IGSL

[liekwang]

help me

?Can anyone help me membambatu I am so grateful for the time I need scema PCB ISGL file type zip when there is a file of type PDF or PNG or JPEG please I

[der_fisherman]

Dear liekwang,

Did you see my post? Was that what you wanted?

Regards

Andy

[Davor]

.LAY files are opened and printed with sprint layout viewer, see here http://www.abacom-online.de/uk/html/...#Layout-Viewer
It is completely free, and it allows you to print the PCB as ever you want. This format is very common so it is good to have this viewer.
From that viewer I printed a PCB layout in PDF using PDFCreator virtual printer.

[liekwang]

davor thanks to its PCB board file it looks for bottom line is you have to look over his lines davor once again thanks for his assistance regards davor

[Davor]

I intend to make one more run on the IGSL mods to make this rig capable of beach hunting. It requires separation of all-metal and ground balance functions. As there are 2 GB channels in IGSL, of which each one can assume one of this functions, the only thing to worry about are phase shifters.

I already played with some advanced phase shifting approaches and posted results at LF project topic. Yesterday I revisited the phase shifting circuitry of IGSL to find that Fe channel lacks regulation span to make it more meaningful. I'm using Fe discrimination at almost the end-position of a potentiometer, and currently it is the position that makes most sense.

Current ranges of regulation are shown in the picture. Both Non-Fe and Fe discrimination ranges share the same span. Many things rely on a phase shift that is achieved in Rx front end that is tuned such that Rx coil resonance is above Tx.



By looking at the picture it is almost obvious that for proper Fe channel operation a tuning range for Fe discrimination must go more to the left, and certainly not that deep into non-Fe range.

It is also almost obvious that the current solution for GB can't possibly reach salts phase, and the lower side is dependent upon the Rx phase shift.

Good news is that all of these shortcomings are possible to fix using the existing chips, and their current layout, with only a few components added on the solder side of PCB-s. For that purpose I'll have to re-introduce the U12 chip (LF351), but with no major changes on it's PCB layout.

The following picture shows my intentions:
a) The existing GB will turn into an all metal channel to provide accurate reference for discrimination. It must remain aligned to the ferrites regardless of ground conditions. violet
b) Next, the Fe discrimination will get rotated to the left where it belongs. It will enable notching of stainless steel, foil and nickels as well. green
c) And the most important, new GB that spans between ferrites and salts to make this rig perform well on all terrains. red

[sini]

Hi all,
I rebuilt IGSL TGSL to IGSL Musketeer. IGSL TGSL worked not so deep as I expected ( 20 cm air test for one euro ) but fine - GB and disc worked well. Parameters of my coils are now: Rx 14.7 mH, Tx 1mH. With 330 nF oscillator oscillates at 8.45 kHz. With 14.7 nF Rx capacitance I measured staic phase shift 32 degrees. Discrimination and ground ballance do not work. For 20 degrees static phase shift is capacitance only 12 nf - resonace frequency is than too far from 8.5 kHz ( not like on IGSL TGSL : Tx resonance=1.1 x Rx resonance ). Is it correct ? Other problem is - on the output of Rx preamplifier is much bigger noise than in IGSL TGSL. I ballanced coil by aluminium foil ( as Davor recomended - thanks, very good idea ) to 20 mV + 40mV noise. Is the Musketeer coil more noise sensitive than TGSL coil ? Thanks

[Davor]

Musketeer coil works as a transformer, same as TGSL coil does, but TGSL has a transformation ratio of roughly 1:1 (sqrt(6/6)), while Musketeer has ratio of about 4:1 (sqrt(16/1)), and hence more air signal. Because frequency is ~half of TGSL it is advisable to double capacitances of all those 100pF phase shifting capacitors against the TGSL solution to remain in the same ball park. Because of larger inductance the coil loading is more severe with Musketeer coil, hence the larger phase shift with same Tx/Rx shift ratio.

This much noise is not what I experience with IGSL, so it's cause must be elsewhere. Most probably Tx, or from some external source.

Guess you kept the oscillator from TGSL with only one PNP transistor and a 100k pot for adjusting operating point. I found that there are a few details that may require a bit of care. The most important one is that the transistor is operating in common base configuration, but base sees high-ish impedance. It would operate much better with some 47-100nF between base and + rail. The idea is to achieve maximum oscillation using a potentiometer, but barely so. Oscillation that is below maximum (set by rails) is prone to amplitude modulation, and it reflects back to Rx as noise. On the other hand setting operation point far into maximum oscillation only increases 2nd harmonic which is also bad. I also noted that introducing a previously mentioned base capacitor also reduces 2nd harmonic.

[sini]

Thanks Davor,
I rebuilt Tx oscillator. Oscillator now is the same as in IGSL Musketeer version ( two transistors ). I adjusted Tx voltage on the coil to 15 Vpp ( because of 2nd harmonic ). Is the static phase shift Tx - Rx 32 degrees good ? Please, could you send me schematic of Tx oscillator ? "Oscillation that is below maximum (set by rails) is prone to amplitude modulation, and it reflects back to Rx as noise" - it is perfectly described - noise looks like amplitude modulation (it is not white noise). Thank you very much.

[Davor]

If you rebuilt the oscillator according to the IGSL Musketeer schematic you have the schematic already. I could post schematics of the oscillators in LTspice format so that you can play with them, but that sums it up.

There are two mechanisms that may severely screw Tx purity: AM and PM or off resonance. An oscillator that has some headroom between oscillation envelope and a supply rail is prone to AM oscillation. It may be controlled by AGC network to improve amplitude stability and some detectors have circuitry that goes to great lengths to do that, but the basic truth is that every oscillator with spare gain will inevitably span it's amplitude to the rail. Too much of the good thing will increase 2nd harmonic, but it is inevitable for single-ended configuration. 2nd will be 20 or more dB lower than carrier, so AM is still your enemy No. 1.
PM problems are (ab)used in off-resonance designs. It becomes severe if it is combined with amplitude headroom where amplitude is affected by everything in the coil's environment. A well designed oscillator will have conduction in phase with oscillator output to avoid PM.

Good practice is to find a position where oscillation reaches maximum, and go just a little bit more. You'll have some more 2nd harmonic than possible, but it is OK.

Attached is a LTspice file with all it needs for simulation of a few oscillators. Not all component values are as in original schematics.

32° phase shift is OK in case you can reach it with GB. Observe my drawings a few posts before for reference. It depends upon the 100p capacitor, which presents itself with ~200kohm reactance at 8kHz. With 100kohm pot you simply can't reach beyond 32°. Increasing these capacitors to 220p will increase GB regulation to a bit over 45° which surpasses 32° phase shift and should suffice for most "normal" terrains.

32°shift is beneficial for good overlap of discrimination setting, at least until I fix it by some better phasing solution.

[sini]

Thanks for answer,
I will try to find Tx amplitude optimum. If I understand well - better is to have more higher harmonics than more amplitude modulation. Second question - if Rx resonance is more far from Tx resonance ( 8.5kHz) than is system more sensitive on AM noise ?? Is the key to have Tx and Rx resonance frequency closer ??

[Davor]

AM noise is a bigger problem than 2nd harmonic, but there is a Goldilocks zone, and it is just past the point where Tx envelope reaches power rail.

Closer the Rx resonance to Tx frequency, sharper the phase change gets. And more phase shift also. It is not related with AM sensitivity. Point is that a parallel tank in Rx front end works as a 2nd order low pass filter that also does some impedance transformation. For that reason you can successfully use op amps much noisier than the coil itself, but at a cost of phase shift uncertainty. Going away from resonance makes it more manageable. A real solution would be a damped series resonance with real low noise input. Op amps in that range of input noise (~1nV/sqrt(Hz)) are pricey, so a good solution would be using BJTs.

Far too many people believe a parallel tank is a band pass filter, and it would be if stimuli were applied on top of it. Trouble is that a stimulus is a voltage source in series with inductance, and the resulting configuration is in fact a L-topology. It has a hump, but by all means it is a low pass filter.

[sini]

Hi,
as preamplifier I use LM833N ( input noise (~4.5nV/sqrt(Hz)). My IGSL Musketeer looks very sensitive to 50 Hz interference. I did not understand it. I thought, that Rx parallel LC ( 15nF II 14.7mH )is band pass filter 10.8 kHz, which damps 50Hz and some higher frequencies ( higher than 10.8 kHz ) . For me, it is little bit difficult to understand, that it is not band pass. Can you draw equivalent circuit of parallel LC tank ? Is the solution to add notch filter after Rx preamplifier ?
This night I will connect Tx coil directly to clear sine external oscillator and than I will measure Rx preamflifier output.

[Davor]

When drawn properly, it becomes quite obvious. L-topology transforms input impedance, and in this particular example you have twice the input voltage and in effect half the noise. Only trouble is that 4k7 gives twice the noise of a LM833/NE5532 4nV/sqrt(Hz) op amp, which in effect defeats whole purpose of the exercise.

Draw your own conclusions. Here is a simulation...

[liekwang]

?I would like to know how wide the pcb Boards ISGL how many cm long x width of anyone on this Board over his answer thank you

[sini]

Hi,
I used small aluminium foil ( recomendation from Davor ) for nulling coil . With foil I reached much deeper nulling. Rx signal is after nulling 24 mV on the Rx preamplifier output ( signal is 24 mV , not 240 mV as is on video - bad setting menu of oscilocope ) . Is the AM modulation on video what you talked about ?

Rx- small signal nulled at 24 mV peak-peak at output preamplifier, synchronized from Tx http://www.youtube.com/watch?v=K329C...ature=youtu.be

Rx- small signal nulled at 24 mV peak-peak at output preamplifier AM modulation, synchronized from Rx
http://www.youtube.com/watch?v=1EvWO...ature=youtu.be


Rx- small signal nulled at 24 mV peak-peak at output preamplifier, synchronized from Rx , aditional 50 Hz interference
http://www.youtube.com/watch?v=5K-ds...ature=youtu.be