Am I losing my mind??, I cannot get this simple circuit to work!!

Thread Starter

Kim Sleep

Joined Nov 6, 2014
38
Ok guys, (and Gals), why the heck can I not get this circuit to work ??!!...seems easy enough.
Have built and rebuilt it several times, am I missing something????!!....is there a possibility that the original design is faulty?
Thank you very much in advance for any help.


Upon reading a description of how the original Sinitsa works, I've come up with a new approach. The original Sinitsa used a diode up front to modulate any RF signals, basically gating them on and off. Then, after band-select filtering, an ordinary diode detector produced an audio signal from the now-modulated RF. I had originally thought that harmonics from the edges of the square wave were mixing with the RF signal directly in the first stage. I came up with a somewhat different approach that I think is functionally similar but doesn't require any "handling" of the RF:

In my version, the analog switch toggles between the DC from the detector diode and a reference diode. To the extent that the reference diode tracks the detector diode (mostly thermally) this should produce about the same result as turning the RF on and off to the detector diode. (In other words, when the RF is off, both diodes should produce the same voltage.) I don't "touch" the RF before the detector and I can null out a steady background RF level. The oscillation can be stopped by grounding pin 11 of the CD4053 with a toggle switch and the circuit will then behave like original All Band Receiver. The details of the audio amplifier haven't been worked out but a simple LM386 is probably sufficient. I might use an op-amp stage of some sort as a preamplifier if I want to synchronously detect the signal for driving a meter (using switch "C").​

Note the snazzy way I made the CD4053 toggle itself. That might have some interesting applications for lock-in projects. It's basically a DPDT self-toggling switch.

I used the 5082-2835 but any RF Schottky diode should work including the common 1N5711. Here's a fun application: The Bug Duster. The transistor amplifier could be replaced with an LM386. It turns out that not much gain is needed. If you try the LM386, add a switch to disconnect the capacitor between pins 1 and 8 to lower the gain for "bug sweeping." Otherwise it will simply be too sensitive.

1694147834823.png
 

crutschow

Joined Mar 14, 2008
34,047
If there any floating inputs on the CD4053, they must be grounded.
CMOS circuits don't take kindly to floating inputs.
 

Sensacell

Joined Jun 19, 2012
3,400
And I have absolutely NO IDEA what this is supposed to do?
Some kind of RF sniffer?

Change the title to something meaningful.
 

ericgibbs

Joined Jan 29, 2010
18,651
PS...it mentions Switch "C"...where the Heck is "Switch C"
Hi K,
It doesn't say it's included in that circuit diagram, it just says it's 'available' which means you have to acquire it if you wanted to fit it into the original circuit.
E
Post the original circuit or a link to it
 

MisterBill2

Joined Jan 23, 2018
17,814
I would not expect the circuit shown in post #1 to do anything useful at all. Certainly I would not expect an analog switch used as an oscillator to provide any useful switching functions on any other section.
The output from a diode detector connected directly to a broadband antenna input will include a lot of assorted noise, in addition to whatever detected carrier may be present.
It appears that the circuit is intended to serve as a "bug detector" to locate hidden transmitters, with the concept being to produce an audio signal by modulating the detector output, with the apparent concept of this circuit being to null the voltage produced by the intentional diode bias with a similar signal from a second diode biased in a similar manner.
An interesting concept but the two opamps mean that you are not switching the original signals any more.

Note to all: This is my guess about the purpose of the circuit. Waiting for a verification by the TS.
 

Alec_t

Joined Sep 17, 2013
14,220
Are you seriously using an LM358 to try to amplify RF signals? It has a gain-bandwidth product of only 1 MHz.
The way the circuit is configured, the outputs of both op-amps are likely stuck as close to the +ve rail as they can get (the LM358 is not a rail-to-rail output type), so wouldn't produce useful output from the 4053.
 

Thread Starter

Kim Sleep

Joined Nov 6, 2014
38
Are you seriously using an LM358 to try to amplify RF signals? It has a gain-bandwidth product of only 1 MHz.
The way the circuit is configured, the outputs of both op-amps are likely stuck as close to the +ve rail as they can get (the LM358 is not a rail-to-rail output type), so wouldn't produce useful output from the 4053.
im not in love with any aspect of the circuit, Im just trying to replicate it exactly
 

MisterBill2

Joined Jan 23, 2018
17,814
It is supposed to be a wide band receiver, receiving many different transmitters as possible
As a wide band receiver it is not going to do very well at all. Just consider that the signal strength ratio is over 60dB in most locations. And receiving more than a very few signals at any time will produce noise and nothing useful.
So now for a question, which is what frequency range of signals do you seek to receive? AND THEN, after receiving all of those signals at the same time, what do you intend to do with them??

OR, is this to be an instrument to measure the intensity of the RF that we are exposed to at every instant?? For measuring total field power density a fundamentally different scheme would be better.
 

Thread Starter

Kim Sleep

Joined Nov 6, 2014
38
This statement is correct;
"OR, is this to be an instrument to measure the intensity of the RF that we are exposed to at every instant?? For measuring total field power density a fundamentally different scheme would be better."
 

MisterBill2

Joined Jan 23, 2018
17,814
OK, now that we have an explanation of the purpose we can consider how to make it work. For starters, the common term for that sort of device is "Field Strength Meter". Usually such a device is used to test the effectiveness of a specific transmitter at a specific frequency.
Measuring field strength is not a new process, and so there is a great deal of information published.
For equipment to provide useful information, it is common to examine individual frequency bands and learn how much energy is present in each segment of the frequency spectrum. Measuring the entire spectrum at once will result in knowing the field intensity from the local high power broadcast radio station while not seeing the radiated power from a nearby microwave oven with a leaky door seal.
 
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