RSP RECEIVER LOW NOISE HF OPERATION WITH LONG WIRE ANTENNAS

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

Re: RSP RECEIVER LOW NOISE HF OPERATION WITH LONG WIRE ANTENNAS

Postby glovisol » Thu Jul 12, 2018 7:52 am

ANTENNA INDUSTRIAL NOISE SUPPRESSION AT 3.5 & 7 MHz WITH HIGHPASS FILTER

More illustrations below.
Attachments
Noise filter schematic.jpg
Filter example for initial testing
Noise filter schematic.jpg (58.95 KiB) Viewed 880 times
Noise filter.JPG
Badly constructed prototype is still effective
Noise filter.JPG (88.16 KiB) Viewed 880 times

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glovisol
Posts: 118
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: RSP RECEIVER LOW NOISE HF OPERATION WITH LONG WIRE ANTENNAS

Postby glovisol » Thu Jul 12, 2018 9:45 am

...But this Butterworth n=6 in a balanced configuration seems to work much better! Industrial noise has gone, 3.5 to 14 MHz. Noise floor is now close to - 135 dBm on all these bands! Await confirmation from other Forum dwellers.

glovisol

IMPORTANT ERRATA CORRIGE as of 13/07/18: The original balanced filter schematic had a serioud error in that all capacitor values were wrong. I have removed the wrong schematic and replaced it with the revised version with correct capacitance values. Sincere apologies, glovisol
Attachments
Noise filter schematic.jpg
REVISED Balanced noise filter schematic
Noise filter schematic.jpg (59.2 KiB) Viewed 833 times

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glovisol
Posts: 118
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Location: Piedmont, Italy

Re: RSP RECEIVER LOW NOISE HF OPERATION WITH LONG WIRE ANTENNAS

Postby glovisol » Fri Jul 13, 2018 11:48 am

Please be aware that in the balanced n=6 filter schematic in the previous post all capacitance values were wrong. I have now replaced the wrong schematic with the correct version. Sincere apologies,

glovisol

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glovisol
Posts: 118
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: RSP RECEIVER LOW NOISE HF OPERATION WITH LONG WIRE ANTENNAS

Postby glovisol » Fri Jul 27, 2018 11:16 am

The advantages of the high pass noise filter can be extended to receivers equipped with the 50 Ohm input only. The uploaded schematic is for an umbalanced 50 Ohm input / 50 Ohm output. Balanced antenna input can still be achieved by placing a balun at the filter's input and isolating the grounds, as shown in the previous posts. The balun could accommodate a variety of antenna impedances by adjusting the PRI/SEC turns ratio. This would bring the advantages of balanced feed to single ended input receivers like the SP1A.

All capacitor values are 5% standard. Capacitors are polyester, stable enough for this non-critical requirement filter. Attenuation of the broadcast band is over 40 dB, thereby removing, in addition to noise, the danger of front end overload by local strong signals.

COMPONENTS:
L1 - 5uH
L2 - 1.4 uH
L3 - 1.9 uH
C1 - 680 pF
C2 - 68 pF
C3 - 470 pF
C4 - 82 pF
C5 - 1000 pF
C6 - 1000 pF
Attachments
Umbal. noise filter n=6.jpg
Umbal. noise filter n=6.jpg (44.55 KiB) Viewed 752 times

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glovisol
Posts: 118
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: RSP RECEIVER LOW NOISE HF OPERATION WITH LONG WIRE ANTENNAS

Postby glovisol » Sat Jul 28, 2018 6:52 am

High pass n = 6 calculated filter performance is shown below. Attenuation in blue & return loss in red.
Attachments
ScreenHunter_157 Jul. 28 08.50.jpg
FILTER ATTENUATION / RETURN LOSS TABLE
ScreenHunter_157 Jul. 28 08.50.jpg (24.56 KiB) Viewed 710 times
N=6 filter graph.jpg
FILTER ATTENUATION / RETURN LOSS GRAPH
N=6 filter graph.jpg (53.34 KiB) Viewed 710 times

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glovisol
Posts: 118
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: RSP RECEIVER LOW NOISE HF OPERATION WITH LONG WIRE ANTENNAS

Postby glovisol » Tue Jul 31, 2018 10:30 am

Application of the high pass noise filter to build a balanced input for the RSP1A, as anticipated in the previus post.

This scheme allows for best ground separation. One side of the balun's input is connected to the antenna's ground. Connection between antenna and balun may be also done using a balanced line.

The ideal situation, as far as noise intake is concerned, is to place the RSP1A + noise filter right at the long wire antenna output terminal/ground stake and to use a long (buffered) active USB cable to connect to the PC.

Below is winding table based on a 10 mm dia. toroid core, F 43 ferrite material. Enamelled copper wire dia. 0.35 mm.
Attachments
Balun ratios.jpg
Balun construction data table
Balun ratios.jpg (47.73 KiB) Viewed 596 times
Xfrmr coupled noise filter n=6.jpg
Balun input for the RSP1A
Xfrmr coupled noise filter n=6.jpg (51.51 KiB) Viewed 606 times

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glovisol
Posts: 118
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: RSP RECEIVER LOW NOISE HF OPERATION WITH LONG WIRE ANTENNAS

Postby glovisol » Fri Aug 17, 2018 6:58 am

Preliminary tests of front end High Pass filter

I enclose two comparisons of reception with and without HP filter on 40 and 20 m. These have been done with a makeshift 15 m long wire antenna and a water pipe ground while on a flat in a sea resort, so they are by no means definitive, but give some indication on possible usefulness of cutting off the lower spectrum while working on HF bands. Far more extensive testing is planned with the Beverage antenna in september next.

The test consisted in quickly inserting/removing the High Pass filter at the balanced input of the RSPduo. The change was done at an average of less than 30 seconds to avoid input signal level variations due to propagation changes during the swap.

The change in the level of the noise floor is impressing, even though a decrease in the received signal level is also noticeable, so there must be a some filter insertion loss, which will also have to be investigated further on.
Attachments
HP filter test 14 Mhz Aug. 4.jpg
HP filter test 14 Mhz Aug. 4.jpg (162.73 KiB) Viewed 381 times
HP filter test 7 MHz Aug. 4.jpg
HP filter test 7 MHz Aug. 4.jpg (163.27 KiB) Viewed 381 times

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