Look in any hamshack today and you’re gonna be hard pressed not to find a computer sharing space with the tranceiver. We them for, most importantly, buying equipment, but also for logging QSOs, looking up someone’s details from their callsign, looking for active DX spots…
For sometime I have had a MFJ-259B that I had purchased from an SK estate. I have treasured the device for a number of reasons. I knew what I had paid for the device was helping that ham’s family and I felt like I needed to honor his memory by using the analyzer. Use it I did! KB5NJD even helped me mod it so it would give us readings down to 470 kHz and I could tune my 630M antenna. As my knowledge has improved, I came to find that there are a lot of things this model of antenna analyzer does not do and that made me think about getting a different device.
One: It doesn’t resolve the sign of X. i.e. is my load inductive or capacitive? W2AEW has a great video on how you can actually resolve the sign of X using a smith chart using an MFJ 259B style analyzer.
Two: The oscillator in the machine is not particularly stable in my opinion. i.e. what freq I was measuring was in doubt by up to 20hz. This isn’t a deal killer for measuring impedance in the field, but is frustrating in a lab environment.
Three: The freq. knob is too sensitive in my opinion. I suppose it makes sense given the tuning range within each band the analyzer covers, but I wanted a little more precision.
Four: All it provides is Freq (approximate as noted above), SWR, R and X (unresolved whether it is positive or negative.)
Again — As a new amateur, it is perfectly adequate as an antenna analyzer. But I wanted something a bit more capable. As it turns out a friend has an AA-600. He was showing me his conventional transformers and how he could measure the frequency response with the AA-600. Not only will it define the sign of X, this thing draws a Smith Chart. It will auto sweep over the entire spectrum of the oscillator enabled on your machine. You can do live measurements where it will show you the rectangular format of impedance and the vector form of impedance. This is a genuine scientific instrument.
Now the question is what frequencies should I cover? I genuinely only have an interest in HF, BUT satellite contacts are interesting. . . and I’ve recently started doing some VHF fox hunts with a local club. At some point I’d really like to build some kind of 2M yagi. If I was doing satellite contacts, it would be ideal to have a 440 beam as well, but the cost differential and the likely hood I would ACTUALLY build such a thing. . . I’ll probably just by a satellite antenna, it’ll be close enough. 🙂
If I decide I really want to experiment at 440 MHz I can always up grade later.
For a long time I have wondered WHY do people always scream a warning at you if you plan on using a small magnetic loop. “Be careful, there is a lot of voltage across the capacitor!” yeah, yeah. . . OK, whatever. . . I’ll be careful.
I asked a number of friends. I heard a lot of explanations. The one that stood out to me was that a mag loop acts like a auto transformer. uhh. . . I’m sure someone reading this is going, “yeah!” You could have told me that it has to do with a wind storm on Mars and particle entanglement. This seemed just as plausible to me.
As you may remember I left you at a metal can with a hole cut out to an incorrect size and then mashed over. You may also remember that there were a few components that I needed to acquire to complete the kit. While I definitely had a stock of BNC panel mounts, I did not have a supply of SPDT switches. This involved me scouring
the interwebs looking for inexpensive, panel mount, SPDT switches. I ultimately chose to order from danssmallpartsandkits.net. If you are thinking that this guy must be a real niche market seller and cater to his customers. . . You’d be 50% right. . . It’s definitely a niche market! From what I can gather he is a nice guy, but he has rules that must be followed. Read carefully and follow the instructions. I’ve never had a problem. I also always order a bunch of other random parts I don’t “need”, but hey. . . next time when I need an NPO bypass cap, I have a stock of them. This is a practice that was recommended to me by an elmer some years ago. It’s why I have parts on hand. . . not always enough, but sometimes enough and sometimes enough to make it inexpensive to order a couple other parts. Get what you need plus 2-3 items you don’t need, but are generally speaking useful.
So a few weeks pass by and a boring, worn package shows up. In it are my parts. They smell as if they have been living in a smokers attic for at least a decade, but they seem to pass the test of working and that is all I need! The next step is getting the case ready for the board. I installed a coaxial power jack from my stash, 2 BNC panel mounts, and the SPDT switch. I choose to wire up all of the internal components so that when I am ready to connect the board there is little work to be done.
This is where I made my second mistake of the build. If you follow the manual, you will build the transmitter. Then when you are done they will give you some options to improve the performance. I read the manual in advance and had opted to install the circuit for preventing chirp ahead of time. IF one were to build this radio and intend to build it with this mod installed from the beginning, one would not burn themselves with a soldering iron while trying to put an electrolytic capacitor between the coaxial power and a ground lug on a BNC ground lug because that capacitor is NOT necessary assuming the anti-chirp mod is installed. The joys of homebrew!
Anyway. . . I had the can wired up and it was time to start on the board. The manual has great step by step instructions. I won’t belabor them other than to say that in the last step, they have you run a capacitor between two terminals near an inductor on the bottom of the board. If you read the manual in advance you would choose to put the capacitor in before the inductor. I think it looks nicer and is less likely to short out any traces. It also fits through the hole just fine if you put it in ahead of time and just bend it over out-of-the-way.
The last step was to build up the home-brew anti chirp mod. It’s a simple circuit and I had all the parts on hand thanks to some prior orders from kitsandparts.com. See how my advice from earlier has paid off in this build! If I had it to do over again, I would use fewer of the manhattan pads. I laid it out exactly as the schematic showed, but you really only need about 5 islands.
The rest of the build was uneventful. I made a short video to show the first smoke test, but unfortunately I must have hit the slow motion button as the video is completely unwatchable and 20 minutes long for something that took about 2 minutes. You’ll have to just enjoy the pictures. It does work and I hope to make an actual contact at some point when the bands are cooperative!
More projects are in the works. Stay Tuned!
The FOBB is a contest put on by the Adventure Radio Society. These are the people who also host the spartan sprint once a month. The idea is to get portable and operate your radio. The FOBB and NJQRP Club Skeeter Hunt are the events that I actually learned radio doing!! I’ll never forget the first contest I took part in, I worked Greg Lane N4KGL. How he copied anything I sent and the fact I copied anything back is a miracle! But. . . I still follow Greg on Google+ and we trade emails occasionally. He has been a very helpful elmer over the years. You’ll hear him in my video! (This is actually just a bizarre coincidence! I happened to hit record right before he responded to me.
JD (K5HH) has been showing me up by Vlogging. I doubt I become a Vlogger, BUT. . . I did make a video of the contest and figured I would share with you. Check it out, share with your friends. Tell me what I can do to make it more useful for the upcoming Skeeter Hunt in the comments below!
Tuna Tin finished post coming soon!
I mentioned previously that I had won a tuna tin 2 at a NORTEX QRP meeting. Well, I’ve finally started building on it. Step 1 is to read the manual. I know. . . shocker. . .
The Manual is pretty straight forward, but I was surprised to learn that it doesn’t actually come with all the parts required to make a working transmitter. You need your own antenna jacks, your own T/R switch, and not surprising. . . Your own tuna can.
For those of you unaware, my wife (KG5WCI) is a vegetarian. Before we got married our prenuptial agreement consisted of this.
- I promise not to cook bacon or eat tuna in the house.
- She agrees to never have a dog that she carries in a purse.
Now. . . before we continue I think I need to address the elephant in the room. Many people feel like I made a poor bargain. But lets be real. . . when I got married my diet consisted of frozen Tony’s pizzas, Burger King (nearest fast food), and Jersey Mike’s (around the corner from work). So its not like I was cooking a lot of bacon.
Back to radio!
As you can see, its not like I can run out to the store and buy a can of tuna. Consuming it at home is not in the cards and consuming it at work, well. . . thats complicated. Primarily because I’ve not made my own lunch in at least a decade and given rule number one exists it’s not like the YL is going to make it.
Luckily. . .
I have friends. A friend at work was listening to my dilemma and rather than running scared, as one should do. . . she mentioned that the next time she makes tuna casserole she will bring me the empty can and even rinse it out. (So as not to even come close to rule number one. #blessed) This actually worked out incredibly conveniently as this friend and her husband are expecting now and canned tuna is expressly not permitted for expecting mothers. Not to mention, she is likely to enact rule number one in her home at least for the next 90 days. 🙂
A week or two later a chicken of the sea tuna can wonders into my life and the adventure it seems is officially ready to start. The first step was to map out the can and figure out the dimensions and how the top will fit mechanically. The manual gives a couple of options, but I’m enamored with the concept of the full open can. This means the bottom of the can needs to be cut out.
Here my friends is where I exhibit the first word in Amateur Radio. What I should have done was put the PC board on top of the can and got a sense of where the hole in the can needed to be. i.e. how big the finished hole should be.
Instead. . . I tried to leave a little bit of the can so I could mount the PC board to the can. Unfortunately after cutting the can out, I discovered that I couldn’t orient the board in a way that did NOT short out a trace. In addition, the edge of the PCB will go right to the edge of the can no matter how big the hole is. There is no need for “structure” to attach it to.
It was time to cut a bigger hole. Unfortunately once I had a hole, it was nearly impossible to cut more metal with a nibbler. It was just too flimsy and wouldn’t “bite” off, which means I just had to bend the metal over. Not an ideal solution, but it worked. We are off to a good start. Hole is cut and its time to mount the hardware.
More to come soon. . .
This episode we’re talking about the WSPRlite flexi.
Now this is a cool little device made by the folks over at SotaBeams in the UK that lets you test your antenna’s actual transmit propagation in real time. It uses the WSPR protocol (Weak Signal Propagation Reporter) originally developed by Joe Taylor K1JT. (Quite an interesting guy, you should look him up.) Now WSPR is open source and still actively worked on. Please find relevant links below.
I’m not going to tell you how to install the support software, as that’s all very well documented when you buy the unit. The point of this episode is just to go over what it does. So, let’s go straight into the setup app where you can update the firmware and set up the device for operation.
After you plug the WSPRlite in to the computer, pick the correct COM port and click CONNECT.
Every so often, I click Update firmware, to make sure it’s current.
Then, enter your callsign and first 4 digits of your QTH locator. Currently WSPRnet only uses the first 4.
Honestly, I’m not sure what the CW callsign checkbox is for, so I ignore it. If you know, please post in the comments below and share your knowledge.
Choose the band you wish to test. Once you pick a band, it will pick a random frequency in the WSPR accepted range.
The flexi version of the WSPRlite has lowpass filters for 20 & 30 meter bands built in. You may need to get some external lowpass filters for any other band you wish to test, depending upon where you are operating from. The WSPRlite will work without them, but you may end up operating out of bounds depending upon your location. Something to keep in mind. I don’t have any other lowpass filters yet, but they’re on the way if I need them.
Then, pick your power output. I’ve just been leaving it at the default 200 mW which, when using the WSPR protocol is equivalent to 1000 watts of SSB. I’m not using an external amplifier, so I leave the Reported power at it’s default.
They suggest leaving the Repeat rate at 30%, so that you’re not hogging the frequency every minute. I’ve also left the Max runtime at it’s default of 3 days.
At the bottom is a very important link. This will send you to your own, personal DXplorer.net report page for your specific device. We’ll get to that later, for now, go ahead and click Open in browser, then, when it opens, bookmark that link. I think it will generate a new link per band.
Lastly, go back up and click Save WSPR Settings.
That’s it, you’re done. Unplug the device and let’s get set up to transmit.
I use my radio power supply,…
… and plug it into the SotaBeams Power Conditioner. When I didn’t use this, the power supply generated an ugly buzz in the transmission. So, I bought this conditioner as a kit, and haven’t had an issue since.
Plug it into the WSPRlite
Connect the feed line…
Which goes to my Emtech ZM-2 QRP tuner which I’ve posted a pictorial write-up on the build previously, see that link below.
Then attach the antenna to the Tuner.
Wait for 2 seconds past the minute on my atomic clock….
aaaand press the button to start transmission.
On the ZM-2, flip the switch to TUNE and fiddle with the knobs until the light goes out, or as dim as possible. If you turn the knobs to the stops and the light stays bright, try Adding picoFarads and keep trying. I took my time here. At 200 mW, I wasn’t too worried about overheating anything. When done, flip the left switch to Operate which takes the LED out of the circuit and give you the least resistance on the line.
Done, you’re now transmitting. Give it a while to transmit for a few minutes, and then go to the above mentioned DXplorer.net link you got from the setup app.
The DX10 Table shows you a list of your best 10, in range every 2 minutes or so.
The Graph is a visual representation of the data points of all your connections. In every report, you can choose a time frame snapshot.
The Spots map is … well, self explanatory.
The Spots table shows you all your spots, most recent on top.
If you’ve tested on other bands, you can swap over to them here.
And there you have it. This is a very useful bit of kit that lets you see just how well your antenna is working based on it’s configuration and current propagation conditions. For around $80 and it’s diminutive size and weight, I highly recommend it. You get a very accurate, real-time picture of how long your radio’s arms are at that moment. Especially in our current solar minimums, it’s quite handy to test out where you can reach.
If this video was helpful in any way, please, give us a thumbs up. If you have any questions on the WSPRlite flexi, please post them below. I’m no real expert, but I’ll be happy to get back to you with what I know.
Thanks for watching the DummyLoads. See y’all next time.
Some friends and I decided to go on a camping trip recently. Camping in June, in Texas is generally NOT a great past time. BUT. . . My friend’s dad had passed away recently and we all felt like we should get together and enjoy nature. Much as his father had.
As with all camping trips, on my list of items to pack is a radio and an antenna. For this particular outing we were going to be at Huntsville State Park in Texas. Since I was the only amateur on the trip, I opted for a small footprint antenna and brought my Buddistick to pare with my KX2.
We arrived late in the day and were greeted with some interesting signs. . .
Like all good trips we had a lot of fun. I managed to set up my buddistick and do a lot of CQing. Unfortunately our location was not very favorable. We were in a low spot and the antenna was vertically parallel and near a very tall tree.
I’m confident that some of my radiation went directly into cooking some of the grubs in the tree. I called CQ for about 20-30 minutes the first night and managed to only work one station (XE1XR). While he didn’t answer my CQ, I did work him. I shut down for a couple hours and came back around midnight Central (0500 UTC) and called CQ again for about 1/2 hour on 30M. Not a single spot. Good SWR so I’m not sure what went wrong other than the location. I did enjoy tuning around the band late at night. I don’t do this much, but I heard an “F” Station and some “I” stations. They obviously didn’t hear me, but it was fun to have a chance!
I forgot to take any pictures of my set up. A couple of noteworthy things you would have seen in my picture. . . had I taken one. The picnic tables at Huntsville State Park are extremely thick concrete tables. I couldn’t get my clamp to open up big enough to go around any part of the table in order to mount the antenna. I was also very close to the water and therefore not very high. So I mounted the antenna to a handicap railing at the base (read bottom) of the stairs up to the vehicles. Again. . . not a great location, but it is what I could do with what I had. . . Next time I’ll bring the PPD. There is plenty of room in most campsites to set that up.
Since the bands were not hopping I opted not to do radio and instead went fishing on the 2nd night. Where I ran into this guy. . .
As you can see I made it home to type this, so it all ended OK. I’ve never seen one in the wild and never dreamed I would be so close to one in the wild.
After buying a WSPRLite I decided I needed a QRP antenna tuner. I was first looking at the QRP Kits SOTA tuner, but after a recommendation I took a look at Emtech’s ZM-2. I looked at a couple others, but after reading a bunch of Eham.net Reviews, the ZM-2 looked to be the best choice for me. The ZM-2 comes as a relatively easy kit, so what follows are some pics of my build. I followed the instructions and the video advice from W5CYF.
Keep in mind, I’m not very good at soldering… yet, so be kind.
Start by winding the toroids.
This was an easier process than I thought it was going to be. Even the little one, I was a bit concerned that I was going to snap the little wire, but it snugged up nicely. I gotta say, I don’t like soldering the heat removable coating on the little wire. I was never sure it was hot enough to melt and get a good connection. I also read the instructions wrong and didn’t leave enough red wire on the large toroid, and so had to create a pigtail for that end. There was plenty of wire in the kit, so that wasn’t a problem in the end.
Setting up the LED
I ended up having to go buy some helping hands and a head mount magnifier to do this part, which worked out for later parts as well. My eyes ain’t what they used to be apparently.
Attaching the front face decal, after spraying 4 coats of Krylon.
Installing the Faceplate.
Here are the switches, connectors, and variable capacitors installed. If you build one of these, don’t attach the right poly cap knob until after you screw the faceplate into the box. The right-bottom screw ends up being under that knob by half a screw width.
Final Components and wiring.
The area near the two main switches was a bit fiddly and mine looks ugly, but there’s no shorts.
It seems to work, but there’s some issues I don’t understand yet. I put out an email to Emtech, but never got a reply. I’ll try calling them. Y’all can expect a video of it in action in the very near future.
The weather in Colorado is spectacular this time of year. Even better at altitude. Crisp, dry, cool mornings are WAY better than the Texas Humidity Enhancer! I seriously need to look for a job up there. 🙂
I am blessed to call Myron Schaffer (WV0H) a friend. He has allowed my family and I to join his family and do field day the last couple years. This video only covers ~30 hours of field day and leaves out most of the details of antennas, etc. I hope you find it entertaining at a minimum!
While on our trip the youngest kiddo mentioned some projects for she and I to work on together. I intend to finish up the Tuna Tin 2 then get after some research and building of our daddy daughter project!
Hope you had a good Field Day 2018!
I was SO excited for field day this year, as it was the first year I’d be operating from the comforts of my own shack. My wife and I recently moved out of a 7th floor loft in downtown Dallas and into a house in the burbs of Jackson MS. This wonderfully opened up my antenna options. Alas, the first antenna I put up failed miserably due to my terrible balun building skills (I’m improving, albeit slowly). The second one did much better, being store bought. At least… I could hear frequencies. I diligently ran my feed line through my attic and out the soffit to hang the center of a 120′ wire dipole off the corner of my house.
I then spent the rest of the week boning up on on digital modes, my CW skills (still not great), the rules, field day operating practices, and testing to make sure my radio could hear on the bands.
It did, swimmingly.
The Friday before Field Day, I tried listening to the W1AW bulletin via phone and CW, but couldn’t quite bring them in. So I pulled it using PSK31, which worked quite well. Which turns out, in the end, to be prophetic.
I also set up my Renogy suitcase solar panel kit and topped off all the batteries I thought I’d need. Turns out my QRP Ranger from Hardened Power Systems worked the whole weekend without needing a recharge, powering both the KX3 transceiver and the PX3 panadapter. Not bad at ALL. I then spent the rest of Friday night cleaning and organizing the shack. So fun….
So, Saturday 1pm Central, station K5HH 1E MS was open for business. I actually heard CQs kick up at 12:58, but who’s counting. I then proceeded to spend the next 3 hours able to hear other stations on 20, 40, and 80 meter bands, but nobody, NO body, could hear me. I just couldn’t reach out and touch anyone. I tried Phone, CW, and PSK31. Heck, I even tried RTTY which I’d never used before. So I thought my field day was a bust. Deciding to run through my whole setup to make sure I had everything connected and hooked up properly, I started with my radio TX settings, then my connectors, then tested my feed lines, which led me to try to change where my feed point was hung. I moved it away from the house (and the metal gutter), and raised it about 6 extra feet. WHAT A DIFFERENCE!! My FIRST try on phone was heard just fine, as they didn’t ask for any repeats. That’s when my day finally started, around 6pm central. I did SSB phone for a while, but one of my goals was to actually work CW for the first time, which I finally did. I did have a hard time breaking through the pileups on CW, so late that night I tried PSK31, which is where I spent the remainder of my field day.
I didn’t rack up a great many QSOs, or points for that matter, but I did double what I got last year, so I’ll take it. I did make contact with a couple friends in Texas though. More importantly, I learned a LOT about setting up my home shack, and had a great deal of fun doing it. I’m incredibly impressed with how long my battery lasted. CW remains a challenge for me, but that’s just going to take practice. Next year, I think I’ll go back to 100w and see what I can accomplish.
Look for a followup on operating PSK31.
The NE602 Direct conversion receiver has been a good project. I’ve learned a lot. This last week of studying the schematic and trying to understand what I can do to peak the performance has been instructional.
Since I was focused on the band spread capacitor I first tried to understand what the spread of the tuning on that capacitor should be versus what it was in my implementation. In the process I manually calculated the max and min value of the schematic. The band spread should have been somewhere between 3.33pF and 8.3pF. A spread of 5pF. As it turns out this is all calculated out in the book. Then I calculated out my values. I have a variable capacitor that ranges from 15-95pF. With a 10pF cap in series that gives me a range of 6pF to 9pF. Only a spread of 3pF. I was right. . . I don’t have enough of a spread to in my band spread capacitor.
What value of capacitor would I need to get my band spread up to the 5pF as suggested in the text. Well I got to bust out my elementary algebra skills and failed dramatically! With the help of my sister-in-law N5LRF (who teaches math) I was able to figure it out.
But what does this mean in reality?
So I decided to calculate out the min/max frequency of the circuit as designed in the schematic and as implemented in my circuit. For this I used an online calculator. But for your reference F=1/(2π√(LC))
As designed the circuit will tune 6.8MHz-7.52MHz. With my implementation it will tune 6.70MHz-7.35MHz.
Hmmm. . . . My LO seems to be right where it should be.
My observation of this circuit in reality is that no matter how I tune the LO, the frequency is unchanged. I clearly have an enormous swing in frequency. I can observe it in the math and I also can observe it on the Oscilloscope. BUT. . . It doesn’t really seem to change the receive station strength. Why is that?
Another set of observations are that when I am measuring with the Oscilloscope I can observe no signal on the LO unless I am transmitting into a dummy load. When I switch the Oscilloscope over to the front end and measure I can observe no signal, whether transmitting into the dummy load or not. Interesting enough when I transmit into the dummy load I also can hear signals on 40M much better. I can still hear the entire band, but I hear them better.
After discussing with my friend Myron (WV0H) I came to understand that when transmitting into the dummy load I am increasing the current flow in my LO. This increased current results in better out of frequency rejection and receiving. The only real solution to this would be to increase the current of LO into the NE602. So the band spread is irrelevant. This receiver is just not very selective. Especially when there are strong adjacent signals. A potential solution would be to have a crystal determine the frequency. I would have a far smaller tuning frequency range, but it would improve the current flow.
I’ve decided that I have learned all that I can possibly learn from this particular endeavor. It’s time to move on to the next project. I’m really thinking about tackling a regenerative receiver and just starting from scratch.
Stay tuned to the site for more updates on building projects and outdoor operating adventures!
I have been disappointed to discover that my receiver is easily overloaded. Also tuning the variable capacitor seems to have very little impact on the received frequency where as the adjustment on the front end seems to have a dramatic impact on the received frequency. Why? What measurements can I take and what can I learn? Well I’ll tell you my story. . .
****Warning everything below this line is my best guess, I don’t actually know. If you know I’d love to hear from you in the comments below.***
First of all I don’t have much equipment, but I do have an oscilloscope that Bill Ellis (N5TXN) gave me years ago. It is a 15 Mhz BK Precision 1472C scope. Unfortunately I don’t have any probes. . . Amazon 100Mhz scope probes ordered. While I’m waiting on those, what else can I do? First I used a dummy load to transmit 7.000 from another radio at 5W and used the variable capacitor on the front end to make sure I was peaking the signal in the CW end of the 40M band. I then used the tuning capacitor to try to tune off the signal. No luck. Then I keyed down into the dummy load and started spinning the VFO. I made it to 7.150 before the signal diminished in any way. Hmm. . . that just doesn’t seem right. Could my LO be on the wrong frequency?
How can I measure the frequency of the LO?
Many phone calls and emails to many friends. A couple of notable quotes.
- Tuning doesn’t matter if the receiver is overloaded.
- You can hook up your oscilloscope or frequency counter, but know that you are loading the circuit and the frequency is not the exact frequency in the circuit.
- Given your LO arrangement, there just isn’t much signal to measure.
I was advised to use a 1″ form and wind 10 loops of wire around the 1″ form for a receive antenna. I could then use this receive antenna to try to get a frequency count by using my MFJ-259B frequency counter OR use my oscilloscope and the antenna. I was also advised that this was likely a futile effort as the total energy in the LO circuit is unlikely enough to get a good reading. Turns out this was correct. . . The MFJ frequency counter gave me results from 400 Hz to 30Mhz and the oscilloscope could see a signal, but it wasn’t enough that I could actually count the waves.
I took a trip to the local Nortex QRP meeting and brought my little creation. I expressed my frustration that the tuning capacitor seems to have no impact on the tuning. After visiting with Dave Lear (NE5DL) and Joe Spencer (KK5NA) I became convinced that the issue was in my band spread capacitor. It’s not a large enough tuning value. When I arrived home my Oscilloscope probes had arrived!
I hooked up the oscilloscope probe to pin 6 on the NE602. I got nothing. I played with the RF gain pot. Nothing. I put my desk radio on 7.050 Mhz and keyed into a dummy load at 5W. Hello. . . I have signal. I guess that the LO runs at such a low current there is no observable signal until a threshold is met on the RF input. I then spun my tuning cap and the frequency changed as did the amplitude. The amplitude and frequency changed dramatically. I interpret this as confirming my hypothesis. The band spread capacitor needs to be adjusted to tighten up the tuning capacitor. As the tuning capacitor exits the tuned portion of the front end the amplitude drops. In my case, its REALLY fast!!
I think my next update will probably be finishing my final experiments with this receiver and start planning my next project. We are approaching the time of year where operating outdoors is nice so I may take a break from building until it gets to be so hot that operating isn’t fun and field day isn’t far away either!
In my last post I had everything wired and simply needed to add power. Why on earth would I leave the devoted readers of this blog hanging on that moment? Well I’ll tell you: It didn’t work!
I said from the beginning I expected to fail, but learn through failure. Mission Accomplished!
If you read my last post you probably caught my mistake. I was mildly distracted while doing the final stages of the build with dad duty. I also did not ever complete an entire circuit in one setting. Even when getting power to the chips I failed to ground the IC ground pins. In retrospect it really was a recipe for disaster!
When I plugged the power in I got a pop. Good news, the LM386 is working correctly! That is the extent of what happened. I attempted to move the RF gain up and down. I tried to “peak” the capacitor in the front end. Nothing happened! I started putting my screwdriver down on different pads on the board. Pin 3 and 4 for the LM386 gave me a noticeable buzz. Seems right. Pins 4 and 5 of the NE602 had the same result. So far no concerns. I put my screwdriver down on the antenna input, no change. Seems strange. I tried adjusting the RF gain, no change. Hmmm. . . Look at the picture, do you see the problem? Well the truth is there were many problems, but the first was that I incorrectly connected the potentiometer for the RF gain. I didn’t realize that a pot is actually a voltage divider network. So your input goes to a resistor on pin 1, your signal feeds through at the voltage divide and you need a lead to ground for the second resistor. You don’t just connect to the next step in the circuit. Speaking of which. . . somehow in wiring all the front end I managed to put all the parts in, but failed to actually connect each of these components to each other to make a circuit. DUH! Even after adding a ground cable for the RF gain control and connecting all the steps for the front end, the receiver was still pretty deaf. Hmmm . . .
I broke out the schematic and started going through each stage and mapping it to my board making sure that I had connected everything correctly. Do you remember my drawing out the schematic. If you look at the original schematic and my sketched schematic your going to see it. Go ahead, compare pictures and tell me. . .
Pin 6 on the NE602 is the input of the local oscillator. Pin 7 is the feedback. I have them reversed. Despite having tried to avoid the crossing of wires by sketching it all out, I have to cross pins 6 and 7 because of how I ran the capacitors. The good news is that a hot soldering iron can help get your wires out and repositioned pretty quick. I managed to do it with out permanently harming myself or anyone else. For what its worth, it’s probably a good idea to wear glasses or safety glasses when hot solder and prying wire is involved. Not that I found out first hand. . . but I’m not going to have cat-like reflexes for my whole life. Ha!
OK. . . all pads connected properly. Time to connect an antenna and give it a try. What I experienced was magic. Initially I was receiving local 96 FM station. As I adjusted the input capacitor I lost the FM station and gained radio Havana Cuba. They are very concerned about our President. . . me too I guess. . . prayed for the last one, will keep praying for this one.
As I tweaked the capacitors I realized that I could here RTTY signals and the occasional CW signal. True to the write up, the front end is pretty wide on this thing. I think I sent an email to everyone I know to share with them my accomplishment. It’s a below average receiver, but I did it!
So what now?
Well, I’d like to study what is actually happening in this receiver. Take some measurements and attempt to optimize my LO tuning to be as selective as is possible with the capacitors I have. Then I am likely to start another receiver. Hopefully one that will be made entirely out of discrete components and also hopefully much more selective. Maybe work on a filter of some kind.
More to come!
If you remember from last post we had the power rail all wired up to the sockets. The next step is to connect the chips with the various capacitors, finish the audio out and start the Local Oscillator. You will see in the picture that I have fixed the power wire for the LM386 and it is now wired to pin 6 which is the proper V+ pin rather than pin 7. You will also note that indeed the power jumper created a small issue jumping from pin 6 and 7 of the NE602 over to the start of the local oscillator. A good foot note for future builds to think about that a little more. Other noteworthy lessons on this section are: 1. My canonical tip for my Weller soldering station is not a great choice for melting the Krylon and getting a good ground solder bead. Nor is my wet pad a satisfactory device for cleaning my tip. There is a significant delay in having a clean tip and being able to melt solder that is sufficiently annoying. As a result I went to Fry’s in Arlington, Tx and purchase an ST2 and ST3 soldering iron tip as well as a Hakko tip cleaning bucket. This definitively made the soldering process better!
The only other notable step from this section was that I purchased a bunch of alleged NP0 caps on eBay. They were shipped on the slow boat from China. When they arrived they looked like ordinary ceramic capacitors and in no way looked C0G or NP0. So I decided to try to test these out. I took out a 680pF capacitor and put it on my AADE meter. It was within tolerance of expected C value. I then pulled out my YL’s (wife for non-amateurs) hair dryer. I then kicked it on low and started heating up the cap. It went from a cool room to hot enough I preferred not to touch it. Total change is capacitance. 1 pF. I’m still learning, but that seems to be well within tolerance for an NP0 capacitor.
The audio chain only needs the actual 3.5mm jack. The LO only needs toroids and the final variable capacitors. Then I will start on the front end. This project is getting real!! Hope to have it make noise soon! When I do get it to make noise I will try to post video!
The title is slightly misleading. While I did go hiking and I did take a radio, each night when I got to camp I was so wiped out I never set it up. I just didn’t have the energy to do it. I did take my GoPro and I thought you might enjoy the story.
More building next week!
At the point I left off last time I nearly had the LO complete. Winding a toroid and connecting all the pads was the last step to close that stage out. For this step I opted to go ahead and do the toroids first. I don’t understand why people dislike toroids so much, it really isn’t that hard. This build was a T-37-6 with 21 turns of #28 wire. (The schematic calls for 26, but I didn’t have any. I did the calculation for what the inductance should be and measured my result. They matched.) Every time you go through the center of the toroid, count 1. Easy!
If your wondering about my L/C Meter. They are unfortunately unavailable. Its a really sad story. . .
Since I already had the pads laid out for the local oscillator I finished up that section. I still hadn’t decided how I wanted to do the tuning capacitors for this receiver. I really am not in the mood to use 2-80pF variable capacitors. I opted to go with a 0-50 variable cap that you need a screwdriver to tune for the band spread and a 20-107 pF air variable for the regular tuning knob. With that decided and done, laying out the pads for the front end began.
The front end is a pretty simple circuit. A toroid that matches the local oscillator, an on the board capacitor and a couple of trim caps. The tricky part of this stage was making sure everything would fit. The particular variable cap I had chosen was pretty big relative to the remainder of the board.
The particular day I was working on this the family had a variety of activities planned and I had to stop a couple of times and then start back up. About 5p I had finished everything. I decided to go through and double-check all the solder joints. Then I realized that I had forgotten the 3.5mm jack for a speaker or headphones! OK fixed that. I double checked all the solder joints and all looked well. I installed the ICs. When installing ICs you will need to bend the leads ever so slightly inward so that they fit in the socket. It is easiest to do when they are IN the socket. Lightly press one edge of leads into the socket to bend them ever so slightly inward. Then gently set the IC into the socket from the back and roll it forward.
Feeling very good about my progress and nervous about the next steps. It’s time to apply power. More to come!
We had our park outing and I took some time to make a video on how to set up the park portable doublet. If you have any questions on how to set it up or make your own, let me know in the comments below.
Now that the board is sized its time to melt some solder. I’m not sure what the real first step is supposed to be. I’ve heard Eric Guth on the QSO Today podcast talk to a number of builders and answers vary from the audio amp to the Local Oscillator. I decided to start with getting power to the chips. Once I had that figured out I’d have a better idea of where the local oscillator would go on the board. I also decided to add a couple of steps to the power input. One is a reverse polarity protecting diode and the second was a 5V regulator. Since I don’t have a real 5V power supply, I am likely to power this with a 9V battery. The NE602 has a max V+ of 8V so I want to make sure that my V+ stays at 5V and not fry anything.
You will see on the board I’ve laid out and superglued the 8 pin DIP sockets as well as the initial pads for the power rail. Lessons learned from this experience. Don’t put superglue on the pad then try to place it on the board. Put the superglue on the board and then set the pad on the glue. If you don’t you will smear superglue on your board as you can see in my picture above. The other lesson I learned was to be a little more thoughtful on where you run the wire from one side of the board to the other. I think I would run it a little closer to the chips so that the Local oscillator could have a little shorter leads over the power wire to the NE602.
If you look closely at my picture and study the schematic from the initial post, you will note that I’ve wired something incorrectly. It can be easily seen in this photo (left). Can you spot it? Leave a comment below when you find it.
The build has begun. . . More to come!
Now that I know how the layout is going to run its time to start planning how much copper will be needed for the circuit board. This will likely be the post where I get the most wrong! To be clear this is being written as the project is in process, so we will find out together if I set this up wrong. . . but a few weeks from now probably.
The circuit is set up around the two ICs, an NE602 and an LM386. Planning how these devices will sit on the board and creating enough room for the various components supporting the inputs and outputs will determine the size of copper board needed. The full size 4″x6″ copper board seems like major overkill for this circuit.
I’ve decided to do the K7QO method of using 8 pin DIP sockets. While the socket adds ~$.15 to the build, it guarantees that I won’t smoke the IC with my soldering iron being too hot. I purchased some MePads when building the Regen last year. They went unused as the particular IC I was using was surface mount and didn’t fit. As you can see in the picture above, these fit the sockets just fine. I also intend to use the MeSquares for the other shared connection points. Now that the sockets are on the MePads, its time to lay them on the 4″x6″ sheet and guess how much board I need.
It seems to me that you would probably only need 1/2 of the board. Measuring 3 inches across the top and bottom of the board I drew a straight line with a black sharpie. I carried the line around the back of the board as well.
Cutting the board using the AA7EE method resulted in a slightly crooked cut, but ultimately successful separating of the board.
I also wanted to do the K7QO method of adding stand offs to the board to raise the soldering level up off the table a little. To keep the holes semi symmetric I measured 3/10ths of an inch from each edge of the board and drilled a hole where the lines intersected.
The last step was to scrub the copper with some steel wool and clean it with alcohol. Then put a couple of coats of matte Krylon on the board. This should help protect the copper a little and allow me to build on it over a period of weeks without the copper oxidizing.
The project is well underway, the next step should be actually super gluing pads and beginning to solder circuit blocks.