View Single Post
Old 1st Mar 2019, 1:42 pm   #1
dave_n_t
Hexode
 
dave_n_t's Avatar
 
Join Date: Sep 2003
Location: Cheltenham, Gloucestershire, UK.
Posts: 298
Default IF 'liner' (alignment aid)

Stimulated by recent discussions of IF alignment aids, I knocked up the pictured aid using bits and pieces I had lying around.

It's based loosely on one I found described online, here

The major changes are:
i) I used transistor IFTs instead of ceramic resonators. I have lots of IFTs and precisely zero ceramic resonators at 470kHz.

ii) I tuned them to 470 kHz (which is more common in the UK than 455kHz)

iii) I used one of the spare 4011 gates with 100k 'linearising' feedback as the 'output' linear amplifier. I haven't checked on the shape of the output waveform, but I don't imagine it's critical.

iv) I powered it from an 'N' cell, using one of the cheap 1.5V to 5V step-up circuits available on eBay. Current drain is 23mA. The step-up circuit has the added benefit of a really dinky pilot LED; and the further benefit of providing a sensible use for all the 'N' cells I acquired from £1 shops as side-effects to buying batteries for my garage and car key fobs.

v) I didn't bother with an output level control (see below).

vi) I pre-set the modulation depth. Possibly 50%, but 'good enough'.

Housed in a plastic box, it radiates 470kHz (and harmonics...) like mad, so 'connecting' it it the receiver-under-repair will be quite easy!

Quite a fun thing, which should be a bit easier for quick alignment touch-ups than my full-sized sig. gen.
Attached Thumbnails
Click image for larger version

Name:	DSC00430.v01.jpg
Views:	243
Size:	73.5 KB
ID:	179233  
__________________
Dave Teague
dave_n_t is offline