DX Engineering DXE-HR-2P Instruction Manual

Hot Rodz®

Adjustable Capacity Hat

for Screwdriver Antennas

DXE-HR-2P

DXE-HR-2P-INS Revision 1f

Shown installed on an
optional screwdriver antenna

© DX Engineering 2019

1200 Southeast Ave. - Tallmadge, OH 44278 USA

Phone: [phone] ∙ Tech Support and International: [phone]

Fax: [phone] ∙ E-mail: [e-mail]

Introduction

DXE-HR-2P - Parts List

Quantity

Description

1

Stainless Steel Mast, 22" with 3/8-24 threads on both ends

1

3/8-24 Trim Nut (installed on bottom of the 22" Mast)

1

3/8-24 Hex Nut (installed on top of the 22" Mast)

6

6" rods

6

12" rods

6

24" rods

1

Hot Rodz® Hub with internal threads

1

Allen Wrench

8

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

1

3/8-24 x 1/2" long Stainless Steel Hex Bolt

1

Rubber Washer

24

Black Tip Caps, for rods

The DX Engineering Hot Rodz® is an adjustable capacity hat system that increases the
efficiency and gain of screwdriver antennas. Hot Rodz® achieves this, in part by enabling the
use of a smaller coil, so that RF energy typically lost trough a larger coil is transferred to the
antenna for a more powerful signal. W reciprocal action occurs in the receiving mode so that
the received signal increases by a similar amount.

Part List for the DXE-HR-2P Hot Rodz®

Additional Requirements

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

SWR Meter: The Frequency Selection guide 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, Dbl-Braid
Dacron/Polyester Rope may be used.

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Theory of Operation

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 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 related wave.

Antenna Length and Performance

The more the antenna is shortened, the larger the coil necessary to compensate. However, the larger coil
increases the resistance and consumes more power, resulting in greater loss. The loss resistance is also seen
at the feedpoint and is partly responsible for making it easy to match this shortened antenna. to the 50 Ω
feedline and radio. The base impedance will drop to about 16-22 Ω after the Hot Rodz® system is added.

We suggest using a mobile matcher, such as the DXE-MM-1 - Dual Impedance Transformer, to ensure your
system operates at optimum efficiency.

The impedance at the feedpoint consists of the radiation resistance, coil loss and ground loss, with the

radiation resistance of a full size vertical antenna equal to about 35 Ω. As the antenna is shortened, the

radiation resistance decreases, but the other losses remain or even increase. To reduce the loss in a loading
coil, we try to use one with the least inductance and resistance that still resonates the antenna.

Greater Efficiency at Half the Size

If the base impedance is reduced from 50 Ω total to 20 Ω total when the actual radiation resistance of the
antenna is 3 Ω, then you will have more than doubled the RF power coming out of your antenna by raising

its efficiency from 6% to 15%.

Half the Length on the 10-80 meter Bands

The Tarheel model 200A screwdriver antenna uses a 6-foot whip for the 10-80 meter bands (3.1 - 28.5
MHz). When combined with a Hot Rodz® system with three 12-inch rods, a 22-inch mast and a safety
spring, the total of the antenna is 6-feet 11-inches, less than half the size of the standard 12-foot Tarheel. This
makes an enormous difference in how often you have to get out of your vehicle to shorten the antenna.

The screwdriver antenna covers large potions of the HF spectrum with just three 24-inch rods, but antenna
efficiency increases with a greater number of rods. Using more (or longer) rods is like extending the whip on
a conventional antenna. The reason is that Tarheel and other screwdriver antennas are examples of the art of
engineering for the mobile environment. Due to design considerations for screwdrivers, the Q (a measure of
efficiency) of the coil is low - approximately 75-100 - and the smaller the coil, the better.

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Hot Rodz® enable operators to use a smaller coil for any given frequency, which increases the radiated
power and the feedpoint impedance. These increases result in stronger signals for transmitting and receiving.

Installation and Maintenance

While DX Engineering Hot Rodz® make it easy to modify screwdriver
antennas, 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. If you are not using a whip, place the rubber washer on the 1/2" long hex head bolt, and screw

this into the top of the hub.

2. Mount the hub on the mast and tighten the locking nut.

3. Insert the stainless steel rods into the hub and tighten in place using the short set screws and the

supplied Allen wrench.

4. Place the small black caps on the ends of the rods.

5. Install the mast and the Hot Rodz® assembly to the antenna or to

the optional resonator spring, and then tighten the locking nut.

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Selecting the Frequency

The rods can be adjusted to nearly any frequency with a few simple adjustments. Follow the
directions below to fine-tune your system to the desired frequency.

Lowering the Frequency

To lower the frequency of a Hot Rodz® equipped antenna, do the following until you achieve the
desired results:

1. Move the rods out from the center to form a larger capacity hat.

2. Add more stainless steel rods (6 maximum).

3. Use longer rods.

4. Add a whip.

5. Extend an existing whip further in length.

Increasing the Frequency

To raise the frequency of a Hot Rodz® equipped antenna, do the following until you achieve the
desired results:

1. Move the rods in toward the center to form a smaller capacity hat.

2. Add fewer stainless steel rods.

3. Use shorter rods.

4. Remove an existing whip.

5. Retract an existing whip (less length).

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Matching the Modified Antenna

The base impedance of the antenna drops to about 16-22 Ω when you
increase the efficiency of the antenna with the
DX Engineering Hot Rodz®. In most cases,
matching problems are solved wit the use of an
antenna matcher such as the DXE-MM-1 ­Dual Impedance Transformer.

Using the Modified Screwdriver Antenna as a Base Antenna

Hot Rodz® works for base systems as well as for mobile antennas, enabling you to operate at lower
frequency bands than you might be otherwise able to do. Hot Rodz® also creates a lower profile
antenna with increased efficiency so more of your RF power is transferred to the signal. A smaller
antenna also improves aesthetics - replacing a 6-foot whip with a 24-inch capacity hat makes your
system considerably less obtrusive.

Modifying the Screwdriver Antenna

Most screwdriver antennas are sold with a mounting bracket that can be attached between the main
unit and a mounting tube of any outside diameter up to about 1.25-inch. To convert a screwdriver
mobile antenna for base operations, do the following:

1. Drive a 1.25-inch OD pipe about 4 feet into the

ground. Leave about 2-feet of pipe out of the ground.

Note: The 1.25-inch OD is approximately the size of
a 1-inch water pipe. Place a cap on the pipe to keep
it from deforming while you hammer it into the
ground.

2. Slip an optional DXE-RADP-3 Stainless Steel

Radial Plate over the pipe and attach the radial plate
to the pipe using a DXE-SSVC-2P Stainless Steel V­Clamp. Position the radial plate approximately 1­inch above the ground level to allow access to the
radial wire hardware. When installing stainless steel
hardware, it is suggested that JTL-12555 Jet Lube
Anti-Seize be used to prevent thread galling.

3. Attach the radial wires to the radial plate. The radial

plate comes with 20 sets of hardware, although
additional hardware can be purchased to attach up to
60 radials. Visit the DX Engineering website for tips
on how to hide radial wires without digging.

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4. Use the mounting bracket from the screwdriver

manufacturer to attach the antenna to the pipe.

5. Attach the coax to the radial plate by using the optional

DXE-363-SST Bulkhead Fitting. Run a short section of
coaxial cable to the bottom of the antenna feedpoint
from the Radial Plate. Additional size rods are available,
including 48-inch and 72-inch long rods for use on the
160 meter band.

Tarheel Screwdriver Antennas
with DX Engineering Hot Rodz®

Optional Items

DXE-MM-1 - Transformer Dual Impedance

The MM-1 is a dual ratio UN-UN (unbalanced to unbalanced transformer). Great for coupling your
50Ω coax to an antenna with a feed point impedance of either 25 or 12.5Ω, typically found in a mobile
environment. Ideal for antennas that have been enhanced with a Hot Rodz® Capacity Hat. Unit is
housed in an aluminum enclosure and uses PTFE SO-239 connectors.
MM-1 Power handling capability depends on the match:

Using the 25Ω to 50Ω port, with SWR below 2:1 on the 50Ω side, 750 watts PEP
Using the 12.5Ω to 50Ω port, with SWR below 2:1 on the 50Ω side, 500 watts PEP

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SYN-DBR-125-100 - 1/8 in. Diameter, Dbl-Braid Dacron/Polyester Rope, 100 ft. Roll

Synthetic Textile Industries Double-braided Dacron/Polyester ropes are not weakened by decay or
mildew and provide excellent resistance to abrasion. The color sealed black polyester yarn used in the
braided jacket also protects the cord from damage due to ultra-violet light.

 100' spool - 1/8'' diameter rope - Double-braided Dacron/Polyester rope - Excellent resistance to

abrasion - NOT weakened by decay or mildew - UV-Resistant - Rated for a load of 420 lbs

JTL-12555 - Jet Lube SS-30 Anti-Seize, .25 lb plastic jar

Jet-Lube SS-30 Pure Copper Anti-Seize is designed for use on taps, lugs, wiping contacts, drum switches,
slip rings, and more. An environmentally preferred thread lubricant and conductive termination compound,
Jet-Lube SS-30 helps keep your equipment in serviceable condition. It contains a high concentration of
copper flakes, a requirement for heavy loads or compression; controlled frictional characteristics allow the
surfaces of nuts and bolts to be tightened to their design torque specifications. This anti-seize product
assures full hydraulic efficiency by allowing the metal surfaces to slide over each other without damaging
metal-to-metal contact.

This part is classified hazardous and is limited to domestic UPS Ground shipping only

Technical Support

If you have questions about this product, or if you experience difficulties during the installation, contact DX Engineering at (330)
572-3200. You can also e-mail us at:

[e-mail]

For best service, please take a few minutes to review this manual before you call.

Warranty

All products manufactured by DX Engineering are warranted to be free from defects in material and workmanship for a period of one (1) year from
date of shipment. DX Engineering’s sole obligation under these warranties shall be to issue credit, repair or replace any item or part thereof which is
proved to be other than as warranted; no allowance shall be made for any labor charges of Buyer for replacement of parts, adjustment or repairs, or
any other work, unless such charges are authorized in advance by DX Engineering. If DX Engineering’s products are claimed to be defective in
material or workmanship, DX Engineering shall, upon prompt notice thereof, issue shipping instructions for return to DX Engineering (transportation­charges prepaid by Buyer). Every such claim for breach of these warranties shall be deemed to be waived by Buyer unless made in writing. The above
warranties shall not extend to any products or parts thereof which have been subjected to any misuse or neglect, damaged by accident, rendered
defective by reason of improper installation, damaged from severe weather including floods, or abnormal environmental conditions such as prolonged
exposure to corrosives or power surges, or by the performance of repairs or alterations outside of our plant, and shall not apply to any goods or parts

thereof furnished by Buyer or acquired from others at Buyer’s specifications. In addition, DX Engineering’s warranties do not extend to other
equipment and parts manufactured by others except to the extent of the original manufacturer’s warranty to DX Engineering. The obligations under

the foregoing warranties are limited to the precise terms thereof. These warranties provide exclusive remedies, expressly in lieu of all other remedies
including claims for special or consequential damages. SELLER NEITHER MAKES NOR ASSUMES ANY OTHER WARRANTY
WHATSOEVER, WHETHER EXPRESS, STATUTORY, OR IMPLIED, INCLUDING WARRANTIES OF MERCHANTABILITY AND
FITNESS, AND NO PERSON IS AUTHORIZED TO ASSUME FOR DX ENGINEERING ANY OBLIGATION OR LIABILITY NOT STRICTLY
IN ACCORDANCE WITH THE FOREGOING.

©DX Engineering 2019

DX Engineering®, DXE®, DX Engineering, Inc.®, Hot Rodz®, Maxi-Core®, DX Engineering THUNDERBOLT®, DX Engineering Yagi Mechanical®,
EZ-BUILD®, TELREX®, Gorilla Grip® Stainless Steel Boom Clamps, Butternut®, SkyHawk™, SkyLark™, SecureMount™, OMNI-TILT™, RF­PRO-1B®, AFHD-4® are trademarks of PDS Electronics, Inc. No license to use or reproduce any of these trademarks or other trademarks is given or
implied. All other brands and product names are the trademarks of their respective owners.

Specifications subject to change without notice.

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