KB6NU's Ham Radio Blog

My second contact this evening was with WN5Y, a high school teacher in Pampa, TX. Looking him up on QRZ.Com yielded the URL to his website. Take a look and you’ll see that solid state receivers can indeed glow.

Dave, you see, sells what he calls The Electroluminescent Receiver Kit. His receiver uses low noise dual gate MOSFETs in which all the drain/source current travels through an LED. If a circuit is working properly, its LED will glow brightly. If the circuit is not working, the LED is dark, just as dead tubes were dark in the old days.

The kit is only $90, but if you really wanted to, you could build the thing yourself from the excellent circuit diagrams and description that Dave provides. Chances are, though, that you’ll end up spending a lot of time and probably close to $90 rustling up the parts yourself. In addition to the basic kit, you could easily spend another $90 on accessories, including an S-meter and digital frequency display. When all is said and done, though, you get a receiver that not only works well, but also looks pretty cool.

Dave also has several pages describing a transmitter to be used with his receiver. There’s no kit available for the transmitter, though.

Another cool feature of Dave’s website is his links page. On the page, you’ll find links to a bunch of sites that cover basic electronic construction techniques, including soldering basics, and QRP projects.

Stan Horzepa, WA1LOU, writes the “Surfin'” column for the ARRL website. This week’s column is on web logs, or “blogs” for short. He includes a link to Dan KB6NU’s weblog and a picture of our president.

Here’s what he has to say about the blog:

No matter what your interest, there is a lot of interesting reading to be found in ham blogs. Take the blog of KB6NU, for example: Dan Romanchik’s Blurty Entries discusses a variety of ham radio topics that interest KB6NU, but it is so well written that it is interesting and entertaining reading even if your interests are different than KB6NU’s.

Thanks, Stan!

Like most hams, I’m kind of a pack rat. I’ve got boxes of resistors, capacitors, and even vacuum tubes that I’ll probably never use. But you never know….

I’m kind of like that with e-mail, too. When I receive an interesting e-mail, I save it to a folder or to a file on disk where it will sit until I junk the computer. You never know, though. Every once in a while I’ll come across one that’s actually useful.

This afternoon, I was searching through my voluminous saved e-mail looking for something I sent to a business associate, when I happened upon an e-mail from a local ham. The message included a URL to a web page that described an interesting QRP antenna, the RockLoop. The RockLoop is a small, square loop antenna measuring 33-in. on each side, tuned with a 100 pF variable cap and a 4:1 toroidal transformer. (Heres’ another URL describing the RockLoop.)

It looked easy enough, and I thought I might actually try to put one together, except that I didn’t have any of the T-50-2 cores on which to wind the transformer. So, I called up my local radio store to see if they had any. Of course, they didn’t have any T-50-2s, but they did have a bunch of T-50-6s. That got me to wondering aboutthe difference between the two cores. So, I did a Google search.

One of the first URLs I came up with is a great tutorial on ferromagnetic core inductors. It talks about the different types of core materials and how to choose the right core for your application. There’s also a chapter on winding tips. This is a very cool site.

Next, I found the Amidon website. This website has a product selector online that describes the properties for all the various. ferromagnetic cores they sell.

Finally, it struck me that I sell a book that talks about all this stuff, namely Ferromagnetic Core Design and Application Handbook by Doug DeMaw W1FB. This book talks about all the different applications of ferromagnetic cores, rods, bars, and beads, as well as give technical data on the various materials and commercially-available products. It’s cool because it not only delves into the theory, but also gives you some circuits to build, if you’re so inclined.

Using these three resources, I was able to determine that the T-50-6 would indeed work for the RockLoop antenna. Its frequency range of 10 MHz – 50 MHz, while the T-50-2 has a frequency range of 2-30 MHz. Since the RockLoop is designed to operate on the 30m, 20m, and 15m bands, the T-50-6 should work OK, although I’m a little concerned that I may be pushing it on 30m. So, while it may work just fine, I think I’ll ask them to actually order some T-50-2s. They look to be a lot more versatile, anyway.

Update 4/26/04: Since writing this, I’ve been searching for sources for these cores. I’ve come up with three:

• Universal Radio
• Alltronics
• CWS Bytemark

The first two sell Amidon cores, but the selection is limited. For example, in one article, the author used an FT-240-67 core for a balun, but neither of the first two sources seem to carry them. CWS Bytemark does carry them, though, and you can order right from their website. They also carry all the wire and tape you need to build your baluns.

I am now the proud owner of an Elecraft KX1, serial #577 or #575. (The serial number kit envelope is stamped “00577,” but the label inside says “00575.”)

From a kit point of view, it’s pretty impressive. The components appear to be quality components, and the instructions are clearly written and well illustrated. What I really like, though, is that the parts lists has photos of all the components. Several times, I looked up the photo of a part before installing it just to make sure that I had the right part.

I’m just two hours into building the thing and have just completed the Part I assembly, alignment and test. So far, so good. It passed all of the initial tests without letting any of the smoke out. At this rate, it’s should take me less than ten hours total to build the thing, including the 30m board and the antenna tuner, as I’d estimate that I’m about 30% done with the base unit.

I will really be interested to see how well the antenna tuner works. From all reports–from guys on the mailling list and from a guy I actually worked on the air–it works really well. I once worked a guy who said he was operating a KX1 sitting on his dining room table with a wire stretched out on his deck for an antenna.

There are several websites that will allow you to take tests and gauge your readiness for the real thing, including:

• Ham Test Online,
• QRZ.Com,
• eHam.net, and
• AA9PW FCC Amateur Radio Practice Pages

Only the latter seems to have practice code tests, though. Since the code test is currently one of the biggest hurdles new hams have to face, I want to thank AA9PW for making this available. I used a practice test last night with my General class and it worked very nicely.

I recently corresponded briefly with a guy on the Elecraft mailing list about his difficulty in understanding antennas. As I’ve pointed out in the past, I’m no expert, but my purchase of an antenna analyzer has certainly helped, and I advised him to also buy one. He replied that he did have one, but…

I’m clueless whether those values of Z, L and/or C are good/bad when it comes to trying to maximize ERP.

This really bugs me because I KNOW the antenna is the most important element (“a dime in the antenna is worth a dollar in the transmitter”). Yet for me my antenna system is the least understood portion of my equipment.

If I could just find a ‘dummies guide’, something that just ‘boils it down’ in laymans terms to give me a foundation to start from I’m sure I could then progress to the more technical explanations.

My response was,

The short answer is that, for the most part, it doesn’t really matter. As long as an antenna’s SWR is less than 1.5:1 (and some would say 2:1), then it will radiate just fine. You know, there are many factors which contribute to an antenna’s effectiveness, and for most amateur installations, you’re not going to be able to optimize all of those factors.

How well an antenna matches the feedline and the transmitter is only one of those factors. Other things, such as the height above ground, location of nearby metal structures, etc. will all have an effect. Look at it this way — connecting a 50-ohm resistor to the transmitter output will give you a 1:1 SWR, but you’re not going to be radiating a lot of power with it.

To me, the big reason for trying to keep the SWR down is to reduce feedline losses when you’re using coax. Coax was designed for systems where the transmitter output impedance matches the feedline impedance and the feedline impedance matches the antenna input impedance. When there’s a mismatch, then the coax contributes greatly to the losses.

Another thing about coax, I think, is that the quality can vary quite a bit. I’m just getting into this, but I think it’s a good idea to actually measure how lossy a particular piece of cable is. I haven’t done this yet, but there are articles out there that describe how to do this.

You can, of course, avoid these losses by using open-wire feedline or ladder line. Because of the way they are constructed, they are not as lossy as coax, even when there’s a high SWR on the line. How cool, eh? The trick, however, is that you have to use an antenna tuner to make sure that the impedance at the transmitter input is 50 ohms. The reason for this is not because the antenna won’t radiate effectively, but rather so you don’t damage your transmitter.

The more I think about it, the more I think that coax is really the culprit here. Sure, it’s easy to work with–it’s flexible and you can run it just about anywhere. To get the best results, however, you have to use qualiy coax and use it with an antenna whose input impedance is close to the characteristic impedance of the coax. If your coax is less than optimal, or the SWR on the line is high, then you’ll get poor results.

I think this is one reason that the guys who have K1s and KX1s and use them with random wires and the internal antenna tuners seem to have such good results. The output power may only be 3-5 W, but nearly all of that power is going into the antenna. There’s no coax to suck up precious watts.

My next antenna project is going to be a loop antenna fed with 450 ohm ladder line. I’m going to string up as much wire as I can around the backyard and run the ladder line down to my antenna tuner. I should have enough space for a full wave on 40m and maybe even 80m. Should be fun.

One of the nice things about teaching the General class is that I actually learn a few things from time to time. For example, last Tuesday, we covered RF safety, a topic that was definitely not on the test when I took my General class test 30 odd years ago. In order to adequately explain the topic to my charges, I had to do some quick boning up of my own.

I found out some interesting things. For example, the resonant frequency of the typical human body is somewhere between 30 and 100 MHz. That’s why the maximum permissible exposure (MPE) for that frequency range is so much lower than the MPE at 1.8 MHz. It’s so low, in fact, that the FCC guidelines state that you must perform a routine RF safety evaluation if you are outputting more than 50 W on the 10m band. For comparison, note that you don’t have to do this evaluation if your output power is 100 W or less on 15m, 225 W on 20m, 425 W on 40m, and 500 W on 80m.

Not sure what’s required to comply with FCC Guidelines? Well, if not, you’ll want to pick up a copy of Evaluating Compliance with FCC Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields, OET Bulletin 65. Supplement B of this publication deals with information for amateur radio stations and includes worksheets that step you through the process. You can get it by mailing the FCC or from the FCC website. It’s a pretty large PDF file, so you might not want to attemp it unless you have a broadband connection.

Going through this material really got me thinking about my own installation here. I’ve been thinking about a tower, but now I’ve pretty much decided against it. One reason is the lay of the land here. My house is situated on a hill, and my neighbors to the rear are uphill of me. A beam on a 50-foot tower would probably beam right into their house when pointed in that direction. Couple that with the difficulty in erecting one in the first place, and I think that I’ll just forget about it for now. It may just be time to move to a better antenna site…..errrrr, new house anyway.

For the last week, there’s been three or four big pileups on 30m every evening. (It may be the same on other bands, but I pretty much stick to 30m lately). The pileups are so big and spread out that between them and the weird QRM on the band, there’s practically no room for “normal” QSOs.

Why the pileups? Well, there are two high-profile DXpeditions on the air these days. The first is the 3B9C DXpedition to Rodrigues Island. Rodrigues Island is about 400 miles east of Mauritius in the middle of the Indian Ocean. The operators are very good and they’re ripping them off one after the other. The website notes that they’ve already made more than 50,000 contacts.

The other is the HK0GU DXpedition to San Andres and Providencia Islands in the Caribbean. This is a somewhat lower profile operation, as there’s only one operator – Gerd. He’s spending four weeks on Providencia to celebrate his 25th wedding anniversary. His operation might be lower profile, but he still creates some good pileups.

I complain about the pileups, but the upside, of course, is that band conditions have been very good. If band conditions weren’t so good, then there would be fewer stations in the pileups (at least fewer stations that I can hear). There’s also a lot of DX stations on. Mostly, they’re trying to work the DXpeditions, but I’ve worked several, who I conjecture got tired of the pileups and just started looking around for other contacts.

I was, in fact, going to rant about the pileups, but Wednesday night, I was just hanging around the shack, and decided to tune around the band. I copied 3B9C, and even though there was a good-sized pileup, they were putting in a pretty good signal, so I decided to give them a call. I got them on the third or fourth try!

A little later, I was tuning around again, and happened on HK0GU calling CQ. He copied me on my first call. I just happened to be in the right place at the right time. As soon as he sent 73, there was again a big pileup.

At any rate, I guess I can’t complain too much about the pileups.