It's not anything to do with the coax itself 959. To tune your antenna properly with the mfj antenna analzyer you need to either use an electrically tuned 1/2 wave coax jumper cut for desired freq using the coax of your choice. Just use the formula I gave you. And use the VF (velocity factor) of the coax being used, whether it be rg8x, lmr400, and so on. Or do like said and just use a PL259 to PL259 at the antenna feedpoint. This would be easier as far as parts are concerned. But for a coax jumper using rg8x the coax needs to be 14.82ft for 27.205mhz. Or 177.83". You can order this from most any shop that sells coax and such. And yes, rg8x will work fine like stated. Once you have your antenna tuned with the electrically tuned 1/2 wave coax jumper, and get values of
R=50
X=0
VSWR: as low as possible. But the numbers above should remain the same.
After this is done, you can use whatever length coax you wish from the antenna to the radio and it should not change any of the readings if done correctly.' Like said, there is more than tuning for a low VSWR.
JMHO, but best bet for you it would seem is to use the mfj meter directly at the antenna feedpoint. This will remove any chance of having skewed readings. Again, JMHO. Once you get the meter and start using it, you will understand what we are speaking of when it comes to tuning an antenna with the analyzer correctly. If you do it right, any length coax will work after the antenna has been tuned to the above readings I posted. If you are just concerned with tuning for lowest VSWR, a smile swr meter will work. You want to tune the antenna correctly and get it right, use the analyzer at the feedpoint or get yourself an electrically tuned 1/2 wave coax jumper or one that falls on a 1/2 wave length. Again, JMHO. And again, have fun with the MFJ meter. Once you get used to using it, you'll ask yourself how you managed without one LOL!!
