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.
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.
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.
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.
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.
https://www.abc.net.au/listen/programs/nightlife/tech-talk-with-peter-marks/104924906
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:
Documentation on Hackaday:
https://hackaday.io/project/
SolderSmoke YouTube channel:
https://www.youtube.com/@
SolderSmoke blog DCR posts:
https://soldersmoke.blogspot.
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.
Discord is a kind of chat board where a group of people can create topic channels and basically talk back and forth in real time - if they wish.
Bill and Dean at Soldersmoke have embraced the form and created a fantastic place where many of us are sharing our issues, if they arise, and helping each other to debug things. The "smokers" are both there but also there's a good deal of constructors helping each other out.
My receiver has been re-built a few times and currently looks like this:
Bill urges us to stick to the design but some of us have had to substitute components or, in my case, due to the lack of an audio transformer that works, add a bit of extra audio gain in the form of an LM386 module.
Several builders have found that we get less output from the VFO than Bill or Dean do and the tell-tale squared off waveform at the input to the diode ring mixer isn't there. It's hard to know what the root cause is but presumably it's component variations or perhaps the "brass" screw material, which, in my case quenches oscillator level as it goes in to the coil. (Adding a 0.1uF cap across the resistor in the source of the buffer FET helps).
The Discord is broken out into channels for the oscillator, mixer, bandpass filter and audio amplifier.
You can join via this link (which will expire in a week). After that check out the Soldersmoke blog for new info.
Congratulations to Bill and Dean for this innovation.
My receiver is working quite well, thanks in particular to VK3ZZC who gave me some NP0 capacitors that have stopped the massive thermal drift in the VFO. It is very satisfying tuning 40m listening to stations - sounding really good - on a home made receiver.
If you are new to home brew radio construction, this is a good way to get started with a community of helpful people.
One important note, if you are going to attempt this project, there have been some changes to the schematic and the latest version is on the Discord in the #schematics channel.
https://www.abc.net.au/listen/programs/nightlife/tech-talk-with-peter-marks/104869386
