[MacLoggerContest] Fun with theology

[Don Agro]

Hi Bill,

On 15-Mar-05, at 11:06 PM, Bill Coleman wrote:

> There are several programs in the PC world that use a "short" space. 
> For example, CQPWin (yeah, I know) allows you to insert a "*" instead 
> of a space character. I don't know how many dit intervals this is 
> precisely, but it does result in faster sending.
>
> 2 dit intervals between characters seems somewhat too short to me.

When you say "seems" is this from actually listening to the CW that 
MacLoggerDX produces or just a theoretical concern ?

MacLoggerDX version 4.0.7b7 features a user-selectable number of dit 
intervals between words.

<http://www.dogparksoftware.com/MacLoggerDX.html>

I suppose we could further complicate the user interface by making the 
number of dit intervals between characters variable as well (maybe 
include fractional dit intervals ?), but to be honest you are the first 
one to mention this.

> For all those generating CW on the serial port RTS line -- I wonder 
> how much fixed and variable latency there is on these USB / serial 
> adapters.

In the adapters - little to none. In the whole bus - it depends. I 
think this is a theoretical concern with little bearing on practice. 
USB 1.1 supports four basic types of data transfers which are Control, 
Bulk, Interrupt and Isochronous. Control transfers are for configuring 
a device and also control of other‘Pipes’on the device. Bulk transfers 
are used for relatively large and bursty data and have variable latency 
constraints. An example is printer data from PC to an USB printer. 
Interrupt transfers are for timely and reliably delivery of small data 
like mouse co-ordinates or key characters. Isochronous, also called 
real time transfers occupy a prenegotiated amount of USB bandwidth with 
pre-negotiated delivery latency. However, for lost data there is no 
retransmission and hence cannot have reliable delivery. An example is 
audio and video capture or playback devices. Typical data rates are 1.5 
Mbit/s (Low speed) and 12 Mbit/s (Full speed). Currently the new 
version of the standard ver 2.0 addresses a facility of High speed (480 
Mbit/s).

The lowest data rate (1.5 Mbits/s) is many times faster than required 
to handle the nyquist frequency implied by the duration of a dit pause.

> I suppose it would depend on the other activity on the USB port as 
> well, since USB, unlike Firewire, doesn't have a guaranteed level of 
> service.

The whole bus bandwidth would of course depend on the CPU controlling 
it and the controller chip used but I find it hard to believe that 
normal bus load would introduce any measurable or perceptible variation 
in the relatively glacial time frame of the dit pause.

I suppose if you were trying to send CW while you were simultaneously 
streaming audio and video from a USB web cam you might run into trouble 
(I haven't tried it) - but in any real practical useful sense - there 
is no problem.

But rather than spending all this time on theoretical conjecture 
(amateur radio is based on empirical science after all) why not listen 
to the CW that MacLoggerDX actually generates and base your 
recommendations on that ?

Auditory perceptions will introduce their own subjective errors but at 
least we will be judging the engineering rather than the theory :)


73 Don Agro VE3VRW

D o g   P a r k   S o f t w a r e   L t d .

email: dagro at dogparksoftware.com
   www: http://www.dogparksoftware.com
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