Comments for "FM Detection Experiments"

13th May 2014 19:53

Gary Grove wrote ...

I would not use toroid coils, they might work but not my pick. The old tube circuits are the best to understand a "bifilar winding", and you can see by taking the can off and examining it. The transistorized circuits are small and the cans are very small and you cannot see how the windings are wound. Most older books show the ratio det and also the foster/seeley discriminator circuits. Emulate from them, or tear apart an old FM radio to look at the cans. Books show very standard ratio det's and also foster/seeley discriminators. All parts have kept the basic format for 45 years. Take the circuit board out of a 25 year old transistorized FM receiver and use the circuit board with all parts in tact and wire it into what ever your building-- Saves a lot of work!!! G.L. Grove C.E.T. Retired

27th June 2013 02:52

Davor wrote ...

Hi, a very late reply...

I found your solution to a ratio detector here as a very interesting variation. Maybe I have a solution to your asymmetry problem. Point is that a tank on the diodes side is supposed to run at ~90° against the middle connection input. It was achieved by very loose coupling to the primary, or otherwise you'd lose the ability to shift phase about the resonance. Phase shifting the middle connection does not do the trick because you are after resonance. Such loose couplings are very impractical, and that's the main reason for ratio detector's demise.

You could provide some alternative mode of coupling that does the trick. A toroid provides near perfect coupling for the bifilar coil.

11th March 2013 15:37

k2lcn wrote ...

To construct a stable 2 mtr local oscillator, use the third overtone of a 14 mhz microprocessor crystal into a tripler stage. 14.8 x 3 = 44.4 mhz. 44.4 x 3 = 133.2 which brings you close to a 10.7 mhz if.

15th November 2011 23:02

Petr wrote ...

Hello Alan,

I recall you having some odd kind of J310 JFETs with Idss ~ 100mA and Up -3.6V or less. Is the same batch also used here for the VCO buffer stage?

I'm not sure what's up with those 100mA Idss JFETs (maybe rebadged PN4391?) either, but genuine J310s tend to have pretty uniform Idss round 40mA. That's also what I use. Philips (PMBF)J310 ones are an exception. Lower avg Idss and more variation.

13th January 2011 04:55

NAJEEB wrote ...

you did a great work. why don't you try ratio detector as it works much better than yours one. you can use a Ratio detector coil. if you need any help to build Ratio detector coil let me know I can help you.

Leave a comment on this article.