Re: ubitx spurs? Added LPF

Joe Puma

The power mod is easier then figuring out spurs and harmonics.  You certainly don’t need that expensive scope for it :) I just did mine and I guess I’m getting the 14w on 80 and 6w on 10 like Allison mentioned. She does best power wise on 20 meters for me, not Alison but my uBitx :)

I’m watching your work here though as I want to do the filtering Farhan mentions and use my poor mans analyzer to see if I notice a difference. 

And....I don’t mean to hijack the post by hey Raj what do you think about my L5, L7 work? :) 


Can someone tell me what C215 does? Mine went bad on me from attaching the IF out for SDR so for a while I was getting poor performance until I replaced it. I didn’t have a 1206 and not the right value of 0805 so I used a 22uf pin hole ceramic cap. Just curious what that part dose right before it goes into the filter.  Now with the new, part my SSB audio is peaking to full wattage nicely. 


On Apr 13, 2019, at 6:50 PM, John Sutter <jds@...> wrote:

This is a V3 that has new relays and the L5/L7 fix and working on the LPF
that I believe is before the mixer, but I'm not sure.

I've been taking measurements at each step.  So far not significant drops.
I had some crazy readings which where later explained by one of the techs saying,
"don't use that one..." but at least it was consistent in relative readings.

That said, I do see power go down with frequency across all changes regardless of mods.
I think I saw a mod for that, but that one's probably not for me.  We'll see.

On 12m I saw 32, 16, and 12Mhz

On 10m, I had 32, 16, and 12MHz and then 7.86 MHz

On 4/13/2019 3:22 PM, Curt via Groups.Io wrote:

very good - I am interested in your results on this, and which ubitx version you have. 

on 12m you might notice 2 spurs on either side of the carrier about 5 MHz apart,  the v5 comes with a LPF similar to you have drawn already installed.  I tried one using SMT inductors on my v4 -- not much change -- not surprising since the spurs are close to carrier.  I did change R26 on mine, but I still have stock 2n3904 transistors (if I were bored I might see what better old stock transistors I might have for 45 MHz - but that might be an adventure). 

on your 12 and 10m readings you are mostly focused on harmonics of the RF output.  either your close-in spurs are good -- or you didn't notice them? 

you could be a little confused as this LPF is described as filtering harmonics of 45 MHz.  one of those 2 spurs I mentioned seems to be 90 MHz - the LO frequency.  the other spur I think is the PA signal leaking back to the mixer, and mixing again.  

with any changes you make in this part of the circuit - do see if you get any reduction of CW output power -- mine does a bunch on 40 and 80 meters.  

73 Curt


Join to automatically receive all group messages.