You may have listened to a local 2m net and heard people saying “This Is” before they give their call sign during check-ins. An alternative is they may say “Net Control” instead of “This is”. Plus there is the combined effort of “Net Control, This is”. Why are they doing this? If you have wondered about that, here is the answer…
One problem when the net control station calls for check-ins is that stations all try to check-in at once and thus can double. Doubling is when two or more competing stations transmit at the same time, one station captures the receiver and gets through rendering the calls of other people transmitting moot since they are not heard. Another type of doubling is where two stations are equally strong to the repeater receiver and neither station is understandable. Both of these cases are due to what is called the capture effect on FM.
So how do we separate these stations out so they are not doubling? A useful technique is to say “This is” and unkey. You unkey momentarily to see if you hear anyone else transmitting. If you do not hear anyone else, then key up again and state you callsign (phonetically) and your name. For example, if I wanted to check into a net, I would do the following:
Key my radio and say, “This is” then unkey. If I do not hear anyone else, I then key up and say November Yankee Four India, Tom, No traffic”. If I did hear anyone when I unkey after “This is”, I wait for the station to finish and start the process again. The reason this works is that saying “This is” takes far less time than you stating your whole call, name and status and thus, the chance for doubling is far less.
I was listening to another local net and heard so many stations saying, “This is <callsign>, Joe in Anytown” (I made that generic of course). There are two issues with this procedure. First, the “This is” does not add anything and it is certainly not preventing doubling”. Second, giving your whole callsign, etc. increases the chance of doubling.
I hear this on the UPARC Tuesday night net quite a few times as well. I suspect people hear others say “This is” but do not realize why the pause/unkey is in there so they just parrot “This is callsign, Joe No Traffic” in one transmission.
I encourage you to try this on the next net you attend and see how much smoother the operations go. Listen to the people that say “This is” or “Net Control”, unkey and then state their call and name. There is a reason they are transmitting this way. It will certainly help to minimize doubling during the check-ins.
One note that this applies to repeaters that are not linked. There is a special issue with linked repeater systems like NI4CE that the links all take a second to start transmitting. If you unkey and key up again to give your call, the beginning of your callsign may be cutoff. In that situation, you just have to wait until the roar of check-ins dies down and find a spot to check-in.
Please let me know if you have any questions or other thoughts on the subject.
