[RESEND] Re: [Coco] COCO 3 for LowFER transmitter?

[jdaggett at gate.net]

On 12 Dec 2003 at 21:07, KnudsenMJ at aol.com wrote:

> In a message dated 12/12/03 11:31:46 AM Eastern Standard Time, 
> bathory at maltedmedia.com writes:
> 
> > Correct in that a pure CW signal is better than an amplitude
> > modulated
> >  carrier is for 
> >  reception. The narrow bandwidth requirements of a receiver for slow
> >  on off 
> > CW carrier will reflect in lower noise power density within the
> > bandpass.
> 
> True.  FWIW, MCW (modulated CW, that is, AM modulated with Morse code
> beeps) is used on the Beacon Band just above the 150-190 LOWFER band.
> 
> One mistake made by the aircraft beacon stations is using a very
> high-pitched tone, maybe 1000 Hz or more.  It requires too much
> receiver BW to copy.  If you use MCW, try a lower pitch, 400 Hz or
> less.  That will allow the receiver to tighten up its bandwidth
> against the horrendous light-dimmer noise on this band.
> 
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The problem is below 400 Hz you start to get into the subaudible range and I think 
the intentions were to make the tone audible.


> > Also at that frequency and that low a power I would
> >  recommend 
> >  a tuned loop antenna for transmitting. It will meet the
> >  requirements. The efficiency can be made quite high. Much higher
> >  than any loaded vertical. 
> 
> I've not heard much about transmitting with loops much smaller than an
> equivalent dipole antenna.   Loops are definitely the best for
> receiving at these low freqs, whit much less noise pickup.   A small
> loop may indeed be as good a transmitting antenna as anything you
> could fit in your yard, and ISTR that the Lowfer rules limit your
> total antenna length to 20 feet or the like -- not that you'd expect
> to abide by that, but since a quarter wavelength is almost a mile,
> you'll not get much more out of a long wire in your backyard.
> 
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Transmitting loops at low power are not to bad. They are generally about 1/10 th 
wavelength and no greater than 1/3rd. On this band they will be more like 1/100th 
wavelength. I still believe that it can be made more efficient than any loaded 
antenna. The main drawback is that the "Q" of the antenna is extremely high and 
thus very narraow bandwidth. 

As receiving antenna sub-wavelength loops are okay. The loop area and/or number 
of turns will affect induced current. Small receiving loops tend to be insensitive to 
man made electrical noise. 

james

> I wonder if Lowfer experimenters have tried Coherent CW, where each
> dot and dash is synchronized to the WWV timebase of NBS/NIST.  --Mike
> K.
> 
> 
> 
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