I too, K1JWJ-- think that your best bet is to go with a base mounted tuner- an auto tuner is good, but even a manual tuner is infinitely preferable to using that toroid transformer arrangement.

.

All that aside, I will throw in a variable that is often overlooked with verticals- the resistive ground losses. You want to get the base of your antenna as high off the ground as practical- and keep the counterpoise up there as well. Ground losses are frequency dependent- the longer the wavelength, the higher the base needs to be. You can loose 3 dbs - half your power- alone to ground losses. That is in addition to the other losses- feedlines, loading coils---- that are working to decrease the radiated signal. The following formula does not address the efficiency of the counterpoise- it can be assumed for a mobile setup it will be 'lousy.' The antenna base height above ground is what important.

.

.

.

Okay, want some math to go along with this? (probably not- but you ignore the physics at your peril...

)

.

.

The following is a Coyote formula for computing the efficiency of an HF mobile mounted 'whip' antenna.

________________________________________

Terms used:

.

.

h = height of the antenna in degrees (ie: a "quarter wave" is 90 deg.)

L = the length of the vertical in feet

E = Antenna Efficiency in %

Rg = Ground loss in Ohms*

Rc = radiation resistance of the loading coil **

Rr = h squared/312

_____________________________________

.

The "Formulas:"

.

.

h = L/984 log (Frequency in Mhz) x 360

.

.

plug this into ---

.

.

E = Rr/(Rr+Rg+Rc(Cos squared x h)

.

.

This will give the relative efficiency, in percentages-- of that vertical, - It will be dependent on frequency, ground losses, and loading circuit losses. (Notice that from the table below, it doesn't take much to raise Rg's Ohmic values- and hence drop the efficiency a lot)

.

.

_____________________________________

.

.

Maybe the math is a bit overwhelming- but anyone with the interest, and taking the time to work out some figures can see why a bumper mounted vertical stinks alongside the same antenna mounted high on the vehicle body. The big thing to take away from this is what that Rg figure does to the E %.

.

Professionally I have used vehicle HF radios for many years- keeping my formula always in mind- Its nothing for one of our units to talk 800 miles daytime on 8 Mhz- 150 Watts SSB into a 6 foot base loaded vertical.

.

.

..........................CF

.

.

___________________________

.

*Rg -- the ground losses, assuming the heigth of the base above ground... you can use 2 Ohms for ~4-5 feet, .... 10 Ohms for ~1-2 feet.... an obvious reason why the base needs to be elevated.

.

.

Rc -- the Ohmic losses of a loading circuit. We'll assume this is a coil with an average Q of 300 Ohms, placed at the base of the vertical.

Rc for various Ham Band frequencies, assuming a whip length reasonable for a mobile station--

4 Mhz -- 6 Ohms

7 Mhz -- 3 Ohms

14 Mhz -- 1.4 Ohms

21 Mhz -- 0.5 Ohms

28 Mhz -- negligible

.

.

.