[RTTY] Wow - thanks Dr Flowers!

[Kok Chen]

On Dec 26, 2013, at 7:47 AM, Kai wrote:

> BIG error here:
> *"**So, before the FCC removes the symbol rate and allow higher bandwidths ..."*

That was my paraphrase.  I should perhaps have said "Before the FCC removes the symbol rate and allows techniques such as Serial Tone modems to be used..."  

You need to read Andy's comments yourself to see that the focus of his comment is not about bandwidths — Andy argues that the intent of the Symbol Rate limit, together with the non-encryption clause, allowed transparency of the messages even when the path to the monitoring station is poor.  And that 

"The proposal to simply replace the current symbol rate limit with a bandwidth limit does not fully fill the vacuum that would be created."

Here is a very simple example from me: create a Serial Tone modem that uses 1.8 kbaud 64-QAM instead of 2.4 kbaud 64-QAM (after all, the data rate would only be 25% lower than the 9600 bits per second STANAGs).  

This 1.8 kbaud QAM signal would actually be narrower than a Pactor-3 signal, and yet, to make it work on an HF channel, you *still* need to equalize the channel at the receiving end.  Anything much higher than about 100 baud would need to be equalized since HF channels often have multipaths of over 10 msec.  That means effectively scrambling the data at the transmitting end.  So, even though such a signal is no wider than what is practiced today on the ham bands, it is equally non-transparent, and unless the PN polynomials are openly published does not allow self policing.

BTW (again, my point, not Andy's), although not as bad a problem as the multiple subcarrier case, the QAM modems still require transmitters that are clean of IMD.  Pactor-4 for example is spec'ed with a 4 dB crest factor.  That is better than even Pactor-3 SL1 (which has a worse case crest factor of 6 dB), and certainly better than Pactor-3 SL2, SL3, etc.

Transparency of the messages is at the bottom of much of Andy's arguments.  That is why he specifically pointed out the fact that people who use email on the ham bands and expect privacy, are deluded.  Self policing requires that all messages over the Amateur service be transparent and readable by any other ham.

Amateur ops have always use the phrase "reading the mail" as a euphemism for legally eavesdropping on an ongoing QSO.  In the case of reading email that is passed through an RMS, "reading the mail" becomes literal.

73
Chen, W7AY