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ADX-S IF Adjustment

 

Hi Adam,
?
Besides the enjoyment I get from doing the assembly, your kits also ?give me the opportunity to learn more about how receivers, transmitters and their software work. ?I've been studying the ADX-S to understand it better and find it's very interesting.
?
The ADX-S v2 manual states:
?
Since the ceramic filter has tolerance on bandwidth and center frequency, it is better that you fine?tune your own beat frequency, so you can get higher SNR and less interference. In order to do so,?you do a search in the source code and you will find two different beat frequencies. One is 460570,?the other is 449430. For now, 449430 is only for 20 meter band. Adjust them at 500-1kHz step and?compare with the default setting, so you will get the best value for your kit.
?
Can you suggest the best way to evaluate the highest SNR and lowest interference when adjusting the IF's? ?For example, could I supply the ADX-S with RF from a signal generator then peak the IF for strongest output as seen on a WSJT-X waterfall? ?Please tell me the method you would use.
?
Thank you,
?
John L.
AA7US
 

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Hi John,

Signal generator is my method. Actually I used a TinySA plus a 40dB fixed coaxial attenuator. Set the signal -80dBm or around. Check the spectrum waterfall.

AGC makes it less apparent to observe the improvement. Also, the settings of the waterfall also impact. To temporarily disable the AGC, you can short the 10uF at pin 5 if I remember correctly.

Since the response of the ceramic filter is not very steep, the improvement is minor if it does have some.

Thanks,
Adam

在 2024年10月8日，11:26，AA7US via groups.io <landrjoh@...> 写道：

?
Hi Adam,
?
Besides the enjoyment I get from doing the assembly, your kits also ?give me the opportunity to learn more about how receivers, transmitters and their software work. ?I've been studying the ADX-S to understand it better and find it's very interesting.
?
The ADX-S v2 manual states:
?
Since the ceramic filter has tolerance on bandwidth and center frequency, it is better that you fine?tune your own beat frequency, so you can get higher SNR and less interference. In order to do so,?you do a search in the source code and you will find two different beat frequencies. One is 460570,?the other is 449430. For now, 449430 is only for 20 meter band. Adjust them at 500-1kHz step and?compare with the default setting, so you will get the best value for your kit.
?
Can you suggest the best way to evaluate the highest SNR and lowest interference when adjusting the IF's? ?For example, could I supply the ADX-S with RF from a signal generator then peak the IF for strongest output as seen on a WSJT-X waterfall? ?Please tell me the method you would use.
?
Thank you,
?
John L.
AA7US
 

Thanks Adam.
?
I'm curious about something (just trying to learn)…
?
Does the value of the capacitor connected to pin 5 of the CD2003 or Toshiba TA2003 affect the behavior of the AGC? ?I ask because the data sheets suggest that a 33uF capacitor should be used, yet the ADX-S uses a 10uF capacitor?
 

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John,

Here is a write up in Chinese:



Thanks,
Adam

在 2024年10月9日，03:49，AA7US via groups.io <landrjoh@...> 写道：

?
Thanks Adam.
?
I'm curious about something (just trying to learn)…
?
Does the value of the capacitor connected to pin 5 of the CD2003 or Toshiba TA2003 affect the behavior of the AGC? ?I ask because the data sheets suggest that a 33uF capacitor should be used, yet the ADX-S uses a 10uF capacitor?
 

That explains things quite well.
?
Thank you Adam.
?
John L.
AA7US

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