Ne602 balanced inputs

[dr pepper]

I threw this circuit together, my intention being to generate a stable clock signal using the carrier o/p on pin 7, using a radio stations carrier.
I didnt have a dual gate fet so I used a J113, it works.
I dont get how the fet is connected to the '602 via C2 and C3, with the source and drain resistors being very different wont the signal levels be unbalanced?, doesnt make sense for an i/p thats sposed to be balanced.
The circuit works better than expected, I made some alterations on the front end so it can be used in a shipping container with an external active whip aerial.

am-receiver-with-synchro-detector - MIKROE

5.3.2 AM Receiver with Synchro Detector

www.mikroe.com

 

[danadakk]

Seems like the mixer has some insensitivity to input level per this from
datasheet (eg.2 of these approaches are imbalanced) -

If you look at structure the input is a diff stage.


Regards, Dana.

 

[dr pepper]

If I get it right a and b will give less noise than c.
I dont know why the designer of the receiver applies different amplitude signals to the 2 inputs, there must be some advantage.
I'm thinking of adding a unity gain phase splitter to provide the 2 signals, easier than a trans.

 

[danadakk]

b definitely rejects common mode, a I am thinking, as wells as C,
not so much.

Regards, Dana.

 

[dr pepper]

Agreed.
a & b are similar, tuning is a little easier with b and bandwidth will be wider, and both lend themselves to an agc circuit.
I'm thinking the circuit I posted connects both inputs of the '602 to the input buffer because there will be some benefit from connecting the source to the input instead of grounding it as this will at least apply partial balanced input to the '602 improving things a little, and just for the cost a connection change.
A while ago I built a Vlf receiver with a '602, I had issues with hum from the ground line, I never fixed it, maybe I could make the loop antenna into a centre tapped affair and double up the input circuitry and feed the '602 with a balanced feed.
It was odd in the fact it hummed like crazy but when turned off there was no hum at all untill the bulk cap discharged, but only if both - and + leads were disconnected.