The algorithm is not super time-efficient, but it does get the reactive impedance under 300mΩ, which is better than I can do by hand most of the time!

#AmateurRadio #HamRadio #electronics #maker #Python #Curses

My thinking was using binary number values from 0-4 to select which relay to enable, while I'd have a 7 (0b111) indicate a reset signal. After creating the truth table on paper, I converted it into AND and NOR gates and simulated it in Qucs-S.

Then I made footprints for the 74HC00A-series ICs that contain the gates I'd be using, and lastly created a schematic showing the routing for all of the lines I'd need in KiCad.

With that, I had what I needed to actually create the board on perf board. I also made a test fixture using buttons and LEDs to verify that it was correct.

The only bug I ran into was where the Relay4 line was high whenever I held all buttons down, which should only trigger Reset. Turns out I only forgot to connect a couple of traces. With that fixed, it worked 100%!

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I spent a few days earlier this week struggling with transistors, but it ended up being worthwhile since I learned a lot. For example, an n-type MOSFET will only allow voltages that are up to the gate voltage across, which means that it really needs to be on the ground side of whatever component is being controlled. You can see the behavior here (with BJTs for comparison):

The bottom right circuit in the above diagram matches how I eventually successfully used the 2N7000 MOSFETs to control the RF relay in the video here:

This project also had me working on my first PCB design in KiCAD, since there was no way I was going to do all that fiddly soldering of these SMD relays to through-hole perf board multiple times!

Now to wait for PCBway to get back to me…

#AmateurRadio #HamRadio #electronics #kicad #PCB #circuit #maker

But for some reason, the resonant frequency was much too high no matter how I adjusted the clamps, so I started playing around with capacitive hats.

My experimentation eventually led me to making hats that look kind of like flower petals, as that's what I saw when looking around online at the time.

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One thing I kept seeing was a strange SWR spike at about 50 MHz, which I still can't explain to this day. Maybe the balcony railing was resonating?

I also tried a resonant stub to see if that would do anything interesting, but the SWR spike remained.

DD8SF wondered if the autotransformer was hitting resonance, but that occurred at around 69 MHz.

While this experimentation didn't really pan out thanks to that weird SWR spike, don't think I'm done with this dipole! There's more experimentation to follow.

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I had a bear of a time trimming and tuning it, mostly because I went down the nasty “too focused to eat” kind of rabbit hole as I worked on it. I was placing the reflector far too close to the driven element to get proper gain, all because it provided a good feed point impedance. I eventually ended up with elements that were too small, too, so I had to solder extensions back on in order to restore their size. Despite all that, though, it works!

I have it pointed at Capitol Hill here in Seattle, since that's where the main amateur radio towers that I can see from here are.

This project also involved building the feed point in the little blue enclosure, which went through a few revisions as I went from targeting a dipole to targeting the loop shown here. And during the trimming and tuning of said loop, an earlier incarnation's internal solder joint broke, so I had to rebuild it to what's shown here. Oh, and this was the first time I've ever used a panel mount N connector, which is more suitable for UHF than “UHF” connectors, albeit with an adapter on the coax line for now.

Reflector Placement

After discussing reflector spacing with DD8SF, he sent me this from the Rothammels Antenna Book:

This was proof enough that I had been working with the reflector far too close to the driven element earlier today, and that the final spacing I ended up with at 0.15λ was good enough for my use.

#AmateurRadio #HamRadio

But since I didn't have an appropriate antenna for 1.25-meters, this also prompted experimentation into loops of proper sizes (which also included more playing around with 70cm).

At this point, I'm not sure why I started playing around with alternate feed point designs, but here are photos of what I ended up with.

It was at this point where I was starting to get strange readings with the Amazon Special SMA to SMA coaxial line I'd been using, so I finally built a new line using LL-240 coax and higher quality connectors.

Much better!

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After cutting it down to a suitable length for the 6-meter band, I started playing around with capacitive hats for the first time

This also prompted playing around with autotransformer baluns some more.

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Since the initial feed proved not durable enough, I built a better one out of box section PVC that is still my go-to to this day.

I started having a lot of trouble getting reliable and repeatable results with this gamma match, which I only later realized was because the aluminum hoops were painted, and paint obviously wouldn't conduct electricity. That also explained why I was having a bear of a time getting any solder to stick.

In the meantime, with the issues with the gamma match, I decided to switch to a “plain” feed instead.

While this did prove to be a somewhat viable antenna, the feed point impedance was far too low.

The low feed point impedance prompted me to go to the same style of twin coax impedance match that I'd used for the 6-meter dipole.

That all sounds great, right? Well, the signal and audio quality were garbage because I'd cheaped out and used Amazon RG-6 instead of coax of higher quality. That certainly taught me a lesson, and I'd go for LMR-240-75 cable for 75 ohms in the future.

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The first time I used it was later the same month, when I walked around Everett, Washington while my wife was at her motorcycle permit course. I tried joining a net without having thought to configure my radio for the repeater offset, so nobody could hear me. To this day, I never forget to do so because I felt so dumb back then!

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