HIGH PASS FILTER FOR OPTIMUM HF RECEPTION
Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION
HIGH IMPEDANCE FILTER CHEBYSHEV N=9 / 0.1 dB RIPPLE / 560 to 560 OHM #10
Amplitude testing setup
Amplitude testing setup
- Attachments
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- Noise Gen Testing 1.JPG (162.82 KiB) Viewed 80332 times
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- Noise Gen. testing 2.JPG (91.52 KiB) Viewed 80332 times
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Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION
Hi I not understand Swr. in figure 6 is different to 8 pre explain.
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Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION
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
Cheers,
glovisol
Reason: No reason
Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION
HIGH IMPEDANCE FILTER CHEBYSHEV N=9 / 0.1 dB RIPPLE / 560 to 560 OHM #10
Filter performance in use
Filter performance in use
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- HP filter in use.JPG (114.8 KiB) Viewed 80302 times
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- LF Spectrum - no Filter.jpg (196.1 KiB) Viewed 80302 times
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- LF Spectrum - Filter.jpg (195.34 KiB) Viewed 80302 times
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Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION
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.
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
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- Filter schematic-grounding.jpg (88.92 KiB) Viewed 80278 times
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- All filters.JPG (83.72 KiB) Viewed 80278 times
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Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION
Made filter 50 to 50 ok works good i post result photo later
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Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION
Here is my no filter- filter pic.
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- No filter-filter.jpg (141.71 KiB) Viewed 80020 times
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Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION
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.
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.
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- Figure 1: Strong signals in the MW broadcast band generate spurs & artefacts
- VOA from Washington D.C - Spur.jpg (206.22 KiB) Viewed 79743 times
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- Figure 2: Insertion of Hi Pass filter cleans the show.
- VOA from Washington D.C. clean.jpg (200.37 KiB) Viewed 79743 times
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Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION
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.
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.
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- Figure 2bis. Giant signals on 49 m and still a clean spectrum!
- Giant signals on 49 m.jpg (197.04 KiB) Viewed 79725 times
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- Figure 3. Gain reduced but spur & artefacts do not go away
- BBC spur.jpg (192.92 KiB) Viewed 79729 times
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- Figure 4. With HP filter inserted all interference gone even at max. gain
- BBC no spur.jpg (188.9 KiB) Viewed 79729 times
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Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION
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.
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.
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- Remove ground lead with some local interference
- Filter schematic-grounding removed.jpg (87.07 KiB) Viewed 79678 times
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- Ground lead removed
- Ground off.jpg (183.49 KiB) Viewed 79678 times
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- Ground lead connected
- Ground on.jpg (184.45 KiB) Viewed 79678 times
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