Hi Paul,
you are correct, sending a side-tone for CW identification is a
non-starter for a mode that is designed to utilize a constant envelope
type of modulation. Apart from that requiring users to use linear
amplification, quite an ask when expecting to utilize up to half hour
transmissions using aerial with no better than 1% efficiency and the
necessary high input power required to get even close to the usual 1W
EIRP limits. Extra bandwidth used for the extra tone and the mixing
products with the wanted data signal would also be unwelcome.
I note also that the length of time to successfully transmit the senders
callsign cannot be a new issue, QRSS techniques have surely already been
used that take several tens of minutes to complete a callsign
transmission. A quick Goole search says that QRSS rates as slow as one
minute per dot/dash (dual frequency keying) have been successfully employed.
73
Bill
G4WJS.
On 28/09/2020 15:34, N1BUG wrote:
Not to ignore the regulatory aspect, but on a technical note:
Correct me if I am wrong but wouldn't sending a CW ID simultaneously
with message tones require linear amplification to produce an
acceptable signal? Many use nonlinear class D and E amplifiers on LF
and MF. Actually I suspect the vast majority do.
73,
Paul N1BUG
On 9/28/20 9:41 AM, David Tiller wrote:
Thanks, Joe, K1JT, Steve, K9AN, and Bill, G4WJS for all your hard
work and these new modes.
I don't want to be a stick in the mud and I am not trying to stir the
pot, but is there any issue with modes that transmit for >= 10
minutes and the US requirement to ID at least every 10 minutes?
I don't think part 97.119 addresses IDs that take longer than 10
minutes.
I admit I don't fully understand all of the details of the
transmitted data in FT4/FST4, so if I'm off-base, please forgive me
(and kindly correct me!). If the FEC employed spreads the callsign
bits out over the message, then my analysis is incorrect from the
git-go.
For FST4, if the message bits are symbol-encoded and transmitted in
the order as shown in the QEX Article on FT4 [See QEX 2020 Jul/Aug,
page 7] and assuming the sender's callsign is sent as the second c28
call, it looks like in most cases the sending callsign is within the
first 57 bits of the 77 bit raw message. That means that 57/77 = 74%
of the raw message has to be transmitted before the sender's callsign
is transmitted. That means the longest transmission that gets the
sender's call in at/under 10 minutes is about 13.5 minutes or 810
seconds.
If I have the callsigns backwards, then the sender's call is sent
first in most cases. That makes the longest transmission more like
27.5 minutes, but then the last 17.5 minutes of the transmission are
unidentified (barring FEC repetition of the callsign bits). That
means the longest tx in this case would be 20 minutes - The first 10
are identified in the message and the last 10 would be identified by
an explicit ID by the operator.
I know this won't be a popular idea, but adding a low power CW ident
at a standard (low, perhaps sub 100 Hz) frequency in addition to the
transmitted signal every 10 minutes would unquestionably address
this. Remember that the requirement is for each station to ID, not to
ensure that the ID doesn't clash with other ID transmissions. If
every FST4 signal over 10 minutes id'ed via CW on VFO + 50 Hz, say,
that would be sufficient to satisfy 97.119.
Ideas/comments?
Again, I'm just asking the question, please don't shoot the messenger.
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