Saturday, February 25, 2023

80m dipole stretched significantly

Very lucky here to have the space, and appropriately placed trees, to allow me to put up a full size dipole for 80m. By all reports it works very well. This week, prompted by VK3LRJ, I tested the antenna and found that resonance had moved down quite significantly.

The band edges (black bars) are 3.5Mhz and 3.8Mhz.

The weekly club net is on 3685 so that's quite a bit away from where the antenna is now. I pulled it down, cut off a bit and folded back the ends. I think I shortened it by about 500m.

Much better! The 7300's built-in tuner has no trouble but it's good to not suffer the losses in the tuner if possible. 

The wire I'm using is figure-8 speaker wire split so I guess it stretches quite a bit. So far it looks to be in good shape but I don't expect it to last forever.

Thursday, February 23, 2023

High School Direct Conversion receiver

After deviating from Bill's design I have come back to the fold and built the mixer as he described. Another insight is that I've come around to putting each functional stage on a board of its own rather than trying to build the whole project on one board. I don't have a 1k:8ohm audio transformer so I used a powered speaker purchased at the MRARC auction last week and that seems to hum for some reason when connected (I tried battery power on the radio).

My VFO drifts wildly but with care it can be made to work. Here's a bit of reception from 40m this morning.

Next I connected VK3HN's VFO up and see how that sounds.

Rock stable as expected but I get clicks as I tune. 

Friday, February 17, 2023

VK3HN's Si5351 VFO in a DC receiver

I built a DC receiver using the PTO VFO based on the "High School" receiver described by Bill, N2CQR, recently. It's a beautiful thing to behold but for various reasons (no NPO caps for one thing) my build drifts like mad. It would make a fine Theremin.

I mentioned this to Paul, VK3HN, and he commented that analog VFOs do drift. He had kindly sent me a sample VFO / Controller board he's been developing for his amazing home brew "Summit Prowler" rigs.

It's a nicely conceived board with an Atmel chip that can be programmed as an Arduino Nano, Si5351 clock generator - with output buffers, connections for a parallel LCD but also I2C, connections for a rotary encoder and spares for various buttons. I had promised to give him feedback on it many months ago.

Here's VK3HN's blog post about itHere's the circuit. Here's his firmware.

Paul's code has all sorts of specialisation for his various rigs but my needs are much simpler so I've created a stripped back version that is just a VFO. Here's my code. I'm using a 128x32 OLED display instead of the LCD and have swapped in a different rotary encoder library.

The rotary encoder tunes and pushing the button changes the tuning step.

Feeding a TUF-1 mixer and then to a few transistor stages and an LM386 module it does actually receive although I have hum which is not uncommon with DC receivers. My "bench spread" construction doesn't help of course.

Arduino boards.txt

There's always something to learn on these little projects. Paul's board inadvertently ended up with an ATMega328 instead of the ATMega328P that the Arduino IDE expects to see in a Nano. Paul suggested turning on logging of the upload phase, capturing the generated avrdude command line and editing the processor type to drop the "p". 

I did that for a while, and it worked fine, but I wondered how hard it was to add a slightly modified board to the IDE. I'm using Arduino IDE 2.x but the support files (on macOS) are at:


Documentation on how to add boards is here.

I just copied the Atmega328p and made a Atmega328noP

Thanks to Paul, VK3HN, for sharing his code and design.

Friday, February 10, 2023

VR Presentation at the Kyneton Men's shed

Kyneton local Tim Sullivan from Sullivan Studios kindly put on a presentation about VR (Virtual Reality) at the men's shed this morning.

We took turns experiencing a visit to Venice, fishing, shooting and flying in a Meta Quest 2 headset (which I see sells for A$629).

While this was totally new to most of the people present, (there was a suggestion that some had come to learn about Vic Rail), I had played with an Oculus Rift headset some years ago.

The response to head movements was pretty good and the graphics was much improved over the past but I feel there's a way to go and certainly the price of headsets needs to come down for mass market appeal.

Tim predicted that mobile phones will be "gone" in three years, which rather surprised the audience.

Some stories of people with restricted mobility being able to virtually travel and see the world - or in one case visit their home country of Italy during Covid - illustrate the power of this technology.

I look forward to even more resolution in the future and I showed Tim how Apple's "Look Around" feature in their maps looks to be ready for VR headsets already.

The headsets will need to get much less bulky to be worn for extended periods but that day will come.

It was great to have such an interesting presentation at the excellent Kyneton Men's shed.

ACMA should do more to prevent and trace scam SMS messages

Like everyone I'm sure, I receive regular SMS messages and calls which are clearly scams. While I think I'm pretty good at recognising them it wastes my attention and I worry about people less able to realise what they are.

This morning ACMA announced a penalty for a Telco who was allowing customers to send SMS messages with text names without having processes in place to check that they weren't being sent as part of a scam pretending to be a trusted organisation. I have received messages that appeared to come from NAB.

The ACMA scam page is worth a read. Here's a few recent messages I've received (The numbers are certainly fake and may belong to real people so please don't harass them):

OK, maybe that last one isn't strictly a scam...

Surely we have the technical capability to trace who is sending these and either prosecute or at least block them? I see the ABC has a report on this.

Thursday, February 09, 2023

Stephen, VK2BLQ's excellent build of the Soldersmoke Direct Conversion receiver

While I deviated from the design, mostly due to deficiencies in my parts collection, Stephen, VK2BLQ, has built a faithful copy and it works!

Stephen is on the way to fame and fortune (well, fame) and it's well deserved.

Here's bill's original post, but check the blog for updates.

Sunday, February 05, 2023

Ballarat radio fest - another excellent show

Today was the Ballarat radio fest. About an hour's drive from my place at Drummond and well worth the trip. There was a big turnout and we weren't disappointed with the second hand, and some new, gear on offer.

I bought some BNC through panel connectors, (female on both sides), some BNC crimp connectors, some adapters and the big purchase was an Emtron tuner for $90. It seems to be in excellent condition.

Since moving back from Sydney to Melbourne I've been very impressed with the quality of hamfests here. Perhaps not as big as Wyong but arguably better gear on offer at better prices.

My thanks to the Ballarat club who did an excellent job of organising the day.

Saturday, February 04, 2023

My terrible build of the Soldersmoke DC receiver

Bill Meara of the wonderful Soldersmoke blog and podcast, recently published a nice design for a direct conversion receiver. He was looking for people to build it as described to check that the design was reproducible. I'm sorry to say I diverged in a few ways:

  • Used a TUF-1 mixer
  • Used an LM386 audio amplifier
I've done all sorts of things wrong, leads are too long, I didn't have any temperature stable (NPO) capacitors so the VFO drifts terribly.

My lame excuse is a poorly stocked junk box.

It needs to be boxed up and shielded but it is now working and with care I can listen to stations on 40m sideband quite nicely.

This morning I watched Bill's video of his version and spotted a ground strap to the nut in the PTO. I thought that might have solved all my problems! I think it helps but it's certainly a good idea to reduce the effect on tuning of a hand being near by.

Not good but it's satisfying to build something and use it to do ham radio. This is just a start. I can certainly recommend a direct conversion receiver project for anyone who longs for the joy of oscillation.


I didn't have a 9.1V zener so had substituted a 6V three terminal regulator with two diodes on the earth pin. There was oscillation which I had reduced with bypass capacitors but still the waveform was a bit fuzzy on the peaks. Today some Zeners arrived so the regulator is gone. The VFO signal now looks excellent.

Temperature stability is poor and my hand affects the frequency. Paul, VK3HN, kind of predicted this. Still a fun project.

Wednesday, February 01, 2023

Tidy bench for a new month

My bench in the shack got very very messy. I had a desk lamp on there and all sorts of junk.

Of particular note is the LED strip light I bought at the Wyong field day a few years ago that I've screwed under the shelf. Removing the desk lamp was a big help. Electronic projects are sure to work for me from now on!