On the cover of Rolling Stone!

Regular readers will know that I'm a big fan to the SolderSmoke blog and podcast. Inspired by their recent direct conversion receiver challenge I built the receiver. It did not go smoothly and in retrospect that's good as I learned many valuable lessons along the way.

After the success of the receiver, it's not a big leap to make a double sideband transmitter. I built one for 80m using some circuits described by Peter VK3YE and Drew VK3XU. It went amazingly well and last Wednesday I called in to two 80m nets and got good reports. My audio was described as "highly fidelic" and a glance at an SDR showed that my audio bandwidth was over 10kHz (and because of double-sideband twice that). Bad boy!

Along the way, I made videos of the receiver and transmitter, including audio sent in of my signal received in Tasmania and Bill posted a nice item about it all on his blog.

I would be calling for Bill and Dean to grace the cover of Time Magazine but that may not be a positive thing any more. 

Now I'm worried that he'll have a link to this post which links back to his post and this could cause internet feedback.

Thanks Bill.

Tech talk on ABC Radio

A breakthrough in computer chips, a new and supposedly cheap phone from Apple and how to avoid to paying higher prices for Microsoft Office 365. Peter Marks, a software developer and technology commentator from Access Informatics, joined Philip Clark on Nightlife to discuss the latest news in technology. 

https://www.abc.net.au/listen/programs/nightlife/nightlife-tech-talk-with-peter-marks/104981308

Joined two 80m nets with the double sideband transmitter

Great fun tonight. First I joined the Tasmanian tech net with the double sideband transmitter and later the Macedon Ranges net. Good reports from both. It's a pretty rough and ready transmitter:

There were reports of my wide bandwidth, not just the other sideband, and I can see on a local SDR that my signal is very wide.

Despite all this reports were quite positive and I'm grateful for that.

It's a very encouraging start. Thanks for the valuable feedback.

Victorian country train radio chatter

With all the government radio going to digital trunk radio I was surprised to find that communication between driver and guard, and sometimes station and driver, is via standard FM radio. Today I caught a train from Kyneton to Southern Cross station and recorded what I heard.

Mostly it's the guard saying when passengers have finished getting on and off but at about 48 seconds you'll hear Sunbury station ask us to wait due to a train broken down ahead.

To record this I made a 30dB pad with DC isolation so I could listen in headphones and also feed audio into the powered mic input on a voice recorder.

Amusingly I heard the driver refer to a city train as "the sparks". I guess they are electric while the country trains are diesel electric.

A visit to the National Communications Museum

Today Nigel, VK3DZ, Ralph, VK3ZZC and I visited the National Communications Museum in Hawthorn, Melbourne, Victoria. It's a very modern museum, a bit expensive to get in the door but they have a great collection of old communications gear of historical note.

There's a huge collection of telephones, from payphone, to dial to mobiles.

There is also a working telephone exchange and some wonderful switchboards.

A fine collection of test gear is on display although we have some concerns about the CROs which are left on sometimes with a very bright spot showing.

I particularly enjoyed the optical disk talking clock.

We had the place to ourselves today although I imagine at times it's teeming with kids. I do recommend a visit although I'd have to say at $30 to get in it's a bit steep. The website is very modern looking and very bad to use. The staff seemed nice though.

Double sideband is back (well, maybe)

There has been some discussion on the Soldersmoke direct conversion receiver Discord chat area about a possible next project for builders who have got the circuit (as described) going. One idea that comes to mind is to re-use the VFO and perhaps the diode ring mixer and make a double sideband transmitter.

On Wednesday I participated in the excellent Northern Tasmania Amateur Radio Club's tech net on Wednesday and was entranced to see VK3DGE was running double sideband. (7:30pm on 3567).

It sounds a little bit funky but fully readable to me. He mentioned he's using a home brew amplifier but didn't mention anything about the exciter.

Tech talk on ABC Radio

Last night on ABC's Nightlife program Philip Clark and I discussed AI going mainstream, in that it was featured in Super Bowl ads, the UK wanting a backdoor to Apple's iCloud encryption, and will the US mandate AM radios in cars as part of emergency communication infrastructure?

https://www.abc.net.au/listen/programs/nightlife/tech-talk-with-peter-marks/104924906 

Soldersmoke Direct Conversion Receiver - Lessons learned

There's nothing more satisfying than listening to a radio you've built yourself. The Soldersmoke Direct Conversion receiver has given me that satisfaction in spades. Here's a little demonstration and discussion of things I learned along the way.

Now, to re-visit the shelf of shame and try to get some past failed projects working!

Join the discussion - SolderSmoke Discord Server:

https://discord.gg/Fu6B7yGxx2

 

Documentation on Hackaday:

https://hackaday.io/project/190327-high-schoolers-build-a-radio-receiver

 

SolderSmoke YouTube channel:

https://www.youtube.com/@soldersmoke

 

SolderSmoke blog DCR posts:

https://soldersmoke.blogspot.com/search/label/TJ%20DC%20RX

Beware of FNIRSi transistor testers

The Soldersmoke DC receiver project has been great fun but also quite frustrating. I got it working nicely if I used an external amplifier but the described three transistor high gain audio chain gave hardly any volume into my speaker. This has out-foxed me for far too long. I'm using 2N3904s with no particular manufacturer marking on them so had determined the leads using my fancy new FNIRSi component tester.

It's a bit hard to read in the photo but facing the flat side, the tester says the leads are C B E. The audio chain was working and had gain but I never got enough volume in the speaker. Nate, KA1MUQ, questioned the orientation of the transistors. I turned one around and there was lots more gain! Testing again, with my old clunker component tester gives the correct pinout.

Again, facing the flat site, but now the pins go E B C. Surprisingly different gain too hFE=170 compared to hFE of 215.

I was able to listen comfortably to sideband contacts with the amplifier driving a speaker directly.

Now my problem is "heartache of oscillation" (contrasting the "joy of oscillation" when building the VFO). The audio chain is very keen to take off at hundreds of kHz.

I found that even having the volume control off the board was enough to create instability. I've put it right back on the board and now all is working well.

Lessons learned: Component testers might not be right and transistors will work to some extent if wired with C and E swapped.