DX Engineering DXE-HR-1P Instruction Manual

Hot Rodz®

Adjustable Capacity Hat

DXE-HR-1P

DXE-HR-1P-INS Revision 1f

Shown installed on an
optional Hustler resonator

© DX Engineering 2019

1200 Southeast Ave, Tallmadge, OH 44278 USA

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Introduction

DXE-HR-1P - Parts List

Quantity

Description

6

6" stainless steel rod

6

12" stainless steel rod

6

24" stainless steel rod

1

Hot Rodz® Hub

1

Allen Wrench

3

8-32 x 1/4" - Long Set Screw (includes one spare)

8

8-32 x 1/8" - Short Set Screw (includes 2 spares)

1

Black Cap, for resonator tip

24

Black Tip Cap, for stainless steel rod

The DX Engineering Hot Rodz® is an adjustable capacity hat system that increases the efficiency
and gain of single-band vertical antennas, such as those from Hustler and Pro Am. Hot Rodz® can
even shorten the height of the antenna by eliminating the need for a whip. Hot Rodz® can also be
used on the Hustler 4, 5 and 6-BTV series antennas by experienced antenna practitioners; however,
the directions in this manual are specifically for mobile antennas.

Part List for the DXE-HR-1P Hot Rodz®

Additional Requirements

You may need the following items that are not included in this package:

SWR Meter. The Configuration guide (Table 2 ) will help you get close to the ideal

antenna size, but a SWR meter is necessary to fine-tune the final assembly.

Antenna Matcher. To match the impedance between your feedline and antenna, use a mobile

matcher such as the DXE-MM-1 Dual Impedance Transformer

Guy Ropes. Depending on the configuration of the Hot Rodz®, your antenna system

may require additional support. SYN-DBR-125-100 1/8 in. Diameter, Dbl­Braid Dacron/Polyester Rope may be used.

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Theory of Operation

Radiation Resistance of

6-Foot Mobile Whips

Frequency

Radiation Resistance

1.8 MHz

0.05 Ω

3.5 MHz

0.17 Ω

5.0 MHz

0.35 Ω

7.0 MHz

0.69 Ω

10 MHz

1.42 Ω

14 MHz

2.77 Ω

18 MHz

4.59 Ω

21 MHz

6.24 Ω

24 MHz

8.15 Ω

28 MHz

11.1 Ω

The radiation resistance increases dramatically as

the frequency increases

When an antenna is shortened from its natural resonant length, the feedpoint becomes capacitive.
To offset the additional capacitance, it is common to add inductance in the form of a loading coil to
restore the resonance. However, the additional inductor increases the resistance, which increases the
loss of the antenna. Hot Rodz solve this problem by using a capacity hat - a series of horizontal rods
that counters the effects of shortened vertical antennas.

A Capacity Hat Increases Antenna Efficiency

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. The currents in Hot Rodz horizontal
elements offset one another and preserve the vertical polarization of the radiated wave.

Table 1 illustrates the real radiation resistance of a 6-foot mobile whip. There is a lot of confusion
about radiation resistance, but one definition is "the resistive component of an antenna feedpoint
impedance caused by radiation from an antenna". Mathematically, radiation resistance is the total
electromotive power divided by the square of the net current causing the radiation. In general, the
greater the radiation resistance, the more efficient the antenna.

Table 1 - Radiation Resistance of 6-Foot Mobile Whips

For instance, a 72-inch, 20 Meter whip antenna with a SWR of 1:1 has a feedpoint impedance of

50 Ω. However, Table 1 shows the true radiation resistance of the antenna is somewhere near 3 Ω,
which means the loss in the system is 47 Ω (50 Ω - 3 Ω) and the radiation efficiency is 6%
(3Ω / 50 Ω). Therefore if an operator uses a 100-watt transmitter in the car, 94 watts are used to heat

the air and only 6 watts remain for communication. The loading coil and ground system generate a
loss of 94 watts; but if we remove the loss from the loading coil, then the base impedance drops by
the amount of the loss in the coil.

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When we add a capacity hat, the inductor (resonator) can be reduced, which lowers the resistance.
As stated above, a reduction in the resonator resistance is reflected in the feedpoint resistance. In
this case, the base impedance of the antenna drops to about 16-22 Ω when you increase the
efficiency of the antenna with Hot Rodz®.

If the base impedance is reduced from 50 Ω to 20 Ω when the antenna's radiation resistance is really
3 Ω, then the loss is reduced from 47 Ω to just 17 Ω and the efficiency improves from 6% to 15%

(3 Ω / 20 Ω). This improved efficiency more than doubles the RF power radiating from your

antenna. Any matching problems at the feedpoint will be handled by your rig's antenna matcher or
with the DX Engineering DXE-MM-1 Dual Impedance Transformer.

Installation and Maintenance

While DX Engineering Hot Rodz® make it easy to modify Hustler mobile resonators and whips, we
suggest you read these instruction carefully before you begin the process.

Safety Considerations

 Hot Rodz® create additional aerodynamic drag. While Hot Rodz® have been made as

aerodynamic as possible, additional guying of your antenna may be necessary.

 Install the plastic caps over the ends of all exposed rod ends. The ends may be sharp and can

cause injury.

 Keep the end of the rods inside the body lines of your vehicle.
 High voltage exists on your antenna and the Hot Rodz®. Transmit only when people are a

safe distance away.

 Be aware that Hot Rodz® makes your antenna diameter larger. Use caution when driving

near pedestrians, and in crowded or confined areas.

Assembling the Antenna

1. Refer to Table 2 to select the resonator and stainless steel rods for the desired frequency.

2. Mount the Hot Rodz® Hub to the Hustler resonator flush with the flat area below the whip

mounting threads as shown in Figure 1.

3. If you are not using the whip, then use the larger plastic cap over the end of the threads.

4. Place the correct number of the smaller caps over one end of the stainless steel rods you have

chosen to use.

5. Insert the stainless steel rods into the hub in the configuration shown in Table 2.

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