-pull 2SC5739 pair as the PA (my new favorite full QRP gallon transistor). I built my own version of the circuit using parts that I had on-hand. The only substitiutions that I had to make were the cores for T3 and T4 (the output transformers), but I have the correct cores on order from Diz. With an input signal level of 0 dBm (1 mW), I was able to get nearly 5 watts output into a 50 ohm dummy load from 160 to 30 meters. The power output started to droop above 20 meters, but I suspect that is because I used the wrong core types on the PA circuit. There is also a control to adjust the power output using a PIN diode bias control on the driver amp emitter. It seemed to work fairly well on some bands, but on others was not very well behaved. Once again, I’m going to wait for my correct cores to arrive before making any final judgements about this.  The great thing about using a PIN diode design like this is that you are using a DC bias to control the gain, which means you can run a long cable to a panel-mounted potentiometer. This looks like a great amp and I look forward to getting it built completely correctly once the parts get here. Stay tuned for another update with detailed measurements once that happens.

…for now.

I just found out that my employer is forcing us into a company-wide week-long shutdown. Most of the company will be taking mandatory vacation at the end of the year. However, since I work in manufacturing and we have a year-end production goal to meet, our “vacation” is scheduled for the beginning of the year. Combined with the company holidays that we have for Christmas and New Year, I’ll be off work for nearly three weeks. I’m fortunate to have just enough vacation time to cover this shutdown, but it’s going to wipe out my vacation time reserve. I had a feeling that this would be coming, so I have been pretty diligent in the last six months in minimising my vacation time usage. Guess I’ll have some time to do some serious solder melting.

The other fun thing that I learned is that our next scheduled merit pay raise has been cancelled. Awesome news. I’m just waiting for the next kick in the nuts to come. Isn’t this economy great?