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Radio Shack sound level meter

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Re: Radio Shack Special

I'm a little bit confuse right now. You said before that Radio Shack Special is regenerative radio but when I surf to the author website it said this Radio Shack Special is SUPERregenerative radio. Here's the snapshot

**broken link removed**


For the sweep generator and scope, scope here you mean oscilloscope right? and May I know where should I connect the probe? Is it at the transistor or the coil?
 

Re: Radio Shack Special

Patrick Cambre copied the shortwave regenerative radio designed by Charles Kitchin then converted its frequency to around the FM broadcast band.
https://www.electronics-tutorials.com/receivers/regen-radio-receiver.htm

It is a regenerative receiver that has a manual regeneration sensitivity control.

A super-regen receiver uses some extra parts that automatically adjust the sensitivity by causing a quenching oscillation of the RF amplifier/oscillator that keeps it at a very high gain but reduces the gain if the signal is strong.

Connect an oscilloscope to the audio spot on the circuit to see the bandwidth when a swept signal is fed to the circuit.
 

Re: Radio Shack Special

In Patrick's circuit he used L1 as 3 tap coil wire and the antenna is connected to the middle leg.

**broken link removed**

So that means this Radio Shack Special still regenerative radio. Now I see.


One more thing is there anyway I can reduce noise from this Radio Shack Special?
 

Radio Shack Special

Where did you find the 3rd schematic that is different from the two schematics that I found?

It makes sense for the antenna to be connected to a tap on L3

It is a very cheap and simple "radio". Noise is expected.
 

Re: Radio Shack Special

I found it here on the author's website **broken link removed**
but to access it I used www.archive.org.

So there's no other way to at least minimize the noise? like modified a little bit the circuit or ading some capacitor?
 

Radio Shack Special

It is a cheap simple circuit that makes noise if the sensitivity control is turned too high and it makes noise whrn the signal is weak.

You can reduce hiss if you increase the value of the 0.01uF capacitor at pin 3 of the LM386 to reduce high audio frequencies and make it sound muffled like an AM radio.
 

Re: Radio Shack Special

If I change the value of the capacitor at pin 3 to certain value, do I need to change the value of other component? May I know what should be the suitable value for the capacitor at pin 3 to reduce hiss like you've said? Is 0.1uF ok? Like in the improved version of RSS it used 0.001uF and add one more resistor, should I add the resistor?
 

Radio Shack Special

When the 10k volume control is at half resistance then each side is 5k and the effective driving resistance is 2.5k. The FET has an output resistance of about 1k so the total driving resistance is 3.5k.
With the 0.01uF capacitor then the audio begins to be reduced above 4570Hz.

FM broadcast stations have pre-emphasis (treble boost) which is a boost above 3200Hz in Europe and above 2133Hz in North America. Radios have a treble cut at the same frequencies.

If you increase the 0.01uf capacitor to 0.1uF then frequencies will be cut above only 457hz and it will sound horrible.
 

Re: Radio Shack Special

If you don't mind can you please give me manual about this thing, I mean the formula. What about pre-emphasis of FM broadcast around Asia region? If my calculation is right, if I want the pre-emphasis to cut above 3500Hz, I need to increase the capacitor value to 0.013uF, is it and will there be any capacitor sell with 13nF value at the store nowadays?
 

Radio Shack Special

Ask the engineer at a local FM radio station if the pre=emphasis is like in Europe or in the USA.

The formula for the cutoff frequency of a simple passive lowpass filter is one divided by (2 pi R C).

3.5k and 13nf makes a cutoff frequency of 3516Hz.
Use 12nF or 15nF or add two capacitors in parallel to get what you want.
 

Re: Radio Shack Special

Audioguru,

Is there any other thing I can do to improve this circuit, I mean in term of minimizing the noise? I've increase the capacitor value and still thinking is there any other thing to improve my circuit.
 

Re: Radio Shack Special

On more thing for 12nF capacitor, mylar type capacitor is acceptable right? Just need your comfirmation. Thank you.
 

Re: Radio Shack Special

Kekkaishi said:
On more thing for 12nF capacitor, mylar type capacitor is acceptable right? Just need your comfirmation. Thank you.
Click to expand...
A 12nF metalized plastic film capacitor with 5% tolerance is good for audio filters. A Mylar type of capacitor is fine.
 

Re: Radio Shack Special

Audioguru,

Whe I was trying to make a report for this radio project I found out one thing that made me curious about voltage rating for the electrolytic capacitor. From the schematic of the author of this RSS, it sad that voltage rating for the electrolytic capacitor must be at least 10V or higher. Then I tried looking at the other schematic of the original and improved version of Radio Shack Special and found out some used voltage rting of 35V and some 50V.

Would there be any difference about this for the performance of this radio since I made a search on google about voltage rating, they only said don't use below its rating othrwise the capacitor will not operate on its original value. So I wonder if there will be any difference on this Radio Shack Special interm of performance if I use larger voltage rating for the electrolytic capacitor, which currently I used 10V? Thank you.
 

Radio Shack Special

The supply voltage for the "radio" is 9V so an electrolytic capacitor rated at 16V or more will work fine. I don't use 10V capacitors with a 9V circuit.

35V capacitors were spec'd because they are available at Radio Shack.
 

Re: Radio Shack Special

Audioguru,

After finishing my project and report, my friend asked me why I'm not using variable diode sice it is easier to tune variable diode than my plastic varicap which required screw driver to tune it. Is it ok to replace my 15pF varicap with variable diode and if it is what value should I use for the variable diode? Thank you
 

Radio Shack Special

A varactor diode has its capacitance changed by a DC voltage.
The diode must have the correct capacitance and voltage to work properly.

An ordinary diode or transistor junction is a varactor diode. Look in Google for Varactor diode.

I use a plastic screwdriver to adjust a trimmer capacitor because it doesn't have stray capacitance like a metal blade screwdriver that affects the tuning.
 

Re: Radio Shack Special

Hello everybody, i'm making the RSS but instead of the MPF102 i put a F245C and i wanted to know if it's going to work with it?
Thanks in advance...:)
 

Radio Shack Special

F245C is not a complete part number.
Please post its datasheet or a link to its datasheet.
 

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