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Have you compared your board with the scope images at the end of the HH article (page 15)?
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I changed the FET today. Here is the pulse on the gate of the FET;
But the Preamp output is still not correct. I don't know why...
The signal looks good but it's on the wrong edge of the TX pulse.
So that seems to say the TX is upside down somehow.....
The pictures in the HH article do not really show much. I'd like to see
each TP and maybe the TX pulse vs sample 1 and sample 2.
I guess I'll have to go back to active turn on and one gain stage to get it running....Comment
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Well I went back to the passive turn off and one gain stage. I left the gain at 33 for now.
I still get the wrong thing for the recieve wave. It looks lit the current signal as I do not
see the TX voltage. I'm stumped. I tried 2 FET's, 2 Coils and active/passive turn off...
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SD are you happy with the pulse from the 555 ?Comment
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Well it's 50 us wide and repeats at 1 khz it should be OK...
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SD can you post up a CRO pic with the CRO lead connected connected directly to the gate of the Mosfet and also a a pic with the cro lead connected to the drain of the mosfet.Comment
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I hadn't tried looking at the drain as I assumed there would be high voltage there;
Gate
Looks like it's not firing;
Drain
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Gate drive looks ok. More than likely the Mosfet is faulty.Comment
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Hi Silver Dollar, since you have a drive pulse on the Gate and have already replaced the MOSFET. There may be problem with the positive 12v from the battery getting through the circuity to the Drain. Or the negative 12v side may not be getting to the Source of the MOSFET.
With the battery removed and the power switch on; measure continuity from the positive battery connection to the cathode of D10; it should read the resistance of the coil; check D10 front to back resistance and insure that it is installed correctly.
From the negative side of the battery measure continuity to the Source of the MOSFET; it should read the 1 ohm resistance of R10.Comment
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I'll have a look today. I tried 2 different FETs so have to imagine the problem is elsewhere...Comment
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I know you set your board up differently than the standard VCO option. What are you using R52,53.54 to accomplish on you board? If I were to install them on the standard VCO set up would I gain any benefit?
I learn allot from threads like this.
Thank you all.Comment
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Well R52, 53, 54 are for the low battery circuit. Many people leave them off.
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Thank you I could not find that in the document and explains why D5 doesnt work on my board. Cool Ill play with that.
Im learning still and trying to teach myself electronics (almost a year now) so sorry for the lame questions I may ask.
Also thanks for all your posts you devote allot of time to the forum.Comment
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Not a problem!
I found my problem, R10 was open! I know I measured it when I installed it.
I'm not sure if it popped due to excessive voltage or just failed when the leads
were bent but we are back in business. I am going to go back to the active
shut off and 2 stage gain as I think it will make a faster detector!Comment
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