coil experiment

[mykaitch]

Did a little experiment today. I knocked up a voltage doubler and used it for the txcoil of my bandido copy.
it gave me 10vpp across the coil (clean sine wave).
It was crap.
Thought I would share this.

[golfnut]

What was it like before?

S

[Skippy]

This is an experiment I had considered doing. I'm intrigued - tell us more about your experiment. Did you linear-regulate the doubled voltage, or was it noisy and raw? Was the switching frequency of the doubler free-running, precisely controlled, locked to the detector oscillator frequency in some way? Did you halve the receiver gain to bring things back to normal, or did you just double TX, giving double sensitivity? Was it rubbish in an air-test? or just in ground?

[Carl-NC]

If you double the TX voltage then you double the RX residual signal, which might send the X demod out-of-range, depending on the design.

[mykaitch]

This is an experiment I had considered doing. I'm intrigued - tell us more about your experiment. Did you linear-regulate the doubled voltage, or was it noisy and raw? Was the switching frequency of the doubler free-running, precisely controlled, locked to the detector oscillator frequency in some way? Did you halve the receiver gain to bring things back to normal, or did you just double TX, giving double sensitivity? Was it rubbish in an air-test? or just in ground?

I more or less threw the doubler together, 555 etc.
It ran at 4.4KHz. The result was lots of harmonics
and distortion of the Tx sine. I changed the freq to 9.8kHz
which sorted everything out. Although my coils were carefully
made and tested at 10kHz, when measured connected and ready to go
I get 8.6Khz on the Tx (which has not been a problem). I found
that varying the doubler (free running) freq too far away from
its 9.8 brought back the Tx problems ie bad sine etc. I also
realized that the front end gain was now too high but I lost faith
and scrapped it. I intend to revisit it at some time. for now, I
have a set-up problem is so much as I am finding ground balance
difficult - I may get rid if the multi-turn and pot a single
turn pot in today. All in all, it works well in air - 8-9"
for a UK 2p (about 1" diam copper alloy). Unlike my first build-
the one I broke, this one works as per Tesoro manual with all my
'mods' removed bar one; all metal does not work at all without
40m across the AUTO switch. I use quad op-amps of the same type
as the original single ones. I can see why mine works but not why
the original desgin ever worked. I did reduce the 470k on the batt
test to slightly shorten it.

[mykaitch]

Is the pic really you cos if it is I ain't messing with you....

[Skippy]

When you re-do this experiment, please keep us informed. You can sacrifice a volt or two from your doubled supply by using a linear regulator. The difference in 'gain' will be negligable. The fact that you could see disturbances on your sine-wave tells me you will have problems - bear in mind detectors look for VERY tiny changes in coil output.