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AM Murania Radio Receiver Question


Philip Karras <ke3fl@...>
 

From pg 5 of the muraniamanual.pdf:

Power and Voltage Regulator
The Murania circuit uses a red LED as a voltage regulator for the receiver. The LED also serves as both a power-on lamp and a tuning indicator. This circuit will be installed and checked for proper operation before continuing.

Can someone explain what voltage is this LED regulating? For what purpose?

Tnx es 73 de KE3FL,
Phil
ARRL OES, ORS, & VE
ARRL Life Member


Jim, N5IB
 

Hi Phillip,

The little TA642 AM receiver IC chip is designed to run with a very low voltage supply - for battery operated gear. It can run on just a single AA battery.
The red LED has a forward voltage drop generally from about 1.6 to 1.8 V when it's illuminated, so it maintains a steady voltage to supply the TA642.

You could do the same thing with two or three conventional silicon diodes in series, or with a 2V zener, if you could find one.
But in the QRP tradition of doing more with less, we get the required voltage regulation.... and the light we get for free!

Jim, N5IB


Philip Karras <ke3fl@...>
 

Thanks Jim! (Philip has only ONE L)

73 de KE3FL,
Philip
ARRL OES, ORS, & VE
ARRL Life Member


On Thursday, February 4, 2021, 7:57:08 PM EST, Jim, N5IB <n5ib@...> wrote:


Hi Phillip,

The little TA642 AM receiver IC chip is designed to run with a very low voltage supply - for battery operated gear. It can run on just a single AA battery.
The red LED has a forward voltage drop generally from about 1.6 to 1.8 V when it's illuminated, so it maintains a steady voltage to supply the TA642.

You could do the same thing with two or three conventional silicon diodes in series, or with a 2V zener, if you could find one.
But in the QRP tradition of doing more with less, we get the required voltage regulation.... and the light we get for free!

Jim, N5IB