SCANdal said:
Gentlemen,
Since aviation radio traffic is passed in AM and most 2 meter ham traffic is passed in FM, is one a good predictor of another's propagation? Or is the difference between the two modulation schemes negligable? Also, aren't the elevations of the transmitters you're monitoring for ACARS is so much higher then your typical ground station - thus potentially skewing your results?
SCANdal
Hi Scan,
The mode doesn't enter into an opening. FM is a rather poor mode for hearing weak signals, but if the band is open, then any modes reception will be enhanced.
Several have mistakenly assumed I was trying to predict tropo openings. In fact, I am trying to predict when sporadic E skip is likely to be present and if so, what region is the opening to. Sporadic E can be very selective on vhf, but the fact that an E skip opening exists between Maine and Tennessee does not mean that there will be an opening between New Hampshire and Kentucky.
So, an ACARS transmission that identifies an aircraft over Georgia probably means that there is an opening between Maine (my State) and Georgia. As pointed out by several users though, not all ACARS transmissions from aircraft identify the actual latitude and longitude of the aircraft.
The fact that an aircraft might is at 40,000 feet doesn't make any difference in fact......since the reflecting layers in the atmosphere are much higher than that. Since an aircraft at 40,000 feet has a radio horizon of about 200 miles, any aircraft that I hear that are farther away than 200 miles are being reflected by some sort reflective layer within the atmosphere. So, a transmission from the ground or from the air amounts to about the same thing as long as the path is longer than 200 miles or so.
There are 2 types of skip that happen on VHF, although there are variants on each type.
Tropo reception is common in the Summer months, it makes vhf stations that are 200 to 600 miles away suddenly receivable. The signals are relatively weak, sometimes just above the noise. Tropo reception is the type of reception most of us have observed. Tropo enhancement can last for days at a time.
However, I'm after sporadic E. It is very selective and very rare. But, when it happens, signals between 1000 to 2000 miles away suddenly become extremely strong-like S9 or stronger. Sporadic E openings last for minutes to several hours, the vast majority of these openings are less than 1 hour long.
When you can predict a sporadic E opening, it's like hitting a home run! It's so rare and so short. But, if you're on the ball and in front of your radio, you can work station on vhf that are 1000 to 2000 miles away with just a few watts and a modest antenna. So, the lure of sporadic E is great, which is why I became interested in monitoring ACARS.
Hope this helps explain the situation a little better.
Regards,
Art
