No longer in vogue, I am asking if an HF (500 kHz- 30 MHz) preselector is available these days. A typical product in the day was an MFJ-1040, or a Cross-Country RF Pre-selector.
Once upon a time, amateur radio operators (hams) used them to maximize the desired signal and, hopefully, minimize the undesired crud reaching the front end of their receiver. They are particularly useful when a strong interfering signal is present within the bandpass of the SDR (IF).
Just throwing the idea out for discussion. Could be useful when installed prior to a bias-T RF preamp.
Not many all-in-one type circuits around. You definitely get better performance from non-switched individual filters that you have to manually insert and remove in the RF chain, and those can be found easily enough on Aliexpress etc.
Built yourself a Balanced Transmit Loop Antenna (see pictureMagnetantenne – WikipediaDatei:-Balanced-Transmit-loop-antenna.png – Wikipedia ), which provides you very high selectivity. Without the Loop the bad receiver in my Kennwood TS-130 was totally overloaded, with the loop tuned to the operating frequency.
If you use a small DC motor for tuning the variable capacitor.
PS.: Pictures of almost all Balanced Transmit Loop Antenna you will find in the internet use thick tubing to minimize losses when used for transmitting up to 100 W or more. For reception only a cooper wire is good sufficient.
