Re: a simple spur fix
My guess is that the two intended filter frequencies are: 90Mhz (second harmonic of 45MHz 1st LO) and 12MHz (2nd LO). The parts represent the right values for a filter at 90MHz, but it seems that 30M band would be wiped out by the second of the mods (which somebody has already observed). 12MHz should be being wiped out instead, so I suspect a typo.
Perhaps either a 35pF capacitor and the 5µH inductor as stated or a 3.8µH inductor and the 47pF capacitor as stated being about right for getting the filter resonant just on the low side of 12MHz.
On 10/11/18 9:49 AM, Brian L. Davis wrote:
10pf series with .3uhy - resonant about 91 MHz