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Old 02-12-2010, 12:34   #1
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Propagation Quest

I was working on a catamaran which has a PTC2 usb pactor modem via a ic-801e and hp laptop for sail mail.The vessel is on land amongst other boats and chaguaramas is a hilly cove area.He connected successfully to a local sailmail station which he was able to send and receive his mails,but when he tried to connect to a next station he was unsuccessful in doing so.My little knowledge and this is where the question lies is

1ue to present location he will not be able to connect outside

2: Propagation Chart was showing 22Mhz was best frequency to use to connect to the station in florida but from my limited knowledge it is not possible during the day and i suggested to use 10,12 or 18 Mhz to connect.

needless to say he did not want what i was saying but what the propagation chart was saying is his god.so he is annoyed and wants a 2nd opinion.also to note he has the Tx and Rx frequency the same and does not want to put the split of 1.5Khz for Tx an Rx so i am in a rut with this customer
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Old 02-12-2010, 12:55   #2
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The propagation charts are accurate for propagation. But of course they don't indicate noise levels at either end, the distant station being in use but unheard, the channel being in use but unheard, unexpected variations in the atmosphere, etc. I regularly use the propagation chart wavelengths that are less than optimum, often with excellent results. You were correct to suggest other wavelengths.

Can't speak to the 1.5kHz split...Sailmail takes care of this with no interaction or configuration actions on part of the user, thankfully.

Other boats nearby are no help at all as they can absorb much power while generating plenty of noise. Plus the ground plane will be less as the boat is out of the water.
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Old 03-12-2010, 07:24   #3
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22 mHz will typically be useful for long distance communication ONLY during the day. With the solar flux at current levels (i.e. not very high) then even daytime communication in this band will be spotty. If you can tell us the exact locations of his transceiver and the RMS station he was trying to connect to, the time of day and the date, we could look at a propagation map and give a more informed opinion on what bands might have been best for the connection.
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Old 03-12-2010, 08:06   #4
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The other consideration, as you alluded to, is the local topography. To get to Florida, the radio wave would need a low takeoff angle from the boat. If the mountains to the NW are high enough and close enough, they may be obstructing the radio waves. Lower frequencies will reflect with higher takeoff angles, but come back to earth closer to the transmitter. This may explain the ability to make the nearer contact. If the station is really close, within a few tens of miles, the contact could be made with ground waves instead of sky waves.
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Old 03-12-2010, 09:26   #5
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his boat was 2 miles in land in chaguaramas trinidad which is a hilly coved area,with other boats also on land around and the station he was trying to connect to was in daytona florida.the time was 9:45am local 13:45 utc
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Old 03-12-2010, 09:38   #6
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The propagation chart in sailmail is very reliable, depending of hour and location.
But are you sure that you have enter the good coordonates in sailmail.
In my configuration, (PTC-II pro end laptop with airmail) i have to enter my location manually.
Jean-Pierre
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Old 03-12-2010, 09:47   #7
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HMM.good point capt.the customer had entered the coordinates
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Old 03-12-2010, 11:30   #8
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Using HamCap, it looks like there was a decent 22 mHz window between 1300 and 1600 UTC, and then again around 2200 UTC.

I suspect that local geography is going to be a problem there for making distant contacts. See if he is willing to move his boat to a mountaintop for better results.
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Old 03-12-2010, 11:52   #9
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Originally Posted by Sheriff View Post
HMM.good point capt.the customer had entered the coordinates
With user input, many time they will confuse UTC with local time when determining the best frequencies and forget to figure in the offset. Chuck
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Old 06-12-2010, 08:24   #10
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good points guys will take all advice thanks
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