You are welcome Andy. Also keep in mind that you two are much more than 300 miles apart and are going to experience QSB and even QRN that you would not have using NVIS antennas only 300 miles or less apart. As you know, noise arrives at low angles (see the explanation of why the Beverages are so quiet), and a NVIS antenna, about only 12 feet high, will discriminate against noise arriving at low angles, because its takeoff angle is almost straight up. In addition, propagation changes (QSB) affects the NVIS short-range communication much less than using a longer skip zone.
Nevertheless, we did extensive tests and had many successful ARQ transfers over 500 miles or greater on 40m and 80m using MFSK16, and sometimes MFSK32, which is the best performing mode we have in the NBEMS suite for handling deep QSB fades and static crashes. It is just that those long circuits are never as solid as a NVIS circuit, so it is not a very good measure of NBEMS performance on either HF (up to 300 miles distant) or VHF (up to 100 miles distant), which would constitute the distances for almost any real emcomm situation. 73, Skip KH6TY NBEMS Development Team ----- Original Message ----- From: "Andrew O'Brien" <[EMAIL PROTECTED]> To: <digitalradio@yahoogroups.com> Sent: Thursday, September 04, 2008 7:00 PM Subject: [digitalradio] Re: NBEMS opeation procedure Thank you Skip, this helps a lot. I was blindly sending beacons !!! Andy --- In digitalradio@yahoogroups.com, "kh6ty" <[EMAIL PROTECTED]> wrote: > > To minimize interference to others and to have the most success with NBEMS, we wish for everyone to follow the prescribed contact procedure for using NBEMS. Here is an except from the Help in the Flarq application: > > Initiating an ARQ connect session > > > Start by sending a 'CQ NBEMS' or some similar unique way of indicating that you are seeking to send ARQ traffic. Do this from the digital modem program and not from flarq. The potential station for receiving your ARQ traffic will answer in the clear. Negotiate what digital mode you will use for the ARQ connection; ie: PSK-63, PSK-125, PSK-250, MFKS-16 etc. Then try that mode without ARQ to be sure that QRN and QSB will not seriously disrupt the connection. Ask the responding station to send an ARQ beacon using flarq. You will then see his ARQ callsign appear in the callsign window. > > Click the CONNECT button to connect with that station. The text next to the diamond will change to CONNECTING and remain that way during the connect time out period. During the connection process the CONNECT button will be disabled (greyed out). > > After a connection has been established the button label changes to 'Disconnect' and the text next to the diamond indicator will read CONNECTED. Pressing this button will then execute an orderly disconnect from the other station and return the program to the CONNECTED state... > > Blindly sending a beacon and waiting for a response is strongly discouraged! > > Please follow the above procedure so as to minimize interference to other users and to establish what mode is most suitable for ARQ transfers under the current conditions. Note that DominoEx and the PSK modes are intended to be used for VHF use and the MFSK modes for HF use. On VHF, when operating near the noise level, it is helpful to start with PSK63, as the idle signal stands out most clearly over the noise background, even if DominoEx modes will produce the most error-free copy, having a lower minimum S/N requirement. Then, once tuned in PSK63, shift to DominoEx 11 without changing the tuning. If the path S/N is sufficient to use the PSK modes, and both transceivers are stable enough (probably using TCXO's), PSK125 or even PSK250 can be attempted, but before changing to a faster mode, copy should be error free when using the initial slower mode. The faster the mode, the better the S/N needs to be for minimum repeated blocks. When using PSK125 or PSK250, keep a little squelch active in order to prevent large amounts of garbage filling the screen in the absence of a signal, and enable AFC. On HF, start with MFSK16, with AFC enabled. > > 73, Skip KH6TY > NBEMS Development Team >
