A calling frequency is intended to provide some certainty about where stations will operate. On VHF bands activity is generally low so it makes a lot of sense for people wanting contacts to use an agreed frequency for issuing CQ calls. However if there are more than two stations wanting to use that frequency, its purpose as a calling frequency has to be respected, and anyone who is in contact should move off the calling frequency.
This arrangements works by “gentlemen’s agreement” during non-contest periods, but falls down in the heat of a contest. It is often found that a strong, well located station can dominate a calling frequency and make it very difficult for any others in their local area to use the calling frequency at all. This requires discipline on the part of all operators and the willingness of all to gently remind frequency hogs to QSY (move frequency) once they have set up a contact.
I think there is a case for abandoning the calling frequency concept during contests.
1. If all stations want to use one frequency for calling CQ, there must be a queue. Why a queue on a band with hundreds of KHz of free space?
2. If just one station decides to run a contact on that frequency, all others must wait. see 1.
3. If there is a mixture of technical capability, ie. power, location, antenna gain, quality of fittings combining to give variations in range capability of the stations in any area, the use of the calling frequency by the stations with less technical capability makes it useless for the others. A couple of stations running 20w to discones can make the frequency useless to everyone else until they complete their contacts. And if they don’t hear the dx, won’t they simply call CQ again?
4. There is also the “hidden transmitter” problem. eg. two well located stations 600km apart are capable of a contact on 2m. Unless they happen to call on a frequency free of interference from lower powered/equipped stations calling CQ (randomly and without asking QRL? first) * they will never make initial contact. So they cannot possibly use a “calling frequency” even to make initial contact, because they won’t hear each other beneath the qrm even from a city 300km away.
5. As has been observed by many others, notably a recent vhf column in QST, most contacts made on the bands above 144 arise by “throws” from 144. There are few random contacts made by calling cq on the higher bands. This makes it sensible to use the same offset on the higher band as is in use on the lower band. Eg. contact on 144.180, then 432.180, 1296.180 etc. if you go to 432.160 you may well run into others who moved up from 144.160. If you use .150 you may well be QRMd by someone calling CQ and the odds are they won’t be aware of your dx contact.
These are just the beginning and I’m sure everyone who has ever been on a decent hill in one of these contests would have other examples and scenarios.
The only situation where net frequencies or calling frequencies are practical is where there is a very low level of activity, or a very low possibility of contacts, making it vital that frequencies are co-ordinated. The EME and MS operators need coordination or they would never get anywhere (though modern SDR receivers are making that less necessary than it has traditionally been). But for a contest, where there is a wide range of stations operating, with plenty of opportunity to work the higher and medium powered stations at good distances, a calling frequency creates QRM, sends the wrong message to new operators and hinders contact rates.
A comparison with HF operating techniques is useful. Imagine too how the operators on 40m would react to being told they need to make contact first on 7050, then QSY up the band. They would simply say, don’t be silly, that will never work. They would be right.