SNR improvments

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PY2PLL
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Last seen: 7 months 1 week ago
Joined: 2009/01/09 - 23:13
SNR improvments

Hi:

Does WSPR 1.1 have any sort of roofing filter implemented on its input (say 200Hz BW). Or detection of any signal that falls on 200Hz passband consider 2.4KHz BW for SNR calculations?

If I use a 200Hz IF BW at the receiver will it improve SNR threshold because of the software behaviour (e.g. I'm feeding sound card with an already limited BW on input) or this 200Hz IF filter will only helps the receiver itself (e.g preventing RX AGC from being pushed by out of the 200Hz BW signals)?

I'm asking this because I've been detecting signals as low as -33dB SNR and even running a bit more power than several stations that I detect between -15 ... -30dB SNR I never was received by any station. Most signals are declared +37dBm TX PWR at the log, I tried set my TX from 30dB to 43dBm without any success.

I'm using a Kachina 505DSP with 200Hz RX filter and average antennas (e.g inverted vee on 40m, a MFJ Mag Loop from 30m till 10m), normally enough for other digital modes QSOs (PSK31, RTTY etc) running low power (10 ... 20W). I even checked the sound card generated signal using Spectran and it seems ok. The sound card uses a realtek chipset, clock is not vy accurate I know but I'm not sure how much any clock inaccuracy affects the TX signal (example: for a correct RX picture from GOES/METEOSAT the board clock must be compensated : the default 11025 Hz became 11107Hz on any wefax software or the Chirp Sounding software from Andrew Senior, which uses L channel to receiver signal and the R channel to GPS 1pps pulse, to lock soundcard PLL. The compensation is the same +87Hz).

Any ideas?

73
Marcus, PY3CRX/PY2PLL