Re: Post #1. Amongst the listed circuits is one entitled "An automatic signal generator". There is no circuit - it is only the idea and a discussion of what it does, how it works and how you use it. The basic idea is a generator that can be used to check & adjust the RF alignment of the 'front end' of a superhet radio. The principle on which is works is as follows.
The unit contains a frequency changer. The two inputs to this are (1) a loosely-coupled capacitive probe that picks up the local oscillator signal from the set under test and (2) a free-running oscillator at the IF of the set under test. Consequently, the mixer output is at the RF of the receiver under test. As the receiver is manually tuned, the RF output of the automatic signal generator always presents the correct frequency to the receiver's 'front end'. And so you adjust the RF circuits accordingly.
O.K. fine; very clever. Or so I thought at first. Then I thought again: there's something not quite right with that idea
: it assumes that the calibration of the receiver is correct to start with 
. I'll expand on that: suppose the calibration is incorrect. Then the RF output from the generator will be of the same error. Subsequently, the adjustment of the RF 'front end' circuits will also be out by the same error. Therefore, the prime function of this 'automatic generator' is defeated.
Now in 'real life', when re-alignment is performed, after the IF strip has been adjusted - with a calibrated signal generator - the next step is to adjust the local oscillator for correct calibration and tracking - again, using a calibrated signal generator. Now that the IF and L.O. are known to be 'on frequency', only then can the RF stages be adjusted - and adjusted correctly.
The whole article seems far too long and detailed for someone who has created an April Fool's joke - or even a hoax. Am I missing something in my analysis? :-/
Al.
The unit contains a frequency changer. The two inputs to this are (1) a loosely-coupled capacitive probe that picks up the local oscillator signal from the set under test and (2) a free-running oscillator at the IF of the set under test. Consequently, the mixer output is at the RF of the receiver under test. As the receiver is manually tuned, the RF output of the automatic signal generator always presents the correct frequency to the receiver's 'front end'. And so you adjust the RF circuits accordingly.
O.K. fine; very clever. Or so I thought at first. Then I thought again: there's something not quite right with that idea
: it assumes that the calibration of the receiver is correct to start with . I'll expand on that: suppose the calibration is incorrect. Then the RF output from the generator will be of the same error. Subsequently, the adjustment of the RF 'front end' circuits will also be out by the same error. Therefore, the prime function of this 'automatic generator' is defeated.Now in 'real life', when re-alignment is performed, after the IF strip has been adjusted - with a calibrated signal generator - the next step is to adjust the local oscillator for correct calibration and tracking - again, using a calibrated signal generator. Now that the IF and L.O. are known to be 'on frequency', only then can the RF stages be adjusted - and adjusted correctly.
The whole article seems far too long and detailed for someone who has created an April Fool's joke - or even a hoax. Am I missing something in my analysis? :-/
Al.
