Title: Intermodulation V0.7
Post by: funky on 19. April 2021, 15:38:54
Hi,
I have a mcHF V0.7 and I would like to reduce the in-band intermodulation products. For this I have already implemented the potato-mod. This mod improved the IMD of about 3-5 dB.
However, I can still see strong intermodulation products. E.g.
3.6 MHz: -17 dB
14.2 MHz: -25 dB
28.5MHz: -25 dB
(I will upload some screen shots after this post)
Are there any other mods for V0.7 which will help to reduce the IMD?
Many thanks in advance!
73
Michael
PS:
PA bias is set properly and IQ calibration has been verified with the spectrum analyzer.
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Title: Re:Intermodulation V0.7
Post by: funky on 19. April 2021, 15:39:36
Title: Re:Intermodulation V0.7
Post by: funky on 19. April 2021, 15:40:09
Title: Re:Intermodulation V0.7
Post by: funky on 19. April 2021, 15:40:39
Title: Re:Intermodulation V0.7
Post by: satoryboy on 24. April 2021, 08:36:33
It is worth trying to reduce the bias at the inputs-outputs of the TX mixer switch to 1.65 V. This will dramatically increase the linearity of the switches. Read the attached article. It is also worth reducing the offset of the bandpass filter switches. You can also increase the quiescent current of the transistors in the PA driver, select a pair for it according to the gain. In the final stage, if possible, there should be a pair selected for the cutoff voltage and the slope of the characteristic. The quiescent current of the mosfets is adjusted according to the minimum level of the third harmonic of the signal, most conveniently in the 18 MHz range, the low-pass filter does not filter the harmonic so much. If you conduct experiments, please report the results, it is very interesting. I do not have professional measuring equipment yet. It would be great if someone could measure the clogging dynamic range (ARRL method, 14 MHz, 500 Hz bandwidth, spacing 2, 20, 48 kHz) of several instances of mcHF.
https://disk.yandex.ru/i/csRgBBzr8XatlQ (https://disk.yandex.ru/i/csRgBBzr8XatlQ) |
Title: Re:Intermodulation V0.7
Post by: SP3OSJ on 24. April 2021, 09:31:42
You need to adjust the transmission path well.
[youtube d25hLhPcHYs]
73
Artur |
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