King Cobra PCB

[Davor]

I may suggest a simple mod for this rig: make an input amplifier a true differential one. Point is that input impedance of an inverting input is ~half the series resistance (e.g. R3) while input impedance of an inverting side is a sum of both resistors there (R4+R6). Tank loading hence depends only upon the inverting input impedance. I also expect it to be much noisier than it is supposed to be.
Fixing it would require a mere resistor values change. For a true differential operation R4=58ohm and R6=2k5. Joint input impedance falls from over 220k to 5k1 (which is not that bad because the tank Q is not that good, and it is not tuned exactly to Tx freq.), and it will reflect beneficially noise-wise. Additionally it will be much less prone to E-field interferences due to the impedance symmetry.

True differential amplifier is a next best thing to an instrumentation amplifier, and only a bit tricky to calculate.

[kt315]

on your smart judgement-seat brought. what you think I have to add and change in the PCB?

[Davor]

Nothing at all. My suggestion was about resistor values, so no PCB changes are needed at all.
The idea of true differential amplifier is balancing input impedances, so that common mode signal (e.g. E field, notorious wet grass etc.) does not produce signal on the opamp output.
It is a common practice to use same resistor values for inverting and noninverting side, but it makes for very different input impedance on each input. High input impedance solution is an instrumentation amplifier, but it is not needed here.

[Patrick]

Are you sure to Q8 ?

[kt315]

Are you sure to Q8 ?

thanks. I do fromthe original. there are another mistakes in the schematic made by guru W.Lahr too.

[ivconic]

Sheeesh... kebab!

That's nice job!

[kt315]

hi all,

The PCP is in stage of making now. You can order already it, via PM, while I do not still know an finish price. Will inform you as soon as I get a resume.

all the best

[WM6]

hi all,

The PCP is in stage of making now. You can order already it, via PM, while I do not still know an finish price. Will inform you as soon as I get a resume.

all the best

Thanks KT315

Please inform us when all will be ready for distribution and prices to (for 1 PCS and for 5 PCS).

[kt315]

Filed!

top side pic attached.

[Merc]

thanks again. can anyone give a logo King Cobra in good quality at PCB more than this I did?

Here is a the logo on the coil of my Cobra II.

Merc

[kt315]

thanks Merc! but I did not find a way to do EMF file from graphic one.
P-CAD accepts only EMF file, but kinda specific EMF. so I placed only text.
MARAUDER, SUPER COBRA, KING COBRA - - and GMT 2012. that's all enough I think.
nobody also did not reply on my appeal to write Geotech and the link of site, that was ignored. but I am not damped first bunch will be too small, 6 pcs, - I would like to fix all mistakes before to order more.

good luck

[kt315]

hello,
the result. got first party. will inform about price later. something expensive, may be have to order second bunch not in Lietuva but in China silk mask is absent - that is strange because I ordered with it.

akk the best

[satdaveuk]

Thanks Kt315, your a gent

Regards

[kt315]

1 board - 35USD and 8USD for shipping. sorry again for the some expensive price , must looking around another manufacturer.

sincerely

[WM6]

1 board - 35USD and 8USD for shipping. sorry again for the some expensive price , must looking around another manufacturer.

sincerely

Not cheap really, dear KT315, but main question is: if one of those PCB was populated and checked in real, on working abilities, and what results outcome?