Rasmus SA5RJS

Python · Linux · Gemini · Embedded · Software Toolsmith · Electronics · Amateur Radio · Homebrew Radios · Security · Programming Language Design · Electromagnetism · Astronomy · Physics · Linguistics · Skeptical Mystic · Bass Clef · All over the place nerd.

Gemini: gemini://raek.se/
Blog and links: https://raek.se/
Amateur Radio: SA5RJS
IRC: raek @ libera and quakenet

Public Key

npub133kx3vtsccvrn4uxjn85wacm45uqglre8qz7z7tr86p6lhy0whsqmhfazx

NIP-05 Address

raek_at_tilde.zone@momostr.pink

Profile Code

nprofile1qqsgcmrgk9cvvxpe67rffn68wud66wqy03unsp0p093naqa0mj8htcqe2gxuj

Author Public Key

npub133kx3vtsccvrn4uxjn85wacm45uqglre8qz7z7tr86p6lhy0whsqmhfazx

Show more details

Last Notes

2025-01-23 21:24:41

I bought a very affordable PS30SW VI power supply from AliExpress. It turns out that the power poles were oriented the wrong way for amateur radio use. Luckily I managed to take it apart and reorient the power poles. Much better!
There are some other interesting quirks of this power supply. The 2×2 power pole output is not that easy to use. To plug in two 2×1 plugs you first need to slide them into each other and then connect both simultaneously. The plugs cannot have rubber boots.
Also, the voltage knob, which ranges from about 8 V to 15 V, seems to be logarithmic. The 8 to 10 V part takes up about two thirds of the range. 13.8 V is at about "90% setting*.
But it seems to work. And so far the fan hasn't run. The fan is connected via a thermal switch and I haven't pulled more than 1 A so far.
#AmateurRadio #HamRadio
https://media.tilde.zone/media_attachments/files/113/879/774/141/502/881/original/6d308f6cc8147f4b.jpg
https://media.tilde.zone/media_attachments/files/113/879/774/511/117/318/original/3810b3fb50e0072c.jpg
https://media.tilde.zone/media_attachments/files/113/879/774/948/913/154/original/e0958e70380d8949.jpg

2025-01-19 23:05:32

- reply

8) Question for you who have built amplifiers like these
1. What is an appropriate drain current?
2. What is an appropriate power supply voltage?
3. What is an appropriate input drive power?
These are all for a push-pull linear amplifier using IRF530s.
I would love to hear what values you have tried out! Other transistors (such as IRF510, or whatever you have tried, really) are interesting for me too!
I'm looking for learning about both "hard limits" on these values, but also sweet spot values or ranges.

2025-01-19 22:56:48

- reply

7) Some things on the to-do list
So far I've run into some problems that probably need to be solved for me to be able to use this amp with my 7W BITX40 to get 20 - 50W SSB.
Get a more capable power supply. The one I ordered is on its way.
Output low pass filter. I have one built with T37-6 toroids, but I would like to have one with larger T50-6 toroids instead. I need to order suitable capacitors.
Lower feedback resistors. As usual, F5NPV provides great advice. The kit comes with 150 ohms, but I want to try with 100 ohms or 47 ohms to get better linearity (at the cost of lower output power).
Add source degeneration resistor and capacitor? Another way to add negative feedback to get better linearity, I think. Try what F5NPV and NA5Y did.
Add temperature compensation. I don't know exactly what to do here. I like a different bias circuit that I saw in one a video from Charlie Morris ZL2CTM. It had a current source and two diodes for each MOSFET.
Make a power attenuator for use on the input. This requires me to first figure out the suitable input power to drive the amp.
Wire up the fan. The heatsink comes with a fan. I just haven't used it yet.
Add temperature switches. I have 40 °C NO, 100 °C NC, and 120 °C NC temperature switched. The idea is to used them to turn on the fan (when above 40 °C) and kill the bias (when above 100 °C or 120 °C). I don't know how to fit them to the heatsink at a proper place yet, though.
Fix the BFO / crystal filter alignment on the BITX40. Currently, the high side of the passband seems to only be about 1.5 kHz instead of somewhere like 2.5 - 3.0 kHz. This is a know problem and I know of ways to fix it. (Add tuning capacitor to the BFO, or disable the BFO and use an output from the Si5351 instead.)

2025-01-19 22:42:31

- reply

This kit uses two IRF530 MOSFETs made for power switching (and not RF amplification). Do you know what kind they are? I don't think they're LDMOSes...

2025-01-19 22:38:48

- reply

6) More power measurements, at two bias levels
I wanted to know how the input power and gate bias voltage together affected the output power. So I ran some tests for two bias levels. The first series of tests were made with 38 mA total quiescent current, so about 8 mA Id for each FET. The board draws 22 mA with zero drain current. The second series of tests were made with 64 mA total quiescent current, so about 21 mA drain current per FET.
The results can be seen in the table in the picture. I might edit this post later and type it to text. See the ALT text for definitions of the columns.
Since the current (and output power) changed over time, I read the meters some seconds (maybe 5) after I turned on the input signal. The values varied a lot, so these measurements are not super reliable.
Also, the power supply seems to current limit about 6 A. It's a 4.5 A power supply anyway, so the results at these levels are doubly unreliable.
https://media.tilde.zone/media_attachments/files/113/857/396/043/992/824/original/eff668f4c50a0b68.jpeg

2025-01-19 22:28:19

- reply

5) Second test, where thermal runaway was very noticeable
I let the amplifier run with constant 13.2 V power supply, fixed gate bias voltage, and constant 0.2 W input power. The transistor tabs reached 70 °C in about a minute. The current consumption kept increasing.
This is in line with what F5NPV wrote about on his blog and @npub1v2z…0xqq pointed out here on mastodon. The bias circuit doesn't have any temperature compensation. So this is to be expected!
Links to YouTube and MakerTube videos:
https://youtu.be/kbxbTp3CwPo
https://makertube.net/w/5Nx4uXhbry3zhF468iNwru
#AmateurRadio #HamRadio #electronics
https://media.tilde.zone/media_attachments/files/113/857/373/357/724/154/original/1524e4ba5cd7b12d.png

2025-01-19 22:23:41

- reply

In that setup, did you use any thermal compensation in the gate bias circuitry (like thermally coupled diodes, or something like that)?

2025-01-19 22:05:57

- reply

This PSU actually has a knob to tweak the switching frequency so that the noise can be moved away from the reception frequency. According to another user, the knob doesn't make any noticeable difference. I've also heard that it is most noisy on the 160m band and maybe a little on 80m.

2025-01-19 21:21:19

- reply

4) First Test
I hooked up a current meter in series with the power supply and started to tweak the gate bias. The board draws 22 mA with the bias completely off. I turned the potentiometer until the current reached 42 mA, which should mean that each FET get about 10 mA of current.
I tested with the PA connected to the 13.2 V power supply and a few different power levels:
* 0.08 W in, 0.51 W out, (current not recorded)
* 0.16 W in, 4.07 W out, 2.3 A
* 0.26 W in, 11.0 W out, 3.6 A
* 0.51 W in, 28.8 W out, 5.8 A
The harmonic content was pretty terrible, as expected. I haven't added any low pass filter on the output yet. I've also heard that lower gate bias means more crossover distortion and non-linearity, so that makes sense.
https://media.tilde.zone/media_attachments/files/113/857/091/263/667/674/original/0399f7ef4a5e7898.jpeg

2025-01-19 21:01:06

- reply

3) Signal Generator
My options for generating the input signal are basically by BITX40 and my QMX. The BITX40 has a trimpot for its PA driver. But instead I went with the QMX and used its "SWR meter" mode.
The QMX lets you adjust the SWR test output power as a percentage of the voltage used for full power. So "100%" is full power, but "50%" is a quarter of full power (due do P∝V²). I measured the power for various settings using my oscilloscope (12.0 V, 7.100 MHz):
* 10%, 5.8 Vpp, 0.08 W, 19.2 dBm
* 20%, 10.1 Vpp, 0.26 W, 24.1 dBm
* 30%, 14.2 Vpp, 0.50 W, 27.0 dBm
* 40%, 18.6 Vpp, 0.86 W, 29.4 dBm
* 50%, 22.8 Vpp, 1.30 W, 31.1 dBm
* 60%, 27.0 Vpp, 1.82 W, 32.6 dBm
* 70%, 31.0 Vpp, 2.40 W, 33.8 dBm
* 80%, 35.2 Vpp, 3.10 W, 34.9 dBm
* 90%, 39.2 Vpp, 3.84 W, 35.8 dBm
* 100%, 42.6 Vpp, 4.54 W, 36.6 dBm
I also looked at the QMX output on the TinySA Ultra spectrum analyzer. There weren't any visible harmonics at all, so I trust that this signal is suitable as a test signal.
https://media.tilde.zone/media_attachments/files/113/857/024/638/161/881/original/d0ab2c3e093b2985.jpeg

2025-01-19 20:16:13

- reply

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.
https://media.tilde.zone/media_attachments/files/113/856/848/475/248/924/original/e22af96b3711e203.jpeg
https://media.tilde.zone/media_attachments/files/113/856/851/444/556/360/original/d07fecd45b19d383.webp

2025-01-19 20:05:05

⚡ 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
https://media.tilde.zone/media_attachments/files/113/856/795/553/948/056/original/f847bba97819504f.png
https://media.tilde.zone/media_attachments/files/113/856/799/164/209/808/original/76f118c5bc9b1b75.jpg

2025-01-19 17:29:45

- reply

I will post about the last days' tests later this evening when the kids are asleep and the chores are done!
https://media.tilde.zone/media_attachments/files/113/856/195/646/669/279/original/4c6cbe445200980b.png

2025-01-17 18:34:37

Got some power amplifier components in the mailbox:
• Switch that closes when hotter than 40 °C
• Switch that opens when hotter than 100 °C
• Switch that opens when hotter than 120 °C
• 2 × BN43-7051 ferrite binocular cores
• 10 × BN43-202 ferrite binocular cores
https://media.tilde.zone/media_attachments/files/113/845/117/501/233/684/original/e739a6b14836501c.jpg

2025-01-13 23:10:49

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
https://media.tilde.zone/media_attachments/files/113/823/567/594/146/821/original/bbfe3f182ff7ed2e.jpg
https://media.tilde.zone/media_attachments/files/113/823/568/277/877/627/original/fae725edaaffeb53.jpg
https://media.tilde.zone/media_attachments/files/113/823/568/806/962/750/original/6f334c8b400a4268.jpg
https://media.tilde.zone/media_attachments/files/113/823/569/970/506/160/original/1b56e8da0dc78ef2.jpg

2025-01-09 21:45:45

- reply

13) Checked bias and soldered FETs and feedback resistors
First I familiarized myself with the bias circuit. The pot adjusts the gate bias between 0 and 4.8 volts. Clockwise = increase bias. The pot also had stops at min and max, unlike what I've seen on others' videos.
Then I added the insulating pads and screwed the FETs in place. With everything at the right spot I soldered the FETs and the feedback resistors.
The amp should be ready for testing now, so this concludes this build thread! I'll start a new test thread next evening when I work on this, and probably more ones later for an enclosure and a LPF.
Thank you all for your encouragement and interest in this project! I've learned so much from the discussions that sparked off and carried on in their own directions!
#AmateurRadio #HamRadio #electronics
https://media.tilde.zone/media_attachments/files/113/800/583/998/657/236/original/afecedfed4ea8f3f.jpg

2025-01-09 11:32:10

- reply

I also run it on my server (which is reachable from anywhere) and on my Synology NAS (for backups).

2025-01-09 11:30:12

- reply

Syncthing for computers and Syncthing-Fork for Android.

2025-01-09 09:37:10

- reply

From the recording I can tell that everything above 1500 Hz or so is significantly dampened, which explains the muffled sound. I had a hunch that the BFO and crystal filter passband might not be properly aligned. It seems like that could be correct!
http://skywired.net/blog/2017/04/replacing-the-bitx-40-bfo/
I also found an explanation of how the BFO and filter are "factory aligned" from a BITX20 group.io post:
"11.059mhz is the nominal parallel resonant frequency of the crystals
The series resonant frequency (as used in the crystal ladder filter) is a few khz lower.
The old Bitx40 made use of this, the BFO oscillator used the 12mhz crystal in parallel resonant mode,
and happened to wind up at just the right frequency down from the 12mhz IF filter.
All those crystals were first sorted to be within 100hz or so of each other before stuffing."
https://groups.io/g/BITX20/topic/69443005
So the difference between the series and parallel resonance is cleverly used to get the offset from the BFO and the filter center frequency. Too bad that this apparently didn't work that well...
The PCB has an unpopulated place for a trimmer capacitor. I could add a cap there, or I could just go ahead and replace the BFO with one of the Si5351 outputs, which I wanted to do anyway (to get away from the 7.2 MHz spur and 41m broadcast band interference by switching between low side and high side injection).

2025-01-08 22:42:14

Tried a thing that has been on my to-do list for ages: listening to the signal that the BITX40 puts out! Here I transmitted into a dummy load and let the QMX pick up the RF using a small wire.
Here's an audio recording: https://raek.se/dump/bitx40_audio_test.mp3
A good thing is that the BITX40 both has a trimpot for the IRF510 bias *and* for pre-driver gain. That way I should be able to transmit at power levels below 7 watts too. The MINIPA70 power amp I'm building can't handle 7 watts on it's input, IIRC, so it's great that I can turn it down a bit.
#AmateurRadio #HamRadio
https://media.tilde.zone/media_attachments/files/113/795/108/088/087/674/original/9e55e13ad2dfe55d.jpg

2025-01-07 22:29:22

- reply

I just ordered a bag of 25 pieces. That'll give me some room for experimentation without worrying too much about running out of parts. I also ordered some binocular cores for future projects. Did you use BN43-7051 and BN43-202 cores for your amp?

2025-01-07 22:03:18

- reply

Maybe later this week I'll have the FETs in place with a heatsink so that I can tweak the bias.
I also have to find a suitable power supply. And probably an input attenuator of I'm going to be able to use/test the PA with the BITX40 (7W output).

2025-01-07 21:58:39

- reply

11) Soldered most of the remaining stuff
Next I soldered the ends of the transformer wires, the low pass filter bypass header, a temporary PTT switch, and the two SMA connectors.
All that's left now are the IRF530 FETs, the feedback resistors, and an external low pass filter.
https://media.tilde.zone/media_attachments/files/113/789/310/325/356/787/original/fbf7de5e5d4a044b.jpg

2025-01-07 07:35:47

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

2025-01-06 21:54:27

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

2025-01-06 21:46:02

- reply

11) Calculated Coupling Coefficients
I added calculated coupling coefficients to the spreadsheet in the previous post. "Coupling 1→2" means "Measuring at winding one with winding two opened and then closed an applying k=sqrt(1 - (Lshort/Lopen))".
https://media.tilde.zone/media_attachments/files/113/783/597/992/310/817/original/34443bc96e4247d8.png
https://media.tilde.zone/media_attachments/files/113/783/598/593/138/748/original/351cf1b64d7a1309.png

2025-01-06 21:20:07

- reply

10) Added transformer wires and performed lots of measurements
The measurements can be seen in this spreadsheet (screenshots added to this post for convenience): https://docs.google.com/spreadsheets/d/1481s1TLiWwiSgU1UrxgSDXqTYwXUrslObALEj7EQkOw/edit?usp=sharing
Most of these measurements were performed on yesterday's live stream on YouTube: https://www.youtube.com/live/wQLbCVtNCCQ
I measured both transformers at all thee windings with all the other windings open and shorted. I also measured the two "tube" windings in series as separate entries.
Any interesting patterns? Tell me if you find any!
So far I've seen that the one tube doesn't "see" whether the other tube is shorted or not, *except* when the wire joining the tubes is shorted. Others in this thread has argued that the coupling between the two tubes are so low that the halves of each transformer could be seen as its own transformer, only connected in series by the wire winding.
#AmateurRadio #HamRadio #electronics
https://media.tilde.zone/media_attachments/files/113/783/453/501/078/219/original/f08c074a31c08dca.jpeg
https://media.tilde.zone/media_attachments/files/113/783/456/351/959/822/original/bf9af1815e02370e.png
https://media.tilde.zone/media_attachments/files/113/783/458/734/300/902/original/5fe0f1bdc645c427.png

2025-01-06 16:00:08

- reply

How do you define "primary"? I always assumed it meant "input side", but from context I assume you mean the "wire" side (as opposed to the "tube" side).
If tube B is open and the wire side is terminated into a 50 ohm antenna, then surely the tube A side doesn't see 25 uH anymore? 25 uH is what you see when the antenna is unconnected, right?

2025-01-05 20:12:16

- reply

And I'm live!

2025-01-05 20:03:55

I'm about to live stream about the MINIPA70 build! Let's see how this goes.
https://youtube.com/live/wQLbCVtNCCQ?feature=share

2025-01-05 17:38:49

- reply

Hmm. Maybe I'll just measure all the combinations tonight. Livestream on my YouTube channel, maybe? (Anyone interested?)
#AmateurRadio #HamRadio #electronics

2025-01-05 17:30:24

- reply

Since last night the project looks like the attached pictures (haven't posted these pictures yet).
What measurements are you interested in? Measure one tube with A) yellow wire open (already did that, I guess) and B) yellow wore shorted? Any more? Maybe measure the yellow wire with the "tube winding" shorted/opened.
I need to measure this before soldering the yellow wires later tonight. 😄 Won't be until about 21:00 CET when the kids are asleep and the chores are done.

2025-01-05 08:57:40

- reply

9) Inductance check of tube windings (input secondary and output primary)
I measured both half-turns together in series:
Output transformer: 5.57 uH
Input transformer: 0.97 uH
https://media.tilde.zone/media_attachments/files/113/774/915/576/638/525/original/73f0ea5b556d074e.jpg
https://media.tilde.zone/media_attachments/files/113/774/916/740/371/908/original/0361a9bc9c80c7c7.jpg

2025-01-03 11:20:25

- reply

It's an independent search engine made by one guy in Sweden on his at home server(s). I like the kind of pages it finds. It won't find "everything" right now, of course but it's impressive that you dont have to be a tech giant to make a search engine that's actually useful!

2025-01-03 11:17:29

- reply

Have you checked out Marginalia? https://search.marginalia.nu/

2025-01-02 09:13:58

- reply

My home antenna has an SWR of about 1.5-1.6 on 40m. Do you think that will be an issue?

2025-01-01 21:59:05

- reply

An additional measurement: The red loop closed, but only through core "A": 0.9uH
https://media.tilde.zone/media_attachments/files/113/755/340/018/558/532/original/814ce7979e275220.jpg

2025-01-01 21:45:03

- reply

I ran the experiments now for the "double tube" case. I measured all these inductance values at the three windings around core "A".
Core with 3 turns (blue): 5uH
Add a second core ("B") next to it, thread a red wire through them but leave it open: 5uH
Join the red wire ends: 2.7uH
Short the three wires around core "B": 1uH
I don't have any spare binocular cores unfortunately. I've already soldered the ones from the kit in place!
https://media.tilde.zone/media_attachments/files/113/755/260/070/636/432/original/1120f01dcabd032f.jpg
https://media.tilde.zone/media_attachments/files/113/755/260/510/434/284/original/dec1376b27ec78a3.jpg
https://media.tilde.zone/media_attachments/files/113/755/260/935/896/147/original/6ba4f4e9a5d3d6fe.jpg
https://media.tilde.zone/media_attachments/files/113/755/261/377/335/466/original/bfb2447811c51cf4.jpg

2025-01-01 17:20:08

- reply

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
https://media.tilde.zone/media_attachments/files/113/754/241/957/728/151/original/c35219d25afc187c.jpg
https://media.tilde.zone/media_attachments/files/113/754/243/321/498/691/original/546d095835085c11.jpg

2025-01-01 16:48:31

- reply

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!
https://media.tilde.zone/media_attachments/files/113/754/114/863/437/748/original/7ed2b45e95cb1c4a.jpg

2025-01-01 16:13:38

- reply

Thanks for this! This explains exactly the part of transformers that has always been unclear to me. I'm in the middle of retracing your steps with pen and paper, so that I understand it myself!

2024-12-31 10:11:23

- reply

Exactly! If you put something like a 10 to100 ohm resistor in series with the sig gen you will limit the current to safe levels, I think (assuming you only put in a volt or so.

2024-12-31 10:04:22

- reply

Nice! I like the simplicity of that "interface"!

2024-12-31 10:03:00

- reply

Yeah, with the sig gen and scope you can already do most of the basic measurements! Video signals are usually in the hundreds of megahertz range, so at 2 MHz the signal might see a lot of attenuation if filters or tuned circuits are involved. My hunch is that you would still be able to see the difference between switched open and closed, though!

2024-12-31 09:06:27

- reply

Sorry for the VNA tangent, but the NanoVNA is just such a useful RF multitool!

2024-12-31 09:05:05

- reply

What do you want to use this switch for? Its original purpose? Or are you about to rework it to some other kind of switch?
As "You're all idiots" pointed out, it can make sense for all the circuit nodes to be shorted *at DC*. The appropriate tool to measure how much of an RF signal propagates through from one port to another is a VNA. The NanoVNA is a *very* affordable one for hobbyists, should you want to get one.
Basically it sends out a sine wave signal into one port and measures how much bounces back to that port and also how much is received at the other port. You get both the change in amplitude and phase and from that the VNA can calculate all sorts of useful values, such as complex impedance.

2024-12-30 21:24:38

Found a book with ALL the meters. 😂
https://media.tilde.zone/media_attachments/files/113/743/879/047/129/518/original/b08f8dc182dfab8d.jpg
https://media.tilde.zone/media_attachments/files/113/743/879/476/054/188/original/0c8411bd4198df20.jpg
https://media.tilde.zone/media_attachments/files/113/743/879/707/475/338/original/39fd8223651a6773.jpg
https://media.tilde.zone/media_attachments/files/113/743/879/929/058/461/original/549f4ea79a309b5f.jpg

2024-12-30 09:31:31

- reply

The original schematic says "13.8 V". I don't know now if it's possible to get 70 W at that voltage, though. Feels like too low voltage? The IRF530s might put out more power than the IRF510s for the same voltage though. My QRP Labs 50W PA (which uses IRF510s, also in push-pull) puts out 38 W at 19 V (not linear), for reference.
Here's a very nice write-up by F5NPV I forgot to mention before: https://f5npv.wordpress.com/irf530-mosfet-amplifier/ A lot of good information there (as well as the original schematic)!

2024-12-30 08:28:08

- reply

Wow, that looks very cool!

2024-12-30 08:06:15

- reply

I bought this one: https://www.aliexpress.com/item/1005005067657667.html
There are plenty of sellers that sell the same kit on AliExpress and Ebay. There is a 100 W variant too that has one of those white double transistors instead of the two IRF530 transistors.
Note that the one I linked does not come with a heatsink, but I think there are others that have that included.

2024-12-30 07:55:15

- reply

Oops! That should have been 5.6 ohms. 50 ohms divided by 9.

2024-12-29 21:35:13

- reply

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
https://media.tilde.zone/media_attachments/files/113/738/068/672/033/250/original/9587d0e6c2288b5f.jpg
https://media.tilde.zone/media_attachments/files/113/738/068/975/922/522/original/893d9bba8d78a2d0.jpg
https://media.tilde.zone/media_attachments/files/113/738/251/292/597/636/original/031611d03efaaad7.jpg

2024-12-29 19:44:38

- reply

Yes, and I have a QRP Labs 50W (non-linear) PA that works really well for those modes! It's interesting how much simpler the design seems to be if linearity is not required.

2024-12-29 19:40:37

- reply

I did use a center punch, but the drill moved sideways a bit anyway. Maybe I pushed unevenly. (My drilling machine is heavy and bulky.) A pilot hole might have helped?
I'm not sure what the appropriate amount of speed and vertical pressure is. The shavings/dust appeared very slowly. It took a long time and I felt that not much happened most of the time. Maybe the drill bit was dull too.

2024-12-29 16:15:48

- reply

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
https://media.tilde.zone/media_attachments/files/113/736/957/273/393/370/original/040976c21a00fb46.jpg
https://media.tilde.zone/media_attachments/files/113/736/957/610/702/922/original/25c82379f1ac7f55.jpg
https://media.tilde.zone/media_attachments/files/113/736/957/905/009/368/original/b60cd7c86a2abbe7.jpg

2024-12-29 15:54:12

- reply

4) I would like to thank @npub1dgh…gkrs and @npub1gyz…sgj4 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

2024-12-29 15:48:28

- reply

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!

2024-12-29 15:36:05

- reply

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.
https://media.tilde.zone/media_attachments/files/113/736/845/259/401/727/original/b42d505298746b7b.jpg

2024-12-29 15:24:02

⚒️ 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
https://media.tilde.zone/media_attachments/files/113/736/712/363/492/495/original/f4cfae0dd1a07523.jpg

2024-12-28 23:04:23

- reply

Thanks for sharing this! I listened to "Liturgy of Light" from this album a lot a while ago (I don't remember how I found it). Your post made me curious about the rest of the songs, so right now I'm listening to the whole album from the beginning!

2024-12-23 11:36:35

- reply

I don't know how keyboard drivers react to that, but the corresponding thing with serial ports (one USB device, multiple serial port functions) does work in exactly that situation. Example code: https://github.com/hathach/tinyusb/tree/master/examples/device/cdc_dual_ports
TinyUSB had keyboard examples too. Sounds like a fairly easy and doable experiment to try the dual keyboard combo!

2024-12-07 12:40:20

New video: #4: SAQ Grimeton 100 year anniversary Dec 1st 2024
A short, not very detailed, recording of last Sunday's transmission.
https://youtu.be/zlng3dPs2xM
#SAQ #Grimeton

2024-12-05 19:37:15

- reply

"pudb some_script.py"! (PuDB is a Python debugger with a TUI)

2024-11-30 22:20:39

New video: Day before SAQ Grimeton 100th aniversary - audio setup and morse decoding
https://makertube.net/w/59bCS2QyacTwvpb9rHWQBB
https://youtu.be/K2HJZrTma5o
#AmateurRadio #HamRadio #SAQ #Grimeton

2024-11-27 09:26:41

40m low pass filter done. Next: measure with NanoVNA H4.
Then I also want to try the noise source I brought a while ago and measure with the TinySA Ultra
#AmateurRadio #HamRadio
https://media.tilde.zone/media_attachments/files/113/554/197/452/094/622/original/8fac7c69c78504d7.jpg

2024-11-26 08:18:44

- reply

What antennas have you used? Any favorites?
Mine is simply the one from the kit (the coil former was pre-made and I just wound the wire). I hope it will receive well. I live somewhat nearby, so I'm optimistic.

2024-11-26 07:56:44

Hey, there's another ham (@npub1zft…c7tn) 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

2024-11-25 22:45:00

Spontaneous evening project: Halfway finished an external 40m low pass filter for the QRP Labs 50W PA. I built the PA with the 20m internal LPF, and this new board allows me to connect an external 40m one on the output to make the PA dual band.
To switch bands I'll insert or remove this board from between the PANand the antenna coax
Thanks to Adam Kimmerly K6ARK, who came up with these boards and kindly sent some to me!
This was also a good time to browse through the tribal wisdom from GQRP Club regarding harmonic filters. It saves a lot of time when someone has compiled the relevant data like that.
https://www.gqrp.com/harmonic_filters.pdf
https://www.gqrp.com/Datasheet_W3NQN.pdf
I was also lucky that the caps left over from the 20m internal LPF were exactly the values needed for a 40m LPF. I also had some T37-6 toroids, so the only parts I didn't have at home were the BNC connectors. I will use SMA connectors and adapters in the mean time.
#AmateurRadio #HamRadio #Electronics #QrpLabs
https://media.tilde.zone/media_attachments/files/113/545/959/076/166/568/original/b91ff02a5eb6c9f7.jpg
https://media.tilde.zone/media_attachments/files/113/545/963/909/952/273/original/5254978519c2ea57.jpg

2024-11-19 13:53:29

- reply

I got an Rigol DS1054Z for about 400 USD some years ago and I'm happy with it. It's an entry level four channel oscilloscope. The DS1054Z+ variant also has digital inputs, so I think it can be used as a logic analyzer.
https://eleshop.eu/catalog/product/view/id/625/s/rigol-ds1054z/category/82/
Pros:
* Very affordable
* Four channels
* Simple protocol decoding
* Screenshots to USB or ethernet
* XY mode
* Automatic measurements (frequency, Vpp, Vrms, etc)
Cons:
* UI slightly laggy
* FFT function not very useful
The Rigol DHO914S also looks sweet. I've seen one IRL. but not played with it yet.
The Saleae logic analyzer is a sweet tool to have. If you don't care about fancy analog measurements, it might be an even better fit for you. (The Saleaes do analog too, but I haven't tried it.)
https://www.saleae.com/
There are very cheap logic analyzers available. I've used one of them together with the Sigrok software on Linux.
https://www.ebay.com/itm/315741037663

2024-11-18 22:11:53

The Grimeton receiver works!
https://makertube.net/w/3SuzodSsMBXaxoSWQNSpse
https://www.youtube.com/watch?v=ZcDiItMRFJ0
#AmateurRadio #HamRadio #electronics #SAQ #Grimeton

2024-11-09 20:20:05

#LambdaCalculus described using #TokiPona.
https://github.com/japi012/nasin-lanta-kakulu
I love these deep/profound-cute/silly combos...

2024-10-31 10:28:23

The Swedish Social Insurance Agency (Försäkringskassan) has now open sourced (MIT license) their "design system":
"The main objective of the design system is to create accessible reusable components. It is composed of the component framework along with related design documentation. We aim for all components to fulfill WCAG 2.2 AA (or higher) and the EU accessibility directive (EN301549). All components are tested both manually and with automated tools on a large range of devices."
https://github.com/Forsakringskassan/designsystem

2024-10-28 11:28:14

- reply

I liked this variant (slides for a presentation) even better: https://indianaaes.org/wp-content/uploads/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf

2024-10-28 09:37:08

I learned a lot from this article:
"Understanding, Finding, and Eliminating Ground Loops" by Bill Whitlock
https://lab.wempec.wisc.edu/wp-content/uploads/sites/657/2018/01/EST016_Ground_Loops_handout-1.pdf
#electronics

2024-10-26 07:31:38

I made a video!
https://makertube.net/w/tDbiq6nvq85bWSdSWQPWmN
https://youtu.be/SR93dgEMDGA
#AmateurRadio #HamRadio #electronics #Grimeton #SAQ #VLF

2024-10-15 11:47:01

GPS disciplined signal generator / UTC shack clock. Sweet!
Kit from QRP Labs.
#AmateurRadio #HamRadio #electronics
https://media.tilde.zone/media_attachments/files/113/311/272/614/375/159/original/f5d0eade873708ca.jpg
https://media.tilde.zone/media_attachments/files/113/311/273/024/057/807/original/99665566a0c2dc0a.jpg

2024-10-09 07:30:15

- reply

I like to browse Cryptomuseum and just look at the cold war radio tech. Take a look at these two, for example!
HVĚZDA IV by Správa 6 (Czechoslovakia, 1961)
https://www.cryptomuseum.com/covert/radio/cs/hvezda4/index.htm
RF-015 by Panasonic (Japan, 1977)
https://cryptomuseum.com/covert/radio/panasonic/rf015/index.htm
https://media.tilde.zone/media_attachments/files/113/276/287/393/304/634/original/23fc20e77c594452.jpg
https://media.tilde.zone/media_attachments/files/113/276/288/854/484/459/original/c15ae23c4e616d6e.jpg

2024-10-01 17:40:14

- reply

Yeah, I was told later by M0TTQ that it is a special event station (and I know they tend to have unusual callsigns). I think I was interpreting the "G" as part of a "GM/GA/GE/GN" following.

2024-10-01 16:50:51

- reply

It turned out I got their callsign wrong. It was supposed to be "IR2RMAG"! I listened back to the recorder audio. The other station misheard my callsign as "SA5WJU"...
Now that I think about it I actually remeber seeing that on the QMX decoder display, but I didn't trust that the QMX "knew better" than the other operator.
Mistakes happen. I'm glad that I recognize when someone else repeats my callsign. But I think I need to pay attention and make sure all the letters are correct too. That'll come with time, I'm sure.
#AmateurRadio #HamRadio #CW #MorseCode #morse

2024-10-01 12:21:39

- reply

The first QSO I also recorded thanks to the QMX implementing a USB sound card. It was just a matter of starting Audacity and hitting the record button.

2024-10-01 12:15:15

Made two #CW QSOs today! Now I have three in total.
20m is not very noisy at my QTH, so I could use the QMX to help me decide the #MorseCode. I responded to the other person's CQ with a simple "BK RR UR 599 599 BK" in both cases.
In the second contact I used the PoLo #POTA spots tab to find the operator. It's very convenient to have the spots in the logger, because PoLo allows you to just tap the spot to fill in the callsign, band, mode, frequncy and POTA reference into the new log entry automatically!
This time I used the Morserino "CW practice gadget" as my (touch) CW keyer. I've gotten used to the touch keyer and I quite like it!
#AmateurRadio #HamRadio #morse
https://media.tilde.zone/mastomedia/media_attachments/files/113/232/064/590/874/790/original/9b6ccba5d9ac66b3.png

2024-10-01 11:50:07

- reply

There is a nice list of ham radio mastodon instances here: https://fediverse.radio/
Some of them work very closely (at least mastodon.radio and mastodon.hams.social and probably one or two more) and have some kind of link so that the local timelines are common.
There is a Ham Radio Workbench episode where Christopher (admin mastodon.radio) is a guest and Smitty (admin of mastodon.hams.social) is one of the hosts.

2024-09-26 07:27:41

mi alasa e kiwen kasi. ni li musi li pona tawa mi. #tokipona
https://media.tilde.zone/system/media_attachments/files/113/202/666/860/901/567/original/b96f5cab7b294b3c.jpg

2024-09-24 04:45:56

- reply

That explains why Jadon KJ7RBS on the QRP Labs managed to get Vara working on the QDX:
"QDX/QMX VARA settings and Winlink" https://groups.io/g/QRPLabs/message/119189

2024-09-23 20:18:48

- reply

It receives SSB but cannot send SSB. It can send a single "carrier" though, so most of the WSJT-X modes work. The QMX does that by emulating a sound card and measuring the frequency of the audio waveform the PC sends to the QMX. It then uses the Si5351 chip to synthesize the corresponding RF frequency directly.
One ham on the QRP Labs groups.io group supposedly had success with using one of the Winlink modes in the slowest settings, even though it wasn't supposed to work.
I might need to research if there are any VHF/UHF nodes nearby so that I can use my HT.

2024-09-23 20:00:53

- reply

Thanks for the rekommendations! Others have pointed to KM4ACK's video series as well, and I watched one of them. Looks promising!
I tried to get my user credentials using pat and telnet, and that actually worked! (I haven't run any "native" Winlink client yet.) I will continue to play around with pat a bit.

2024-09-23 17:54:35

- reply

That looks very interesting. I will take a look!

2024-09-23 13:40:05

- reply

...- .. ...- ..- ...-

2024-09-23 13:27:12

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

2024-09-23 13:13:53

- reply

.--- .. -.-- .- .---
- .-.. .... .. -. --. .- -. .... --- .-.. -.. .- .--- .- - .-.. .... .-.. .- .... .----. .- .----. ..--..

2024-09-22 19:23:40

- reply

There is also the Morserino project, which does all kinds of things. It is well worth checking out if you haven't seen it already!

2024-09-22 19:21:56

- reply

You could use any of the Arduino boards with native USB (Leonardo is one, but there are probably lots of them) to turn your key into a USB keyboard (which send a spacebar key down/up event when you press/release the key). I think they mentioned such a project on the Ham Radio Workbench podcast.
I made a similar project to connect an NES controller to a computer by emulating a keyboard: https://gist.github.com/raek/e8ee0b7e0801ef27c477c4333ec3e066
That example could be stripped down to only check a single bit instead of reading eight bits from a shift register

2024-09-22 13:27:49

- reply

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

2024-09-22 13:24:51

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

2024-09-19 09:52:29

- reply

poki toki mi li laso mute.
mi toki e nasin ni kepeken ilo uta:
"toki toki toki! ni li Sijela Alapa luka Lomejo Julije Sijela, Sijela Alapa luka Lomejo Julije Sijela. o toki tawa mi. mi kute."
taso tenpo ni la, jan ala li toki tawa mi. tenpo ante la, mi toki kin.
poki toki mi ni li wawa. mi pali e poki pi poki toki mi. lupa ilo tu tu lon sinpin ona li ni:
* ilo kute
* ilo uta
* ilo nena tawa toki
* ilo luka tawa sitelen kepeken kalama pi tenpo wawa kepeken kalama pi tenpo lili
#TokiPona #AmateurRadio #HamRadio
https://media.tilde.zone/system/media_attachments/files/113/163/565/863/458/882/original/661f9cee977af640.jpeg

2024-09-19 09:02:19

I started think about #TokiPona again. There's something delightful about the semantic space spanned by the Pu word list and how the words are so broad in meaning, but still point to such immediate and experienceable concepts.
mi wile pali e sitelen tawa lipu linluwi mi. sina wile ala wile lukin?
mi sona ala e ni: "radio" li seme kepeken toki pona? ijo "radio" li "poki toki" tawa mi. taso, toki "radio" anu kon "radio" li seme? ni li "radio waves" kepeken toki Inli.
ken la, ona li "kon toki sewi"? ijo "antenna" li "linja sewi" tawa mi."
mi tawa.

2024-09-16 07:50:31

- reply

An FTDI USB to serial cable and a NanoVNA.

2024-09-13 19:49:55

- reply

Thanks for the tip! Using the "pile-up control system" linked from the QRZ page, I managed to get a slot in the pile-up with my 7 watt BITX40. I got a 51 report (not very surprising). I'm very happy to actually make a QSO with this kit-build radio (I can count them on one hand)!
#AmateurRadio #HamRadio

2024-09-07 17:16:20

- reply

Cool! What is that thing under the QMX? A tuner? Its size matches the QMX very well..

2024-08-30 16:40:46

- reply

Yes, IIRC you don't get the sbi/cni instructions with GCC unless you enable some optimizations. Otherwise you get the c-ish "naive" machine code. -Os is a nice level too (optimize for size)