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Author Topic: If the FEDS say go Digital  (Read 1824 times)
AA4HA
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Posts: 1640




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« Reply #15 on: March 30, 2010, 10:33:09 AM »

One problem with digital voice modes is that it requires channelization in order to be convenient. They require the receiver to be exactly on frequency at the start of the transmission in order to synchronize. It doesn't fit very well into the normal amateur activity.

Yep, if this was to be a widespread technology then we would need a digital decoder application that would recognize "pilot tones" for the different modes. If this was integrated with a CAT interface the software could autotune the radio to give a good lock. (hmm, ideas abound in my head). When using a two-tone digital mode all you needed to do was to split the difference between a mark and a space tone. For multi-tone systems it would require a more complex way of locking (as I mentioned a pilot tone, phase locked loop and either a CAT interface or some sort of software/hardware tuning indicator so we could manually adjust a radio onto frequency).

The other alternative would be to create channel blocks across a chunk of spectrum. I am not too keen on this idea for a lot of reasons.

Tisha Hayes, AA4HA
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
AA4PB
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« Reply #16 on: March 30, 2010, 10:37:59 AM »

"Data modes are not permitted in the HF voice subbands"

That's true but the FCC considers the digital transmission of voice to be a "phone" mode and it is permitted in the phone (voice) subbands.

That seems really odd to me. I can have exactly the same digital modulation scheme and spectrum but if I transmit voice with it then it belongs in the phone subband and if I transmit text or binary data with it then it belongs in the CW subband. Unless someone is able to decode the digital data, they would have no way of knowing what content was being transmitted.
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AA4HA
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« Reply #17 on: March 30, 2010, 10:44:27 AM »

1) FCC wants to be able to monitor our transmissions.

2) Data modes are not permitted in the HF voice subbands. It is not good amateur practice to put wide modes in the CW/data subbands. There are also restrictions on data rate and frequency shift. End result is a the data modes US ham use tend to be narrowband.
[/quote]

On Point #1 I agree with the FCC, there should be nothing that we transmit that we should feel secretive about. The FCC regs are a pretty good guideline on prohibited information (business traffic, broadcasting, certain types of personal information during a disaster response/ relief operation).

On Point #2 there is a bit of a loophole on ALE transmissions. It has been debated that ALE is classified as a voice mode. To quote the FCC "Incidental tones for the purpose of selective calling or alerting or to control the level of a demodulated signal may also be considered phone." You can find a reference to this distinction at; http://hflink.com/articles/

According to the FCC we are limited to 300 baud for "digital modes" in the HF spectrum. This data rate may have been relevant when working with FSK keying where the Shannon limit was very low. With advanced modulation techniques (modulo-N, the varieties of PSK and STANAG-like systems) we should draft a recommendation to the FCC for rule-making to make the standard indicate "any data mode that can be constrained in a 3 KHz SSB channel that does not use techniques to mask or encrypt the contents".

Again, that is a personal opinion on digital modes and I will shift further discussions of that over to the appropriate forums.

Tisha Hayes, AA4HA
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
AA4PB
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« Reply #18 on: March 30, 2010, 11:35:35 AM »

Thats one of the confusing issues with the FCC rules that I alluded to above. There is no "digital" mode defined by the FCC. There is a "data" mode, a "phone" mode, and others. They are actually defined by the content of the transmission rather than the way in which it is encoded and transmitted. As a result, "phone" is "phone" regardless of whether you transmit it as in an analog AM or SSB signal or encode it and transmit it using a digital method. What makes it "phone" is that your are transmitting someone's voice.
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WD8T
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« Reply #19 on: March 30, 2010, 04:15:49 PM »

Guys, don't be silly...we all know that we live in a country where nothing can be forced on us by the Government.
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KA2UUP
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Posts: 388




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« Reply #20 on: March 31, 2010, 10:37:42 AM »

Quote:  "Guys, don't be silly...we all know that we live in a country where nothing can be forced on us by the Government."

That is, unless the Great and Dear Leader wants it to be forced on us, but that is another topic!
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