HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

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glovisol
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Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Post by glovisol » Wed Feb 20, 2019 8:50 am

HIGH IMPEDANCE FILTER CHEBYSHEV N=9 / 0.1 dB RIPPLE / 560 to 560 OHM #10

Amplitude testing setup
Attachments
Noise Gen Testing 1.JPG
Noise Gen Testing 1.JPG (162.82 KiB) Viewed 3101 times
Noise Gen. testing 2.JPG
Noise Gen. testing 2.JPG (91.52 KiB) Viewed 3101 times

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sdrom33
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Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Post by sdrom33 » Wed Feb 20, 2019 9:03 am

Hi I not understand Swr. in figure 6 is different to 8 pre explain.

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glovisol
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Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Post by glovisol » Wed Feb 20, 2019 9:54 am

Hi sdrom33, the difference in the SWR plots, especially the better SWR at high frequencies, is due to the addition of the built-in wideband 560 to 1 KOhm transformer in 8, while in Figure 6 the testing was done 560 to 560 Ohm only.

Cheers,

glovisol

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glovisol
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Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Post by glovisol » Wed Feb 20, 2019 5:22 pm

HIGH IMPEDANCE FILTER CHEBYSHEV N=9 / 0.1 dB RIPPLE / 560 to 560 OHM #10

Filter performance in use
Attachments
HP filter in use.JPG
HP filter in use.JPG (114.8 KiB) Viewed 3071 times
LF Spectrum - no Filter.jpg
LF Spectrum - no Filter.jpg (196.1 KiB) Viewed 3071 times
LF Spectrum - Filter.jpg
LF Spectrum - Filter.jpg (195.34 KiB) Viewed 3071 times

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glovisol
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Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Post by glovisol » Thu Feb 21, 2019 8:39 am

CONCLUSION

HIGH IMPEDANCE HIGH PASS FILTER CHEBYSHEV N=9/0.1 dB/560 to 1 KOHM - LW & MW BAND ELIMINATION
LOW IMPEDANCE HIGH PASS FILTER CHEBYSHEV N=9/0.1 dB/50 to 50 Ohm - LW & MW BAND ELIMINATION
HIGH IMPEDANCE LOW PASS FILTER CAUER C 05 15 40/N=5/0.5 dB/560 to 1 KOhm - MW & HF BAND ELIMINATION


In this thread and the related one concerning the LW band, three filters have been presented, starting with the theoretical calculation, prototype development and test and final realisation. These filters, which are simple to build and pose small building difficulties, will provide RSP Receiver improved operation by eliminating strong unwanted signals that would overload or otherwise impair operation of the RSP receiver under unfavourable propagation/interference conditions.

The practical schematic of the High Pass balanced filter for use with long wire antennas and HI Z RSP receiver input is presented below.

One final note regards the realization of low noise isolation/impedance scaling of wideband ferrite toroid transformers. To obtain noise rejection, primary-secondary capacitance must be reduced as much as possible. This means that there is a trade-off between number of turns and hence inductance and noise performance, because the lower the inductance, the higher the losses at low frequency, but the lower the inductance, the lower the capacitance and the lower the noise leaking through. For this reason one must make a compromise, which depends on the antenna characteristics: the bigger the antenna aperture, the higher the signals and therefore the more loss affordable by reducing the number of turns.

It is up to the individual operator to find the best compromise. As an example the 560 to 1 KOhm transformer should have, by calculation:

Xl = 560 * 2 = 1120 Ohm @ 2 MHz
L = 1120/(2*3.14*10^6) = 0.180 mH
Np = 1000*SQRT(0.180/400)= 20 turns
Ns = 20*SQRT(1000/560) = 27 turns

The best compromise I found betwen loss and noise was to halve the number of turns, as shown in the schematic.
Attachments
Filter schematic-grounding.jpg
Filter schematic-grounding.jpg (88.92 KiB) Viewed 3047 times
All filters.JPG
All filters.JPG (83.72 KiB) Viewed 3047 times

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sdrom33
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Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Post by sdrom33 » Sun Mar 03, 2019 10:10 pm

Made filter 50 to 50 ok works good i post result photo later

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sdrom33
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Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Post by sdrom33 » Thu Mar 07, 2019 8:39 am

Here is my no filter- filter pic.
Attachments
No filter-filter.jpg
No filter-filter.jpg (141.71 KiB) Viewed 2789 times

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glovisol
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Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Post by glovisol » Sun Mar 17, 2019 5:46 pm

Using SDRplay Ver. 1.3

I am uploading screns pics showing HI PASS filter performance while receiving Voice of America, Washingtong D.C. on the 19 m band as if it were a few km away. Figure 1 shows spurious and artefacts caused by strong local signals in the MW broadcast band. Figure 2 shows a clean spectrum after inserting the High Pass filter. Decrease in signal level is due to fading conditions, not by filter insertion loss, which is negligible. This can be verified by the level of noise on dial.
Attachments
VOA from Washington D.C - Spur.jpg
Figure 1: Strong signals in the MW broadcast band generate spurs & artefacts
VOA from Washington D.C - Spur.jpg (206.22 KiB) Viewed 2512 times
VOA from Washington D.C. clean.jpg
Figure 2: Insertion of Hi Pass filter cleans the show.
VOA from Washington D.C. clean.jpg (200.37 KiB) Viewed 2512 times

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glovisol
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Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Post by glovisol » Sun Mar 17, 2019 6:27 pm

In Figure 2bis we have giant signals on the 49 m band (up to -26 dBm) and still a clean spectrum using the internal MW notch filter.

Note that in the previous post RF gain is at maximum in Fìgures 1 & 2, but what happens if we reduce the gain?

Figure 3 shows 19 m band reception of BBC on 15,400 KHz (VOA Washington still there). I have reduced RF gain to minimum level ( this is a gain reduction of 61 dB) but spurs & artefacts remain. In Figure 4, with HP filter inserted, the spectrum is clean and we can afford to keep RF gain at max. level. These tests demonstrate the usefulness of the HP filter cutting below 1900 KHz when in presence of strong local MW broadcast signals.
Attachments
Giant signals  on 49 m.jpg
Figure 2bis. Giant signals on 49 m and still a clean spectrum!
Giant signals on 49 m.jpg (197.04 KiB) Viewed 2494 times
BBC spur.jpg
Figure 3. Gain reduced but spur & artefacts do not go away
BBC spur.jpg (192.92 KiB) Viewed 2498 times
BBC no spur.jpg
Figure 4. With HP filter inserted all interference gone even at max. gain
BBC no spur.jpg (188.9 KiB) Viewed 2498 times

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glovisol
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Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Post by glovisol » Mon Mar 18, 2019 8:47 am

HIGH PASS FILTER GROUND CONNECTION OPERATION

Please refer to the balanced HP filter schematic that I again upload below for convenience. I have found that for certain LOCAL NOISE conditions it essential to disconnect the ground lead to remove interference, as shown in the pics below.
Attachments
Filter schematic-grounding removed.jpg
Remove ground lead with some local interference
Filter schematic-grounding removed.jpg (87.07 KiB) Viewed 2447 times
Ground off.jpg
Ground lead removed
Ground off.jpg (183.49 KiB) Viewed 2447 times
Ground on.jpg
Ground lead connected
Ground on.jpg (184.45 KiB) Viewed 2447 times

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