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PY3CRX_PY2PLL
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Filter with 1500 Hz center frequency
« on: 19. April 2021, 22:46:02 »

Hi all ...

Is it possible to include 1500 Hz as center frequency to the existing filters? Just to match WSPR from WSJT-X. I've been using it for a few days on mcHF V0.4 (CAT + PTT + USB audio), lots of fun at 27dBm 

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Re:Filter with 1500 Hz center frequency
« Reply #1 on: 20. April 2021, 05:47:05 »

I will not say for UHSDR, in my mod-firmware I already worked with filters, in particular, I added CW filters with a width of 200 and 100 Hz. What exactly do you need? Give a normal, well-voiced technical task.
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Re:Filter with 1500 Hz center frequency
« Reply #2 on: 20. April 2021, 09:38:34 »

I read about WSPR. If you select a 2.7 kHz BPF filter, you just get a 2.5 kHz bandwidth with a center 1.5 kHz. 73!
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Re:Filter with 1500 Hz center frequency
« Reply #3 on: 20. April 2021, 10:43:44 »

Please explain - I do not see any sense in this discussion...

You get the audio for WSJT-X via USB - correct?

If so: there is not any filter added in the chain between output of audio codec and USB audio stream - it is 100% full 48KHz.

So about what filters in respect of WSPR do you talk?

vy 73
Andreas
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Re:Filter with 1500 Hz center frequency
« Reply #4 on: 20. April 2021, 12:09:06 »

Gentleman;

I use WSPR on USB mode, as it should be. Of course I use regular SSB filters (low pass, band pass etc with high cut at 1.8, 2.4 whatever), any of them which allows those 200Hz BW around 1500Hz to pass thru. Everything's perfect.

I noticed that even at USB I can select "CW" filters (e.g. 900Hz center frequency 300Hz BW I use when decoding DSC on HF or RTTY on ham bands etc, when I set 900Hz at those softwares as the center freq).

Since WSPR software by default uses a 1500 Hz "tone" +/- 100Hz what I suggest was sort of data modes filter @ 1500Hz with 300Hz BW.

It's a way to avoid nearby signals driving agc. Is the same CW filter with a few extra center frequencies (500, 550, 600 etc ... 900 ... jump to 1500).

Regards;
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Re:Filter with 1500 Hz center frequency
« Reply #5 on: 20. April 2021, 14:49:20 »

Accepted, in the next version of the mod-firmware I will add a filter with a center of 1500 Hz and a bandwidth of 300 Hz. 73!
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Re:Filter with 1500 Hz center frequency
« Reply #6 on: 20. April 2021, 14:55:28 »

If you use WSPR via USB audio all filters you select are not in the signal path. So it makes no difference what filter you use. No need for any new filter. AGC is driven by signals outside the filter bandwidth anyway.

vy 73
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Re:Filter with 1500 Hz center frequency
« Reply #7 on: 20. April 2021, 16:51:43 »

Ok , got it. I saw 48KHz when I use DIQ = EXT, but using DIG = EXT I have a filtered audio and the filters have effect on it. But if AGC is not sampled inside the filter passband there's no advantage at all to have a narrower filter for digital modes. Attached a picture from WSJT-X input monitor in wide band mode. mcHF filter = 1.8K wide, 1.3K CF.

73.
 wsjt.jpg
« Last Edit: 20. April 2021, 19:22:37 by PY3CRX_PY2PLL »
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Re:Filter with 1500 Hz center frequency
« Reply #8 on: 21. April 2021, 04:36:16 »

Yes - thats it! I am only usig DIQ mode and demodulate signals via PC applications. Why using ARM-based filters and demodulation routines when you already have attached a much more powerful PC  ... So I forgot that there is a possiblity of a "mixed operation".

Hint:
You gain some more dBs if you use DIQ and demodulate the signal via PC programm (like Quisk), then pipe the audio output to WSJT-X.

vy 73
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Re:Filter with 1500 Hz center frequency
« Reply #9 on: 21. April 2021, 14:16:08 »

I understand. My use is pretty standard like an analog radio, except that the serial CAT port and audio interface are embedded @ USB port. I did'n see lack of CPU, to be honest performance is very acceptable. Run for hours with 27dBm no frequency drift nor power variations. The only "issue" is that PC clock must be compensated for something like 100ms to match NTP synched PC time. The same apply when I use RTTY PSK31 etc using FLDigi, except that CAT does not work ok.

I tried DIQ once on DreAM DRM software, but those RX only modes I run with SDR# or HDSDR and AirSpy SDR.

Still a surprise that AGC is not derived after IF filters. Does this solution reduce a desired weak signal inside filter pass band while there's another strong signal within the 48KHz baseband? I did not notice this behaviour btw.

73!
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Re:Filter with 1500 Hz center frequency
« Reply #10 on: 21. April 2021, 15:52:37 »

Warren Pratts WDSP is a very complex thing - ideal for portable devices with hardware like mcHF...

Of course you do not see any CPU issues in standalone mode - you have to comare all stuff in parallel with a PC SDR software (I by mysel prefer Quisk on Linux) which is fed by DIQ. If you do this you will notice big differences in overall RX and TX performance. On Linux you can simply create an audio sink and an audio source where you connect the SDR software with any other (AF using) digital modes software. On Windows you can use special applications for this - I don not 100% remeber the name because of I do not have Windows. Maybe the name is "VAC" (Virtual Audio Cable)?

If I am at home and want to use digital modes I always use DIQ and PC applications - not a mix of both. That makes no sense. In protable use you have a good performance regarding mcHF is a QRP transceiver running STM32 firmware. Of course the filter coeffs which are used in PC programs are much more powerful.

vy 73
Andreas
« Last Edit: 21. April 2021, 15:52:56 by DF8OE » Logged

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Re:Filter with 1500 Hz center frequency
« Reply #11 on: 23. April 2021, 01:53:53 »

Yes, virtual audio cables, I use them to plug SDRs that run at the same PC of external decoders, screen capture recorders etc.

This WSPR app was just a test, I was away from a long time (my first log was at 2009 1st quarter), and I like the idea to run it using mcHF because its ease of low power setup. Mine still without PA, just an MWH591 hybrid amplifier that delivers 800mW maximum from 1 to 250MHz. So I set "5W" to have 500mW for now.

But the future is a regular (and modified) PA, with a pair of BFG591s at the driver and some bipolar at the output pair (2SC1971 may be). CW and SSB. I did not like the original mosfets for a portable QRP, too much bias current to have enough gain at higher frequencies. But this is another story.

Thanks for all info. 73.
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Marcus Ramos
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Diskussions- und Newsboard des DARC-Ortsverbandes I40  |  allgemeine Kategorie  |  UHSDR Firmware (Moderators: DF8OE, DL1PQ)  |  Topic: Filter with 1500 Hz center frequency <- zurück vorwärts ->
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