Yaesu FT-897 Audio noise reduction mod
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- Опубликовано: 15 апр 2019
- 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. 
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did the mod a couple of weeks ago. happy happy happy. did reverse it for a moment today and the stock audio was horrible :):) its back in for ever now
Nice to see my WEB inspired someone. Cheers, 73 Petr OK1FIG
Petr Malý this is a seriously good, and simple, little mod that has changed my radio for the best. Thanks for sharing the information. The best part of what do is to share the knowledge we gain and the results we found from implementation.
You inspired me also, I have bought the tantalum caps to do the job some time ago, nice to hear it in action on here
Did this mod yesterday (added a switch to see the difference), it does cut off the top end a fair bit - also (obviously) reduces the audio output from the amp as well so you have to turn the volume up an 8th more to get the same output - slightly easier to listen to, but not by much
Thanks for the comments Ian, I too noticed a slight drop in audio output, more on the external speaker I use than internally. I have quite a high noise level here so notice a much larger difference than I might do away from the home QTH, but now I may add a switch to experiment more.
Hi, sounds great! How have you connected the capacitors together? They both look polarised and connected - + - + ? Or does it need to be or act as a single non polarised capacitor?
paisteformula6021 I can’t recall from memory but the link to the mods online gives very detailed information on the methods.
how much more is the amp draw with that mod ?
I haven’t taken any measurements but the data sheet indicates that the addition to the circuit is just there as a high frequency cut off filter.
What you pay new for these radios, makes you wonder why the manufacturer can't place these components inline. I mean let's face it it does not cost very much.
My question is...why did Yaesu allow this model to hit the market with so many improvements needed and quickly discovered by technicians in the field? In other words, they tossed it on the market without regard and just wanted our money!!!
Good question. Perhaps sometimes good enough isn’t the same as the best possible.