You might be surprised Joe. Demodulating double sideband AM with a 6 kHz I.F. filter is hardly different from demodulating SSB AM with a 2.7 kHz filter. You are only losing 300 Hz of audio bandwidth doing that.
I got into the habit of running SSB mode to receive AM, particularly SW AM, because injecting the "carrier" locally eliminates selective QSB distortion caused by the carrier fading out of phase with the sideband. In the K3/K3S, that's handled automatically by enabling "Sync AM". Very few AM stations transmit audio above 7 kHz these days. Many restrict the bandwidth to between 2.5 and 3 kHz total (5 to 6 KHz RF bandwidth). By doing that the AM stations can sell some of their channel space for other services (using subcarriers on the main carrier). Also, most car radios for the past few decades limit the audio bandwidth on AM to 3 kHz or less because customers complained about the background hiss coming up on weak stations. I read that became a real issue when AM/FM car radios appeared and the typical consumer did not understand why AM stations got "noisy" while FM stations did not. As a result, many AM broadcast stations today use very heavy high frequency pre-emphasis to help overcome the limited bandwidth. 73, Ron AC7AC -----Original Message----- From: Elecraft [mailto:[email protected]] On Behalf Of Joe Subich, W4TV Sent: Saturday, June 25, 2016 12:51 PM To: [email protected] Subject: Re: [Elecraft] k3s AM receive > Is there any reason to equip my my K3S with either the 6 kHz or FM > filter roofing filters for AM reception or will the DSP filter do the > job. I realize that if I want to tx AM I will need to install the > 6kHz filter. If you expect to receive AM as AM you will need either the 6 KHz (AM) filter or 13 KHz (FM) filter. You can receive BCB AM using the stock 2.7 or 2.8 KHz filter but you must receive the AM signal as if it was USB or LSB and zero beat the carrier. Doing so will give you significantly restricted frequency response - barely good enough for "Talk Radio". 73, ... Joe, W4TV ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
