What’s
New in cocoaModem 2.0 v0.31
Kok
Chen, W7AY [w7ay (at) arrl.net]
Last updated: January 22, 2007
Click here
for the previous (v0.30) What’s New page.
What has changed in v0.31 ?
This version of cocoaModem has a new Synchronous AM Reception interface.
A small optimization was done to the CW Interface. The decoding latency is increased by 100 msec for the sake of slightly reducing the CPU utilization.
%o and %N have been added to contest macros to handle "cut" numbers for CW contesting. Also, a bug fix was made to the %n macro.
Synchronous AM Interface
cocoaModem now has an interface for Synchronous AM
reception.
Selective fading can cause the carrier of an AM signal to
be attenuated to the point where the AM signal appears
over-modulated and thus sound distorted when envelope
detected. One way to overcome this is to filter out the
carrier and one of the sidebands and then using a product
detector for demodulation (i.e., receive the AM signal
using an SSB receiver). The remaining problem is the need
to precisely tune the receiver.
Synchronous demodulation is usually done in the
intermediate frequency stages of a receiver and involves
extracting the AM carrier and phase locking a local
oscillator to that carrier for use in the product detector.
The phase lock loop automatically fine tunes the product
detector.
cocoaModem implements synchronous AM demodulation by
applying DSP techniques to an SSB receiver's output that is
slightly off-tuned. It requires no hardware modification to
the receiver.
CW Cut Numbers
If %o is used instead of %n, QSO numbers
will be sent with the number 0 (zero) substituted by the
letter T. If %3o is used, the number is sent with enough
leading zeros (leading Ts) to make up at least three
characters (e.g., 91 will be sent as T91). If %4o is used,
the number is sent with enough leading zeros (leading Ts)
to make up at least four characters (e.g., 91 will be sent
as TT91).
If %N (capital N) is used instead of
%n, QSO numbers will be sent with the number 0 substituted
by the letter T, the number 1 substituted by the letter A
and the number 9 substituted by the letter N. If %3N is
used, the number is sent with enough leading zeros (leading
Ts) to make up at least three characters (e.g., 39 will be
sent as T3N). If %4N is used, the number is sent with
enough leading zeros (leading Ts) to make up at least four
characters (e.g., 39 will be sent as TT3N).
There was a macro bug where %n was always padded with
leading zeros to create a QSO number with at least three
digits (e.,g sending 001 for 1, sending 024 for 24, etc).
That bug has been fixed. %n now sends the minimum number of
digits (QSO number 1 is sent as a single digit 1, etc). To
get 3 digits, please change to using the correct form that
was documented earlier, i.e., use %3n to send enough
leading zeros to make it at least a 3 digit QSO number.