"Bob Henderson" <[EMAIL PROTECTED]> made an utterance to the drakelist gang ---------------------------------------------------------------------- Esteemed reflectees
My odyssey continues....... In order to make some rapid progress, I opted to remove the Telladyne relays from the Sherwood switching pcb and directly wire these into the circuit. This approach worked well and completely resolved the problem caused by leakage across the switching pcb. I haven't figured out why the pcb caused this problem but this one must be faulty in some obscure way, as hundreds of folks have installed these without problem. Anyway, that unwanted signal is now way down at the noise floor, instead of S9+15 where it was before. Now here's the sad thing....... I returned the R-4C to the shack last night expecting the interference from BC signals on 20 & 40m to be thing of the past BUT they were as loud as ever. On 20m still peaking within a few degrees counter-clockwise rotation of the preselector and on 40m peaking within a few degrees clockwise roatation. My heart sank. I left the receiver set to 40m with the preselector peaking the interfering signals i.e that few degrees clockwise from the 40m peak and I retired to bed. This morning I set the TS570 to produce an S9+30 signal on 7020 (preselector still peaked for the maximum strength from the BC interfering signals) I then swept the TS570 from 1.7 - 30 MHz and noted signals audible on the R-4C. This is what I found: 1882 S1 2340 S6 (3rd harmonic is 7020 hence a measure of the bpf in the TS570) 2824 S1 3510 S2 (2nd harmonic is 7020) 5596 S1 5645 S9+10 (poor 1st i/f rejection and a measure of the rf bpf in the R-4C) 5695 S1 (2nd I/F good rejection) 7020 S9+30 >7020 Nil Everything looks good with the exception of first I/F rejection and its hard to see how that might be causing this particular problem. I puzzled over how these signals might be being generated and wondered if some kind of third order problem was to blame. I decided to use a TS930 as a second signal source to see if this might reveal something. Leaving the TS570 producing an S9+40 signal at 7020, I set the TS930 to produce an S9+40 signal at 7010. I then tuned around on the R-4C looking for 3rd order products. I found some but all at the noise floor. Certainly no significant unwanted signals were detectable. I've scratched my head so much I've got splinters in my fingers. Where on earth do I go next? 73 Bob, 5B4AGN ---------------------------------------------------------------------- On Behalf of "Bob Henderson" <[EMAIL PROTECTED]> Submissions: [email protected] Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost: [EMAIL PROTECTED] - help in body of message Zerobeat Web Page: http://www.zerobeat.net Brought to you courtesy of TLCHost.net http://www.tlchost.net/ ----------------------------------------------------------------------
