Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
开云体育Emanuele People would love to have a single conversion receiver that has no images up at 28Mcs. ?signals that are too weak wont be heard, but stronger ones and the sig gen should come in 910Kc apart, one weaker than the other. ?I guess you turned the trimmers for 1,2 all in before doing the alignment again and they had to be shifted all out again? And still not good enough. Maybe you could pull the RF tube and inject after the tube so there is only one set of coils to do… as a test. Do you have ?scope so you can look at the RF close to the various coils? It is a mystery. ???? ? From: [email protected] [mailto:[email protected]] On Behalf Of Emanuele Girlando via groups.io
Sent: Tuesday, February 4, 2025 5:29 AM To: [email protected] Subject: Re: [HallicraftersRadios] S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak! ? Thank you for the advises guys. The problem is not solved though. ? Bands 3 & 4 RF alignment went very well, even if the trimcaps were very touchy. I went through the bands 1&2 alignment process again. On bands 1 & 2 I am injecting a -90dBm signal from an HP 8640B sig-gen. I don't expect to have any close in image signal under these conditions. I looked for them tuning around the two alignment frequencies and found none, nope.
? Now the questions are: ·?????? why is this happening in the first place? ·?????? how to try to further reduce the trimcap capacitance without destroying them and avoiding to dismantle the relevant RF sections? ·?????? Can it be C7A and C7B went out of value, enough to influence band 1&2 but not enough to influence bands 3&4? ·?????? can it be my RTMA dummy antenna? ? Thank you very much. -- don??? va3drl |
don Root