minimum sample delay

[bklein]

Ahhh ok, see it with my ipad blowup. What are the three line traces? Special shielding, or?

[KingJL]

Your Q5 is right but the schematic doesn?t show the ?dot? b-c.

Actually, it does. Look carefully, it is easy to miss... I almost missed it myself.

[green]

Carl's method of measuring resonance is most accurate, as the result will have included ALL of the capacitance (intended and unintended) of the TX circuit (i.e. coil, MOSFET, cable, internal wiring/routing, etc.). Also the correct damp resistance is not just a function of resonant frequency, but more importantly a function of the ratio of inductive reactance relative to capacitive reactance (which corresponds to the ratio of L to C as well as frequency). In other words if 2 coils have the same resonant frequency but different ratios of L to C, they require different damp R values.

Where is Carl's method described ? thanks

Rd=pi*L*resonant frequency

[bklein]

Your Q5 is right but the schematic doesn’t show the “dot” b-c.

[KingJL]

is there a schematic error with Q5/6 bases?

I don't believe there is. I created the circuit in LtSpice and the circuit works... It implements a low noise preamp with a gain of ~150. I had to substitute Q4 (better performance could be obtained with a better match for Q4). The circuit offset is controlled by R14.

[6666]

"... Carl mentioned in another thread to disconnect Rd with an operating PI to check resonance..."

Thanks

[Polymer]

@bbsailor -
I get "server not found" error with the link, even with the base address.
Sometimes this happens with US websites whwn accessed from Europe.
Could you please test from your location!?

Works ok from Australia

Thanks. Just tried via a proxy server, it works! Might be geo-blocking or similar.

[KingJL]

Where is Carl's method described ? thanks

"... Carl mentioned in another thread to disconnect Rd with an operating PI to check resonance..."

[KingJL]

... Also the correct damp resistance is not just a function of resonant frequency, but more importantly a function of the ratio of inductive reactance relative to capacitive reactance (which corresponds to the ratio of L to C as well as frequency). In other words if 2 coils have the same resonant frequency but different ratios of L to C, they require different damp R values.

Amen!!!

[6666]

is there a schematic error with Q5/6 bases?

Maybe DaveJ can answer that, but does look a little unusual .

[6666]

Carl's method of measuring resonance is most accurate, as the result will have included ALL of the capacitance (intended and unintended) of the TX circuit (i.e. coil, MOSFET, cable, internal wiring/routing, etc.). Also the correct damp resistance is not just a function of resonant frequency, but more importantly a function of the ratio of inductive reactance relative to capacitive reactance (which corresponds to the ratio of L to C as well as frequency). In other words if 2 coils have the same resonant frequency but different ratios of L to C, they require different damp R values.

Where is Carl's method described ? thanks

[bklein]

Thanks Kingjl, is it this circuit ? always been curious about it, DaveJ has said a few times its worth investigating.

is there a schematic error with Q5/6 bases?

[6666]

@bbsailor -
I get "server not found" error with the link, even with the base address.
Sometimes this happens with US websites whwn accessed from Europe.
Could you please test from your location!?

Works ok from Australia

[Polymer]

Thanks for all your replies. It looks like HARD ferrites are used only for permanent magnets. I had a misconception of this.
The ones we are interested in are SOFT ferrites and there seem to be two main categories of these:
NiZn and MnZn.

@KingJL -
Thank You for the confirmation. The ones that don't work well with PI are apparently the NiZn ones (e.g. am radio antenna)
Am lucky enough to have many MnZn rods - they are not as cheap or as easy to get as you say.

@bbsailor -
I get "server not found" error with the link, even with the base address.
Sometimes this happens with US websites whwn accessed from Europe.
Could you please test from your location!?

[bbsailor]

I have lots of Soft Ferrite Rods that I have used in Pin Pointers.
They work pretty good.

Here is a link that will explain soft ferrites:http://www.magneticsgroup.com/pdf/mmpa%20SFG-98.pdf

Basically, soft ferrites do not hold much energy after the TX pulse turns off.