In your searching did you find any "mainstream" pcie gen4x1 SFP+ cards? I only found the H!Fiber model - which looks perfect, except that our work won't buy from that supplier.
Audio codecs are very good at retaining signal phase as the human ear is very sensitive to errors in this. Whilst I'm not saying it is impossible, I think it would be very unlikely that the interval change is due to transcoding.
Also, as it is a moving receiver this effect is almost expected.
Sadly the towed pinger locator (TPL-25) is omni directional.
But by analysing the inter-ping interval you can determine a CPA point. Something below I wrote on reddit about this technique:
Due to the pulse length (10ms) there is an inherent 100Hz bandwidth in the signal, which is equivalent to the frequency shift you would expect if moving at 4m/s. In other words, Doppler measurements of a single pulse is NOT going to be useful in attempting to localise.
However, because the pinger has a relatively stable repetition rate (about 1.106s from what I could see) you can do a cool trick to localise it (assuming the source is stationary):
- Perform a pass over the area of interest (ie where the pinger is)
- measure the ping times of arrival (either manually with waveform inspection or write an envelope detector)
- plot the ping times of arrival versus the time of arrival modulo ping interval. ie in MATLAB: plot(toa, mod(toa, 1.106), '.');
- The plot indicates the relative distance from the source / receiver. Hopefully the plot should contain a local minimum representing a closest point of approach (ie like http://imgur.com/v1ZclaX ). This means that the source lies in a line perpendicular to the vessels course centred at the location of the receiver (ie TPL-25) at CPA time
- Perform another pass over the area of interest on a course perpendicular to the first
- measure the ping times of arrival and look for CPA as before
- You should now have two intersecting lines. Guess what should be at the intersection? :)
This relies on having a stable ping repetition rate.
BTW this is the author of the linked post here :)
Rodney
Edit: @ISL has hit the nail on the head there. Hyperbolic trilateration using multiple simultaneous receivers is the way to go. RAAF will be trying this with sonobuoys deployed from P3-C Orions