BNC and coax question

[ptm82379]

I am using a function generator to deliver a signal to my ignition coil project but i need help with the post connector im using.

The front side of the plug is female BNC. The back side has 2 solder tabs, one on the outer casing and a copper center line.

Is it necessary to use coax and both solder tabs or can I just use some solid copper wire soldered to the center copper terminal of the BNC connector without the outer tab that the shielding would normally solder to?

 

[user_88]

The simple answer is that you can connect a solid copper wire between the center post of the generator and the ignition coil. However, it will be necessary to take a separate wire and insure that a clean ground point on the generator, such as the tab on the outer coax casing, is connected to the negative or ground terminal of the ignition coil circuit. If you do not have a ground wire between the two components, your circuit will not be complete, and the function generator will not generate a signal.

The advantage of using a coaxial cable to connect the generator to the ignition coil is that higher frequencies will be transmitted more effectively. The significance of higher frequencies results from the fact that square waves ... or switching waveforms ... have sharper edges that are composed of the higher frequencies.

Coaxial cable is designed to transmit relatively higher frequency signals with as little attenuation as possible.

If you have access to an oscilloscope, you might try to compare the sharpness of a square wave, observed at the function generator output, with the sharpness or attenuation of the square wave measured at the ignition coil, after it has traveled some distance to the coil.

 

[Reloadron]

For lower frequencies the best solution would likely be a BNC to Banana binding post adapter which would give you your signal and ground out at the front panel. If you have to come out from inside the signal / function generator then solder leads to both tabs for signal and ground (common). Aslo when working with a square wave note the output BNC on the front panel. Do you see any small print to the effect of 50Ω ? Should that be the case the signal / function generator is designed to work into 50Ω and it would be best if possible to terminate the output at the load (your coil or whatever) placing a 50Ω resistor across the signal and ground. A plain 50 Ohm carbon resistor is fine.

Ron

 

[user_88]

The primary coil resistance of a typical ignition coil is something like 1 ohm ... If you don't seem to be getting any results, then try putting the 50 ohm impedance matching resistor in series with the primary coil, rather than in parallel with it.