Tuning the Hermes/Angelia pre-driver notch

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marc
Posts: 34
Joined: Mon May 15, 2017 2:40 pm

Tuning the Hermes/Angelia pre-driver notch

Postby marc » Tue May 30, 2023 6:11 am

I'm trying to understand how to set the variable notch filter located at the DAC output and centred at around 71 MHz on all Hermes and Angelia buards (C22, L4, C12 ,L3, C13). I don't think I've read anything about this filter in the OpenHPSDR literature.

VY 73
Marc f6itu
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w-u-2-o
Posts: 5540
Joined: Fri Mar 10, 2017 1:47 pm

Re: Tuning the Hermes/Angelia pre-driver notch

Postby w-u-2-o » Tue May 30, 2023 11:17 am

Interesting question! I didn't have time to put this into LTspice for simulation, but a quick few iterations at https://rf-tools.com/lc-filter/ produced this:

Capture3.JPG
Capture3.JPG (317.19 KiB) Viewed 1550 times

Strange how L3 and C13 are inverted in their order on the schematic.

If no one answers here you might try reaching out to Kjell Karlsen, LA2NI, he might know.
marc
Posts: 34
Joined: Mon May 15, 2017 2:40 pm

Re: Tuning the Hermes/Angelia pre-driver notch

Postby marc » Tue May 30, 2023 9:10 pm

Thank you, Scott

You had the same reaction I had :- D (except that I'm a lazzy guy, I used Elsie)

I'll try to ask Kjell the question (I already bother him too often about the Munin400/Aries suite etc, I don't dare bother him too much).

I'll simply measure with an analyzer what comes out of the DAC "without" the filter, just to see if there isn't an unsuspected/unwanted birdy.

Thanks again Scott

73'
Marc f6itu

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