On Tuesday, June 8, 2021, 10:27:00 PM CDT, jerry@... <jerry@...> wrote:
All,
To help me post-mortem the Chinese linear,
I was checking the output of the uBITX on various bands.? I used a Bird
4410 wattmeter with the 10kW slug ( which can be switched down to 10W
full scale ), and my trusty Narda attenuator as a load.? Here's what I
got
3.615? MHz - 4.2W
7.029? MHz - 4.9W
10.115 MHz - 3.7W
14.030 MHz - 17W <======= HUH?
21.03? MHz - 2.5W ( more like it )
28.35M MHz - 3.9W
? That 14MHz reading is a doozy - no WAY is the uBITX making SEVENTEEN
WATTS.
My wattmeter ( a recent Ebay purchase ) must be defective!? Specifically
the slug, where all the RF stuff is.
? Let's double check this.? I lugged out a scope ( Rigol 1054z ).?
Plugged it directly into the output of the 30dB Narda attenuator.? No
termination feature on the scope inputs, and I was too lazy to go get a
tee fitting and a 50ohm mini-load.? So the readings of the scope would
be 6 dB off.? Fine, I could live with that, I was interested in the
difference, if any, between 20M and the other bands.
? 40M Hit the mic button - got a reasonable looking sine wave.? Little
fuzzy.
? 20M? Hit the button - wow, what a mess!? Looked like multiple
unrelated sine waves at the same time..? Or something.? What was it?
? Let's look at this in the frequency domain...
Got out the tinySA, plugged it into the output of the Narda.? Starting
at 80M, I looked for the 3rd harmonic:
? 80M - 3rd harmonic -32 dB
? 40M? - 3rd harmonic -18 dB
? 20M? - All heck broke loose.? Big mess.? Spurs all over, in a more or
less symetrical pattern around the fundamental.? The two biggest ones
were at 11.3 MHz ( -10dB ) and 16.55MHz ( -8 dB ).? Looked like the
unfiltered output of a
mixer.
? ? ? ? ? ? ? ? ? ? - Jerry KF6VB
