My wideband loop helper project should let you eliminate overload from strong nearby broadcasters while enjoying HF reception with most wideband software defined radio receivers.
After a few years of experimenting with wideband loop antennas, I have recognized their fundamental challenge. Overload from local medium wave broadcasters with very strong signals. You will find this problem manifesting in several ways. Namely, we can experience mixer distortion, ADC overload and AGC gain reduction when trying to use a wideband antenna with a wideband SDR receiver.
So, these challenges led me to create the wideband loop helper project. I will describe the purpose, design, build and performance of my project in a series of articles, starting today.
I wanted a simple, switchable solution that accomplished three things. First, a switchable attenuator that would reduce strong signals before they entered the front end. Second, a switchable filter to reduce medium wave strength without affecting signals higher or lower in frequency. And third, I sought a dual channel design for use with a pair of loops and a two-channel diversity receiver.
Mission accomplished. You can see my prototype wideband loop helper project in the photo above. My parts count and cost was quite low, under $20. Four BNC bulkhead connectors, four DPDT miniature toggle switches, a milled printed circuit board, all wired within a small plastic case about 90 by 120 millimeters in size.
You can switch in either an attenuator or bandpass filter, or both, on either channel, all independently.
Wideband Loop Helper Project with Readily Available Parts
Everything I needed for my wideband loop helper project was readily available in my parts drawers and boxes. And the design is easily adjustable to fit with what you might have available. Or readily available on eBay. Six each of resistors, capacitors and inductors with some matching involved.
For most of you, a 20 dB attenuator should be enough. So should a bandpass filter with at least a 30-40 dB drop across the medium wave band. You will find these are quite easy to achieve with even the most rudimentary construction practices. I finished the plastic box with a metallic paint coating to provide shielding.