A "Starter Project for after the RAE"
I was thinking about a 'starter project' for the 'newbies' after the RAE. It used to be something like a 'Crystal Set'. Because the AM transmitters are few and far between nowadays, it should be a 'simple DCRX.' And to make it more 'interesting' it should receive SSB, CW and PSK31 and RTTY.
Direct Conversion Receivers have been around for several decades.
Lets try putting an AI on the task...
Based on a search of technical literature and recent hobbyist projects, there are many articles and resources dedicated to direct conversion receivers (DCRs), ranging from historical overviews to modern, high-performance designs.
Academic and Technical Articles:
Numerous technical papers and articles exist on ScienceDirect, MDPI, and ResearchGate covering DCR design, specifically addressing challenges like DC offset, LO leakage, and I/Q imbalance.
Main Themes in Recent Articles:
Simplification:
Many designs focus on minimizing component counts, often using under four transistors.
Performance Improvement:
Articles discuss techniques to overcome traditional DCR limitations (hum, Microphonics) using I/Q demodulators and modern DSP.
Direct Conversion vs. Superhet:
Several articles compare the cost and complexity benefits of DCR, especially for integrated, zero-IF designs.
Overall, the number of articles is substantial (over 20+ prominent technical, academic, and hobbyist resources found in the search results).
So what do 'we' want to build?
Some design features:-
1) The ZS article used a 420mm loop antenna
2) Use an 'active antenna'
3) An IC "Balanced Mixer" to suppress the local oscillator leakage to the antenna.
*** Whoops! That might be a problem...
4) Which 'Band' do we want to use?
5) How sensitive should it be?
Example Picture showing simple construction method 1.
You can't get the wood, you know!
There 'used to be' many integrated circuits for the Direct Conversion Receiver.
SO42 - SL6440 - TIxxx - CA3086 NE602/NE612 and so on. Most are no longer in production or available for purchase. [Also fake ones are available!]
See the note 'Dilbert Cell.' [Not a typo]
A recent Youtube described how a 'Gilbert Cell' worked. Take a look. The simple version would do the job nicely - using 'readily available' - 'general pupose' transistors!
The Gilbert Cell (084d)
https://youtu.be/mQ36yy7mloA?si=2W3HRTWym6j-LcsR
Now we are scavengers
This is where I get on a 'soap box' and tell you about how many transistors I have recovered/scrounged/scavenged from old/wornout electronic circuits. The list includes ATX Power supplies, VHS recorder/players etc.
Just Found this:-
"There are many conflicting technical requirements for a good-quality front-end in an SW receiver. The noise figure and the intermodulation level should be low, the RF insulation between ports LO, RF and IF should be high, and some amplification is desirable. The Type SL6440 high level RF mixer from Plessey ensures a noise figure of around 10 dB, and offers sufficient suppression of the LO signal." - Oh dear! No longer available.
Dilbert Cell ???
In electronics, the Gilbert cell is a type of frequency mixer. It produces output signals proportional to the product of two input signals. Such circuits are widely used for frequency conversion in radio systems.[1] The advantage of this circuit is the output current is an accurate multiplication of the (differential) base currents of both inputs. As a mixer, its balanced operation cancels out many unwanted mixing products, resulting in a "cleaner" output. Gilbert cells can also be used as variable-gain amplifiers (VGA).[2]
It is a generalized case of an early circuit first used by Howard Jones in 1963,[3] invented independently and greatly augmented by Barrie Gilbert in 1967.[4] It is a specific example of "translinear" design, a current-mode approach to analog circuit design. The specific property of this cell is that the differential output current is a precise algebraic product of its two differential analog current inputs.
NE602/612 ICs
The NE602 and NE612 (including SA602/SA612 variants) are essentially identical, interchangeable Gilbert cell mixer/oscillator ICs often used in RF applications. Originally, the NE612 was introduced as a slightly updated, redesigned version of the NE602 for better high-frequency performance, but they are often identical in modern production and share the same specs, datasheet, and Pinout.
Both are designed by Signetics (now NXP/Philips). The distinction between "NE" (commercial) and "SA" (industrial/automotive) is more relevant than 602 vs. 612.
40m Direct Conversion Receiver
https://community.element14.com/technologies/open-source-hardware/b/blog/posts/simple-dcr-assembling-a-7-mhz-40m-direct-conversion-radio-receiver-part-1
https://qrp-labs.com/images/news/dayton2019/FDIM2019ConfProceedings.pdf
A 40m Direct Conversion Receiver project to upgrade from ZR to ZS
Hannes Coetzee, ZS6BZP, B.Eng Elektronic (Pretoria)
Also in :-
https://zs6wr.co.za/anode/AnodeJuly2010.pdf - Hannes Coetzee ZS6BZP
A 'Work in Progress' JB ZS6WL 2026-05-12
