Re: Signal generator question]

[Jean-François Ménard-5]

Thanks Don.

Again, I will keep and print this email has a reference in my shack.
Clear explanation... very instructive. I am actually building the signal
generator found in the K2 manual. Now it works ! I

I will now experiment using this device. I also found a good explanation
the ARRL handbook, in the section «troubleshooting», chapter 27. I
really want to use more my scope and learn on how to use it... and how
to read it. A good practice.....

Best 73 and thanks again for your time !!!!

J-F VA2VYZ

Don Wilhelm a écrit :

> Jean-Francois,
>
> Signal tracing can be quite effective - I applaud your goals.
>
> Signal tracing of a transmitter path can usually be done with only an RF
> probe since the signal levels are usually large enough to measure easily,
> although a 'scope is more informative because you can see the relative
> frequencies involved.  For the K2, just follow the steps detailed in the
> Transmit Signal Tracing section of Appendix E in the manual.
>
> Receive Signal Tracing is a bit more 'iffy' - although the method in
> Appendix E of the K2 manual works well, one must use a relatively strong
> signal source (such as the oscillator shown in the manual) to have a large
> enough signal in the receiver to measure (very small readings are likely
> just noise picked up by the probe).  One must remember that in the RF and IF
> stages, a signal that can be observed on a 'scope or RF probe is much
> greater than the normal signal levels handled by the receiver -
> none-the-less, the procedure can be informative in identifying a failing
> stage, but it cannot be used to evaluate distortion levels since the stages
> are being overdriven by the generator with this elementary test.  If one
> uses a normal receiver input level signal, there are devices to effectively
> measure those small signal levels (Spectrum Analyzer for instance), but the
> signal path must usually be broken and the signal level transformed to 50
> ohms to do proper measurements.
>
> A more effective method of troubleshooting a receiver is to use a signal
> generator to do 'signal injection' at each stage of the receiver - for the
> sudio stages, that requires a generator that will produce audio frequencies,
> and for the IF stages it requires a signal generator that can produce a
> frequency equal to the IF frequency.  The RF stages require a signal
> generator at the receiver tuning frequency.  This generator should have a
> controllable output level so the levels can also be evaluated.  Normally one
> would start at the audio stages and move toward the antenna one stage at a
> time, injecting the level and frequency that each stage should respond to.
> Using that procedure, it is sufficient to measure the ouput of the receiver
> either with an AC Voltmeter or just the ears listening to the speaker.
> There ued to be 'signal injectors' available that produced an audio square
> waveform that was very rich in harmonics that could be used as a relative
> indicator of functioning receiver stages - if you can hear a good response
> when moving from the audio stages toward the antenna, it can quickly
> identify a failing stage.
>
> Bottom line - receiver signal tracing begins at the antenna and works toward
> the receiver audio stages, signal injection works the other way around.
> Both methods verify the operation of each stage in turn until the failure
> point is found.
>
> The generator that you referred to is a Function Generator which is great
> for evaluating audio and low frequency IF stages, but if you are using a K2
> for this 'education', the IF is at 4915 KHz and that generator will not go
> above 3000 kHz.
>
> As I indicated, if you are just trying to isolate a failing stage, the large
> signal injected at the antenna (tune the receiver to the signal generator
> frequency) will usually suffice, but if the problem is more subtle than just
> a failing stage (distortion for example), the controlled level signal
> injection at each stage is required - along with a good knowledge of 'what
> is normal'.
>
> 73,
> Don W3FPR
>
>
>  
>> -----Original Message-----
>>
>> I would like to learn and explore more «signal tracing» procedure and
>> technique. I actually have a Fluke 196C. But I don't have a signal
>> generator.
>>
>> A friend of mine have his signal generator for sale. The model is an
>> Instek GFG-8216A. I would like to know if the device will be good for
>> signal tracing or the specification of this device is not enough for
>> this purpose??? I know that I could build the one in the K2 building
>> manual or at least use the technique «Cheap'n Dirty» from N0SS... but
>> that's not my point.... ;-)
>>
>> The specification can be viewed at
>> http://www.instek.com/pdf/Generator/GFG-8216A8215A.pdf
>>
>> Thanks for all your advice.
>>
>> Best 73
>>
>> J-F VA2VYZ
>>
>>    
>
>
>  

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