Circuits with complex

Thread Starter

PaulEngineer

Joined Dec 21, 2016
217
Hello

In this days I would like to make a more complex circuit! But I have 3 questions:
1) Could this circuit be used as a "beginner walkie talkie"? I know it is just a transmitter, but I will try to adjust a circuit as a receiver! Between this 2 circuits will be adjusted a small button switch or an "on/off" switch!
2) In the circuit plan there is a trimmer that have a value 4-40 pF! I have a trimmer that have a value 4-50 pF! Will it have any changes on circuit function?
3) the trimmer have 3 pins, but in the circuit plan, the trimmer is joined with ONLY 2 pins! How to understand that? How its possible? The trimmer have 3 pins! I became confused!
 

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bertus

Joined Apr 5, 2008
22,292
Hello,

Are you using a trimmer capacitor as in the picture?

trimmer_capacitors.png

The two pins on the sides are joined together.
The middle pin is the other side of the capacitor.

Bertus

PS picture is taken from a dutch catalog.
 

Thread Starter

PaulEngineer

Joined Dec 21, 2016
217
Yes its almost like this but 4-50 pF
So! The 2 pins across over (I don't know how to say that but in Greece its translates like "απέναντι") is connected and the middle is the tunning pin? This appears in all the kinds of the trimmers that have 3 pins?
 

bertus

Joined Apr 5, 2008
22,292
Hello,

With a 4 - 50 pF capacitor the tuning range will be bigger as with the 4 - 40 pF capacitor.
The range will be extended to the lower side of the frequency range.

Bertus
 

Thread Starter

PaulEngineer

Joined Dec 21, 2016
217
Hooooof I thought I will have problem :)! This isn't any kind of advantage? I think as many pF have a trimmer so many frequencies it can hold. I'm right?

So, could this circuit to be used as a "beginner walkie talkie". Or it needs more complex circuit?
 

bertus

Joined Apr 5, 2008
22,292
Hello,

Yes, it can cover a larger frequency range.
The only disadvantage can be that the tuning can be a bit harder.

Bertus
 

bertus

Joined Apr 5, 2008
22,292
Hello,

I usualy take a smaller capacitor when I do not have the correct value.
You can shift the range by changing the coil.
Pushing the turns together will enlarge the coil value.
Pulling the turns apart will lower the value of the coil.

resonance_formula.png

Bertus
 

Thread Starter

PaulEngineer

Joined Dec 21, 2016
217
Wow this formula is helpful! But the trimmer have not one value it have many! A range let's say correct, that is usually 4-30, 4-40, 4-50 etc! So what you say is that I should to take a value ie 35pF from the range of 4-50pF and depending of that I should to "prefer" (I want to use the word "ρυθμίσω") the shifting of the coil? Let's make an example:

Trimmer value=35pF
(for trimmer with range 4-50pF)
Coil value=7-8 turns turned around a 1/4 bolt with gauge #18
2π=3,14*2
~~~~1~~~~~~~~~~~~~1
f=—————— =>~~~~ f=——————
~~~2π*√LC~~~~~~~~ 2*3,14*√L(a value of an inductor in uH)*35

Did I right listen you? This is what I should to make? Or something else?
PS the character (~) is just for spacing don't be care for this!
 
Last edited:

bertus

Joined Apr 5, 2008
22,292
Hello,

The trimmer capacitor you show is a ceramic one.
Also with this type the outer pins are connected together and the middle pin is the other side of the capacitor.
The colored dot is likely to indicate the gange of the capacitor.

Bertus
 
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