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Hot Rodz™ Patented Hot Rodz™ consist of:
How to install DX Engineering Hot Rodz™on your Hustler Mobile Resonator.  Important: Note that there are (6) short setscrews and (2) longer setscrews. The longer setscrews are used to hold the hub to the Hustler resonator and the shorter ones are used to secure the stainless rods to the hub.
Tech Notes DX Engineering Hot Rodz™ The DX Engineering Hot Rodz are meant to increase the efficiency and gain of the Hustler Mobile antennas. They can also be used on the Hustler 4, 5 and 6-BTV Series antennas by experienced antenna practitioners; however, the directions contained here are specifically for the Hustler Mobile antennas. The DX Engineering Hot Rodz are an adjustable capacity hat system that will allow the use of a resonator (coil) of smaller inductance (20m coil on 40m, 40m coil on 80m, 80m coil on 160m, etc) which will reduce the amount of RF energy lost through the coil and will result in that saved energy being radiated by the antenna. The reciprocal action will occur in the receiving mode, which will increase received signal strength by a similar amount. Some Basics When an antenna is shortened from it's naturally resonant length at the frequency of interest, the feedpoint becomes capacitive and it becomes necessary to add offsetting inductance in the form of a loading coil. This restores the resonance of the antenna. Unfortunately, the additional inductor also has resistance that adds loss to the antenna. The resistance in the coil eats up your power and you are not going to be as loud as you would be if the coil loss were not present. The more that you shorten the antenna, the larger the coil that you need to use. The larger coil has more resistance and eats up more of the power. Mobile antennas are usually pretty short, require large coils and hence have large losses. This loss resistance is also seen at the feedpoint and is partly responsible for making it easy to match this shortened antenna to the 50-ohm feedline and radio. The impedance seen at the feedpoint is made up of the radiation resistance, coil loss and ground loss. The radiation resistance of a full size vertical antenna is about 35 ohms. As the antenna is shortened the radiation resistance goes down quickly but the other losses are still there or even increase. The table below shows the Real Radiation Resistance of your 6-foot mobile whip.
So, for instance, if you have a 72-inch, 20m-whip antenna and you are measuring an SWR of 1:1 that means that you have a feedpoint impedance of 50-ohms. The true radiation resistance of your antenna is somewhere near 3-ohms. That means that you have a loss in your system of 47-ohms (50-ohms minus 3-ohms) and a radiation efficiency of about 6 percent (3-ohms / 50-ohms). So, if you have a 100-watt transmitter in the car, 94-watts are being used to heat the air and only 6-watts are being used to communicate! The other 94-watts are used up in the loading coil and ground system. If we were able to suddenly remove all the loss from the loading coil that we were using then we would see the base impedance drop by the amount of the loss in the coil. How do we reduce the loss in the Loading Coil? Basically, we try to use the one with least inductance and resistance that we can still get to resonate the antenna. One way to reduce the size of the required coil is to install what is known as a capacity hat. A capacity hat can be thought of as an extension of the Marconi antenna design that adds horizontal elements to the design of an otherwise vertical antenna to add length. If the capacity hat is designed correctly the currents in the horizontal sections of the hat offset one another and preserve the vertical polarization of the wave radiated by the antenna. The DX Engineering Hot Rodz™ are designed to have balanced currents necessary to preserve the vertical nature of the wave. As seen in the table below, the resonant frequencies of mobile antennas using the Hustler MO-2 vertical mast and the indicated resonator can be configured over a wide range by using the DX Engineering Hot Rodz™.  Extended – means that the rods are moved out from the hub as far as possible. Centered – means that the centers of the rods are located at the center of the hub. Choosing The Correct Configuration To obtain the highest efficiency from your antenna, use the smallest resonator possible to attain the desired frequency.
Adjusting Hot Rodz™ To An Exact Frequency Hot Rodz™ can be adjusted for the exact frequency that you need. To lower the frequency of your Hot Rodz™ equipped antenna, do one or more of the following:
To raise the frequency of your Hot Rodz™ equipped antenna, do one or more of the following:
A word about matching. The base impedance of the antenna will drop to about 16-22-ohms when you increase the efficiency of the antenna with the DX Engineering Hot Rodz™. Any matching problems will probably be taken care of by your rig's antenna matcher, however DX Engineering will have an inexpensive matcher available soon. How much did the efficiency increase? Well, if the base impedance was reduced from 50-ohms total to 20-ohms total when the actual radiation resistance of the antenna is really 3 ohms then you will have gone from 6% efficiency to 15% efficiency. This more than doubles the RF power coming out of your antenna. Let's look at an example of the use of the DX Engineering Hot Rodz™. Suppose you want to operate 40 meters. Normally, you would install a 40m coil and 32 inch stinger on the MO-2 which will result in an antenna of about 102 inches in height -- Fifty-Four inches for the MO-2 and 48 inches for the resonator and stinger. This combination will resonate at about 7.16 MHz. Looking at the chart you can see that using DX Engineering Hot Rodz™ you can install a Hustler 20m coil (RM-20) and the 24-inch rods (supplied) and the 12-inch stinger that resonates even lower at 7.1 MHz but which is only 78 inches tall! As a result you will see the base impedance drop to about 20 ohms which indicates that you have dropped about 30 ohms of resistance from your antenna system! This may or may not present a problem for you. I have used the automatic tuner in an FT-900 to match this in my mobile and gotten great signal reports. Safety Tips
Additional Info For The Daring Use 2 sets of Hot Rodz™ and get additional benefits! Install the same as the original setup plus an additional Hot Rodz™ just below it.  Tech Help available at: 330.572.3200 M-F 8:30AM - 4:30PM EST Or dxengineering.com@dxengineering.com |
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