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Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Posted: Wed Feb 20, 2019 8:50 am
by glovisol
HIGH IMPEDANCE FILTER CHEBYSHEV N=9 / 0.1 dB RIPPLE / 560 to 560 OHM #10

Amplitude testing setup

Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Posted: Wed Feb 20, 2019 9:03 am
by sdrom33
Hi I not understand Swr. in figure 6 is different to 8 pre explain.

Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Posted: Wed Feb 20, 2019 9:54 am
by glovisol
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

Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Posted: Wed Feb 20, 2019 5:22 pm
by glovisol
HIGH IMPEDANCE FILTER CHEBYSHEV N=9 / 0.1 dB RIPPLE / 560 to 560 OHM #10

Filter performance in use

Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Posted: Thu Feb 21, 2019 8:39 am
by glovisol
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.

Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Posted: Sun Mar 03, 2019 10:10 pm
by sdrom33
Made filter 50 to 50 ok works good i post result photo later

Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Posted: Thu Mar 07, 2019 8:39 am
by sdrom33
Here is my no filter- filter pic.

Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Posted: Sun Mar 17, 2019 5:46 pm
by glovisol
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.

Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Posted: Sun Mar 17, 2019 6:27 pm
by glovisol
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.

Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Posted: Mon Mar 18, 2019 8:47 am
by glovisol
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.