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AM receiver not working

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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Yes, it's the total capacitance! (and I confess I calculated it by measuring plates... let's forget it)

Anyway.
Now it works very well with headphones, BUT:
- does not work with speaker (makes different noises depending on which speaker)
- does not work if I don't touch the box (the usual motorboating)
- reaches one radio channel only, at 540-550 kHz
I tried both with one and with two capacitors, same result. It's very strange, because there are other channels above and below that frequency, very close to it.

View attachment 8693 Here's a picture of the situation...

(1) That circuit is not designed to drive a speaker directly.
(2) The world of RF is a different animal. You can't have things hanging out like that.
(3) The Rotor on the cap should be the terminal committed to the 100nF and 120K node..
(4) Anything I may have missed. :D

Chris
 
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Gherbi

Jun 13, 2013
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(1) That circuit is not designed to drive a speaker directly.
(2) The world of RF is a different animal. You can't have things hanging out like that.
(3) The Rotor on the cap should be the terminal committed to the 100nF and 120K node..
(4) Anything I may have missed. :D

(1) Well, isn't the input signal the same? I don't understand...
(2) What do you mean?
(3) Isn't it the same? Anyway I connected the LC this way.
 

davenn

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Sep 5, 2009
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(1) Well, isn't the input signal the same? I don't understand...

its only a single transistor output probably nowhere near enough output level to drive a speaker properly

(2) What do you mean?

RF electronics compared to audio electronics is a who different thing ....
the approach to constructing RF equipment means there needs to be a much more thoughtout and tidier construction and layout and that gets more and more critical as the frequency increases

You can get away with all sorts of rough construction with audio gear that just wont work when dealing with RF signals and equip.

(3) Isn't it the same? Anyway I connected the LC this way.

The rotor (moving vanes) part of the tuning cap should be connected to the ground 0V rail, this will normally substantially lessen the effect of touching the tuning shaft.... using a plastic knob on the shaft will lessen that even more
The stator ( fixed vanes) part connected to the top side of the coil and on to the detector etc parts of the circuit

I cannot quite see what you have done in your pic.
Having the wires from the coils/tuning cap going through holes in the metal case to the rest of the circuit is also a big NO-NO. It will drastically affect the operation of the tuned circuit.

I would be mounting the whole thing in a plastic case instead. Mounting the tuning cap through a hole in the case. Fixing the ferrite rod/coils and circuit board in the case so they dont flop around

As I said earlier in this post. RF construction is much more critical

Dave
 
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CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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I would be mounting the whole thing in a plastic case instead. Mopunting the tuning cap through a hole in the case. Fixing the ferrite rod/coils and circuit board in the case so they dont flop around

Dave

Dave, this too funny. My initial take was ahhh, another cool Aussie colloquialism! I was going to ask you for a definition. :D

Gherbi, I think you'll find that mounting everything on a wood base will afford you maximum latitude and ease of placement and affixing. Remember, when making interconnects think short and rigid. Capice? ;)

Chris
 
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