Noise reduction mod on the Yaesu FT-897.
On my Blog - m0tef.blogspot.com/2019/04/mo...
I have been using my ft-897 for a while now, the main rig has a fault and I have been far too busy to get it sorted and repaired. I found it was not quite right, I have been spoiled by using quality receivers over the last few years and I couldn't quite put my finger on what was missing. Some reading online and some tests quickly helped me identify what it was, the AGC was a little too fast and the audio amplifier adds a certain hiss and noise to a signal.
I found two fixes online, the first one was to add a capacitor in parallel to modify the AGC hang time adding it to C1503 - mod to be found on DG2IAQ modification sheet, a great source of information for any 897 owner. found here. www.ok1kng.netcontrol.cz/rs/do...
The other fix was to reduce white noise, the info can be found here. ok1fig.nagano.cz/FT897D/FT-897...
By adding two capacitors to make up the 0.75uF and a resistor of 68 Ohm between pins 2 and 4 on the IC the TDA2003 then suppresses the high frequency noise, a simple but effective mod that isn't widely seen across the web. I think every FT-897 could benefit form this reducing the fatigue of listening for longer periods of time and makes weak SSB much easier to decipher in the band noise conditions. When working signals QRP it really helps pick signals out of the noise using SSB or CW, It I think it also helps make the DSP noise reduction more efficient when I have made the comparisons from before and after. My only wish is that I added a switch to pop it inline and out of line to make direct comparisons in a second on the same signals.
I have made a video of the impact this made on the RX audio, I feel it has made the radio much better, there is a slight downside in the RX audio on broadcast as the audio filter cuts some of the top end from wide FM broadcasts.
15 апр 2019
