Just go to http://soldersmoke.com. On that archive page, just click on the blue hyperlinks and your audio player should play that episode.
http://soldersmoke.com
In the course of working on my 160 meter AM station I came across a strong AM signal a bit below Top Band. Turns out it is part of something called the "Travelers" Information Service." The signal from this system on 1.670 MHz is very strong here. A Shortwave (Midwave!) Listener in Austria heard it too. Check out the confirmation letter from the Virginia Department of Transportation. Nice of them to do this. Here is the QSL letter sent to Austria: https://remotedx.wordpress.com/2014/06/01/very-rare-reception-vdot-highway-advisory-radio-1680-khz/ They are running 10 watts into a 49 foot tall vertical with 40 radials. They have a text-to-speech system that is constantly describing weather conditions. Quite useful actually. I found a web site that lists all the stations of this kind in the US:
Thanks to Peter Parker VK3YE for alerting us to this beautiful receiver from Bore 4O6Z in Montenegro. This may be our first ever report on a Montenegrin rig. And it is a thing of beauty. Bore says it is based on a phasing circuit by homebrew legend V. Polyakov, RA3AAA.
It is snowing here today, so I am stuck in the hamshack. YEA!
I've had the Hammarlund HQ-100 receiver on the bench because I am building an outboard digital frequency readout for it and for the DX-100. More on this later. But as long as I had it on the bench I decided to do a mod to the audio output that has LONG been needed.
Here is a nice web page that describes the problem and the solution. The problem is the "Auto Response audio output circuit" touted in the add up above. Essentially I had to remove the touted circuitry. The AutoResponseectomy only took me about 15 minutes and the results are quite noticeable. The old receiver sounds a lot nicer. I'm listening to 40 meter AM now. FB.
I listened to it as I aligned my HQ-100 receiver and worked on a digital frequency readout for the old receiver. The interview was the perfect accompaniment for such a project. Inspirational stuff. Lots of great info on QRPp and homebrewing. Mike talks about some of his more famous rigs including the voice-powered New England Code Talker (pictured above).
I loved the story of Michael carting his DX-100 home in a wagon. And I really sympathized when he described the harsh reaction of the phone operator to his early efforts at voice modulation.
Strongly recommended! You won't be disappointed. Great interview. Thanks to Eric and Mike.
Hi Bill I thought I would drop you a quick line to show you something I have been playing around with for the past couple of weeks. It's a SSB superhet using a PJRC Teensy 3.1 microcontroller (YouTube link below), and a great audio library by Paul Stroffregen. Suffice to say I'm really happy with it.
There is a direct conversion front end, albeit using a VFO 15kHz down from the incoming RF. The 15kHz IF is then fed into the Teensy audio line in which can handle up to 22kHz. From there everything is in software. First is a 2.4kHz BPF tuned to the LSB, followed by mixer with a 15kHz BFO. Finally, there is a 2.4kHz LPF. Next step is to add both CW-wide and CW-narrow filters which can be selected during run time.
As you can tell from the video, my antenna is not the best and I have quite a bit of QRM in the shack. I really need to think about a better antenna, but that's another story.
I have been following your R2 endeavors with interest, and as I said to Pete I will attempt to replicate the R2 on a Teensy. I will try and use the divide by 2 arrangement you tried as the logic looks right.
I will also be adding in a transmitter. For that I'll use the microphone input and then take the audio from the line out straight to the RF pre/power amp.
I must admit that I really enjoy homebrewing hardware/software hybrids as you get the best of both worlds. As i say that, I wonder how much ADCs cost these days to directly digitize RF... Now that would be interesting.
I'll say again that I really enjoy following the podcast. I have loved electronics since I was a small boy when my parents bought me a battery, switch and light bulb. This age of cheap DDSs, microcontrollers and the like is amazing, and I get so much enjoyment putting them all together to make functioning ham radios. I hope more get into the homebrew field as the entry barrier is dropping fast.
Feb 10 at 7:40 AM Hi Bill and Pete, My work is closed today due to the snow so I wanted to show you what I've been up to. I built sort of a test fixture a while back for those cheapie EBay AD9850 boards based on AD7C's DDS circuit using an Arduino Uno as a controller. Last summer someone posted a link to Analog Devices App note AN-423 on QRP-Tech I think. It was always on my list of things to try. Armed with a schematic of the eBay DDS gleaned from Doug Pongrance's website, I got to work. It involved cutting a trace or two on the DDS board using an X-Acto knife. Two outputs of the DDS chip are fed into a wideband transformer as in the app note's second page and I hung a scope probe off the secondary of the transformer. Basically you are removing the Rset resistor on the DDS board (marked R6 on mine) and using a 2N7000 MOSFET as an electronic version variable resistor and modulating the MOSFET. This lead to much frustration over the afternoon. No output on the scope!! Did I make an error or connect something up wrong? I was using the 600 ohm output of my HP652A audio generator. I thought about it during lunch and decided to try the 50 ohm output. Bingo!! At the 3V RMS range setting on the generator I now have some kind of signal. Not a nice sine wave shaped AM output but at least something resembling a clipped sine wave. The circuit is really touchy as far as needing a hefty audio signal in. The output of my iPhone at max volume doesn't turn on the DDS chip. I set the DDS for 1200 kHz and can listen to it on a Radio Shack portable radio. Varying the audio generator varies the received tone on the radio just like I was expecting. I just need to figure out what's up with the audio levels. Chris KD4PBJ
Feb 11 at 7:53 AM
I did manage to reduce the audio a little and get clipping to go away. I'll send another set of oscilloscope shots tonight.
The only thing I don't get is why the audio level needs to be so high. The app note said 1 V peak to peak should be enough but I am having to drive it with 7 V p-p audio to get a decent waveform with 0.8 V p-p RF.
I did cut the traces going to pins 12,20 and 21 to the DDS chip rather than pick up the signals elsewhere in the board. This was because once the traces go into vias down in the board, I'm not sure what else they connect to.
Chris
Feb 11 at 1243 PM
Found the original email from May of last year about the app note. It was on the EMRFD list. After hearing you guys lately talking about AM it has me excited about an AM transmitter.
I just got a thought over lunch that I'm going to try tonight and that is biasing the 2N7000 gate with a couple of volts to see if I can get the transistor on. Then maybe I don't need as much audio. I'll definitely put a series cap in though to my audio source so I don't fry my iPhone!!!
More to come this evening!
Chris
Feb 11 11:23 PM
I'm so excited!!
That's exactly what I needed to do-bias the gate of that 2N7000 so I'm not depending on the audio to turn it on, only to modulate it.
I hooked up a 9v battery across a 10 k trim pot and connected the wiper to the gate of the fet. A 10 uF cap is in series with my audio line as not to feed DC back into my source.
I have audio and now the output of a small radio or iPhone modulates it fine.
So this is a great proof of concept! Those cheapie DDS modules from China can be AM modulated.
I need a mic amp now, filter (surgery to the board disabled the on board LPF, but yes Steve I'll install one right away), buffer amp and some kind of linear RF amp to get a few watts.
Wow, you really have to spend 20 minutes and watch the video (above). It is really well done. I loved it. I give it FIVE SOLDERING IRONS!
And big news today! They did it! Gravitational waves finally detected. Here is a good New York Times article that includes a recording of the signal, a nice NYT video that has a good explanation (with phasing!) of how lasers are used in the massive detectors, and mention of Joe Taylor, K1JT, whose Nobel Prize winning work contributed to this great discovery.
Even I, with my luddite tendencies and analog preferences, have recently bumped up against the speed limit of 74 series logic chips. The Si5351 chip in the I and Q VFO for my phasing receiver will run up to 160 MHz. But the 74 series inverters and flip flops that I have attached to the output don't seem to want to go beyond about 120 MHz. Our old friend Thomas LA3PNA tells us how to break this speed limit: http://www.potatosemi.com/
Be sure to go their "Milestones of 74 Series Logic" Page. I like their explanation of the brand name:
Back on 2 February I was on 160 AM with the DX-100, talking to WA4PGI. At the end of our QSO we got a call from a station. I was at first confused -- was this station calling on SSB? Or was he calling on AM? Turns out that he was -- in a way -- on BOTH. K4DBK was -- I think -- running an old Collins KWS-1, the transmit side of the famous Gold Dust Twins. Aptly named: It was built in 1955. 1000 watts output. $2095.00 in 1955. Gold dust indeed.
The really interesting thing about this rig was that it put out CW, SSB and SSB plus the carrier. I think that was what we were hearing from K4DBK. FB.
Does anyone have an e-mail address for K4DBK? I'd like to drop him a line.
Thanks for all the comments and advice. I have come to understand the wisdom of divide by 4 IQ circuits. Fortunately it was very easy to convert the divide by two 74AC74 circuit described earlier to a version of the divide by 4 scheme seen above. (From the SDR Ensemble II Receiver: http://www.wb5rvz.com/sdr/ensemble_rx_ii_vhf/04_div.htm) This change provided a great way to observe 1) the improvement in the output signals from the VFO and 2) the resulting improvement in receiver performance, especially opposite sideband rejection. Here are some numbers. I was very pleased to discover that my Rigol scope will measure duty cycle and phase difference. Thanks Rigol! AD9850 Divide by 4 : 7.212 MHz Duty cycle: 48.3 Phase Difference: 87-90 degrees Si5351 Divide by 2: 7.212 MHz Duty Cycle 49.6 Phase Difference: 83 degrees Si5351 Divide by 4 7.212 MHz Duty cycle 49 Phase Difference: 85-90 degrees Additional improvement came when I switched the power supply to the IQ inverters and Flip Flops. I switched from 3.3 to 5 volts: Si5351 Divide by 4 7.105 MHz Duty Cycle 49.7 Phase Difference: 90 degrees When I took the VFO box and put it back in the receiver with the divide by 4 scheme and the 5 volt supply I immediately noticed a big difference in performance. It was obvious that opposite sideband rejection was back to what I had had with the AD9850, perhaps better. I have a quick and dirty method of measuring opposite sideband rejection: I put an RF signal into the antenna connector. I put the 'scope on the audio output. I tune (on the desired sideband) for 1kHz audio and I measure the output voltage. Then, with the audio gain and RF sig gen output in the same positions, I tune to the opposite sideband, again tuning for 1 kHz, again measuring audio output. With the divide by 4 scheme and the 5 volt supply, the opposite sideband was so weak I had trouble measuring it. I estimate the rejection to be at least 32 db -- this is back in the range of what I had with the AD9850, and significantly better than I had with the divide by 2 scheme.
Now I just need to figure out how to get the Si5351 VFO sketch to tune above 42.94 MHz. For some reason it quits at this point, switching down to 2 kHz output, and keeping me on 30 meters and below. Thanks again to Todd VE7BPO for a lot of help with the hardware and to Tom AK2B for help with the Arduino code.
"SolderSmoke -- Global Adventures in Wireless Electronics" is now available as an e-book for Amazon's Kindle.
Here's the site:
http://www.amazon.com/dp/B004V9FIVW
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