While adding the new 9-band ISO-center graphic EQ today, I
noticed that the IQ correction had somehow bubbled up to the
wrong place in the TX audio input chain. Doubtless an
artifact of the many ping-pongs of the source code between
Bob and me. Now in its correct place.
73
Frank
AB2KT
Alan Davis wrote:
Gentlemen,
On the Setup Menu (DSP page) the Image rejection Phase & Gain balance
controls do NOT work for the Tx (transmitter). Since the Tx is direct
conversion these controls should null out the unwanted sideband. What nulls
out the local osc? Please clarify this.
I discovered the non-working controls while doing some tests on the SDR
transmitter driving a dummy load. The carrier on my rig on 18.120mHz was
about 25 to 30 dB down and the unwanted sideband was about 35 to 40dB down.
I drove the SDR's exciter with a swept sinewave from 100 to 4000Hz @ 10sec/
log. sweep. Examination of the SDR's signal on the Icom 7800's panscope
revealed the poor carrier & unwanted sideband supression of my SDR Tx. I
tried to balance out the 'bad stuff' to no avail whatsoever.
The Tx image rejection feature was 1st incorporated in Beta 1.3.0. I ran
Beta 1.3.0 and it didn't work there either - nor in any other version.
This needs to be corrected, ASAP.
Two other things. The Transmitted SSB spectrum displayed on the SDR's
Panadapter screen is an elegant and useful feature. However, it has a
peculiar behavior that could stand some explanation. With no audio drive
applied to the SDR exciter in keydown, the displayed spectrum does NOT
APPEAR UNIFORM. There is a +25dB 'bump' from about 0Hz to 1kHz that drops
into the noisefloor from about 2kHz on up. Does that 'bump' represent
something real?
Upon driving the SDR exciter with a uniform amplitude, audio sweep
generator from 100 to 4000Hz and examining the SDR's received output on the
Icom 7800, the transmitted frequency spectrum appears uniform, not boosted
at 1kHz! Why is the SDR's Panadapter producing a false Tx spectrum even
though the SDR-1000 is evidently transmitting a uniform spectrum??
Please make the SDR's Panadapter display accurate in transmit was it is in
receive.
73, Alan K2WS
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