Toots for raek@tilde.zone account

Written by Rasmus SA5RJS on 2025-01-31 at 21:13

I might have built a direct conversion receiver from a signal generator, a mixer, and an audio interface...

[#]AmateurRadio #HamRadio #electronics

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Written by Rasmus SA5RJS on 2025-01-27 at 12:45

I just discovered this treasure trove: "Basic Linear Design" / "Linear Circuit Design Handbook"

It's available for free on Analog Devices' website!

https://www.analog.com/en/resources/technical-books/linear-circuit-design-handbook.html

[#]electronics #AmateurRadio #HamRadio

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Written by Rasmus SA5RJS on 2025-01-19 at 20:16

2. Power Supply

The kit states "13.8 V" on its schematic (the "standard" amateur radio voltage), so I'll use about that voltage for testing.

The power supplies I own are a bit limited. My HP E3631A is adjustable, but can only put out 1 A.

I have a fixed 13.2 V (so not quite 13.8 V) power supply that can deliver 3.5 A continuously / 4.5 A intermittently. It's what I've used so far.

During the tests, I managed to pull about 6 A pretty early on, so a new power supply is needed. I ordered a new one from AliExpress called "PS30SWVI" (Power Supply, 30 A, Switching, sixth generation). It even have double Anderson powerpoles on the front! It should arrive in about 2 weeks from now...

With the new power supply I should be able to adjust the voltage and have plenty of current available. My only worry is that it doesn't have any settable current limit, but I guess that I could ad a fuse in series.

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Written by Rasmus SA5RJS on 2025-01-19 at 20:05

⚡ MINIPA70 Test Thread! 🧵

The board is populated and does not put out smoke when powered up. So what's next?

As I see it, the power amplifier has three main parameters that I need to find an optimal value for:

• Power supply voltage
• Gate bias voltage
• Input power level

For each point in this three-dimensional space, I get the following resulting values:

• Output power
• Harmonics power levels
• Intermodulation distortion
• Current consumption
• Temperature

I have some reasonable starting points for the three parameters I need to tweak. A blog post by F5NPV has been invaluable for me, and in it he suggests good values for all the parameters.

https://f5npv.wordpress.com/irf530-mosfet-amplifier/

[#]AmateurRadio #HamRadio #electronics

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Written by Rasmus SA5RJS on 2025-01-13 at 23:10

This project (where I sourced the non-SMD parts myself) required an SMD 7.5 uH common mode choke. I didn't have any, so I made my own substitute!

It turned out to be 62 uH, so I overshot the inductance a little... 😁

Bending the ends around the bottom to match the PCB footprint worked surprisingly well!

I bought the PCB here: https://www.tindie.com/products/mustoradio/ham-radio-antenna-switch/

[#]AmateurRadio #HamRadio #electronics

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Written by Rasmus SA5RJS on 2025-01-07 at 07:35

Today I learned that the 78L05 (the classic 5V regulator, but with a TO-92 "transistor" package) supposedly exists in two variants with different pinouts...

[#]electronics

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Written by Rasmus SA5RJS on 2025-01-06 at 21:54

Dear scratchbuilding radio fediverse,

Sometime I think I heard that someone had made a "proper RF datasheet" for the IRF510 MOSFET. I know that the transistor is "officially" just a switching transistor, so the datasheet doesn't have a Smith chart and many RF details. But supposedly, someone made the measurements and made an unofficial datasheet?

Does this exist, or am I just misremembering? If it exists, where can I find it?

[#]AmateurRadio #HamRadio #electronics

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Written by Rasmus SA5RJS on 2025-01-01 at 17:20

8. Input and output transformers: assembly and mount.

The transformers were fun to assemble. It tries to solder the PCB end caps with the bottom edges as flat and aligned as I could. I put the standing on one end and added a little solder to the other end. Then flipped them over and soldered the other end. Then flipped them back again and soldered properly.

It took a lot of heat to melt the solder and I found it useful to move the soldering iron in circles around a tube's edge to melt all solder consistently.

Next I soldered the transformers to the PCB. This also took a lot of heat and some time. Now the project is much more three-dimensional and has a lot more heft. I look forward to firing up the amp (not literally, I hope, although that will surely happen anyway)!

[#]AmateurRadio #HamRadio #electronics

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Written by Rasmus SA5RJS on 2025-01-01 at 16:48

7. Electrolytics, relay, and DC power cord.

I soldered the remaining components that would be obstructed by the transformers if not soldered before. I also soldered a 5.5/2.1 mm DC power cord (another dumpster find) so that could test the bypass relay by shorting the PTT pins. It went "click" as expected!

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Written by Rasmus SA5RJS on 2024-12-29 at 21:35

6. RF choke.

This is made with two turns of 1mm enameled copper wire around a binocular core. It was difficult to bend and thread the thick wire through the core and I accidentally scraped away some enamel in the process. The turns were stiff and didn't touch, so I didn't worry too much about it. I fixed everything in place with hot glue later.

The inductance of the choke turned out to be 4 μH. The reactance becomes roughly 180 Ω for 7 MHz and 350 Ω for 14 MHz. The 50 Ω output impedance of the output transformer secondary looks like 0.6 Ω from the primary (assuming a 1:3 turns ratio, and thus a 1:9 impedance ratio). So in the current divider formed by the choke and the output transformer, most of the current goes to the output transformer (more than 99% I think?) because 0.6 is much smaller than 180.

Actually, the amplifier is a push-pull design with the output transformer doubling as a combiner. So my back of the envelope calculation is probably off by a factor of two in some direction. If you know how to reason about the output impedance of a push-pull amp like this, please feel free to explain it to me!

[#]AmateurRadio #HamRadio #electronics

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Written by Rasmus SA5RJS on 2024-12-29 at 16:15

5. The first step was to break off the PCB parts used to form the input and output transformers and file the edges. It only took a minute to make all the edges super smooth and nice to work with.

Next I chose a heatsink: an old CPU heatsink salvaged from a trashed computer. Then I drilled and tapped M3 holes. First time for me tapping holes in metal, and drilling in copper. The drilling was harder than I expected. The holes ended up a millimeter or so from where I planned, but it doesn't matter.

[#]AmateurRadio #HamRadio #electronics

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Written by Rasmus SA5RJS on 2024-12-29 at 15:54

4. I would like to thank @quantensalat and @SA6JKK here on Mastodon for sharing their builds of a scratch built and a MINIPA70 amp. You inspired me to try this too!

https://astrodon.social/@quantensalat/111039741265686012/

https://mastodon.radio/@SA6JKK/111344946727316480

NA5Y on YouTube also has a nice build video: https://youtu.be/JgiakIxMjfI?si=eJ8XpO3NIKfLXAIN

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Written by Rasmus SA5RJS on 2024-12-29 at 15:48

3. The kit is not complete. For instance, it does not come with a heatsink or an enclosure. Instructions and a schematic were not included either. And I know the "70 watts" in its name is not realistic.

But I think the kit can be a useful first PCB for me to experiment with HF power amplifiers. There are a lot of tinkerers who have built this before and it's easy to find blog posts and videos showing how to build and test it. So this is a well beaten path and I'm in good company!

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Written by Rasmus SA5RJS on 2024-12-29 at 15:36

2. Why am I building this? My BITX40 transceiver puts out about 7 watts of power, and I have not been very successful getting contacts with it. Other amateur radio operators have said that QRP SSB is hard, but that 20 watts (like that from a Xiegu G90) is plenty enough.

So that's a perfect excuse for me to buy and build yet another kit! I hope this kit will provide linear amplification (needed for SSB) and give me 20-50 watts of transmit power.

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Written by Rasmus SA5RJS on 2024-12-29 at 15:24

⚒️ Build thread! 🧵

Follow along when I build a MINIPA70 amp, a $20 linear "70 watts" amateur radio transmitter amplifier kit for HF.

[#]AmateurRadio #HamRadio #electronics

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Written by Rasmus SA5RJS on 2024-11-26 at 07:56

Hey, there's another ham (@g7kse) who has uploaded SAQ-related videos to Makertube!

https://makertube.net/w/wh3bkKN4eUrVJezwHZfxk3

It's curious that whenever I think that I'm the only one interested in niche topic X in another unrelated niche place Y, there always seem to be someone else there with the same overlap of interests...

[#]AmateurRadio #HamRadio #SAQ #Grimeton

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Written by Rasmus SA5RJS on 2024-10-15 at 11:47

GPS disciplined signal generator / UTC shack clock. Sweet!

Kit from QRP Labs.

[#]AmateurRadio #HamRadio #electronics

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Written by Rasmus SA5RJS on 2024-09-23 at 13:27

Dear amateur radio fediverse,

I have just started to read about Winlink. It seems like there are multiple RF protocols in use. I have a QRP Labs low bands QMX and want to know if it's possible to work Winlink using it, preferably from Linux? (It only supports modes that do not send multiple tones simultaneously.)

Do any of the "RF access" protocols used by Winlink (AX.25? PACTOR? VARA?) have this single-tone property?

I also saw that some of the protocols are proprietary. That doesn't sound too good for portability...

Is there any combo of mode and software this FLOSS-loving amateur should check out?

[#]AmateurRadio #HamRadio #Winlink #QMX

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Written by Rasmus SA5RJS on 2024-09-22 at 13:27

Here is Øystein's legendary first CW QSO video for you who haven't seen it yet: https://youtu.be/mZw_gvOUi5s

[#]AmateurRadio #HamRadio #CW #morse

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Written by Rasmus SA5RJS on 2024-09-22 at 13:24

Today I had my first CW QSO! I "spotted" myself in the calling-cq channel at the https://hamshow.eu/ discord, and Stu M0TTQ replied my call on 20m!

CW QSOs are definitely above my skill level, but I try the "Don't get good to get on the air. Get on the air to get good!" approach.

Also thanks to Øystein LB8IJ for sharing his first CW QSO on YouTube, errors and all. That video has inspired a great number of people, me included.

Equipment: QRP Labs QMX (low bands), QRP Labs 50W PA running at ~37W, black Bencher BY-1 iambic paddle, 40m EFHW antenna in attic.

[#]AmateurRadio #HamRadio #CW #morse

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