Here is a larger image of the schematic (click for a full view):
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Thursday, December 1, 2022
The 40 Meter Direct Conversion Receiver We Have Been Working On -- Comments Welcome
Sunday, November 20, 2022
Watching Shortwave Broadcast Stations on the TinySA Spectrum Analyser
This reminds me of a cool project I have not yet done: modifying the TinySA to allow the user to listen to the station: https://soldersmoke.blogspot.com/2021/10/how-to-listen-with-your-tinysa.html I notice that Dean KK4DAS (my colleague in DC receiver design) was the only commenter on the blog post describing the TinySA mod. TRGHS. We need to to do this.
Here are the reports showing when Vatican Radio and Radio Marti were on the air on November 18, 2022:
Thursday, November 17, 2022
SDR Direct Sampling: The End of Homebrewing (as we know it)
I sometimes hear hams claim that our efforts to build simple direct conversion receivers are "very relevant" to modern technology and are "directly applicable" to today's communications techniques. These hams will say that direct conversion receivers are at the heart of modern rigs.
That's a nice thought, and it might have been true in the past, but I don't think it is true anymore.
I think the future is what you see written on the black box (!) that encloses the receiver in the above video: "DIRECT SAMPLING RECEIVER." In the recent past we did have two direct conversion receivers in the front end of SDR receiving systems. These receivers produced I and Q signals that were fed into the computer (often via the sound card). That was nice.
But the writing has been on the wall for a long time. There is no longer a need for all that direct conversion and I and Q. Just put a fast Analog-to-Digital converter chip at the front end, convert the entire HF spectrum to a digital stream, and send that stream to your computer. Or to another part of your "rig." As in the ubiquitous 7300.
I don't mean to be a Luddite here. That big waterfall is very nice. The receiver sounds great. But I am a homebrewer and I prefer to build my own gear. Ordering this black box on my phone, having it delivered by Bezos to my front step, and then updating the driver, is not what I consider homebrew radio.
A couple of things I spotted: The Si5351 chip in the box -- at least one part was recognizable. And the completely vertical skirts on all the SSB signals -- lots of 7300s out there.
Hey, to each his own, YMMV, whatever floats your boat. Just don't kid yourself into thinking that our beloved DC receivers are still somehow being used in these modern black boxes.
Tuesday, November 15, 2022
Amazingly Cool MONTV Video on Direct Conversion Receivers with Glue Stick PTOs
A Treasure Trove of Permeability Tuned Oscillator (PTO) Info and Links (Plus Info on Direct Conversion Receivers)
There is really great info on this page, and even more in the links at the bottom of it. While the page is about PTOs, the links often discuss their use in Direct Conversion Receivers. I really liked the Tin Ear receiver. And it was great to again come across the work of Alan Yates VK2ZAY. Alan very admirably admits that laziness caused him to use an LM386 audio amplifier in place of a more virtuous discrete transistor design.
https://qrpbuilder.com/pto_mechanism
I bought one of the qrpbuilder PTO kits and I will soon put it together. I have been having good results with a Glue Stick PTO and with a brass screw PTO form designed by Farhan and 3D printed for me by Dean KK4DAS.
LET'S GO PTO!
Wednesday, November 9, 2022
Direct Conversion Receiver -- Simple 2-Diode Mixer Defeats Radio Marti, but Diode Ring is the Best
Here is another update on Direct Conversion receiver construction. In Northern Virginia we get very strong signals from the Radio Marti transmitter in Greenville NC. During the morning hours it is just above the 40 meter band at 7335 kHz. In the evening it is a bit higher in frequency at 7435 KHz. (in the video above I mistakenly give the morning frequency, when in fact they were on the higher evening frequency). In either case, Radio Marti has been a big source of unwanted AM breakthrough in our simple DC receivers. It now serves as something of a test of our bandpass filters and mixers.
In this video I try out the simple mixer described in detail here: https://soldersmoke.blogspot.com/2022...
The following morning, I tested the mixer with Radio Marti (in fact) on 7335 kHz. By adjusting the VFO signal input to the minimum value needed to turn on the diodes, I was able to bring Radio Marti AM breakthrough to minimal levels. But I could still hear it (weakly) in the background. Putting a very simple diplexer at the audio output of the mixer (just a .1uF capacitor in series with a 47 ohm resistor to ground) helped a lot.
I could also hear break through from Spanish-language broadcasts from Vatican Radio on 7305 kHz (using the 250 kW transmitter in Greenville NC) from 11:30-11:45. Perhaps most surprisingly, I was also getting AM breakthrough from 40 meter FT8!
Here is a short video showing the simple two-diode mixer in action during the morning hours:
I also tried out the more common two diode mixer with trifilar toroid. (In this one, the VFO turns both diodes on, then turns both of them off). The results were similar to what I got with the other two diode mixer.
We are trying to develop four circuits -- bandpass filter, mixer, variable frequency oscillator, and audio amplifier -- that will be simple enough for construction by high school students, but not so simple as to compromise performance. We want the receiver to work well.Wednesday, November 2, 2022
Understanding a Very Simple Two-Diode Mixer
What do you guys think? Do I have this right? How would you characterize this mixer: Is it multiplying by 1 and 0? Or is it multiplying by 1 and -1?
Friday, October 28, 2022
SolderSmoke Podcast #241 Mars, Direct Conversion, PTOs and Glue Sticks, Anniversary of the BITX20, Multus Proficio SDR, Boatanchor Station, MAILBAG
SolderSmoke Podcast #241 is available
Audio (podcast): http://soldersmoke.com/soldersmoke241.mp3
Video (YouTube): (215) SolderSmoke Podcast #241 October 28, 2022 - YouTube
Introduction:
Back on Mars. Opposition
approaching. I have a Mars filter. And (like T.O.M.) a Mars
globe.
N2CQR DXCC done
SolderSmoke in the WayBack
Machine
Sticker news
PARTS CANDY -- Don't Scrimp with a Crimp!
Bill's Bench
School DC RX projects -- in
Hyderabad and Northern Virginia.
Direct Conversion Receivers --
Keeping it Simple, Learning a Lot. A step beyond the Michigan Mighty Mite.
Do we really need 100db? Do we really need to shield VFOs? Farhan's
super-simple and stable Colpitts PTO. Audio amps, 1000-8 transformers and
rolling your own LM386
PTOs and Glue Stick PTOs.
Paul Clark WA1MAC. Brass vs. Steel bolts. #20 thread vs. #28
thread. Backlash Blues. The best Glue Sticks.
2 meters and the VWS.
Bill has a Baofeng.
SHAMELESS COMMERCE:
MOSTLY DIY RF
Pete's Bench
20th Anniversary of the
BITX20 Pete's early BITX rigs.
Computer Woes
The Multus Proficio SDR rig
Simple SSB in China
BA7LNN
Things of beauty: Tempo
One, NCX-3 and a SBE-33
MAILBAG
-- NS7V is listening.
-- Graham G3MFJ
sent SPRAT on a stick.
-- Nick
M0NTV FB Glue Stick and 17 Shelf videos.
-- Dino KL0S
HP8640 Junior
-- Mark AA7TA Read the SolderSmoke Book
-- Steve EI5DD Connaught
(Ireland) Regional News
-- Dave
K8WPE Planting the seeds of ham radio
interest
-- Peter VK3YE
Ruler idea on PTO frequency readout
-- Michael AG5VG Glue
Stick PTO
-- Tobias A polymath with UK and Italy
connections. And cool tattoos.
-- Alain
F4EIT French DC receiver
-- Michael
S. was in USMC, working on PCM/TDM gear
-- Alan Yates
writes up Amazon transformer problem
-- Todd VE7BPO, Dale W4OP, Wes W7ZOI
-- Farhan VU2ESE
sent me an sBITX
-- Todd K7TFC The Revenge of Analog
-- Jim Olds Building QRP HB gear
Saturday, October 15, 2022
DC Receiver: 100db Gain? Diplexer? VFO in a box?
Friday, October 7, 2022
How the Diode Ring Multiplies by 1 and -1 -- "The Secrets of the Diode Ring" -- Plus another Bandsweep with the DC RX
Thursday, October 6, 2022
Adding a Diode Ring to the Direct Conversion Receiver, And How the Diode Ring Works
Sunday, October 2, 2022
Update on the Direct Conversion Receiver -- Now only 4 transistors
Friday, September 30, 2022
Bandsweep with the New Homebrew 40 meter Direct Conversion Receiver
-- The mixer is singly balanced using one trifilar toroid and two diodes. We have found out that even with these three simple devices, there is significant variation in how people connect them to VFO, RF in and audio out. I think we have found the best way to do this: Be sure to put the VFO on the primary of the transformer, and let this signal turn the diodes on and off.
-- For the AF amplification, I have one FET, followed by two BJTs. I have a small audio transformer between the speaker and the final AF amp. There is plenty of audio.
You may wonder why, after all the SSB superhet transceivers, I am building a simple Direct Conversion receiver. Well, we hope to help a bunch of high school kids build one, so we need to be really familiar with how it works. And I find that as simple as it is, there is still a lot to learn in a project like this.
Thursday, September 29, 2022
A Bout of Direct Conversion-ism in Northern Virginia -- DC Receivers Under Construction
Saturday, September 24, 2022
Talking about Homebrew Radio with the Williamsburg Virginia Radio Club
Tuesday, September 6, 2022
Michael AG5VG Builds a Sub-Harmonic Receiver and Moves it to Higher Bands
Good Evening Bill,
Saturday, August 27, 2022
SDR on a Breadboard -- But Isn't This an Old-Fashioned Fantasy?
Wednesday, August 10, 2022
Vasily Ivanenko on Vladimir Polyakov's Subharmonic Detector
Vasily IvanenkoAugust 9, 2022 at 12:49 AM
Thanks Bill. My own experiments at HF with subharmonically pumped Schottky diode mixers show clearly that almost every mixer parameter we measure is worse than our classic balanced mixer topologies. Definitely 2LO-RF isolation was better than other unbalanced mixers without the need for a transformer.
I guess it's appealing for low-complexity receiver builders. For zero IF receivers, I like and run my LO at 1/2 RF frequency and then use a doubler -- that's a great advantage for
a DC/ Zero-IF receiver and a built-in feature for the subharmonic mixer.
The SH mixer becomes quite appealing at SHF to mm-wave lengths where making a quiet, temp stable LO gets rather expensive and tricky.
Subharmonically pumped mixers can also work at odd integers if the mixer LO/RF drive is balanced and designed to produce distortion that for example, triples the LO frequency. Rohde & Schwarz had a 40.1 GHz spectrum analyzer with one --- and if the LO was 13 GHz while the RF was 39.5 GHz, this gave an IF output of 500 MHz in 1 particular circuit. Really amazing design work. Here's an interesting URL:
https://www.eravant.com/products/mixers/subharmonically-pumped-mixers
The SH mixer has been around for > 4 decades. The oldest SH mixer paper I've got in my library is from Schneider and Snell from 1975. I don't think they invented the SH, but this pair helped popularize it for the world and design work continues today.I've seen optical SH mixers with I/Q outputs in research papers.
Here's the abstract and citation:
Harmonically Pumped Stripline Down-Converter
M. V. Schneider, W. W. Snell
Published 1 March 1975
Physics, Engineering
IEEE Transactions on Microwave Theory and Techniques
A novel thin-film down-converter which is pumped at a submultiple of the local-oscillator frequency has given a conversion loss which is comparable to the performance of conventional balanced mixers. The converter consists of two stripline filters and two Schottky-barrier diodes which are shunt mounted in a strip transmission line. The conversion loss measured at a signal frequency of 3.5 GHz is 3.2 dB for a pump frequency of 1.7 GHz and 4.9 dB for a pump frequency of 0.85 GHz. The circuit looks attractive for use at millimeter-wave frequencies where stable pump sources with low FM noise are not readily available.
Best to you!
Tuesday, August 9, 2022
Polyakov Direct Conversion Receiver on 80 Meters (video)
In today's episode I put the switch in the open position turning the receiver into an ordinary Direct Conversion receiver with a single diode as the detector. I find that it works pretty well on 80, but probably not as well as it does on 40 (where it is in full Polyakov mode). (Yesterday I demonstrated the receiver in action on 40 and provided details on the circuit. See: https://soldersmoke.blogspot.com/2022/08/polyakov-ra3aae-direct-conversion.html)
You will notice that when I throw the switch, but before I retune the input LC network, you can still hear the signal from the previous band. So when I have it in 40 and I throw the switch to open, you can still hear the 40 meter signal. Apparently one diode will (poorly) demodulate a signal with the VFO running at HALF the operating frequency. I saw this in the real world receiver and also saw it in an LTSpice simulation. In LTSpice the signal level drops significantly when I go to just one diode: From 50 mv peak to 15 mv peak, but it can still be heard. Something similar happens when I go from 80 to 40. When I close the switch and suddenly have two diodes and a 3.5 MHz VFO trying to demodulate the 80 meter signal, I can still hear the 80 meter signal, but it is much weaker and a lot more noise is getting through. Again, I saw this in the real world and in LTSpice. It looks as if with the two diodes, the 3.5 MHz signal is being sampled twice each VFO cycle. This may result in some output in the audio range. But again, it is much weaker.Monday, August 8, 2022
Polyakov (RA3AAE) Direct Conversion Receiver: 40 meter DC RX with VFO at 3.5 - 3.6 MHz (with video)
I've been reading about Polyakov (or "sub-harmonic") Detectors for a long time:
https://soldersmoke.blogspot.com/search/label/Polyakov--Vladimir
But until now, I never built one. Recently, Dean KK4DAS and the Vienna Wireless Makers group have been building a Direct Conversion receiver. Their receiver uses an Si5351 as the VFO, but of course Dean and I have decided to try to do things the hard way by building non-digital VFOs. At first we just came to the conclusion that my earlier Ceramic Resonator VFO wasn't much good (it drifted too much). This led us into standard Colpitts and Armstrong VFOs, and the fascinating world of temperature compensation. Then I remembered the Polyakov circuit -- this would allow us to use a 3.5 MHz VFO on the 7 MHz band. Lower frequency VFOs are easier to stabilize, so I started building my first Polyakov receiver. You can see the results (on 40 meters) in the video above.
I started working with a circuit from SPRAT 110 (Spring 2002). Rudi Burse DK2RS built a Polyakov receiver for 80 and 40 that he called the Lauser Plus. (Lauser means "young rascal" or "imp" in German.) For the AF amplifier, I just attached one of those cheap LM386 boards that you can get on the internet. With it, I sometimes use some old Iphone headphones, or an amplified computer speaker.