Mike, Thank you for the explanation; i understand now that this false "anomaly" is present with the 2k7 and 2k8 filters.
May i "abuse" of your knowledge to explain to me the following behavior : During receive, the 2k7 and 2k8 filter seem to give a ~ 300 Hz at -10dB frequency; it's ok for my use; during transmit, the same filters seems to give a ~ 500 Hz at - 10dB relative to the 1 kHz attenuation; i've tried to shift the bandpass, but naturally, the high frequency is shifted too. As i work essentially with digimodes, i can accommodate with that; but what is the cause of this difference ? (coupling capacitor, etc). I've tried to "play" with EQUALIZER, but the ALC "bars" begin to get non desired values... 73 QRO fr Rudolf, HB9ARI AD6XY wrote: > The "anomaly" is not really an anomaly, it is just the other side of the down > conversion oscillator. For a filter to pass an SSB audio signal the passband > needs to go down to 300Hz or so. For this to happen the attenuation for 0Hz > and image frequencies can't be that far down. That is all it is though it is > probably better with the 8 pole filter. It can also be eliminated by raising > the centre frequency, at the expense of bass response. Unfortunately I don't > think you can do this on transmit, though perhaps you could adjust your > filter offset. That would not work with the USB/LSB inversion below/above > 8MHz. > > Currently the filter is centred on 1.5kHz by default. The best place for it > but if you narrow it down with DSP it is probably better to raise this to > 1.8kHz. I am not sure how the filter shift relates to the DSP filter and the > crystal filter, i.e. which is adjusted, probably both. > > However, I find I always need to reduce the filter centre frequency to > maintain intelligibility as I narrow the DSP bandwidth. So to make sense of > a signal within 1.8kHz I need a 1kHz centre frequency. That is not what I > would expect which makes me wonder what the shift control actually does. > > > > Mike > _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
