[1000mp] 40 Meter unique problem

[W70m at aol.com]

Normally one would conclude the following is an antenna problem and  not with 
my old reliable FT-1000MP.  Yet, now the antenna checks out  okay.  I am 
seeking someone who might have experienced a similar  situation.
 
Last night in the NCCC sprint, when running 100 watts to a two  element 
Cushcraft yagi, the VSWR went to the pin on 40 meters only.   The receive signal 
intermittently dropped by 20db or more.  Application of  power by tripping the 
footswitch, restored the receive signal; only to drop  again later.  The VSWR 
remained high.  I have had the receive signal  drop problem before.  It behaves 
like a relay did not return to the  closed position.
 

Today the antenna checks okay with 100w and full power.  Last  night while 
the antenna gave high VSWR on 40, it showed low VSWR on 17 and 12 as  usual.
 

Any suggestions?  Please reply direct and thanks for the  help.
 
73
 
Rod W7OM