ALC And Digital Modes - Avoiding Harmonics
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- Опубликовано: 25 авг 2024
- Someone emailed me the other day after working FT8 for my first few days with a screenshot of my radios signal on his waterfall, and a third order harmonic.
He attached a document with a lot of good information on tuning a radio for FT8 and other digital modes.
After doing a little research into what ALC(Automatic Level Control) is and what it does, I experimented until I found a "sweet spot" where I could transmit higher power without it resulting in distorted audio, or my radios ALC kicking in.
By tweaking a few settings I was able to achieve a nice middle ground and eliminated my third order harmonic.
I am by no means an expert, so suggestions and corrections are welcome. But I wanted to bring this to light, and share how I fixed this on my ft-450.
This ducument was sent to me by a Mike Black/W9MDB and apears to be created by a Eric Spero/WA1SXK as well.
Full credit goes to these two for this document.
docs.google.co...
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If you all have any special tips to do this better, let me know!
This video helped me so much, doubled my output power with no ALC. Thanks! 73
Now I need to learn enough about audio settings in Linux to duplicate what you have done. Thanks for giving me a lot of starting point info. much appreciated. 73 N8VY Doug
@ModernHam Question. How far away from your QTH is the W9 station who complained about your audio harmonics? If the station is close to you, then the problem could have been RX overload on his end, in which case he should turn down his RF gain. The best way to tell is to enable the radio notch filter, and center it on the main audio signal. If the harmonics are still seen, then the problem is with the transmitting station. If the harmonics disappear, then the problem is RX Overload at the receiving station, and they should turn down their RF Gain, or switch off the pre-amp, and/or enable their attenuator. AC6BW
Great info thanks 🙂
Glad I could help!
Well explained
Wonderful video. I have an Icom IC-707 that does not have ALC. You gave me some ideas to try and see if I can get the levels correct to use it with Winlink Express. I am also using a Signalink USB Sound Card. Thanks es 73 - KF6BL
also dont froget, you change the audio frequency in the wsjtx software when you reply to a CQ etc, that will also have an effect on the ALC as well as one frequency tone will be higher and cause the alc to kick in and a lower one wont
Driving line level audio from a soundcard into a mic level input is why you were splattering. The rig has a data input in the back, use it.
It is connected via the data port.
The ALC reading on the Xiegu G90 reads 98 to 100. That can be reduced by the radio AGC or the PC audio?
Hi, great video. That has cleared up a lot of confusion for me. However, I am using digivox and I am struggling with getting that to work. I that if I reduce my audio to levels where ALC is absent, my digivox will not kick in to TX mode. The other problem I'm having is my ALC meter is not steady. It is pulsing. Could this be caused by RF feedback or grounding issues. Thanks in advance. 2E0MNV
70w!!! Jezzzz. I don’t run over 30 on a much poorer antenna than yours. I wouldn’t never flog my poor radio at 70. I am licensed at 100w PEP so 70 is over that any way
Yeah the trick is to set your output higher, and adjust the actual level with your PC. While my radio is set to 70, I'm actually running 50-60 after volume level controls are introduced.
@@ModernHam The problem with that approach, is that you're not using the full audio range of the radios audio chain front end and modulator. That effectively brings the noise floor, hiss, on the audio lines up closer to the actual signal and degrades the quality a tiny bit. You want the cleanest audio possible when doing digital. It helps your chances of being decoded when your signal is weak at the receiving end.