Re: ubitx spurs? Added LPF
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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:
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John
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
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