Yes, and that was what I wanted to know. I've read in this mailing list that the DSP limits the audio at 4 kHz. I'm seeing it roll off at little above 3400. The low end rolls off at around 300, so I'm getting an audio passband of ~3100 Hz. I wonder if this is normal, or if there's something else I can tweak in the settings.
It depends on your "roofing" filter ... If you have an AM (6 KHz) or FM (13 KHz) filter, you will see 300 Hz to 4200 Hz with FC=2.20 and BW=4.00 (at -3dB). If you only have a 2.8 KHz filter, bandwidth will be around 2800 Hz (900 - 3700 with FC=2.20 and BW=4.00 or 400 - 3200 with FC=1.60 and BW=4.00). If you see roll-off at 3400 Hz you either have a narrow roofing filter or the DSP center frequency (FC) is set too low. 73, ... Joe, W4TV On 8/23/2015 3:51 PM, Pierfrancesco Caci wrote:
"Matt" == Matt Zilmer <mzil...@roadrunner.com> writes:Matt> Hi Pf, Matt> Most tone modes operate at an offset from carrier frequency, so that Matt> the audio frequencies of interest are more or less cenetered in the Matt> filter passband. I believe the JTx modes are already in the 1200 to Matt> 1500 Hz range so no offset is required. Hi Matt, actually, I'm seeing JT9 stations transmitting at 3400 Hz, and who knows if there are some even above that. JT65+JT9 uses quite a wide receive window. Matt> The crystal filter being used only restricts the bandwidth of the RX Matt> chain (1st IF). The DSP imposes its own audio filtering on the Matt> baseband, and that's what you're seeing as rolloff below ~300 and Matt> above ~3500 Hz. Yes, and that was what I wanted to know. I've read in this mailing list that the DSP limits the audio at 4 kHz. I'm seeing it roll off at little above 3400. The low end rolls off at around 300, so I'm getting an audio passband of ~3100 Hz. I wonder if this is normal, or if there's something else I can tweak in the settings. Pf
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