Tag Archives: QRP radios

Amature Radio

Marker Generator and more

20150507_190019Picking up where I left off in the last post, I got the drill bits and finished the 40 meter Helically Wound Vertical antenna. I will get a project page up soon.

Now when I say “finished”, what I mean is the antenna is useable. I still need to seal and cover it but I wanted to get it all tuned up first. As far a receiving goes, the vertical is out performing the dipole strung in the house just sitting on the floor leaning up against the wall next the operating station, so it’s looking good.

I need to finish the tuning with a transmitter on it. Since the only transmitter I have for 40 meters is a CW 250mW transmitter I am holding off on that.

20150508_121409In the mean time I put together a Marker Signal Generator. The design takes an 8 MHz crystal and divides the signal down several time ending up with the desired 1 kHz signal with many harmonics to mark out a tuning dial in 1 kHz increments.

20150508_150243It was fun to build and I leaned a little about some ICs I had never used and some of the basics of working with multiple devices in a single package.

When I came to function, I was very disappointed. The oscillator was anything but stable and we very dependant on an extremely stable input voltage. The onboard diode voltage regulations stunk so I tuned down the power supply from 12 volts to the 5 the ICs need.

20150508_153648At this point I was finally able to calm down the oscillator and get close to 1 kHz I was hoping for. A millivolt up or down and the frequency was out. Not a particularly useable device as it sits but it does give me some ideas for using out of band crystals to generate a signal.

As always, this is the whole point, to experiment and learn about RF design by doing, not just reading and modeling on a computer.

The big news, and the reason I missed a post last week is that I have been doing some research on finding my next big build project. The winning design was the Beach 40 by VK3YE. I have been scouring the web looking for a simple phone (voice) transmitter. I was hoping for SSB (Single SideBand) but the Beach 40 DSB (Double SideBand Suppressed Carrier) is simple and straightforward as is.

IMG_20150513_125237Being me, I had to make some modifications to the design and tweak a few things. One of the great things about this design s that it uses discrete components rather than ICs.

At one point Peter (VK3YE) recommends changing the audio amplifier to one that uses the LM386 chip rather than discrete components because the output is rather low. Since one of the main reasons I chose this project was to keep to available discrete components I went out in search of a different audio amp.

Enter Arv Evans K7HKL and his Discrete Component AF Amplifier paper. By the way, at least via email, Arv is a really nice guy. Thanks for the help Arv!

20150513_170104Now with the circuits mostly settled and parts enroute, Digi-Key arrived a day early! 🙂 I sat down tonight and began kitting the parts for each of the transceiver subsections beginning with the Super VXO. I am only installing one crystal set right now but the plan is to set it up for several banks of crystals. I also had some ideas as to using the banks for multiple bands as well as sections of a single band, but that’s for later.

20150513_202942I also kitted the Local Oscillator/Buffer and the Balanced Modulator/Product Detector sections. There are a few bits that will need some refinement, mostly inductors, but these will be addressed as needed.

And speaking of inductors, since I sent back that crappy one I am still in need of one. I will be ordering one tomorrow because I wont get far in this build without one. The goal is to have this radio up and running before Field Day June 27-28.

Look for a project page soon.

Till next time, 73,
~Jon KK6GXG

Amature Radio

40 Meter Antenna

With the direct conversion receiver now working and tuned into the 40 meter band, it’s time to get to work on a better choice of antenna. The dipole would be great if it were in the proper environment, but this indoor, RF noisy environment is not conducive to picking up much.

Since tuning the receiver to the band I have been picking up both voice and cw transmissions but they are deep in the band noise. The other issue is portability. While the dipole can be pulled down and packed up for field use, it won’t work well in a mobile environment and would be a chore at home to pull down and put back up. So a whip makes the most sense for now. If the whip works at home I can wind up the dipole and keep it in the ready for field use.

Right now my focus is on getting the receiver, antenna, and any needed matching equipment in place. Once that is all together I can turn my attention to filters, amplifiers, and a transmitter.

Scan from the 1975 ARRL Handbook, page 606.
Scan from the 1975 ARRL Handbook, page 606.

The antenna is a helically wound vertical that I mentioned in a previous post All Aboard the Project Train. I ordered a six foot fiberglass safety flag whip for the core and a fresh 1.5 pound spool of 14 AWG copper magnet wire to get the project going.

Yesterday I started the antenna construction by unrolling the 66.5 feet of copper wire and marking it every five feet, mostly so I didn’t lose my count. After dinner I started winding the coil onto the fiberglass in a tight coil. The picture in the header for this post is the fiberglass with about 30 feet wound on.

20150422_093128
66.5′ of 14 AWG copper wound onto a6′ x 3/8″ fiberglass rod

After winding the rest of the wire onto the fiberglass I threaded a dentists tool in between the wire wraps up the full length of the rod to create the uniform spacing for the coil.

On reflection at this point I think I might have opted for an 8 or 10 foot rod. For most applications it might be a better choice but neither would fit well indoors so 6 foot it is. I may build another antenna like this if it works well and try different lengths and diameters for different applications. A 10 foot whip would be better with a 1/2″ core and any longer would need 3/4″ or 1″ to remain stable unless it were placed inside a tube and filled with epoxy resin, another option. I haven’t tested any of these, I’m just spitballing with the structural integrity issue and weather resistance.

20150421_220832Now that the coil is done, the most difficult and time consuming part I think, it is time to move on to the spike and the base.

The plan for the spike is to pick up a small piece of 3/8″ copper tubing about 4″ long and use a coax crimping tool to mechanically center and attach a 1/4″ steel rod to about 2″ then sweat solder it together. After the spike is properly affixed, scoot the coil up a bit and solder the copper wire to the tube, add some epoxy inside the tube and scoot it back onto the fiberglass rod. This should give plenty of mechanical stability to both the spike and the rod as well as a good electrical contact. To help prevent galvanic corrosion I will coat the steel/copper interface with a few coats of lacquer.

The base is where I am going to have to think some more. The diagram calls for a variable inductor at the base of the antenna. I don’t think I will need this because I am planning on using an adapted Z-Match antenna tuning unit from chapter 23 of QRP Basics but that is for the next project.

OLYMPUS DIGITAL CAMERAIn the mean time I am thinking about using a PVC/ABS 90º conduit fitting with an access panel, cutting off and sealing up the right angle (on the bottom of the image), inserting the bottom of the antenna with the wire sticking up out of the box a little and filling the cavity with epoxy resin, leaving enough room to install an exterior lug fitting to attach the wire to on the inside.  For mechanical stability and to provide a secure mounting point I was thinking about using 6″ of conduit around the antenna and filling that with epoxy resin as well.

I hope to get the spike done this week and the base over the weekend. While out and about getting the final parts for the antenna I will be hitting HSC for the parts for the Z-Match. Another busy week for radio. 🙂

73,
~Jon KK6GXG

Amature Radio

All Aboard the Project Train

Sometimes it is indeed a project train, not just a project; occasionally a train wreck, but it’s early so we’ll hope for the best.

Now that I have built several receivers and a transmitter for 40 meters, I probably should have an antenna that does more than pick up all the RF noise around the shack. The antenna, and I use the word loosely, is nothing more than a dipole of 26 AWG insulated wire strung around the house. While it might work well if the wire was straightened out on a hill top, or even in a backyard, elevated 15 feet or more above ground, in its current incarnation, in a word, it sucks.

Next up on the project block, an antenna, sort of…

I have been looking at several small footprint antenna options like spiral coils that look like those God’s Eye yarn and popsicle stick things you may have made as a kid,  the one in the movies from the 40s when the resistance spy transmitting Nazi secrets and the SS storms in. It looks like a X and has thin wire wound around it.
288And Small Loop antennas that look more like old direction finding antennas on aircraft. And by the way, according to the formulas and general information, for 40 meters, not so small, 10′ diameter.

Now there are lots of variations and tons of experimental configurations to run with, and I do want to play with many of the possible configurations, but I need a stable, small, portable option for the immediate future. Something I could mount on the car, throw up on a pole, or stand up on the back porch, all without much effort. I also need to keep the cost down.

Scan from the 1975 ARRL Handbook, page 606.
Scan from the 1975 ARRL Handbook, page 606.

Enter the Helically-Wound Short Vertical. I ordered some 14 AWG lacquered copper magnet wire and a 72″ long 5/8″ diameter fiberglass rod, I need to learn to make these so I also ordered a How-To book on making composite fishing rods, and I’m in $20 so far. I have all of the hardware items including the 12″ spike for the top. What I don’t have is the variable inductor, or a tuner.

Whooooo Whooooo! Here comes the train.

RollspuleLets start with the one I haven’t done any research on yet, the variable inductor. The mechanics are fairly simple, rotate the coil and the follower moves up and down the coil creating a tap point. As long as the coil is perfectly cylindrical, the follower makes good contact, and smoothly moves down its axis rod, no sweat. he he he, no sweat I only need the one variable inductor according to the diagram so I really need to find out what value I need. I already have several small value iron-core variable inductors so I may not need to make this one, but if I do, it will be a homebrew. These things are a high-dollar item otherwise.

Moving on to the antenna matching unit. I have plans for one that is fairly simple and straightforward, I even have most of the parts on hand. What I don’t have is the variable capacitors. Sensing a theme here? Variable…

cav-167-205-71_lgBA funny coinky-dink on capacitors; while I was doing research on the Small Loop antennas I came across several websites that went into some lengthy discussions on making variable caps. Turns out, they aren’t that hard to make, I even have nearly all of the materials to make several. Not only are they fairly easy to make, but the formulas for calculating the capacitance based on the area of the plates, number of plates, and the distance between the plates is also fairly straight forward.

So lets see where we are now…
I have three receiver and one transmitter for 40 meters. There is an antenna for them, but it sucks particularly in this location. My next project is to build another transmitter, But I will need a better antenna first…

  1. Antenna
  2. Resonator for antenna (variable inductor)
  3. Antenna tuner
  4. Variable capacitors for the tuner

Now, after these are done I can move on to the new transmitter. As a side note, with the next transmitter project I wanted to pump up the power all the way to a couple of watts, not just miliwatting it. I also want to include SSB (Single SideBand, voice) as well as CW so I can incorporate digital modes into the shack. For all of this the antenna really needs to be better than what I am using.

That’s all for now, 73,
~Jon KK6GXG

Amature Radio

40 Meter Loose End

20150410_115049Today just started off good. The post came early and an expected package came a few days early, my QSL card order from Vistprint.

I’m not quite sure when I will need to send any out, but now I have them and I am very happy with how they came out. I’m also very proud of them, I spent the better part of a day working on the layout and confirming the text-safe areas around the card. The finish product is just what I was hoping for.

20150408_154753A couple of days ago I got a package in the post from another ham, Brad  (AA1IP) and oh my, what a box it was. A medium sized  USPS Priority Mail box filled to the top with stuff.

I started sorting it out that evening and last night and again this morning. Its all sorted into like or similar components. There is still a lot of sorting to do, particularly with resistors and capacitors. Among the jumble there were a few packets of resistors already sorted by value and those are my project for tonight. Get them all stowed away.

20150408_162644The sorting process will take a while and I’m in no rush, so bag by bag over time it will all find homes. Once I get everything stowed I may ask for another. Mmmm, a masochist, I am *in my best Yoda voice*.

A small follow up project got completed over lunch today. I finally finished the power cable for the 40 meter receiver I built. The original plan was to build the receiver and a follow up transmitter, package them together, and power them both with a solar charger / battery pack. Also in the original plan was to build out the cable from scratch.

Funny thing about plans… I dont have any good multi-conductor cable anymore. The closest I have is some cat 5 and some twisted-pair for telco work. Nether is appropriate for this project. I was waiting to go to the Electronics Flea Market @ DeAnza this weekend but I also have plans to go to a radio builders club meeting on Sunday and check things out there. I was encouraged to bring my project along, and since the build was complete I thought I should power it as planned.

20150410_132528Long story short, I know, too late, I decided to pull an extra USB printer cable out of my computer junk box and use an existing cable, clip an end, and install the power plug. Easy peasy.  The plug isn’t quite big enough for the cable but I adapted it and heat shrunk that end for some extra stability. Thoroughly checked it for shorts and opens twisting it about and we are good to go.

The radio can now be powered by a computer, USB car adapter, or the solar power supply I had originally intended to use. Any standard USB source with the appropriate 5 volts will do.

I’m sure I’ll have more to post about after the Flea and the club meeting.

Until then, 73,
~Jon KK6GXG

 

Amature Radio

Fresh Prespective

Over the last few days I have been working on a direct conversion receiver project I found in the book Experimental Methods of RF Design last month. I had been planning and even started a very similar design back in February. I was having problems with that project so I picked up the EMRFD book to help figure out what the issue was.

EMRFD-40m-ReceiverThere in the first chapter was this design and I decided to scrap the other project and started working on this one.  It wasn’t like “oooo, a new shiney…” because they are very similar designs and the goal was to build a direct conversion receiver for 40 meters, not specifically that receiver.

Now that I have finished unnecessarily defending my position on hitting the reset button on the project, we can continue.

This time I decided to go with the “ugly” method of prototyping. I was not aware of the induction issues with the plastic pinboards or the other problems that can arise with high-speed or precision circuits. I had seen a few things on ugly construction and comments on its superiority over the plastic breadboards, along with other similar prototyping methods like “Manhattan.”

Since I had never done ugly before I was a bit nervous about it. I have used perfboard successfully on other projects and while perfboard does not have the same negatives as pinboards, it doesn’t have a ground plane ether. This can be problematic in RF circuits.

Any hoo. Yesterday I finished soldering the board and started mounting stuff. The project is screaming along and I have been pulling back regularly to make sure I don’t rush to finish. I have been going back an checking the new additions for physical problems, shorts, cold soldering, and the like. So far things have gone nicely.

20150401_193337This morning I sat down and looked at the partially mounted project box and some things crossed my mind. If I only put an antenna port on the back, instead of including a power port, I could actually have an internal battery pack. I could even add the power port and include a charging circuit for the internal battery…

I nixed this idea on this build because I intended to use a battery pack / solar charger that I already have so the power possibilities will be saved for later.

I do plan on adding a transmitter to this case. This brought my attention to the front panel. I am installing a power switch and headphone jack for the receiver, but I would need a jack for the cw key and a TX/RX switch. I could fit both of these components in the front panel integrated with the receiver parts without a problem. I could even install them now to prepare for the inevitable. I even have the parts in stock.

What I didn’t think about last night was the tuning of the transmitter. I don’t have the room for the tuning components on the front panel. I don’t know if I could modify this oscillator/mixer to work in conjunction with a transmitter thus converting the whole thing into a transceiver. I will have to get back to the book and read on.

In all honesty there are a couple of other things too. I would want a beat oscillator which would need a momentary switch and some other logistical elements to think about as well.

I spent a lot of thought on keeping this board small. I didn’t want to crowd things too much, but I wanted a small planform. I got what I wanted and I learned a few things about experimental design.

Planning ahead is not just about where the rest of this circuit is going. It includes thinking about the likely evolution of the project. Would I convert this project to a transceiver? Probably not. I would more likely build a new project ether from a different design already established, or take a lot of time and build modular circuit clusters testing them as individual units and working out the logistics of placement, interfaces, and housing configurations as the project developed.

I am actually surprised at how much I have learned from building this little DC RX, and I’m not even finished with it yet!

73,
~Jon KK6GXG

Amature Radio

BreadboardRadio Kits

Breadboard Radio KitsOn Wednesday I received some awesome mail, the kits I ordered from BreadboardRadio.com arrived! As I am inclined to do, I opened things up and began organizing and inventorying the contents there in. Counter to the habits of a younger Jon, I printed all of the distructions, what I tend call them, and read them all, cover-to-cover. Even before setting up the first project!

I completed the electronics of the Matchstick antenna tuner Wednesday evening. Without a receiver or transmitter I couldn’t do much with it. Yesterday I finished the electronics of the Sawdust regenerative receiver and proceeded to spend over four hours tuning up and down the 40 meter band.

There was some broadcast, not sure if it was AM bleed or SW though I am leaning towards SW, phone (voice), and some digital transmissions. I believe I heard both RTTY (Teletype) and PSK31 (ASCII keyboard-to-keyboard). No CW though. I was really hoping for some Morse Code. Lots of band noise. The solar storm this week is making for some interesting sounds.

Progress shots were taken and will be uploaded to the usual places, here, G+, and Flickr, but I wanted to get them all wrapped up nice and purdy first. Because they are kits and will be done over the weekend most likely, I figured it was worth the wait. I am going to post about each kit separately though.

When I said a kit was completed, I deviated from the distructions in one respect. They called for finishing the wood bases before the electronics so the mounting of said electronics goes directly onto a clean, freshly finished mounting. Well, I didn’t do that.

Matchstick antenna tuner kit from BreadboardRadio.com
Matchstick antenna tuner kit from BreadboardRadio.com

I wanted to finish all of the bases at the same time… and, okay, I wanted to get a radio on the air ASAP. So, yes I will finish the bases, but it will be all at once. I I am not sure with what finish I will be using so for now the kits get mounted on the raw base.

Before the kits arrived I built a simple ½  λ dipole to have something to test the radios with, and it does work, but I don’t like the feed point or the wire spools. I didn’t take any pictures because, well I’m not particularly proud of it. That may sound vane, and it is, but some hack jobs just shouldn’t have pictorial evidence.

To resolve the antenna issues and to address the bases for the the kits I think a little fabricating shop time is in order. This morning I am designing the feed point / spools and after day-job stuff I will look at finishing materials for the kits.

73,

~Jon KK6GXG