Another internet circuit with problems?

Thread Starter

AlbertHall

Joined Jun 4, 2014
10,226
I found this circuit on the internet and I suspect it has a problem. It is a receiver for time code transmissions. In the UK these are broadcast on 60kHz with a 100ms, 200ms, or 300ms break every second.
D1 and C9 are the envelope detector for this receiver, but I see no discharge path C9. I guess it needs a discharge resistor across C9. Given the 60kHz carrier frequency and 100ms minimum gap what time constant should I use here?

I don't propose to breadboard this as I expect it would end up as an oscillator rather than a receiver so it will be going straight to PCB so a 'get it right first time' approach is desired.
Are there any other visible problems?

1595575005904.png
 

bertus

Joined Apr 5, 2008
20,650

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ericgibbs

Joined Jan 29, 2010
10,449
hi,
I agree about the breadboard build, I built some of the old Rugby time transmission/receivers some years ago, worked OK,

E

Have you considered LTSpice'ing it, I know you use LTS.?
 

Thread Starter

AlbertHall

Joined Jun 4, 2014
10,226
It could be that the discharge of C9 is done by the input impedance of the LM1458, wich is about 300K to 1M, given in the dataheet.
Ah, yes, I had it in my mind that it was a jfet input like the TL082. That would make the time constant 3ms to 10ms which seems reasonable for a 100ms pulse width.
The tiny and cheap receivers seem to have vanished hence the DIY job.
 

jpanhalt

Joined Jan 18, 2008
10,068

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Thread Starter

AlbertHall

Joined Jun 4, 2014
10,226
I built this circuit but it receives a constant level of 60kHz. There might be just a hint of once per second pertubation but it would be impossible to decode. It seemed that something in the house was producing a 60kHz signal so I went round disconnecting and switching things off but this made no difference so I was stumped.

Then I remembered that I have solar panels on the roof and a 3.6kW inverter in the loft. I waited for sunset and hey presto a clear MSF square wave. That's OK as it should manage to sync correctly during the night.
 

jpanhalt

Joined Jan 18, 2008
10,068
Night is the best time to do it anyway, at least where I live and signal is weak. A shielded loop will give you some directionality. But that circuit seems to receive everything. Using a microwave three rooms away caused interference with mine too.
 

Thread Starter

AlbertHall

Joined Jun 4, 2014
10,226
I live 17 miles away (by road so less by radio wave) from the MSF transmitter aerial so signal strength really shouldn't be a problem.
 

Thread Starter

AlbertHall

Joined Jun 4, 2014
10,226
That is probably a typo. It means C1 is used to tune the ferrite rod antenna.
I used a LW coil and ferrite and measured the inductance with the in the centre and at the end of the rod and then selected a standard value capacitor which resonate a 60kHz between those those two positions which turned out to be 1.8nF. Then move to coil for maximum received amplitude.
 

Picbuster

Joined Dec 2, 2013
1,020
I found this circuit on the internet and I suspect it has a problem. It is a receiver for time code transmissions. In the UK these are broadcast on 60kHz with a 100ms, 200ms, or 300ms break every second.
D1 and C9 are the envelope detector for this receiver, but I see no discharge path C9. I guess it needs a discharge resistor across C9. Given the 60kHz carrier frequency and 100ms minimum gap what time constant should I use here?

I don't propose to breadboard this as I expect it would end up as an oscillator rather than a receiver so it will be going straight to PCB so a 'get it right first time' approach is desired.
Are there any other visible problems?

View attachment 212983
I think that a sin wave generator and a scope are needed.
make a little coil (5 turns or so) and feed 60Khz from generator.
use scope to measure on the drain adjust C1 or L1 to obtain maximum signal.
repeat at ic1A pin one and so on.
last ic2a lm1458n measure min input and flip the 60Khz off/on observe repeat with pin on1.
test the last lm.
No you know exactly what the bottle neck is.

Picbuster
 
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