- ATS-909 HF Receiver:
- ATS-909
Modifications
- ATS-909
Alignment Procedure
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Alignment Spectrograms
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Software Defined Radio
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I will not repeat the numerous improvements to the
ATS-909 that may be found on other modification
websites, but will limit my comments to a few changes
that mean the most in my shortwave listening experience
with the receiver. I first obtained this dandy radio in 1995,
and have taken a soldering iron to it numerous times.
It is not a difficult radio to work on, but one must
be careful with its surface-mount components. There
are a few cables and delicate connectors that should
be handled with care. Considering those factors, I
suggest making changes described below.
- Anti-Chuffing
- Beep Removal
- Finer SSB tuning (makes steps smaller, but you
lose some ability to tune between 1 kHz increments);
4.7k for 10 Hz steps
- Replace ceramic filter CF6 with a narrower one
for better adjacent channel rejection on FM
- Restore segments of FM tuning range (diode change
enables TV audio in the USA and some assisted
listening devices)
- Short resistor R7 to ground - allows gain
reduction to zero
- AGC mods as described here; IF clipping mod not
necessary
- Audio bandwidth enhancement
Improved AGC response:
- Popular modification sites on the web have
suggested reducing capacitor C57 (on Pin15 of IC1) to
a value of 10 uF. I disagree, and have had better
results leaving it at 22 uF.
- Capacitor C11 should be verified to be 4.7 uF.
- The radio does not exercise enough control
over strong signals. Local amateur and utility
signals frequently slam the S meter to full scale and
distort badly. I have solved the problem by
increasing R181 to 470K. This slows the rate at which
C11 recharges and also allows a more effective
control of IF circuit gain.
AGC Schematic:
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AGC Parts Layout:
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Audio Modifications for Better Bass
Response:
To achieve a low end rolloff around 15Hz,
coupling
capacitors should be increased as
indicated:
- C67 and C68 (output from product detector) 4.7uF
- C80 (AM / SSB audio into IC3)
- C93 and C94 (input to audio amplifier
IC6)15uF@10v
- C106 and C107
(input to the L and R power
amplifiers IC4 and IC5)10uF@10v
- C116 and C117
(output of L and R power amplifiers
IC4 and IC5)1000uF@10v
- C132 and C133
(output of auduo amplifier IC6)
10uF@10v
Product Detector Schematic
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Product Detector Parts Layout
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