[Milsurplus] Tuned circuit design question

[Al Klase]

Hi John,

I think your stated approach in reasonable, but calculations are only 
going to get you into the general neighborhood.  I expect you're in for 
a lot of cut and try.  I'd wind quick-and-dirty test coils on cardboard 
or plastic pipe until I got close.  Perhaps get the highest frequency 
range working, then add turns to that for the next lower band, etc.

Sounds like a potential character-building experience.

Good luck,
Al

J Forster wrote:
> I've been asked about reverse engineering a WW II captured set. It's an HF regen
> receiver with 4 bands. The front end has a main and FB coil. From a pic, the FB
> coil appears to be wound on a bakelite tube that slips inside the main tuning
> coil which is wound on a somewhat larger bakelite tube. The main coil is tuned
> with a 140 pF capacitor in parallel with it, and the FB is adjusted with a 5 -
> 35 pF series cap. One end of both coils is grounded.
>
> Now comes the tricky part. Both coils are tapped and there is a bandswitch which
> grounds a part of each coil for the higher bands.
>
> The question is, how do you calculate the inductances, when a part of the coil
> is shorted out? Do you just assume the flux is totally excluded from the shorted
> section and just compute the inductance of the unshorted part or what? Is there
> some applicable correction factor?
>
>   

-- 
Al Klase - N3FRQ
Flemington, NJ
http://www.skywaves.ar88.net/


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