[ARC5] BC-455 IFT - measurements

[WA5CAB--- via ARC5]

The secondary coil and fixed capacitor is broadly resonant at 2830 KC.  If 
you were to add a trimmer and peak it exactly at 2830, the output increase 
would be negligible.  Although they are all at 455 KC, the secondary of the 
IFT's in the BC-611 (except the -F), BC-745 and the BC-728 are all untuned.  
Someone probably decided that it wasn't worth the additional cost in time 
and materials to install and have to adjust a trimmer.

Back to the BC-455-(*), besides C12, L6 also has trimmer C11 across it.  On 
the wiring diagram page the list does say C11 is 17 and C12 is 180 mmf.  
But the detailed parts lists for RAV, ARA and SCR-274-N all just give the 
Delta-C as 17 mmf.  None of the lists give the min and max.  And if you read the 
fine print, C-12 is either 175, 180 or 185 mmf.  +/- 2.5 mmf.  Presumably 
the actual value was selected at assembly.

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480

In a message dated 10/29/2014 05:45:04 AM Central Daylight Time, 
kgordon2006 at frontier.com writes: 
> I just checked the inductance of the two coils in the BC-455B IFT type 
> number 7277 I have here:
> 
> The pie-wound, larger, coil tests at 2.264 mH. This coil is L-7
> 
> The smaller, single-layer coil, tests at 16.14 uH. This coil is L-6
> 
> So, my measurements follow Les'.
> 
> Now, the capacitor in parallel with L-6, C-12 is 180 pfd.
> 
> The pie-wound coil, L-7, has no capacitor shown in parallel with it on 
> the schematic. In order for it to be resonant at 2.830 MHz, the 
> capacitance required would be on the order of 1.5 pfd.
> 
> I don't understand 1) why L-7 is ~2.3 mH, 2) why it is untuned, and 3) 
> how does this IFT work?
> 
> My instrument must be off a bit. In order for L-6 and C-12 at 180 pfd to 
> resonate at 2830 Khz, L-6 must be about 17.5 uH.
> 
> Ken W7EKB