Pseudo SO2R HF system.
Hi. To be more productive in HF cw contests, I decided to design and build a secondary receiver connected to IC7300 via CiV jack.
It is a basic superhet receiver using a mixture of Analog Device , lots of SMT and 2 obsolete transistors. All modules will be on a single PCB except main controller and DDS generator.
The controller will communicate with IC7300 and Home made QRO to switch from one freq to another , transmit there then return to previous one. The receiver will have USB interface and kenwood emulated codes to be seen by contest software as secondary TCVR. Another feature is to use it in same freq with main receiver but on a different antenna , and headphones split to both receivers. In this way I can listen dual polarization or dual directive antennas.
It is a long process but I believe it would be fun building it, so far I finished designing PCB and waiting JLCPCB to deliver.
End of Part 1
21 January 2021 status update:
Got PCB’s from China and already put some components on it.
So far I ‘ve tested audio pre and amplifier, product detector / Si5351 BFO and 2x AD603 IF amplifier.
Results are great so far apart that first AD603 IF preamp is sometimes self oscillating, waiting for another spare time to address this issue and solder the rest of components.
73’s, Gabriel yo8rxp
24 Jan 2021 status update :
Sometimes I get amazed by my ow stupidity . as such:
Audio amplifier is squeaking on speakers no matter the output power, on headphones is just beautiful
Burned out my last ADE 1/24 mixer so I had to rebuild it from scratch aka 4 diodes and 2 x T37-43 toroids
First audio OP preamp is doing big nada so a low input impedance audio preamp was built
Lucky me DDS AD9850 sine output is not generating birdies at all, happy here as Si5351 is full of shit.
If AD603 AGC voltage is over 5.5 V then some annoying hiss is generated, so AGC module is to be biased and no more that voltage. here it comes differential Opamp value, fingers crossed
Arrl 3 poles bandpass filters are just great, no problems here.
Bottom line is lots of work is to be done , so another PCB version is expected. Also Amtec ot Topnik Zel flux is super ok but lots of grease remaining , gotta clean it up with isopropyl alcohol.
Started to write Arduino code and “borrowed” a bit of know how from UB7KPV project
Work in progress
This project of mine was a bit forgotten but at the end of 2022 I decided to resume work.
ugly weekender style - status update
Added a third AD603 IF stage- a total of 120dB gain on IF stages
Determined optimal AGC values - between 5 and 6 Volts aplied to AGC port to get 120dB AGC range
Added AD8703 RSSI detector - unfortunately only 80 dB range here, will have to cascade / ATT 2 of them
I have to build and set differential Opamps circuitry to get linear response for RSSI input versus AGC output.
Knee time, raise time and fall time will be experimental determined for FAST, SLOW and Medium AGC time.
Also, in keen to test MC1496 as product detector instead of diode ring mixer.
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