DF9CY VHF Broadcast Passband Filter (88 .. 108 MHz)
How to make the filter
In some cases the input filter of a VHF Broadcast receiver for 87.5 .. 108 MHz is not selective enough, or something in the input circuit is sensitive from out-of-band signals.
You must have the selectivity improved and this can be done with a really simple filter circuit. Amateur Radio bands are suppressed at least by about 15 to 20 dB above the passband and by minimum 35 dB below 55 MHz.
I have already built a number of these filters and it even helps in my old "kitchen-transistor-radio", which was up to then my best RF indicator in the house ...
The filter is made on an experimenters' board with SMD (surface mounted device) components and its size is 10*10 mm (without connenctors). No tuning is required.
I designed the filter with the well known PUFF 2.0 microwave circuit design program. If you want to re-simulate don't forget to put some 3 .. 5 Ohm series resistance to the 100nH inductances to get realistic results.
If the suppression of the 144 MHz or 432 MHz amateur radio band is not sufficient for you, have a look at the TVI Stop filter, and add those 144 MHz and 432 MHz devices.
Have fun and 73
Text and All Images are Copyright by Christoph Petermann DF9CY
GO (back) and visit my homepage