John,
What linear supply did you use? Thanks.
Chris - AE6VK
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
Sent: Friday, September 22, 2006 8:06 AM
To: flexradio@flex-radio.biz
Subject: [Flexradio] DC/DC Converter (DC1) Replaced with Linear Supply
Hi Folks,
I just wanted to let you know about a modification I made to my
radio. DC1 is a switch mode converter that provides +/- 15 volts
for the instrumentation amplifiers IC6/7 on receive that interface
the QSD to the sound card.
The DC/DC converter's internal oscillator free runs at ~120 kHz
and is very rich with odd harmonics, every 240 or so kHz, throughout
the HF range.
This manifests itself as low level 'carriers' that drift around and
through receive frequencies. When the SRD is first powered up they
move quite fast, but after the unit has warmed up the move very, very
slowly through your QSO.
These signals were about S4 on my SDR1000 in the 40M band and are easily
removed with the automatic notch. But, loving to tinker like I do I
removed the DC1 and soldered a 7 pin header in its place. I used a
1" x 2" x 2", +/- 15v linear supply wired to the header.
How's it work? Great! No more warbling tones from within the SDR.
I wish I would have done more before and after testing. Now when I
connect the receiver to a dummy load, most of the bands are clear of
spurs with the noise floor at -153 dBm. I imagine that the fundamental
waveform (square wave?) of the DC/DC converter was putting an awful lot
of total integrated power into the QSD and mixing with other signals
there to increase the total spurs.
It just keeps gettin' better.
Regards,
John
k2ox
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