HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

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

Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Postby glovisol » Tue Feb 12, 2019 8:36 am

FILTER CHEBYSHEV HIGH PASS N=9 - 50/50 Ohm - UNBALANCED

From prototype to finished filter


The filter is built on a one side PC board used as a soldering reference ground plane for minimising parasitic inductances. All components are assembled on this board prior to mounting inside the die cast enclosure. I was worried about parasitic coupling among the coils, due to close proximity, but filter attenuation @ 1.5 MHz is very similar to that of the original prototype (#6) so this problem did not materialise. Another worry was what would happen with closing the lid, but no detrimental IN/OUT coupling was detected.

Coil formers were made with 20 mm dia. PVC electrical conduit pipe and no detrimental effects on coil Q was detected. Once the filter is mounted inside the enclosure and tested, it is advisable to glue the base of each coil former to the PC board with bi-component epoxy resin.

Later today antenna attenuation of LW and MW band will be tested on the RSPduo and reported.
Attachments
Chebyshev N=9 HI PASS FILTER DATA.jpg
Chebyshev N=9 HI PASS FILTER DATA.jpg (106.49 KiB) Viewed 2537 times
DSC_1405.JPG
DSC_1405.JPG (73.25 KiB) Viewed 2537 times
DSC_1404.JPG
DSC_1404.JPG (69.49 KiB) Viewed 2537 times

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glovisol
Posts: 643
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Postby glovisol » Tue Feb 12, 2019 10:09 am

FILTER CHEBYSHEV HIGH PASS N=9 - 50/50 Ohm - UNBALANCED

Practical results
Attachments
HP filter in operation.JPG
HP filter in operation.JPG (75.92 KiB) Viewed 2533 times
No HP Filter MW broadcast Band.jpg
No HP Filter MW broadcast Band.jpg (264.92 KiB) Viewed 2534 times
HP Filter in MW broadcast band.jpg
HP Filter in MW broadcast band.jpg (262.72 KiB) Viewed 2534 times

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glovisol
Posts: 643
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Postby glovisol » Tue Feb 12, 2019 4:45 pm

FILTER CHEBYSHEV HIGH PASS N=9 - 50/50 Ohm - UNBALANCED

Practical results


NOTE: For the measurements of previous post and of this one there is a 550 to 50 Ohm toroid transformer between Beverage antenna & filter's input.
Attachments
While @ 3.6 MHz is business as usual....jpg
While @ 3.6 MHz is business as usual....jpg (191.62 KiB) Viewed 2509 times
Spectrum 0-1500 KHz - No HP filter.jpg
Spectrum 0-1500 KHz - No HP filter.jpg (192.99 KiB) Viewed 2511 times
Spectrum 0-1500 KHz  with HP filter.jpg
Spectrum 0-1500 KHz with HP filter.jpg (179.73 KiB) Viewed 2511 times

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glovisol
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Location: Piedmont, Italy

Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Postby glovisol » Wed Feb 13, 2019 3:31 pm

FILTER CHEBYSHEV HIGH PASS N=9 - 50/50 Ohm - UNBALANCED

Filter performance near cutoff with Network Analyser- 1
Attachments
Measurement setup.JPG
Measurement setup with AA30 Network Analyser
Measurement setup.JPG (152.49 KiB) Viewed 2476 times
HIGH PASS R.L. 1-3MHz.jpg
Return loss near the 2 MHz cutoff frequency better than 12 dB
HIGH PASS R.L. 1-3MHz.jpg (113.86 KiB) Viewed 2476 times
HIGH PASS SWR 1-3 MHz.jpg
SWR near the 2 MHz cutoff frequency 1.6 max.
HIGH PASS SWR 1-3 MHz.jpg (65.35 KiB) Viewed 2476 times

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glovisol
Posts: 643
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Postby glovisol » Thu Feb 14, 2019 7:47 am

FILTER CHEBYSHEV HIGH PASS N=9 - 50/50 Ohm - UNBALANCED

Filter performance 2 to 10 & 2 to 29 MHz with Network Analyser- 2
Attachments
HIGH PASS SWR 1-10 MHz.jpg
HIGH PASS SWR 1-10 MHz.jpg (67.37 KiB) Viewed 2452 times
HIGH PASS SWR 1-29 MHz.jpg
HIGH PASS SWR 1-29 MHz.jpg (67.62 KiB) Viewed 2452 times
HIGH PASS R.L. 1-29 MHz.jpg
HIGH PASS R.L. 1-29 MHz.jpg (64.44 KiB) Viewed 2452 times

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mark.
Posts: 51
Joined: Tue Oct 03, 2017 9:14 pm

Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Postby mark. » Thu Feb 14, 2019 10:27 pm

Responding to the original post of the thread..
For the one scenario I didn't see, 500 ohm longwire and 50 ohm radio.

Would I build a 500 in/500 out filter with a 500/50 transformer on the output of the filter or a 50/50 filter with a 500/50 transformer on the input of the filter? Or can it be done through filter values and no transformers?

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glovisol
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Location: Piedmont, Italy

Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Postby glovisol » Fri Feb 15, 2019 7:46 am

Hi Mark,

In the last posts I have finalised construction and performance measurements for the 50 Ohm to 50 Ohm filter. This filter is useful for connecting a 50 Ohm antenna feedline to a 50 Ohm input of the RSP receiver. If you wish you can place a 10:1 low noise transformer at the filter's input (560 to 50 Ohm) and connect through the filter a long wire antenna to the 50 Ohm input of the RSP receiver.

Two days ago I have started the construction of the Chebyshev filter N=9, r=1.5 dB, ZIN/ZOUT=0.6 - PROTOTYPE #7: this filter had been designed for connecting directly a 600 Ohm long wire antenna to the 1 KOhm Hi Z balanced input of the RSP2 or the RSPduo. Unfortunately I have found that the coils developed for the prototype (prototype #7) are too large and do not fit in the 1590 BS Hammond die cast enclosure I have purchased. Furthermore I have found, measuring prototype #7 with the Network Analyser, that SWR becomes too high past 4 MHz and this problem is caused by the 0.6:1 ratio between input and output. For this reason I have re-designed the filter for a 1:1 ratio, eg. 560 to 560 Ohm. This filter will connect to the long wire antenna directly and will have at the output a 1:2 ratio wideband, low noise transformer matching the 1 KOhm HI Z input of the RSP receiver. By changing this transformer, e.g. using a 10:1 ratio, 560 to 50 Ohm, it will be possible to couple a long wire antenna to a 50 Ohm input.


For the practical realisation of this filter I need smaller coils. I tested iron powder toroid coils made with type 1 material, e.g. Micrometals T50-1, but Q is too low: Q<120 @ 2 Mhz. So I have developed a new layout with air core coils (Q=200) and am presently building the filter which will fit into the box. I expect to be ready for measurements and do them over the weekend. I also inted to write a post dedicated to the practical realisation of low noise wideband toroid transformers together with Network Analyser measurement data.

Kind regards,

glovisol

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illllm
Posts: 56
Joined: Wed Jan 23, 2019 10:26 pm

Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Postby illllm » Fri Feb 15, 2019 12:39 pm

can you please let me know what it is that you used to generate the signal so you cold test your filter?

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glovisol
Posts: 643
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Postby glovisol » Fri Feb 15, 2019 2:40 pm

Hi Illlm,

I use a wideband noise generator sold on ebay for 15 USD approx. You can find details & pictures of the measurement setup here:

viewtopic.php?f=5&t=3943

and here:

viewtopic.php?f=5&t=3352

Remeber to use a supply voltage of maximum 10 V with the noise generator. Higher voltages are not safe as I discovered to my own cost.

glovisol

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glovisol
Posts: 643
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: HIGH PASS FILTER FOR OPTIMUM HF RECEPTION

Postby glovisol » Fri Feb 15, 2019 2:53 pm

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

Development and construction of this filter with a new layout & winding coil method went much quicker than anticipated and I am able to upload some measurements taken on the finished filter assembly, before mounting into the die cast box. Filter performs well and offers a SWR below 1.5 up to 15 MHz and a SWR below 3 up to 29 MHz. All details in the next posts.
Attachments
HIP HI Z Bandpass 6 MHz.jpg
High Pass Chebyshev N=9, r=0.1 dB, 560 to 560 Ohm - Bandpass plot to 6 MHz
HIP HI Z Bandpass 6 MHz.jpg (149.65 KiB) Viewed 2353 times
HP Hi Z 1K-3K SWR.jpg
High Pass Chebyshev N=9, r=0.1 dB, 560 to 560 Ohm - SWR near cutoff frequency
HP Hi Z 1K-3K SWR.jpg (102.69 KiB) Viewed 2353 times
HP HI Z 1.5K-10K.jpg
High Pass Chebyshev N=9, r=0.1 dB, 560 to 560 Ohm - SWR to 10 MHz
HP HI Z 1.5K-10K.jpg (103.57 KiB) Viewed 2353 times

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