Todd,?
__Every tuner has a range of impedances it can match (which usually varies by band).? Your 40M dipole will be about 40-70 ohms with minimal reactance ( C or L) at resonance on 40M.? A peak at 20M finds the antenna is a center fed full wave and could approach 2500 ohms, quite a mis-match for 50 ohm coax. You are feeding it with coax that would be about 2 wavelengths long when the velocity factor of the coax is accounted for (VF is the dielectric in the coax slowing the speed of the signal's travel).? !/4 wave of coax after the feedpoint and the extreme high impedance is now just the opposite, very low.? So inside that coax length, at some point, the 'resistance' is about 50 ohms with lots of reactance.
__If you want to stick with the coax, try adding a 10 ft coax jumper in series with the line and test 30M & 20M again.? You may find the ZM2 tuner can now match the complex R +/- J impedance it 'looks' into (or not).??
__All of this gets back to the idea of feeding the antenna with open wire 300-450 ohm twinlead as Larry mentioned.? This has been the time tested way to extend what ever wire you can hang up to cover multiple bands.? I agree with Larry on 80M, you may be able to get a match, but QSO may prove difficult due to losses in the coax and tuner.
? K1TWH? < Tom
