My homebrewed PA0FRI Active Antenna is working well from a very physically constrained location.
Design
3D render:
Schematic:
Results
The antenna is connected to an RSP1 Clone SDR running custom FT8 band-hopping
software. I am using a SOLID 4-Way 5-2400 MHz RF splitter to connect multiple
SDRs to the same active antenna. NB: Plug in 75-ohm dummy loads (terminators)
on the unused splitter ports; MX-282 / MX-280 75-ohm loads work fine.
Time to build: Less than 45 minutes for the PCB. The mechanical aspects (loop construction and boxing) can take a while.
My live reception results from this antenna can be viewed at the following URL(s):
Performance Testing
Testing Update: A 10m EFHW antenna installed in the same 'surrounded balcony' location receives less than half as many countries compared to the PA0FRI active antenna.
Magic might not exist for grownups but the reception results of this Active Antenna from a very limited physical location are nothing short of magical!
Special shout-out goes to Ismo (OH2FTG) and Gajendra Kumar Sir for their guidance on these topics - thank you!
Notes
The first two decodes in the following screenshot are from a "turned off" active antenna. The last two decodes are from the same active antenna when turned on.
Remember the Don't let the perfect be the enemy of the good saying? While
theoretically better active-antenna designs exist, we are not keen on pursuing
them because the results of this PA0FRI AA are good enough (TM).
References
- Simple active receive loop antenna - for physical construction aspects
Updates
Update (14-August-2025): My Active Antenna performed well for weeks, and
then performance suddenly dropped one day. This made me wonder what changed. I
went to the terrace and found that the DC power supply line had been
disconnected (some guest appears to have tripped on it during a recent pooja
event at home).
As you can see, the performance of the "AA" fell drastically without power.
As soon as I reconnected power, performance improved dramatically.