Re: ubitx spurs? Added LPF

Joe Puma

Thanks Curt. I probably meant C212 which is 22pf. Gets a little rough remembering component numbers when youre trying to recount. :)  

On Apr 13, 2019, at 8:56 PM, Curt via Groups.Io <wb8yyy@...> wrote:


C215 is part of the matching circuitry used with the 45 MHz xtal filter -- 0.1 uF is a pretty large value at 45 MHz -- and it is large enough that it resonates with the coil way above this.  it seems to be a capacitive voltage divider to aid in impedance matching the filter.  possibly what you used is just fine -- I don't fret if I have to replace a SMT with a leaded part.  at these low frequencies the physical size of the cap isn't a big deal - when it fits the space. 


FB on your mods - those relays are said to often to fix the harmonics, and sometimes also help with mixer spurious.  the new filter you added is intended to fix SSB spurs on 15/12/10m. 

on 12m I think I see your spurious down at - 39 dBc.  that is ever so close to the goal (much better than my - 34 dBc) that if you experiment with slightly less audio drive you may be compliant enough. 

I think what you did was adding a new LPF placing it between the 'bi-directional amplifier' and the 'final mixer on transmit' (aka first receive mixer) - juslike v5.  I am especially curious with this result - and if you think it gave you some spur reduction - great news.  Raj is doubting the vertical orientation but your results seem to be good.  check your CW output now especially on 40 and 80 meters -- hopefully at least 5w on 40m and more on 80m.  (my rig and some v4's appear to be 'haunted' on CW whenever parts are added here to fix the SSB spurs). 

possibly your rig is doing well.  nice instrument you have there.  enjoy your work.


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