I am using vacuum capacitor, you can find them on e-bay around $200. But I have used small NPO capacitor in parallel for several years. With the right material that can handle current on 1.8 MHz. Most ceramic capacitors, like doorknobs can handle 3 RF Amperes on 3.5 MHz but only 1A on 1.8MHz.
The capacitor I used for several years with no failure is this http://www.electronicsurplus.com/cera-mite-564cc0gaa302el620j-capacitor-cera mic-62pf-3-000v 62pf NPO 3KV, for 1200 PF you need 19 units in parallel, very important the capacitor cannot touch each other, keep them at least 2 mm apart, or 80 mils separation between them. You can find them on DigiKey as well or other vendors, at Eletronicsurplus they cost U$ 1/each. NPO is a must otherwise they will change capacitance with the temperature, some 500pF capacitor can really change the tuning a lot. Three 170pf NPO in parallel does a much better job them one 500ps that is not NPO. My two cents N4IS JC , _________________ Topband Reflector Archives - http://www.contesting.com/_topband