Almost all expert players are playing so, that if they have supermaximum and fit in a 1NT or 2NT opening, they bid NT with 3 card fit, and they bid their doubleton, if they have a four card fit. The bad thing is bidding the highest suit doubleton, because it takes away the place of the 2nd transfer from responder, which we need to play from the strong hand. 1NT-2♦-3♦ is showing doubleton diamonds, 4 cards in heart, and a supermaxinum hand. I have an easy solution to show all doubletons below game contract, and still playing from opener's hand
My idea is, that we should bring the doubleton in the highest suit also to the lowest bid. 1NT-2♦-2♠ should hold either doubleton in ♠, or doubleton in ♦).
If we do so, responder can give a 2nd transfer with 3♦, if he isn't interested in which suit is th doubleton, and he can ask with relay for the identification.
Now, using a small gadget, we can always play from opener's hand, without going too high.
We will have three steps below our fit's suit in the next level: 1NT-2♦-2♠-2NT is asking for the doubletons, and we are 3 steps below our 3♥ contract.
The lower response, 1NT-2♦-2♠-2NT-3♣ will show doubleton in ♠, the pairs can change it to doubleton in ♦, if they want. To that, responder can bid the last step as 2nd transfer, to play fro the opener's hand.
The 2nd step staying out, we may not bid it, because than the weakre hand will play in the next level. 1NT-2♦-2♠-2NT-3♦ doesn't exist, or showes doubleton in the higher suit with a hand, which is better to play from the weaker side., like Axx, KQxx, Ax, Axxx.
If we have the higher doubleton, we bid the 3rd step to the relay, bidding exactlx our fit's suit. 1NT-2♦-2♠-2NT-3!♥ will sow the higher doubleton, landing in our almost always better side.
|3♣||doubleton in ♠, To that, 3♦ is a 2nd transfer to ♥.|
|3♦||doesn't exist, or doubleton in ♦, with a hand, which is better to play from the weak side. To that, 3 and 4♥ is to pass, others are cuebids.|
|3♥||Doubleton in ♦|
The complete convention looks like this:
|2♥||no extra in the opener's hand|
|2♠||Supermaximum, 4+ cadrs in ♥, doubleton in ♠, or doubleton in ♦. To that, 2nt is asking for the doubleton, 3♦ is a 2nd transfer to ♥.|
|2NT||Supermaximum, 3 cards in ♥|
|3♣||Supermaximum, 4+ cadrs in ♥, doubleton in ♣, or doubleton in ♦. To that, 3♦ is a 2nd transfer to ♥.|
|3♥||4+ cards in ♥, good hand, but not a supermaximum. We also need it sometimes as a barrage, when responder has very weak hand.|