Ripples in the Ether

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.

Audio Amplifier Guts

As I mentioned in a previous post a few days ago, I found a nice 2 watt mono audio amplifier board that’s a perfect addition to give speaker capability to a receiver with headphone output. I purchased four of these bad boys since they were so inexpensive (and I was paying for shipping from Hong Kong, so might as well order in bulk). I figured a good test would be to build up a bench amplifier so I could have the convenience of listening to any of my homebrewed phones-only receivers/transceivers (most of them) on speaker.

To the right, you can see the pleasing results of this little project. I had a nice Ten-Tec TPC-17 that turned out to be a perfect enclosure. The 1/8″ input connector is on the left, a power LED in the middle, and a mute switch on the right (the amplifier board has an active low mute line which works extremely well). I created a speaker grille drill template in Inkscape for the 3″ speaker bolted to the top lid of the enclosure (if there’s any demand for this file, I can post it here). The actual 1″ x 1″ audio amp board is on the left and a small 7805 voltage regulator board on the right.

AF Amp on the Bench

Here’s the enclosure all buttoned up for use. You can see that the speaker grille is a bit ugly, but it works well enough. There is no power switch, since the quiescent current is so low that there’s no problem in leaving it powered up. Tonight I hooked it up to my VRX-1 (with a rock on 7030) and listened to the wide-open band with the DX contest in full swing. The audio quality was quite nice; better than I remember it when testing it out in the open on the workbench. I’m guessing this is because the speaker was properly mounted instead of having the magnet rattling against the bench. Even though it’s a simple project, it’s a great addition to the shack that makes me wonder why I didn’t do this earlier. Yeah, I could have purchased a set of amplified PC speakers, but that just didn’t seem appropriate. Besides, the amp in the Ten-Tec enclosure looks spiffy next to all of the other similar looking equipment in my shack.

Update

I got a bit bored tonight, so I took a video to demonstrate the amplifier working with the VRX-1. Yes, I know there’s nothing to really look at, but the audio is a bit interesting.

Sure Electronics EUA2005 Audio Amplifer Lash-Up

Lately, I’ve found that eBay has been one of the best ways to beef up my junk box with inexpensive electronics components (eBay Stores are my preference, the auctions often aren’t that great). I purchased a nice SMD resistor/cap assortment from a company called Sure Electronics and found that they have some other goodies that might be of interest to the homebrewer. One of those is a tiny little (about 1″ x 1″) 2 watt mono audio amplifier based on the EUA2005 IC. The spec sheet states that the IC output power is 1.5 watts, so the manufacturer might be fibbing a bit on their specs. Regardless, it’s enough power to drive a 3″ speaker to a decent volume for shack listening. The IC has a maximum V_CC of 6 V, so I had to create voltage regulator to step my 12 V bench supply down to 5 V using a 7805. The audio quality is definitely what I would call “communications” grade, but the price is great: $2.22 for a 2-pack. One word of warning: your order is shipped from Hong Kong, so expect about 2-3 weeks for your order to arrive.

For those working on W8DIZ’s frequency counter project in QQ, they also have a Atmel STK500 in-circuit programmer clone for a very inexpensive price. I haven’t had a chance to try mine out yet, but if it works as advertised it’s well worth the price (I have no reason to believe that it won’t work, but if doesn’t, I will update this post).

The usual disclaimer applies: I’m not associated with the company in any way, just a satisfied customer.

Software Defined Radio is a technology which has always intrigued me, but something I just haven’t been able to devote a lot of time to yet. I’ve built an early model SoftRock and studied the basics of the theory. Not too long ago, I built up my own little version of a 40 meter SDR based on a different topology from the SoftRock (VXO feeding a quadrature hybrid, driving passive MOSFET mixers). It worked so-so, and it ended up in my pile of experimental boards.

Subharmonic SDR Schematic

Today in my feed reader, I caught wind of a really neat topology for a minimal parts count SDR, courtesy of Joachim, DL1GSJ. His receiver uses a simple phase shift network to create the I/Q LO signals to drive a pair of Polyakov (subharmonic) mixers. It looks dead simple to breadboard and could be an easy way to try SDR without having to order a SoftRock kit. Get over to Joachim’s blog to get the full details of this fascinating design.

A little while ago, I got a hankering to work on a SSB transceiver. It’s something that I’ve never homebrewed before, and it seemed it like it might be fun to tackle. The BITX20 seemed like an obvious choice, and W7ZOI recently published an improved bidirectional amp which would be nice to try in the rig. But I’m one who likes to try stuff that’s a bit off the beaten path, so I decided to try my hand at something a bit different.

VU2PEP has a lesser-known SSB design on his website, that’s a dual-band transceiver. Besides having 20 and 40 meter capability, it also has a different topology than the BITX series. Instead of reversing the flow of the signal to generate a SSB signal, this design sends the RX and TX signal in the same direction through the IF. Take a look at the schematics to get an idea of what I’m talking about.

I decided to make a “remix” of this design. The basic topology is the same, but most of the circuits are revised. The IF was moved to 4.9152 MHz, and the VFO is heterodyne-style to provide a ~19.12 MHz LO signal. My version is only for 20 meters. The front end has a preamp added and uses a cascode JFET mixer instead of a single JFET. So far, the RX strip and VFO is complete (although I might change the VFO because of some birdie problems), but the transmit amplifiers haven’t been built yet. I got a good chance to work out the RX during Sweepstakes. Check out my YouTube video below to hear me describe the circuit so far and listen to the receiver on SS.

New England Code Talker by AA1TJ

Although there are many days when I can barely stand the level of rudeness on QRP-L (and increasingly on qrp-l.org), I am sometimes reminded why I maintain my membership. Some recent events there have helped to boost up the numerator in the signal/noise ratio, and correspondingly, my interest.

In case you haven’t followed much of what has happened on the list in the last few years or haven’t listened to SolderSmoke, there’s a fellow by the name of Michael Rainey AA1TJ, who could be considered the mad genius of the QRP world. He has created what has to be considered some of the most unique and inventive minimalist QRP circuits that our hobby has ever seen. Take a look at his website to get an idea of what I’m talking about. I’ve also attached a YouTube video below showing you how AA1TJ has to operate this very unique transmitter.

AA1TJ trying for transatlantic QSO

His latest flight of fancy is his New England Code Talker voice powered CW transmitter. Yes, you heard correctly; the transmitter is powered 100% by voice sound pressure energy (about 15 mW RF output). AA1TJ has already made numerous successful QSOs with the transmitter, proving that the concept actually works. Recently he, AA1MY and W1PID met at the beach front cottage of W1REX to attempt the world’s first voice powered transatlantic QSO, as well as what was claimed to be the world’s first transatlantic QRP QSO on 160 meters (I think I misunderstood that. It’s supposed to be AA1MY’s first 160 meter transatlantic QRP QSO), both very amazing feats. I won’t spoil the story, so get yourself over to W1PID’s website to read the details of how this expedition turned out. I must salute all of you gentlemen for pushing the boundaries of our wonderful hobby and trying something never done before. Well done!

Update: Here’s the “Rexpedition2009” report about the event from W1REX (PDF format).

Update 2: A great video from W1REX showing the transatlantic 160 meter QRP QSO:

While I occasionally get a bit worried about ham radio having to be dragged kicking and screaming into the 21st century, there are encouraging signs that some hams get it. The two areas in ham radio where this seems most pronounced is in Radiosport and DXing/DXpeditions. Outside of the United States, these aspects of the hobby seem to be doing a decent job of attracting folks under 50 to our nerdy little world (no offense to you crusty old guys; without you our hobby would be non-existent). I’m not quite sure why, but inside of the US, these pursuits haven’t quite had the same pull on the younger crowd. Speaking for myself, I’ve never felt I could seriously tackle either activity without having the ability to deploy a half-decent antenna, something I’ve only recently been able to do because I just purchased my first single-family house. Perhaps other younger folks have had a similar problem.

Anyway, let me show you the efforts of a few people who have helped in blowing a little dust off of our vintage hobby. First up is the website and video blog of XR0Y, the Rapa Nui (Easter Island) DXpedition. These guys have a very visually appealing website with tons of information about the operation, a blog to keep you updated on the latest news, a Twitter feed, and perhaps best of all, a really cool video blog. The production values are top-notch (they are promising HD video of the actual operation) and it’s interesting to get a behind-the-scenes look at a DXpedition from start to finish. Here are the first three videos in the series; it looks like many more are on the way:

Next, a topic a little bit nearer to my heart, courtesy of W2LJ. Larry was contacted by VK1AA regarding a new QRP transmitter kit from GenesisRadio called the Q5. It looks like this kit is geared towards the new kitbuilder/homebrewer, perhaps as something to build on a club “kit night”. The design uses CMOS logic for the LO and driver amp, which feeds into a class-A PA (about 1 watt output). I don’t see any low-pass filtering on the output and there’s no specification on the spurious products, so an outboard filter might be in order.

GenesisRadio got an excellent video spokesman for their kit; young VK2FJDX. Check out the FB job he does in promoting the new kit:

The VRX-1 receiver kit uses a TDA7052 audio amplifier IC, which is a bit different from your run-of-the-mill LM386. Because of its push-pull output, if you use a phones jack, you must isolate it from ground. This isn’t something you have to worry about if you use a non-conductive enclosure or if you have an isolated phones jack. However, more often than not, you won’t have an isolated jack, and many of the enclosures that we use are metal.

This little hint will allow you to modify a “standard” grounded ring phones jack with a conductive enclosure (such as the 4SQRP Clear Top Tin, like the one I used).

Bill of Materials

• 3.5 mm phones jack
• Small length of 3/8″ OD (1/4″ ID) Polyethylene Tubing
• 1/4″ nylon washer
• CA glue (optional)

Instructions

Cut off a piece of the 3/8″ OD polyethylene tubing approximately 1/16″ long (about 1 mm).

Cutting a small piece of the 3/8" OD tubing

Place the small piece of tubing over the phones jack, so that it rests against the body. You may want to glue the tubing to the body of the phones jack.

3/8" OD tubing over jack

Drill a 3/8″ hole in your enclosure to accommodate the tubing, then place your phones jack in the hole so that the 3/8″ tubing is centered in the hole. Place the 1/4″ nylon washer over the jack from the outside of the enclosure, then use the knurled nut to secure the jack to the enclosure. It’s as simple as that!

Isolated jack installed in enclosure

VRX-1 in 4SQRP Clear Top Tin

While I was away on my honeymoon, I noticed that the upcoming kit that I’ve been hinting about for months has finally been released. The Four State QRP Group announced availability of the VRX-1 direct conversion receiver. The VRX-1 is a simple 40 meter VXO-tuned receiver (crystal on 7.030 MHz), but it’s not your typical NE602/LM386 combo. The product detector consists of only a 2N7000 MOSFET, a capacitor, and an inductor. The audio amplifier is a TDA7052 from NXP. This little 8-pin DIP can output 1 watt of clean audio into low impedance headphones or a small speaker. Current consumption is only about 40 mA, which makes the VRX-1 easy on your batteries if you take it out for portable use. The construction of the receiver is done Manhattan-style, but don’t let that put you off if you’ve never built this way before. I provide a precise, detailed layout diagram to show you exactly where each part is placed and how it is oriented. There’s also some very detailed build documentation to walk you through the build, which you can preview at the VRX-1 web page. Even the novice builder can construct this radio!

The VRX-1 was designed to be a companion to the NS-40, or other similar rock-bound 40 meter QRP transmitters. I also include instructions on how to use some of your own parts to modify the VRX-1 for operation on any HF band, so don’t feel like you are stuck on 40 meters if you would like to try to experiment a little. In a future blog post, I’ll walk you through the process of integrating the VRX-1 with a standalone QRP transmitter to make a complete station.

Proceeds from the kit sales go to fund OzarkCon 2010; I don’t make a dime off of it (just the glory, LOL!). So please support the QRP community and try your hand at a new kind of kit. It’s only $25 postage paid in the States, $28 for DX.

20 Watt Broadband Linear Amplifier

QRP is tons of fun on CW, but it gets a bit rough trying to work other stations on SSB with 5W, especially when you are using antennas that are low to the ground. I had been eyeballing the nice RF MOSFETs from Mitsubishi for a while, and since I got a hankering to get a bit more active on SSB, I took the plunge and ordered five of the RD15HVF1 devices. At a current price of $5.25 at RF Parts, they are a bit more expensive than the IRF510 that you see in a lot of 20-40 watt range linears, but these devices have a few advantages over the IRF5xx series. One of the biggest, in my opinion, is that these RF transistors are designed to run off of a 12 volt drain voltage, unlike the IRF510 amps which don’t really work well until they get around 24 volts on the drain. These things can also take quite a beating from poor mismatches, and have the convienice of having the source connected to the metal tab on the case, making for a nice solid ground connection.

20 Watt Broadband Linear Amp - Inside

Having the appropriate parts in hand and some designs on the internet to steal from, I set out to build my own linear. There isn’t a ton of creativity to be used when designing a linear of this class (Push-pull Class-AB). Every design that I’ve seen looks nearly the same. Not surprisingly, the real focus of the design is in optimising the input and output networks. Feeling lazy and anxious to just get on the air, I pretty much did “cut and paste” from some different circuits to find out what works best. I know, not the best method, but sometimes the desire to just put out some RF trumps proper procedure. I don’t have a scehematic to post at the moment, but if you click through on the photo to the right, you can see a close-up with descriptions of major circuit blocks. Below, I’ve posted links to the two circuit resources that I used the most for this design. I’ll have more details about the designs to comment on at a later date, when I can pull some proper notes together.

• HPSDR Pennywhistle
• TF3LJ SoftRock Amplifier

One of my weakest homebrewing areas is in the mechanical engineering, but now that I have a bit of a real “shop” in my garage, things have been getting better. A bit of scrounging at the surplus stores around town led me to some cheap heat sinks that looked like they might be suitable for this project. After attacking them with an angle grinder to get a lip off of the bottom side, I was able to bolt two of them to the lid of an aluminum Hammond enclosure. I nibbled a nice square area right out of the middle of the copper clad I used to build on, soldered the RD15HVF1 devices to some pads etched out with a Dremel, then bolted the MOSFETs and copper clad directly to the lid of the enclosure. Drilling the holes for the BNCs and the LED was a piece of cake with the aluminium box material.

Without getting into too many details at this point, I was able to get the amplifier working right off the bat. I didn’t get quite as much output power as I initially liked (only got about 10 watts), but the amp was working correctly. More troubling was the fact that output on 6 meters was only 2.8 watts. Not too great when you are putting in 2.5 watts. I figured it had to be something with the input or output network. The input return loss measured quite good; -15 to -20 dB across all the bands. So I figured that left the output network. My initial iteration of the amp used a transformer similar to the one in the Pennywhistle amp (this is a configuration that I’ve also successfully used before in a push-pull class-C CW amp). Without doing any actual measurements and calculations, I dropped in the broadband transformer pair used in the TF3LJ amp, and immediately improved my output power by a few watts. But I was still a bit low on 6 meters. A bit more searching showed that I might need another compensation cap on the output, so I experimented a bit more until I found that a 1200 pF silver mica in series with the drain transformer outputs worked wonders and boosted my power on 6 meters to nearly 15 watts CW. I haven’t done any analysis to see why this helped. I know, sloppy…but sometimes expedience wins.

Since there’s no output filtering built into the amplifier enclosure, I had to assemble some outboard filters in order to get this thing on the air. I was going to use 7-pole low-pass filters until I realized that everybody else uses 5-pole filters because push-pull amps already suppress the even-ordered harmonics by at least -30 dBc. A bit of work with the new LADPAC software in EMRFD enabled me to crank out a table of filters for all of the bands (160 m – 6 m) using the silver mica caps in my junkbox plus T68-6 toroids. If you click through the photo below, you can get a glimpse of the copper clad enclosure sticking off the output of the amp.

Backyard Linear Test

Last Monday, after a bit of checking of the signal purity with my dummy load and scope, I was satisfied that everything was working OK and took the amp out for a spin on the back porch. I set up the Buddipole in Versatee Vertical configuration with the Low Band Coil. It tuned right up on the upper end of 75 meters, and I had no problems at all checking into the Oregon Emergency Net. One watt out of the 817 gave me about 25 watts out of the linear on 75 meters. I was too busy to do much else with the amplifier until today (the following Sunday), but I was excited to give the amp a try on 6 meters, since that was one of my biggest motiviations for building the thing. The Buddipole was set up in a simple 6 meter dipole configuration about 10 feet above the ground and I parked the 817 on 50.125 MHz. It didn’t take long before I heard N6OR booming into Beaverton from Southern California (grid DM12). I snagged him on the first call, getting a 57 signal report in return and a report of good, clean audio when asked. He was running 100 watts into a quad, which you can see on his QRZ page. I was really thrilled since this was not only a victory for my mad homebrewing skillz, but was also my first 6 meter QSO!

I’ve been parked on 50.125 for most of the afternoon here at the NT7S shack and have picked up a few more QSOs. So far, all reports of the audio quality of the linear have been FB, so I’m satisfied that it (and the LPF) are working as they should be. I think I’ve about worn out my keys on this post, so I’ll wrap it up for today (I always start with modest ambitions on these posts, they they grow exponentially). I’m having way more fun than I should be, and I’m very pleased to be back out of my ham radio funk.