Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
¿ªÔÆÌåÓýJacques, it is not much maybe but where is the min cap of the BS? What is the dial frequency at the very top of the band [min cap] ?is !.6kc ?really min capacitance. Agree, even with a small change it still looks like come hidden cap ???? Emanule re Jim¡¯s .. at 1360 or 1380 there is no breathing room on the trimmer like one would expect. ? Also many variable caps have the min cap below 10% of the max, so we can wonder what this one was intended to be ? From: [email protected] [mailto:[email protected]] On Behalf Of Jacques_VE2JFE via groups.io
Sent: Thursday, February 20, 2025 10:57 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! Importance: High ? Hi Emanuele, ? From your measurements: BAND 1: C7A = 450pF, L3(C&D) = 200?H Fr = 530.5kHz (1/(6.2832 x SQRT(L x C))) C7A = 50pF, L3(C&D) = 200?H Fr = 1591.5 kHz ? BAND 2: C7A = 450pF, L3(A&B) = 26?H Fr = 1.47 MHz C7A = 50pF, L3(A&B) = 26?H Fr = 4.414 MHz ? From a mathematical point of view, that should work on both bands, or be very close to ! Unless there is a hidden capacitance in the assembly somewhere, like a connecting wire that should stand in free air, but that is pushed close to the GND along it¡¯s path instead.? (I have seen that before: too long story to tell here). Hard to verify because the radio is not right in front of me ¡. I also believe that the schematic is right: on band 2, the A+B section of L3 is connected to C7A, but the antenna signal is fed to L3 C+D and coupled using mutual inductance between the coils. On band 1, L3 C+D section is connected to C7A, antenna signal fed to L3 A+B section with a 1k resistor in series and fed by mutual inductance again. I believe that the 1k resistor is there to ¡°balance¡± the Band 1 sensitivity to the one of the other bands (more or less). ? Sorry to repeat feats or opinions that were mentioned before on the thread, but I caught this boat late¡ ? 73, Jacques, VE2JFE in Montreal ?
-- don??? va3drl |
don Root