Have you got a simple way to test comparative EMI immunity? Maybe just a mobile phone?
I don't think I'm through in that area since I believe some network like the one you have shown or THAT's would be appropriate. Maybe just a pair of ferrite beads and shunt Cs.
Having said that I've not seen problems without it.
Though both similar in some ways, yet different in others, I was curious about exploring the use of a common mode choke that would provide some differential series L along with a big (effective) common mode L.
The Cooper VersaPac inductors are very cool: http://www.ka-electronics.com/images/pdf/Coilcraft_VersaPac_Inductors.pdf
They first piqued my curiosity as mic preamp common-mode chokes (and switching PSU inductors) but they might be usable here.
I'm in a high RF 820 kHz environment already. I had the spectrum analyzer hooked up recently and it showed 820 in the mV level.
The Motorola 2600 I have also has the tracking generator option so I'm good from 400 kHz to 1 GHz.
My 4G Wimax modem (CLEAR) gets rectified by my phone handset cord/instrument so I have a good source of 100Hz pulses in the 2 GHz region.
So, FWIW, I'm not seeing any problems yet.
I do have another long piece of Brand-Rex cable I got from SSL.
The spool is damaged and I can't get at one end.
I may have to uncoil that one to re-spool it and when I do may test it laid-out as a long wire antenna.
John wrote regarding the step:
but another possibility is a simple divider formed by the output R and characteristic cable R that would indeed give a -6dB step function for =R.
John, that's exactly it.
You may also not recall it earlier but I did test it with the cable terminated in it's Zchar of ~100 Ohms.
(The drive level of course was reduced significantly due to the low Zterm.)
The step goes away and the final value is 1/2V.
For an unterminated cable with Rsource = Zcharacteristic:
0, 1/2V, then 1V - 1/2V, then 1/2V + 1/2V = 1/2, then 1/2, then 1.
At t=0, t, 2t, then t final.The explanation:
Please visit "Transmission Lines at Audio Frequencies, and a Bit of History," Jim Brown, Audio Systems Group, Inc.: http://www.audiosystemsgroup.com/TransLines-LowFreq.pdf"Transmission Lines at Audio Frequencies, and a Bit of History," Jim Brown, Audio Systems Group, Inc.
About those "hooks:" Some call it time domain reflectometry. Take a look at the expanded waveform at 500 nS/division.THAT1646 feeding 400 feet of 9451 recovered by a THAT1246. 10 kHz, 1 V P-P, expanded 500 nS/division. Line out top, recovered bottom.
At the top we see the THAT1646 output. Almost immediately we see the signal rise to a plateau at about 60% of it's final value.
This tells us one thing from the beginning: The output impedance is not exactly equal to the characteristic impedance of the cable. If it were, the plateau would be at 50%. But, we're close.
On the bottom trace we see the 1246 start to respond approximately 600 ns later. This is the cable delay. With the delay of 9451 being 1.5 nS/foot it is apparent we have about 400 feet of cable.
The incident wave from the 1646 output is initially terminated by the cable characteristic impedance. Our cable delay is about 600 nS. But the plateau is twice that. Why?
Because the incident wave has to travel 400 feet down the cable and back another 400 feet. The delay of the reflected component is 2T because it has to make a round trip. Thus, the plateau is approximately 1.2 us.
After 1.2 us the reflected wave sums with the incident to converge upon the final value.
Though I have not proved it yet by testing the single-ended case, we have visual evidence to support:
Use of differential circuits at both ends can insure signal integrity at least wrt those two ends.
Fully balanced transmission and reception permit greater time-domain waveform fidelity. Though we usually think of music as sinewaves, we occasionally have to transmit timecode...
What we see in the time domain is also in the frequency domain. It's just another way of looking at things. Just my 2 cents.
Our 10 kHz sqaurewave has components >100 kHz where the line reaches it's characteristic impedance.
“Logic will get you from A to B. Imagination will take you everywhere.”