Building a 145 MHz Low Loss Helical Bandpass Filter
Over on YouTube user Mile Kokotov has uploaded a video showing his home made low loss helical bandpass filter for 145 MHz, but also tunable from 110 MHz to 160 MHz. Bandpass filters are useful for the RTL-SDR as often strong out of band signals can cause overload, causing poor reception. A bandpass filter blocks all signals outside of its pass band. A helical bandpass filter is simply a coiled wire enclosed in a conductive container that can be tuned with a variable capacitor made out of two plates.
In his video Mile shows the inner construction of his helical filter, explains the parts and shows what calculations he used for construction.
145 MHz Low Loss Bandpass Helical Filter by Mile Kokotov
As described this seems over coupled – a wall between the coils about 1/2 the height seems to be about right.
Thank you Mile kokotov and rtl-sdr.com. I needed a good filter . It seems that this works well