I enjoy listening to the classic rock format on WRMI radio, broadcast on 5050 KHz mid evenings, and 9455 KHz late night. With the DC receiver project winding down, I have enough left over parts to ( I think ) build a simple radio for listening to WRMI under good conditions. Having inventoried what I have on hand, I think the "design" goals are going to be: 1. Simple, beginner friendly circuitry, with no complicated circuits, or unobtainium parts; 2. Self contained except for power supply, suitable for daily listening, convenient to operate, hopefully not a toy that one becomes disinterested in after a week or so of use; 3. Sounds good I've always liked the oddball look of this case that someone pretty good at 3D design designed for the bitx transceivers: BitX40 Ergonomic Enclosure by fire5ign - Thingiverse. So, I printed it up, in a really bright color to go with the fun tropical / Caribbean Sea motif that WRMI is using. That takes care of the case. I have the Si5351 based raduino built and debugged - it just needs some minor tweaks to the code, and the 1602 LCD with an I2C drive board fits without difficulty in the case as is shown. That takes care of the VFO. Two out of three already done, that just leaves the radio part. I've been thinking about the best way to go about it, and I think a single conversion superhet is the best solution to meet the design goals, For the front end, I'm choosing a single tuned circuit, because I think the chances of correctly tuning up a double tuned circuit are nil, without some type of spectrum analyzer. Tentatively, I am going with a 50 ohm input. An active antenna, or maybe even a regenerated ferrite rod, might be attempted at some point. I pulled a previously wound T-37-6 coil, and gave up on counting the turns wound on it, and just used an LC meter to measure its inductance at 3.54 uH, then calculated the capacitance necessary to resonate at 5050 Khz as 280 pF. I picked a 220 pF cap that measured out at 210 pF, and a 75 pF cap that measured 69 pF, to get the needed 280 pF. I used a 5 turn link on the toroid to go from a 50 ohm antenna to the 1500 ohm input resistance of an NE602, and assembled and swept the filter with the red pitaya. And it peaked low, by about 30 pF of stray capacitance, when I back calculated the peak. I substituted a random 47 pF cap for the 75 pF, reswept the filter, and it looked close enough. An alternate, easier, approach is to substitute a trimmer cap for the smaller cap, and just peak it for maximum atmospheric noise or signal strength. I made a simple mixer with an NE602, and tested it with an RF input of 0.01 volts at 5000 KHz, and an LO input of 0.1 volts at 5500 Khz and looked at it with the red pitaya to verify it worked. The 500 KHz IF, 5000Khz LO, and 10.5 MHz IF are plainly visible. The smaller peak at 11 MHz is probably an intermod artifact of the two IF's. The 0.01 volt RF input is very strong compared to an over the air signal. All of this is being built on the board that I abandoned when I went a different direction with the DC receiver. Only the regulators were salvaged. The NE602 is using the 8 volt regulator. That's it for now. This is a low priority project, and updates / progress may be infrequent. 73. Win W5JAG

SIMPLE POWER SUPPLY STATION CONSOLE I’ve been using a store bought imported power supply for the homebrew general coverage receiver, with satisfactory results, but wanted a homemade supply for use with it as a matter of principle and appearance. The power supply presented here is nothing special but provides several convenient functions: A low power regulated DC output derived from the AC mains; a rechargeable battery pack and charger; both power sources can be connected to the output connectors which can accommodate multiple loads; and a digital multifunction display. The line transformer is a Philmore miniature 7.5-0-7.5 1 amp secondary device, with the center tap unused and the ends of the secondary connected to a full wave bridge to ensure sufficient DC output voltage. 1N4007 diodes, bypassed by 100 nF disc ceramic capacitors for noise suppression, make up the bridge. The DC regulator is an LM317 device. A 200 ohm sense resistor is used between the output pin and the adjust pin, which is grounded through a 4k7 trimpot to set the desired output voltage. The small heat sink limits power output to about 600 ma or so. The circuit is completely generic - I did not even bother to draw a schematic. The Battery Pack consists of three overpriced pieces of Li-ion 18650 cells, each with a nominal voltage of 3.7 volts and 1800 mah capacity that I purchased locally at a Wal Mart lawn and garden center. Probably the best way to manage Li-ion battery packs is with one of the inexpensive battery protection boards designed especially for this purpose - they limit the charge / discharge current, charge / discharge voltage cutoffs, and probably other stuff like equalizing charge between individual cells in the pack. I tried several different types and had 100% failure rate for reasons unclear to me. So, to move forward with the project, I built a crude charger from another LM317 that limits charge current to 600 ma, about 1/3 C. More charge current would be hard on the cells, and 600 ma is about the limit from the transformer / regulator / heat sink combination. The charger module takes it’s DC input directly from the rectifier output. A trim pot sets the voltage limit on the charger, here set to about 12.3 volts, or 4.1 volts per cell ( 90% capacity ). 18650 Li-ion cells should not be discharged below a certain point, generally about 2.75 volts per cell, so a protection circuit or voltage monitoring should be used to protect the pack from over discharge. An inexpensive front panel digital voltmeter allows for monitoring of the battery pack charging and discharge voltages, and adjustment and monitoring of the output voltage of the DC supply from the mains. The display also contains a 24 hour clock with battery backup, and a temperature sensor, as well as the DC voltmeter. It is a two wire device, meaning no independent DC supply voltage is required. The display can cycle through its various functions at a programmed interval, or continuously display one selected parameter. The attached video shows the display cycling. A series of simple mechanical switches allow: turning the AC power on / off; connecting the battery pack to the charger or the load control switch, or complete disconnection of the battery pack; connecting the output load connectors to the battery pack or the DC output derived from the mains; and connecting the voltmeter to monitor the battery pack voltage or DC output of the mains AC supply, or disconnected ( display off ). Banana / Binding posts are used for the output connectors - only two pairs are presently installed, but the case is fitted for three more pairs if needed. A two wire polarized line cord is used with a 1 amp fast blow fuse inline on the hot side before the switch. The chassis and small contrasting finish bezel around the display are designed on TinkerCad and 3d printed. The display and bezel are press fit into the opening on the chassis; a green display is installed at present - I may change it out to another color. Connectors are used for a mostly modular design - the battery pack and DC supply / charger module can be installed / removed without need to solder / unsolder any connections. 73 and happy building, Win W5JAG

Here are a couple of simple IF amplifiers using obsolete linear IC's. They are not my circuits ( I think - the 3028/3053 might be ) but I have used them successfully and might save someone some research time hitting the books. CA/LM 3028 and 3053 are basically the same chip, the '3028 version being good for much higher frequencies than the '3053, although both are completely suitable for HF frequencies. The '3053 in its day was the less expensive chip, although decades later that has reversed. Neither chip is especially common these days, but are still available. The '3028/3053 can probably be duplicated with discrete components, although I have not tried that. These are through hole parts only. A much higher gain amplifier can be made by using the third transistor, but the circuit here does pretty well gain wise, and is easily made stable. Both '3028 and '3053 were commonly duplicated by proper connection of the transistors in CA/LM 3046 and 3086, the latter being the premium VHF version of the chip. LM3046 was in production until a year or so ago, so should still be readily available in through hole. SMD parts were made, but might be dicier to locate now. The MC1350 is supposed to be long out of production, and to my knowledge was never offered in SMD, but there are still commercial devices in production that use it, and I see them available in through hole and SMD variants on AliExpress, so I'm not sure what is going on with this part. They could be counterfeits or licensed production, or both. I have a lot of old through hole in stock, so I haven't purchased any in years. I'm tempted to try some of the SMD parts. Note that on the MC1350 sheet, VR2 is an adjustable gain control. MC1350 is made for low VHF use and it is capable of substantial gain there and at HF, so caution is warranted in using it. Also note that MC1350 and CA3028 have opposite AGC control voltage action. 73, Win W5JAG

This radio was previously described on the old RadioBoard forum under the title “A Simple Superhet”, and is re-presented here in more detail than previously. It is a general coverage broadcast receiver. OVERVIEW: The radio features digital tuning and frequency readout with memory channels, a low VHF first intermediate frequency for good image rejection, and broadband circuits eliminating alignment. No unobtainium parts are used. Commercial products are used where there is an advantage to do so. The radio is constructed modularly. Three 50 x 80mm BusBoard systems SMD prototype boards ( 200 x 100 format ) hold the RF and audio circuits. The power supplies are on simple perfboard. The completed modules and VFO are installed on a breadboard “chassis” designed on TinkerCad and printed on a simple and inexpensive 3D printer with PLA plastic, thus no complicated metal work is required. A rotary encoder is used for tuning, and directly mounted to the front panel, eliminating the tricky mechanical alignment problems associated with obsolete LC or Varactor VFO’s. The main tuning knob is also 3D printed. Volume is set by an electronic attenuator controlled by a simple DC voltage, eliminating cumbersome shielded wiring to the front panel. The heart of the radio is a commercially produced QRP Labs VFO kit, available for about $33 USD, using the now ubiquitous Si5351 frequency synthesizer chip. The VFO can generate a tunable LO well past 200 MHz, quadrature output if required, tuning steps as fine as 1 Hz, at a square wave level sufficient to drive commercial level 7 mixers without additional amplification. A digital frequency readout and memory channels are provided. Further, an additional fixed frequency local oscillator is provided. The firmware allows the frequency displayed to account for the IF offset from the tunable oscillator. The kit is supplied with a white on blue background LCD, but 5 volt type 1602 LCD readouts are available in a wide variety of color combinations. My radio at this time uses a black LCD with red digits. The Si5351 has many good features and one, perhaps two, significant drawbacks - there is a degree of cross talk between the oscillator channels that is inherent to the device. The output is a square wave, by definition harmonic rich. This is ideal for diode mixers. The Si5351 has a DC component on its output, so a DC blocking capacitor of 10 or 100 nF should be used in circuits where this DC component cannot be tolerated. For up converting superheterodyne receivers, the general rule of thumb is that the first intermediate frequency should be at least 1.5 X the highest frequency to be received. The intermediate frequencies in this receiver are 45 MHz and 450 KHz. Crystal filtering is used at the first IF, and a ceramic filter is used at the second IF. The use of a low VHF first IF, greatly simplifies the construction of the receiver, while enhancing its performance compared to older design techniques. Tunable LO injection is 45 MHz higher than the frequency to be received. The use of the low VHF IF puts the image frequency 90 MHz above the received signal, thus a simple low pass filter is satisfactory to protect a strong first mixer, while eliminating front end alignment and tracking issues. The low pass filters and diode double balanced mixers used are commercial products by Mini Circuits. The IF amplifiers are 50 ohm broadband amplifiers. A TDA1072 Integrated Circuit handles final IF amplification, AM detection, AGC, and provides a meter output voltage that is used for signal strength indication and an additional AGC loop. Audio output is from a DA7052A BTL Integrated Circuit. Each of the modules in the radio will be described in further detail in subsequent posts. 73, Win W5JAG