a short trip north

This past week work led me to Rockville, Maryland for a few days. As always, I had my trusty Yaesu FT-7800R with me in the car to help keep me company on the drive. While my other coworkers elected to fly, I chose to drive so that I could have some flexibility to visit friends and family who I have in the metro DC area.

As far as radio goes–I didn’t make time to program any of the area repeaters in my radio before I left, so I left the rig stuck on 146.52 MHz simplex throughout my trip. Three times over the past three days I was able to make simplex contacts. I sent out QSL cards today to these folks: WA4KEB, W5JMC, and KI4XH. The terrain around Washington, DC is not exactly conducive to long simplex rag chews, unfortunately. Quick chats with WA4KEB and W5JMC were all I could muster, but I had a nice, long chat with Fred KI4XH.

Fred and I made contact on my way to Ham Radio Outlet in Woodbridge, Virginia, where I was headed for some window shopping and to purchase some 15A PowerPoles. We chatted a bit about my travels to Rockville as well as other future work trips I have planned for the spring to Chicago, Anchorage, and rural Pennsylvania. It turns out that he has had extensive travel experiences in Alaska and would be happy to offer suggestions for places to eat and things to do during my time there. What a fruitful QSO!

This weekend I hope to pull out the soldering iron again and work on some aspects of the PSK-20 project. While I was gone, the LP filter I had ordered from W8DIZ at PartsAndKits.com arrived. It should be a quick build as there are only a few through-hole parts and two toroidal inductors to wind. The LP filter will go between the frequency synthesizer and the PSK-20 PC board to transform the signal into a nice sine wave.

a lull in the action

On Monday, I attended the monthly meeting of my local radio club where I picked up a portable oscilloscope from Steve W3AHL to assist in testing the Si570 frequency synthesizer’s output voltage. The past few evenings have been busy with a couple college basketball games of interest to watch (Kentucky on Tuesday, Duke last night) so I haven’t had a chance to work on the PSK-20 project.

I may warm up the soldering iron this evening and fire up the oscilloscope which W3AHL has graciously allowed me to borrow in order to check the voltage from the frequency synthesizer. According to the specs, the SA612AN expects a 200-300 mV signal from the oscillator. The stock output is much higher than that. W3AHL had suggested that I use a Pi attenuator to reduce the voltage from the synthesizer. I followed his initial advice, but without an oscilloscope I wasn’t able to check the voltage. Before I had the chance to test it, I had received this message from him:

The only problem is the 10db attenuator is wrong.  Last night I realized we were measuring voltage — I calculated the attenuation needed based on power ratio, which is what I normally use for RF circuits.   So just to make sure I got it right this time I verified what was needed using the 8924C’s signal generator and a 30 dB attenuator I had.

So to take the 2.2 volt P-P signal (unterminated — it would be 1.1 volts if the PSK-20 board had a 50 ohm terminator resistor on its end of the coax) down to the desired 250mv. signal, requires an 18.9 dB attenuator.  This would require two 62.8 ohm resistors to ground and a 217 ohm resistor in series between them.   Or as close as you can get in standard values.

The current 10 dB attenuator should give 700 millivolts output — a tad too much.

Again, I’m glad to have the experience and expertise of folks like Steve W3AHL to help with projects like this one. I’ll post results when I have a chance to test them–hopefully this evening.

Yesterday I ordered a low pass filter kit from Dieter “Diz” W8DIZ, who runs an awesome site/store called KitsAndParts.com. I explained to him what I was trying to do, and he offered to help me create a low pass filter with a cut-off frequency just above the output of the frequency synthesizer (around 5.3 MHz) to help transform the square wave from the synthesizer to a sine wave (which is preferred by the SA612AN).

John,
I made you a custom LPF for 5.3 MHz
Need to calculate the turns on the T50-2 cores
Caps are 470p and 1000p
All packed and ready to ship tomorrow AM
-Diz

Diz has always been helpful and mindful of his customers’ needs. This can be clearly seen in his reviews on eHam. Hopefully the parts will be in by the weekend and the next phase of the project can be tackled before the beginning of the work week.

PSK-20 nearly complete and testing begins

This past weekend I was able to finish the basic PSK-20 kit (sans the 5.068 MHz oscillator circuit). Overall, this was a very easy build. It’s not a simple one-evening project, but it can definitely be completed in a 2-3 evenings of work with 2-3 hours each evening devoted to the task.

Steve W3AHL, a member of our local club, mentioned to me a few weeks ago at our regular monthly meeting that he had a ton of lab-grade test equipment at his house. Immediately, a light went off in my head, and I made a mental note to contact him whenever I was preparing to do the final checkouts on the PSK-20 project.

Yesterday, I headed down South to Chatham County to visit him (about a 15 minute drive from my home in Carrboro). We spent the better part of 3 hours with his spectrum analyzer and oscilloscope trying to figure out the answers to the following questions:

1. What is the exact frequency of my Si570 oscillator?
2. How far can I pull the 9 MHz LO down?
3. What additional adjustments are needed in order to use the Si570-based signal generator as the second LO?

The answer to the first question was fairly easy to determine. After applying power to the Si570 frequency generator kit and allowing it to sit for 20 minutes or so, the output frequency was 9,999,992 Hz. Its nominal frequency is 10 MHz, so that’s not bad. Saving this value to memory space “000″ in the menu allows the kit to generate more accurate frequencies than if you work with the assumption that the nominal frequency is equal to the actual frequency.

The answer to the second question is important because that will determine if the crystal I have will allow me to operate on USB rather than the LSB (which the kit is designed to operate on). This odd configuration may be overcome in some software packages. At the end of the day, I’d like to be able to operate on USB (the traditional sideband on 20m); however, if this ends up being a costly choice (dollars-and-cents-wise) I may bypass it. Measuring the frequency of the 9 MHz LO while adjusting the trimmer capacitor C38 helped me determine that the lowest frequency of the oscillator is 9.021 MHz. This is definitely not as low as I’d prefer for the generation of the USB signal. Inrad sells USB crystals for the frequency of 8998.5 kHz, but their cost is $12 plus whatever shipping and handling may be involved. Not exactly the least expensive solution. So, the solution for now is to accept LSB as my sideband of operation on 20m digital modes until such point that I feel like spending what will amount to at least $20 to obtain this new crystal.

The final question to be answered of the day was how to incorporate the Si570 frequency synthesizer into the kit as the second LO. Previously, I had thought about using high-side injection at 23 MHz (instead of 5 MHz) “just for fun” and because other folks on QRP-L had suggested it might be a cleaner signal. After speaking with Steve KZ1X I decided that it might be best to stick with the low-side injection method since using high-side injection may require additional changes to the circuit which I may not want to tackle at this point in my learning.

Going with this thought, Steve W3AHL fired up his oscilloscope and began measuring the voltage output of the synthesizer and comparing it to the voltage required by the SA612AN Gilbert cell mixer. It turns out that the peak-to-peak voltage is much higher than what is needed/tolerated by the SA612AN. Steve W3AHL helped design a 10:1 Pi attenuator using commonly found resistors from Radio Shack. In a perfect world (at least, according to the calculator he used), I would have a pair of 96 ohm resistors and a single 71 ohm resistor in the circuit; however, Radio Shack’s selection of resistors is limited to 100 ohm (for the 96 ohm) and 68 ohm (for the 71 ohm). Not a bad compromise at all!

The neat thing about this attenuator circuit is that it will fit on the PC board very easily. Recall that I did not install any of the 5.068 MHz oscillator parts. This has left open C43, C44, R47, R48, and R49 (as well as a few other pads). The Clock + (in the circuit) and Clock – (to ground) from the Si570 kit were fed using RG-174 coax at C44 and a wire jumper was added at C43 to make the connection between C44 and R47. The Pi attenuator was created by adding one 100 ohm resistor at R47 and at R49 and one 68 ohm resistor at R48. I haven’t had a chance to test this yet, but it should provide the correct amount of voltage for the SA612AN (200-300 mV). It still may be the case that I need to add a LP filter to create a sine wave from the square wave the Si570 creates, but I’m going to see what happens when I power it all up before I go that route.

Our regular monthly club meeting is this evening. I’m planning on bringing the kit to the meeting for a little intermediate show-and-tell and eventually giving a full presentation of my project to the club in February or March.

PSK-20 build

This past week has been long on building and short on writing, but I’m okay with that.

As of today, I have completed all but the last two steps in the assembly of the kit. The manual is broken down into “group builds” (e.g., Group 1 assembly installs the DC power circuitry, Group 2 assembly installs the Transmit/Receive switching circuitry, etc.) which help the kit builder have a sense of the purpose of each set of capacitors, resistors, transistors, and the like. Unlike Elecraft kits, which usually have an alignment or “check out” after each step of assembly, there are no such resistance or voltage checks for this kit. So, you must go on faith alone that there are no cold solder joints, misplaced parts, or nonfunctional devices until after assembly is complete. The first “smoke test” is truly that.

In the Group 3 build (the 9.000MHz and 5.068MHz oscillators and related components) I left out all components connected to pin 6 of U7 (SA612AN) since I plan on connecting the signal generator there in lieu of the 5.068MHz crystal. It may be the case that I will need to add some of those components once I determine their necessity, but there is plenty of physical real estate on the board for these parts to be installed at a later time. In face, Dave Benson states that “real men” can install in whichever order they wish, ignoring the “group build” guide laid out in the manual.

The last two portions of the construction include stuffing and soldering the transmitter bandpass filter and driver stages as well as the transmitter final amplifier to the PC board. I hope to finish those either tonight or tomorrow and then take the final product to fellow OCRA member Steve W3AHL’s home to tune the sideband generating circuitry and obtain an accurate measure of my particular Si570 part two days from now. After that, I should be ready to place the kit in an enclosure and start playing around with it on the air!

Once I complete the build, I’ll upload some photos of the board after each “group build” for viewing.

New Year; new project

This past year I have finally come very close to completing my Elecraft K2 (and most of its options), which has been a learning experience. While soldering the multitude of parts to the PC boards can be mind-numbing, the steps involving check-out of the rig help teach a bit of theory. Earning an Extra Class license requires an understanding of the theory involved; however, actually applying it to a project helps cement the concepts in the mind.

In 2010 I will be traveling a bit for my job and may find myself in lonely hotel rooms at night. Rather than spend the evenings flipping through channels on the television, I would prefer to get on the air and make some contacts. Given the fact that I travel with a laptop computer and often travel light, I thought it would make the most sense to try and bring along a transceiver which would allow me to get on the air and operate some of the digital modes. Dave Benson’s PSK-xx kits fit the bill.

I chose the PSK-20 because of the high activity on 20m PSK31 and because the other kits are for bands which would require an antenna of greater size than I would prefer to manage on business travel (PSK-30 on 30m, PSK-40 on 40m, The Warbler on 80m).

I’ve previously operated PSK31 on my Yaesu FT-817D with a Tigertronics SignaLink interface and been quite successful, earning the QRP-ARCI 1000 Miles Per Watt award (see post here about those adventures). Using a transceiver with a built-in interface would save space and weight when they are at a premium.

I ordered a PSK-20 rig in the summer of 2009 and finally received it in the fall, but have yet to begin the project. With increased confidence in my homebrewing abilities and greater understanding of theory, I have set out to modify the PSK-20 kit to tune the entire 20m band and allow me to reach the calling frequencies of digital sound card modes other than PSK31.

The PSK-20 rig itself is an interesting rig. It has a ~4KHz bandwidth centered around the PSK31 frequency for 20m (14.070MHz) and operates on the non-traditional lower sideband (LSB). The sideband is of no consequence for some variants of PSK31 (e.g., BPSK) but matters more for others (e.g., QPSK).

According to Dave’s documentation about the receiver…

U1 is fed with a 5.07 Mhz Local Oscillator (LO) signal and converts the incoming 14.07 Mhz received signal to the 9.00 MHz Intermediate Frequency (IF).

and

Product detector U2 receives the 9 Mhz IF filter output and multiplies (mixes) it with a ~ 9 Mhz LO signal.

Also (for the transmitter side of things)…

Single-sideband filtering is performed by a second filter comprising Y7-Y10 and related capacitors. After passing through the transmit IF filter comprising Y7-Y10 and related components, the signal has been reduced to a 9 MHz SSB signal. Its output drives 2nd mixer U7. This mixer is also driven by a signal from the 5.07 MHz LO, Colpitts oscillator Q9 and associated components.

The output of this mixer consists primarily of both the sum (14.07 MHz) and difference (3.93 Mhz) frequencies applied to the mixer. Q7 is an emitter follower used to buffer the high-impedance output of the mixer. U8 is a Monolithic Microwave IC (MMIC) and provides approximately 12 dB of gain.

My plan, as it currently stands:

1. Pull the 9.0MHz local oscillator LSB signal to USB by adding a level of inductance in line with the trimmer capacitor already on the board
2. Replace the 5.068MHz crystal and its supporting circuit with a frequency-agile signal generator
3. Mount the entire rig, including a digital frequency readout, in a Ten-Tec enclosure (the enclosure that Small Wonder Labs provides for the PSK-xx rigs is not large enough to accommodate the size of the digital frequency readout and dial)

In order to make this a fully portable digital station, I’ll need to bring along an antenna (I’m thinking either a 1/2 wave wire antenna cut for 20m) and perhaps an antenna tuner. The tuner, should I need it, will be filled by my Elecraft T1. It offers small size and excellent performance that will be appreciated when packing my bags for my business trips.

Should be an exciting few weeks. My first trip will occur in the third week of January, and I hope to take the rig along with me. First, to construct the signal generator of choice–the Si570 Controller and Frequency Generator Kit #2 by K5BCQ and K5JHF.

Field Day at the beach

The second in a series of previously published articles from the OCRA (Orange Co. Radio Amateurs) newsletter. This appeared in the July 2009 issue.

Surf City, NC

My Beach Vacation: A way to earn ARRL awards and make QRP contacts
By John Shadle, W4PAH

Participation in OCRA’s Field Day activities has been a tall order for me the past few years. Last year I was with my wife at UNC Hospitals welcoming our first child into the world, and this year we were headed to the beach for our first family vacation to celebrate our anniversary and his first birthday.

Thankfully, since it was “my vacation” too, my wife was okay with me bringing along some radio gear to take advantage of the near-legendary effects of saltwater ground on antennas!
Planning for the trip began with considerations of antenna options. I began chatting over the repeaters and email with Bruce N1LN and Steve KZ1X about possibilities. They both highly recommended loop antennas. Given the house’s layout (3 stories high, 450-500 foot pier into the sound off Topsail Island) the loop made a lot of sense. I could’ve probably used a single long wire from the house to the pier, but the loop offered quieter reception and more gain.

In my antenna junk box I had a 500 foot roll of #14 AWG stranded insulated wire (the kind you can pick up at Lowe’s or Home Depot for pennies by the foot) and some of those white plastic insulators that are ubiquitous at hamfests. One evening, I headed over to Bruce’s house to create the loop. Bruce had offered up the use of a balun he had created which was currently not being used. It was either 4:1 or 6:1, but we were unsure of its properties beyond that. We measured out 140+ feet of wire, threaded the insulators on the wire, and soldered each end to the balun to complete the project. After coiling it up, I was ready to pack it in my bags for the beach.

My wife, son, and I had planned to leave on Saturday afternoon and head down east, but my son had a low-grade fever that morning so we ended up leaving closer to dinnertime instead. Field Day was already in full swing by the time I was able to set up my antenna during my son’s morning nap Sunday, June 28th. I attached two of the insulators with 1/8” rope to the balcony of our third floor bedroom and the remaining wire of the antenna was stretched to a point and tied to the side of the pier over the saltwater marsh below. The feed point was at one of the corners of the balcony and a stretch of RG-58 connected my station in the screened-in porch below to the antenna above. The high end of the antenna was at least 25’ and the low end wasprobably 8’ above sea level in a sloping inverted delta configuration.

After connecting the coax to my SWR meter, antenna tuner, and rig (a Yaesu FT-817D), I was ready to go!

Despite the fact that I had a full-wave on 40m, I operated exclusively on 20m SSB for the duration of my participation in Field Day. My first contact was with W1QI in Connecticut at 14:35 UTC and my 25th and final contact was with K4F in Florida right before 18:00 UTC. I was surprised that my 5w and simple antenna were able to net 14 states and Canadian provinces over the two and a half hour period I operated. Hunt and pounce were the words of the day, and I had a great time with the quick “contest” exchange of Field Day.

A map of the contacts I managed to make can be seen here:
http://www.flickr.com/photos/shadle/3669789986/in/set-72157620687360544/

After Field Day had concluded, I decided to add PSK31 to my operating modes, but not before making one last SSB contact on 20m. Right before bed on Sunday night my meager 5w was able to get my voice all the way to N6JW’s station in Riverside, California (near Los Angeles). Perhaps it was the salt water, or perhaps it was the fact that he was running an Elecraft K3, but the contact was made and logged.

1000 Miles Per Watt from QRP-ARCI!

During the rest of the week, on 14.070MHz, I had QSOs with operators in 22 states and 5 DXCC entities (outside of the USA) including Canada, Italy, The Netherlands, Spain, and Alaska (yes, Alaska is a DXCC entity). The QSL cards and Logbook of the World confirmations have finally started coming in, and I’m proud to state that my 2.5w PSK31 contact to KL8DX in Denali National Park in Alaska qualified me for the QRP Amateur Radio ClInternational’s “1000 miles per watt” award. The strange fact about this contact is that it was made as my battery power was beginning to drain. I had to QRP to 2.5w from 5w for the last few QSOs of that particular day. Amazingly enough, KL8DX still heard me loud and clear—up until the radio shut off!

All in all, it was a wonderful trip to the beach. I’m hoping to make it back to this location for future vacations and eventually earn the ARRL’s Worked All States award with the endorsement for QRP. The QRP-ARCI also offers an “All States” award for QRP contacts with 20, 30, 40 and 50 states.

More photos of my adventure may be seen at Flickr.
http://www.flickr.com/photos/shadle/sets/72157620687360544/

Information about the QRP-ARCI and their awards may be found at their web site.
http://www.qrparci.org/
http://www.qrparci.org/content/blogsection/4/116/