Is this a major advance in PI sensitivity ??

[moodz]

... the bifilar wound coil and front end is a project that is sitting on the shelf.

The CCPI project overtook it.

[bishop_slayer]

Is this idea still worth following up on or are there newer developments that give better sensitivity?

[6666]

Hi picked up a bunch of SF18G diodes from E14
using their free code '0FREIGHT' at the checkout!

that's a zero, put the code in "special instructions" in delivery area at checkout and free postage till end of Nov in Oz.
$5.80 for 25

[Davor]

Yes, and not too high frequencies because of quite high capacitance. The only drawback is that the voltage-capacitance curve is not perfect as with the full blood varicaps, but for every VCO application that is driven by a PLL they are just perfect.
Day by day we witness some traditional components simply vanish into obsolescence oblivion, and real varivcaps are long gone. Use what you can

[sido]

Is that IN4.... series a Varicap behaviour in HF Frequencies??

Sid

[Davor]

Yes, 1N4001 is a varicap in disguise.

[mickstv]

No worries moodz. From memory I initially used some UF4005,6 which came out of an old smps. Definitely the 1n400 series are too slow for the job.

[moodz]

Moodz would you mind telling me where you are getting the SF18G diodes ?
thanks
6666

Mick is right ( thanks Mick ) ...element14 have them ... I tried 1n4004s and there is a distinct speed / recovery difference using the SFs.

[mickstv]

Hi Mick thanks
I had previously tried there, but must have typed it wrong
cheers

No worries

[6666]

Hi Mick thanks
I had previously tried there, but must have typed it wrong
cheers

[mickstv]

I can help with that one Element14.




Cheers
Mick

[6666]

Moodz would you mind telling me where you are getting the SF18G diodes ?
thanks
6666

[Davor]

THAT1510 is a nice thing when applied where it belongs, and that would be a balanced input. It works best at higher gains, and the only drawback I can think of are the "miller" capacitors that take care of the stability, but in turn also reduce gain at higher frequencies. Guess they'd be just fine for up to 100kHz bandwidth.
It is quite possible to make such preamp on your own, and optimise it for your purposes. It comprises a CFIA amplifier that is made from two opamps and two BJTs in current feedback configuration. All the feedback components are of very low resistance, thus introducing a bare minimum of additional noise.

The cornerstone in audio preamps was the Graeme Cohen pre, and THAT1510 is a near replica of that particular design. They both use CFIA frontend, but Cohen's pre had a cross coupled differential amp balanced output, while THAT has something else.

It is funny, but CFIA is a nice example of mind over electronics, where an intelligent design outperforms most of the off the shelf components. Yes, our detectors are using low impedance sources, and sure they can benefit from low noise pre.

[moodz]

May I ask, what are you talking about? An average/amateur PI machine would have over 10000X amplification to get descent results. The that1510 has been tested my me over 3 years ago and it has major flaws. You get a bit over average, sensitivity, but it's still far away from a good commercial PI detector.

May I ask the same question .... I have only ever used the THAT1510 as an amplifier ... I have never thought of using it as a metal detector ...

Since it was designed to be an amplifier I would have to agree with you that it is still far away from a good commercial PI detector

[straton]

Speaking of using an A/D converter, I have used the AD1671 12bit complete, 1.25MSPS, A/D converter with good results, for discrimination purposes but sensitivity went down. If anyone is interested I have a few of them for sale. They are compete/monolithic!!!, easy to use, parallel interface(easy interface), unipolar/bipolar input,with internal reference, excellent choice for this kind of job. Most atmel and microhip micros are suitable.