I forgot the attachments!
On Tue, 20 Mar 2018 20:40:15 -0500
"Tim Gorman" <tgorman2@...> wrote:
Henning,
I've looked at the balanced modulator in the ubitx. It is set up
differently than what I am used to but it should work.
The arrangement I am used to is shown in the first attachment. The
ubitx is in the 2nd attachment.
In looking at T7 the windings are not very well spaced on the core.
They are crammed together at the bottom near the circuit board. I
don't know if this could cause some stray capacitance that would
upset the balance of the circuit.
I might see if I can take a probe and separate the windings and get a
little better spacing and see if that helps to balance the carrier
out.
I have to say that I am a little surprised that no one else has any
suggestions on how to better balance the carrier.
tim ab0wr
Tue, 20 Mar 2018 05:29:59 -0400 "Henning Weddig
via Groups.Io" <hweddig@...> wrote:
Tim, this is a nice measurement-
At which output power did You take the measurement? What is the
attenauation of the power attenuator between the output of the uBITX
and the Input of the spectrum analysser? Your measaurement shows a
thrid intermodulation of 34 dB/ related to a tone, in relation to
PEP please add 6 dB results in 40 dB of d3! BUT: marker 1 shows the
supressed carrier is only 20 dB below the carrier, or 26 dB to PEP.
Commercial rigs suppress by at least 40 dB or better. This result
is a"proof" of my worries concerning the unsuffiecient carrier
Suppression of the balanced modulator and xtal-filter..
Henning Weddig
DK5LV.
-----Urspr¨¹ngliche Mitteilung-----
Von: Tim Gorman <tgorman2@...>
An: BITX20 <[email protected]>
Verschickt: Mo, 19. Mrz 2018 22:46
Betreff: [BITX20] two-tone test on ubitx
Attached is a screen save from my spectrum analyzer for a two-one
test of my new ubitx.
The tones were driving the finals to about 10watts output (not
quite, but close). I had a 30db external pad and a 10db internal
pad in the SA.
The carrier was only down about 20db (marker 1). That's not as good
as I expected. I'll have to look at that and see what can be done to
improve it.
The 3rd order IMD (marker 4) was down about 34.5db which is
adequate.
The heat sinks get *hot* while running a key down measurement like
this. If you are going to use the rig for a digital mode it probably
needs to be set for about half-power out of the rig. That or a
significant increase in heat-sink capability should be installed.
tim ab0wr
