[TenTec] Titan II Mods

[Dr. Gerald N. Johnson, electrical engineer]

There's nothing fundamentally wrong with ceramic capacitors in that
loading circuit, BUT they must be the right capacitors. General purpose
high voltage ceramics are not the right capacitors. NPO or COG
capacitors come the closest to working OK. IN the old days Centralab
type 829 transmitting capacitors are the most appropriate. Likely
purchasing found a better deal on general purpose capacitors and ignored
engineering's demand for temperature stable capacitors. If I were an
engineer at TenTec, I'd be reading the riot act to purchasing (via top
management). Unless, some prior owner changed them improperly.

Using smaller capacitors for 80 meters will reduce the loading range of
the final for mismatched antennas. Otherwise the transmitting mica is
the right component for that location. Circulating current in a KW PA is
significant.

At 29 pf per foot, RG-58 coax makes convenient capacitors unless the
length of cable gets to be more than a fraction (1/10th) of a
wavelength. Then transmission line effects switch in and make the
apparent C more than that computed by 29 pf per foot. That's OK at the
fundamental, but is bad for harmonics because the C is not constant with
frequency and can cause enhanced harmonics.

73, Jerry, K0CQ

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