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D4D: Modification for better IMD

Adam Rong
 

Folks,

Please refer to the photo to make modification to improve IMD. The RF output will be impacted but it is worthwhile to do so. Replace C5 by 103. Remove C6. Add a 1uF-10uF cap. Add a resistor of 22-27 ohm. Make connection as follows. Connect the positive pin of 1uF to the upper pad of C6. Connect the negative pin to the interconnection of 22-27 ohm and the original 330 ohm. Remember to adjust the audio output to just stably trigger the relay.



Thanks,
Adam

Adam Rong
 

Folks,

For the modification 2 in the full manual, you can try a better solution. Cut a PCB trace and add a 1N4148 diode as the following picture. It will improve the carrier leakage by about 10dB. So far I haven’t seen any significant side effect. This modification is suggested by BH4DCL.

Thanks,
Adam

在 2019年5月25日,下午10:56,Adam Rong via Groups.Io <rongxh@...> 写道:

Folks,

Please refer to the photo to make modification to improve IMD. The RF output will be impacted but it is worthwhile to do so. Replace C5 by 103. Remove C6. Add a 1uF-10uF cap. Add a resistor of 22-27 ohm. Make connection as follows. Connect the positive pin of 1uF to the upper pad of C6. Connect the negative pin to the interconnection of 22-27 ohm and the original 330 ohm. Remember to adjust the audio output to just stably trigger the relay.



Thanks,
Adam



<image1.jpeg>

Mark Sykes
 

Adam,

The 1N9148 diode in the cut trace for modification 2 carrier leakage:  That is instead of the 1M Ohm pot?

Thanks,
Mark
KD8RG

Adam Rong
 

Correct. 1M Ohm pot is no need.

Thanks,
Adam

在 2019年6月12日,下午11:39,Mark Sykes <mark@...> 写道:

Adam,

The 1N9148 diode in the cut trace for modification 2 carrier leakage:  That is instead of the 1M Ohm pot?

Thanks,
Mark
KD8RG

tommi647@...
 

I'm a little late to this group and am not aware where the 1 meg pot was to be connected, or why. Also what does the diode actually do to improve reception or transmission?
Thanks very much Tom.

Adam Rong
 

Tom,

We were discussing the way Elecraft K2 adopted in their SSB option board that you can download from here. See page 24 for balanced modulator portion. The 1M pot is connected to pin 1, 2, 3 of the NE602.
https://ftp.elecraft.com/K2/Manuals%20Downloads/ksb2%20manual%20rev%20G.pdf

However, we found that this way is not effective most of the time. The way to add a diode will reduce the power supply voltage and it is kind of design of experiments from BH4DCL.

Thanks,
Adam

Adam Rong
 

Folks,

Please read the deep modifications from BH4DCL. He modified LPF, PA bias, VOX and the power on transient transmission. Again, please use Google translation to read this page in Github:
https://github.com/cnsit/radio/blob/D4D/articles/D4D.md

Also, if you find it is easy to get the VOX mis-triggered in TX after you modified the #1 in the manual to improve IMD, you can add a 103 cap at the Audio In connector.

Thanks,
Adam