MPP Beach Rev-E - partial fail at STEP 6, TP 6,8,9,10

[waltr]

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[Polymer]

What I do is Quote your post.
Then manually add end of quote and beginning of quote tags and insert my comments between them.

The beginning quote tag is "[ q u o t e ]" but without the spaces.
End of quote tag is "[ / q u o t e ]"

The multi quote button is to include quotes from several threads. Check the muliti quote on more than one post then quote on last post.

Thank You waltr! I will go about answering post #14 now.

[Polymer]

Step 3 Tx oscillator:
The frequency is relatively unstable compared to the baracuda or surf PI.
I may be splitting hairs here, but I do get a variation of around 20 Hz "jumpiness" @ 1300 Hz (or PPS?) which is visible on the scope. The vertical traces twitche/stretch sideways.
Tried different 555's and decoupling caps. No change. Could it be the high ohm pots variability? I don't have to turn them much to get big changes in frequency/pulse width.

Could be the pot is a little flaky. Try pulling the pot and measure what resistance it is set to. Then put a fixed resistor into the circuit.
If now a steady pulse rate the pot is bad. Having a fixed resistor for pulse rate is fine.
Or put in a fixed resistor a bit smaller then what you measure off the pot and add a smaller value pot in series.

I have been thinking about which pots to externalize. The pulse width is now fixed @ 38us after experimenting.

The frequency I have fixed at about 1700 Hz and with an external 10 turn pot +- 220 Hz for EMI adjustment.
Going up to 3400 or 6800 PPS didn't give me much more sensitivity and gets very power eaty.

It is interesting to observe how you can also tune in to interference. That's really noticible.

The frequency wobble is now gone - must have been the pots.

Thank you for the assurance of everything "OK" with the Tx curve and preamp wiggles.

I am quite happy with the detection results so far.
My coil is 12.6" x 4.7" and has around 320 uH.
Detection of a US-Nickel starts at 11" and gets really good at 10".
Silver rings and such only get half as much distance.
Pulse delay ist set to 12us

I have yet to play with the "gain" PL6 - it is shorted at the moment.

At the moment I am trying to figure out a good volume control.
Not happy about this yet, have been playing with a pot 5kΩ in place of R33,R36 & R39.
It's the only pot I have with an on-off switch.

Gosh, I'm rambling again ... Over & out for now.