Hello guys Sam's 142 gtl alignment calls for a output of signal generator through .01uf to tp 16 Thanks. Don't understand the .01uf part what is need it thanks
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Question about alignment procedure
- Thread starter kaos513
- Start date
Umm, okay.
TP16 is where you hook a 'scope input to peak L18 for max.
I think what you're referring to is on the next page, the first step in the receiver alignment. Says to feed 7.8 MHz from your signal generator to TP13, collector of TR10.
We don't bother with that, and peak L3 and L4 using an on-channel signal, tuned in the normal way.
Not sure why they tell you to do it this way. Makes no sense to me.
Does serve to remind me why we ditched the alignment procedures in so many of the Sams books, and use our own.
73
TP16 is where you hook a 'scope input to peak L18 for max.
I think what you're referring to is on the next page, the first step in the receiver alignment. Says to feed 7.8 MHz from your signal generator to TP13, collector of TR10.
We don't bother with that, and peak L3 and L4 using an on-channel signal, tuned in the normal way.
Not sure why they tell you to do it this way. Makes no sense to me.
Does serve to remind me why we ditched the alignment procedures in so many of the Sams books, and use our own.
73
Having never worked on one myself I was wild guessing. That’s a good point, why do they tell you to do some of those things and yet they don’t work? Or work properly? Or it’s easier another way...
Feeding the 7.8 MHz IF-frequency signal into a receiver is something I would only do if the receiver is dead, not hearing any antenna input.
Then again, I would probably just lay one finger alongside the shaft of a small screwdriver and touch the tip to that spot.
If you hear a raucous noise, the receiver is functioning okay downstream from that spot, most likely.Tells you the problem is upstream, between there and the antenna input.
73
Then again, I would probably just lay one finger alongside the shaft of a small screwdriver and touch the tip to that spot.
If you hear a raucous noise, the receiver is functioning okay downstream from that spot, most likely.Tells you the problem is upstream, between there and the antenna input.
73
Well, in this schematic of the Cobra 142GTL, TR15 is the squelch sense transistor. Don't see a test point near it in the diagram shown on this page.
[URL]http://www.cbtricks.com/radios/cobra/142gtl/index.htm[/url]
73
[URL]http://www.cbtricks.com/radios/cobra/142gtl/index.htm[/url]
73
you have to remember when these procedures were written, the modern test equipment we all use was very expensive, if it was available.
Many radio shops had old equipment, and (im guessing) SAMS and the manufacturers wanted to cover their butts by suggesting the use of a .01uf cap in series because there was a chance that the sig gen at the shop might not already include one, and might put a DC voltage into the radio.
as for the reason they call out the IF freq and the TP instead of just telling you to throw a 27mhz signal into the antenna jack is because (guessing again) these were the same instructions given to the people in the factory giving the radios their initial alignment, and the receivers could be totally dead. in that case, you might need to peak the stages individually before you could do the final tune up on frequency.
LC
Many radio shops had old equipment, and (im guessing) SAMS and the manufacturers wanted to cover their butts by suggesting the use of a .01uf cap in series because there was a chance that the sig gen at the shop might not already include one, and might put a DC voltage into the radio.
as for the reason they call out the IF freq and the TP instead of just telling you to throw a 27mhz signal into the antenna jack is because (guessing again) these were the same instructions given to the people in the factory giving the radios their initial alignment, and the receivers could be totally dead. in that case, you might need to peak the stages individually before you could do the final tune up on frequency.
LC
Good point. And if you encounter a radio that has had every slug twisted randomly, you'll need to do it this way.
73