Hi all, In a recent post, Ramakrishnan, VU3RDD, referred to raised cosine and root raised cosine filters. Yes those filters are used on digital data systems, for minimum inter-symbol interference a raised cosine filter is quite good and he correctly says the system works best if the filtering is shared between the Tx and Rx. But is that any good for CW, are my ears raised cosine? The ITU has a recommendation, which as an ex member I cannot now access, on the occupied bandwidth of a transmission (AM = 2*Fmod max etc) and covers data and CW. It is the shape of the rise and fall of the envelope which determine the occupied bandwidth. Pulses give a comb envelope with a frequency domain 'harmonic' or spur at 1/t where t is the pulse width; on a (sinx/ x) pattern spaced at 1/T where T is the pulse repetition rate. However here the pulse width is better described as the rise time rather than the dit rate. (yes I did mean dit (as opposed to dah)) The compromise is adequate clarity between two pulses with a dit interval and excessive key click. from memory the ITU rec gave a figure between 100 and 200Hz for manual keying. Suggestion, set up a perfect keyer, ie vertical sides, filter in one of the digital audio filters, reducing the bandwidth (removing key clicks) until copy is poor. Post the findings. I'd do it myself but don't now have the bits.
Regards Alan G0HIQ. ___________________________________________________________ Copy addresses and emails from any email account to Yahoo! Mail - quick, easy and free. http://uk.docs.yahoo.com/trueswitch2.html _______________________________________________ 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