Re: Mode Comparison

"kh6ty" <hteller@...>

----- Original Message -----
From: "Bev & Jerry Chambers" <btjc1997@...>
To: <NBEMSham@...>
Sent: Sunday, January 13, 2008 3:54 PM
Subject: [NBEMSham] Mode Comparison

Has there been any comparison study between NBEMS and "Air Mail" via 2 Meter Packet?

I know Packet requires a lot more band width than PSK31, but that wouldn't seem to be a problem as there is hardly any Packet activity now. There also might be an equipment advantage to Packet with all the old FM rigs and TNC's gathering dust.

Also, what frequencies are being used by NBEMS at the present?

73, Jerry - W6LQR


The idea behind NBEMS is to be able to reliably bridge a disaster area for up to 100 miles, without dependence upon a repeater system, which may be inoperative.

By using PSK63, NBEMS is able to do that on 2m with small, portable, antennas, or on HF, using NVIS antennas.

The range using packet is considerably less than 100 miles, as without any repeaters in a high location, I believe that the typical reliable range on FM simplex is usually considered to be only around 30 miles, depending on the terrain. In a system like FM, once you have achieved full limiting, ARQ is probably not needed anyway to insure error-free message transfer.

The initial frequencies for 2m NBEMS operations have been chosen to coinside with the nationally agreed upon PSK31 calling frequency, which is 144.144 MHz, USB, and extending 2.5 KHz higher. When NBEMS becomes widely used, it is recommended that PSK63 activity might have to be moved starting 2.5 KHz higher than PSK31 activity, as is the convention on the HF bands. This would be done to prevent PSK63 signals, which are twice as wide as PSK31 signals, from interferring with adjacent signals using PSK31.

Due to the "resuable" nature of 2m frequencies (i.e. they do not travel long distances very well), it will probably be a very long time before PSK63 activity on 144.144 MHz becomes a problem to PSK31 operators, if ever. Here in South Carolina, we run a twice-weekly PSK63 net on 144.144 MHz, USB, around 1500 Hz tone frequency, and there is never anyone else in the bandpass, but we wish there were more activity!

73, Skip KH6TY


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