The Dummyloads

Where ham brains come to fry

Where ham brains come to fry

Archives for June 2018

Slow start to Field Day 2018 for K5HH

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.

-73-

Interesting Tube of cloud rolled through Sat afternoon.

 

Final Write Up Direct Conversion Receiver

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!