Re: LPF kit for ubitx v3


Donald <donwestpwl@...>
 

Jerry, Many thanks! I found the relay part number, and will continue reading.--Donald, KB5PWL

On 2/8/2019 5:03 PM, Jerry Gaffke via Groups.Io wrote:
The easiest and quickest spur fix is probably Raj's suggestion to just swap out L5 and L7
with a specific kind of shielded 1210 inductor.  That might be good enough.
https://groups.io/g/BITX20/topic/27154925#60453
https://groups.io/g/BITX20/message/62948

But be sure to buy the right 1210 inductors:
https://groups.io/g/BITX20/message/62948

Farhan has suggested a totally different spur fix:
https://groups.io/g/BITX20/topic/28088828#61752

This forum has not managed to agree upon a "best" spur fix.
Here's some additional reading if you are game, it gets complicated.
https://groups.io/g/BITX20/message/64136
https://groups.io/g/BITX20/message/62931
https://groups.io/g/BITX20/message/63985

Regarding spurs, I have not made my own measurements, so am not an authority here.
But:  Farhan's spur fix attacks the 90mhz harmonic coming out of the 45mhz IF amp,
also deals with some leakage from the 12mhz BFO on CLK0 into the VFO on CLK2
that then sneaks on out through the power amp and LPF's as a 12mhz spur.
Raj's fix prevents energy from the power amp from coupling back into the 45mhz IF amp,
a totally different strategy and would seem to not address the same spurs as Farhan's fix does.
How they can both (mostly) work is beyond me.

I suggest that for most of us, the best spur fix is the simplest one that mostly works.
Any mods much more ambitious than swapping out L5,L7 may well wreck
more radios than it fixes.  Especially if you don't have instruments to check the results.

Jerry

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