Ron The R4B does have a "roofing" xtal filter at the first IF. But you are right, in that the main selectivity (at four switched bandwidths) is at the second IF at 50kHz with LC filters. The problem here is that at the input to the second mixer grid, the bandwidth is only 250Hz after the supposed "roofing" filter. 73s
Gwyn ________________________________________ From: Ron [[email protected]] Sent: 18 July 2010 11:39 To: [email protected]; Griffiths G. Subject: Re: [Drakelist] R4B xtal filter bandwidth problem Gwyn, Are you really meaning a R4B? I am fairly sure that the B series RX has an LC circuit in the 60Khz range for its selectivity. I didn't think the RX had xtal filters till the C series. 73, Ron WD8SBB --- On Sun, 7/18/10, Griffiths G. <[email protected]> wrote: From: Griffiths G. <[email protected]> Subject: [Drakelist] R4B xtal filter bandwidth problem To: "[email protected]" <[email protected]> Date: Sunday, July 18, 2010, 4:47 AM Folks Does anyone have experience of the R4B as-fitted xtal fliter showing a -3dB bandwidth of just 250Hz, from 5644.910 to 5644.660kHz This suggests to me that only one crystal is in circuit, but I do not have the circuit of what is in the can so I can be sure. Is there a circuit available? Before I dismantle, suggestions welcome as to any other diagnostics I can do. many thanks 73s, Gwyn Griffiths G3ZIL _______________________________________________ Drakelist mailing list [email protected]</mc/[email protected]> http://mailman.zerobeat.net/mailman/listinfo/drakelist -- This message has been scanned for viruses and dangerous content by MailScanner<http://www.mailscanner.info/>, and is believed to be clean. _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
