At 01:35 PM 9/14/2007 -0700, you wrote: >Why does the HD hash QRM the lower frequency more than the upper one? >In the case of 650-KSTE, the QRM is worse on 640 than 660 (splits, 639 >is worse, 666 is clearer), in the case of KEX 1190, 1180 is worse and >1200 is clearer (splits 1179 is trashed, 1206 in clearer). > >73, > >Patrick
Patrick, The IBOC hash ought to be equal on both sidebands; however most tube transmitters use Pi output tuning networks which tend to attenuate the upper sidebands slightly more than the lower sidebands. The math is simple: a Pi network, as usually con- figured for a broadcast station, is a low-pass network with the carrier frequency being the cutoff frequency. Since HD is wideband, anything above the rolloff, or cutoff frequency is excessively attenuated. This requires a redesign of the output networks for symmetrical bandpass. Once everyone goes IBOC, this won't be a problem anymore; or at least not nearly as big a problem. But, of course, IBOC will never be universal unless someone prices HD (the latest nonce-word to avoid the four-letter word "IBOC") low enough. Ain't going to happen. Too many stations are right on the financial edge. A good idea in the wrong place. 73 de Charles _______________________________________________ IRCA mailing list [email protected] http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: [email protected]
