LOW PASS FILTER FOR OPTIMUM LOW FREQUENCY RECEPTION

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glovisol
Posts: 449
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: LOW PASS FILTER FOR OPTIMUM LOW FREQUENCY RECEPTION

Postby glovisol » Wed Feb 13, 2019 5:05 pm

MEDIUM WAVE REJECTION WITH A CAUER C 05 15 40 PASSIVE LOW PASS FILTER

Network Analyser measurements

The two enclosed PC screens show the SWR performance of the LF Low Pass filter in the operating range.

- In the 560-1000 screen the AA-30 Network Analyser is connected to the antenna input and shows the SWR with the filter terminated or not terminated with a 1 KOhm resistor, simulating the load of the RSP balanced HI Z input.

- in the 1000-560 screen the network Analyser is connected to the 1 Kohm port while the antenna input is terminated with a 560 Ohm resistor. This screen also compares this reverse SWR with the forward SWR of the previous screen.

In the two screens the worsening of the SWR at low frequency is due: (a) to the proximity of the measurement limit of the AA-30 and (b) to the natural low frequency roloff of the ferrite isolation transfomer. These measurements underline the excellent performance of this filter.
Attachments
LOW PASS SWR 560-1000.jpg
LOW PASS SWR 560-1000.jpg (127.5 KiB) Viewed 629 times
LOW PASS SWR 1000-560.jpg
LOW PASS SWR 1000-560.jpg (124.65 KiB) Viewed 629 times

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glovisol
Posts: 449
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: LOW PASS FILTER FOR OPTIMUM LOW FREQUENCY RECEPTION

Postby glovisol » Fri Apr 12, 2019 8:45 am

CLEAN FILTER PLOTS AND TEST SETUP

As mentioned here:

viewtopic.php?f=5&t=4130&start=30

when working at low frequency the Spectrum Analyser plots would show strong interference generated by the switch mode PSU feeding the Noise Generator. These plots were shown in the early posts of this thread. This problem has now been solved by replacing the PSU of the Noise Generator and clean low pass filter plots are uploaded below.
Attachments
Low Pass LF Filter 1.jpg
Low Pass LF Filter 1.jpg (144.32 KiB) Viewed 122 times
Low Pass LF Filter 2.jpg
Low Pass LF Filter 2.jpg (158.03 KiB) Viewed 122 times
Low Pass filter test April 19.JPG
Low Pass filter test April 19.JPG (271.63 KiB) Viewed 122 times

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