Since you want to roll your own, here are the coil specs from Texas Bug Catcher site. The #640 sounds like what you want - Minimum 72" whip with no cap hat. This should work with your 102" whip.
# 680 COIL
The #680 HQ Coil is 6-3/8 inches in diameter and 7 inches long. It is wound with 12 Ga. wire at 4 turns per inch. Because of its larger diameter, shorter length and wider turn spacing the Q of the coil is higher than the #480 which improves the radiation efficiency. The #680 HQ has a total inductance of approximately 85 microhenrys which will allow 75 meter operation with a whip length of 72 inches without the use of a capacity hat. Adding a capacity hat will allow whip lengths as follows:
20 Inch Hat----- 36 Inch Whip
16 Inch Hat ----- 48 Inch Whip
12 Inch Hat ----- 60 Inch Whip
These whip lengths are intended as a reference only. The length of the whip should be kept as long as practical. The “Higher Q” makes this coil the best choice for 40 and 75 meter operation.
# 640 COIL
The #640 HQ coil has the same mechanical construction as the #680 but is only 4 inches long . This coil is best suited for 10 through 40 meter operation. The # 640 will require a whip at least 72 inches long for 40 meter operation. As with all coils the whip may be shortened by adding a capacity hat.
HD80 MATCHING COIL
As with all high “Q” mobile antennas (especially on 40, 75 & 160 meters) the feedpoint impedance is quite low. This necessitates some method of feedpoint impedance matching. This matching can be done several ways. An inductor, capacitor, toroidal transformer or other method can be used. Because of the ease of use we recommend the shunt inductor. The GLA Systems Heavy Duty Matching Coil is easy to tune and will match our antennas in all cases. It can also be used to match other types of HF antennas with great success.
The HD-80 matching coil is 2 inches in diameter and 2.5 inches long. The base of the coil is a solid piece of copper that is the full diameter of the coil. This copper plate has a 3/8” hole in the center that allows the stud of the mast to secure the coil to the mount. The coil wire is wound on a solid CPVC form. The coil form has a 1 inch hole in the center to allow the mast to pass through and secure the coil to the mount. This greatly increases the strength of the coil and also reduces coil vibration.
The coil is shorted to ground with a jumper and coil clips that are provided with the HD-80.
[URL unfurl="true"]https://www.mtcradio.com/texas-bugcatcher-hf-mobile-antenna-info/[/URL]
