Re: a simple spur fix

Ashhar Farhan
 

allison and others,

the traps are capable of adding a notch of -20 db. so even if you don't hit the bottom precisely, a 10 db reduction is all that is necessary to clean it up to the required level.

these are meant to be fixes that work with existing boards : from v1 onwards. i tried to choose a method that was easy to do.
we will need a different post mix if amp design going forward
yes the traps are for 90 mhz and 12 mhz.

the 10 mhz insensitivity is something i will look into today, I havent experienced it. perhaps we should move the trap to tx filters for the 21 mhz to 28 mhz band? the 12 mhz is filtered for the lower bands in any case.

the other place to apply the 12 mhz trap would be the local oscillator output?

another simple mod to be applied is to change R26 and R46 from 470 ohms to 220. the darlington pair was having insufficient current adding to distortion woes.

- f


On Sat, 10 Nov 2018, 05:48 Mike Woods <mhwoods@... wrote:
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. 

Mike ZL1AXG

On 10/11/18 9:49 AM, Brian L. Davis wrote:
10pf series with .3uhy - resonant about 91 MHz
47pf series with 5.0uhy resonant about 10.4 MHz
Is this correct?
Brian - WA5RDG


--
Mike Woods
mhwoods@...

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