W6SDO.COM SAN DIEGO, CALIFORNIA USA
Now that the antennas
for the home shack are
completed and I have
finished up the bicycle
mobile, I have been
able to work on the
installation of a mobile
station into my Sprinter
Camper van. It is now
almost completed and I
like to think of it as my
base station on wheels.
Photo above: This is my Sprinter camper van, before installing the mobile rig.
The Roadtrek SS Agile Sprinter van camper conversion pictured is my daily driver as
well as my “home away from home” whenever I am on the road. This van is used as a
staging platform for bike rides, flying kites and RC model airplanes, trail hiking, walks
along the beach and the occasional picnic. It is also used as the desert and mountain
camper for me and my wife (and our two small dogs) as well as a truck to occasionally
haul lumber home from the local Home Depot. It has most recently become my mobile
ham radio station and the basis for one of my favorite ham radio subjects, antenna
development and experimentation. It has been almost two years since I first started
work on this mobile station. The following is a description of where it stands today and
some of the things that still remain to be done in the future.
Before starting the detailed design, layout and construction of the mobile station, some basic
design guidelines and goals were established for this mobile installation as follows:
1. No “usable” space inside of the camper van should be consumed by the mobile installation
and there should be no negative visual or physical impact on the interior of the van.
2. The installation should be designed for maximum flexibility and adaptability so that future
modifications and improvements can be easily implemented.
3. The radio and antennas must operate with relatively high efficiently on all bands from 440 MHz
to 160 meters.
4. The plan should include several antenna packages that are optimized for mobile operation
on the road, mobile (parked), camping, field-day and emergency style operation.
5. It should be easy and quick to shift between the different operator positions and antenna
configurations during mobile, mobile (parked), camping, field-day or emergency operation
6. High transmitting power (of at least +6db) should be available whenever it is necessary.
7. Long battery life should be available at both low and high power operating levels.
8. The van should be equipped with solar charging capability for the house batteries
9. Internet capacity should be available for navigation, logging, monitoring band conditions,
QRZ, email, entertainment, etc.
10. The mobile installation and operation must not degrade the van’s safety, performance or
usability while driving or when parked.
11. The mobile equipped van should be packed and ready to go on short notice for any
emergence requirement. Contents should include food, clothing, camping equipment, tools,
water, propane, ac and battery power, optional antennas and a fully equipped EMT medical bag.
The basic mobile station components are attached to the side of the kitchen cabinet in the space
between the cabinet and the driver’s seat. At this location, these components do not use any
usable interior space, have virtually no visual impact, get air flow for cooling, and are easily
accessed for adjustment and service. The components that are mounted here include:
1. The ICOM IC-7000 100 watt all-band transceiver.
2. The Ameritron ALS-500M 500 watt solid state linear amplifier.
3. The interface module that buffers between the transceiver and the amplifier.
4. A four position antenna switch to provide an easy way to select any of the antennas associated
with this mobile station including: (a) the rear mounted screwdriver, ( b) optional rooftop vertical
whip, (c) an under wheel mounted or roof-top mounted push-up mast, and (d) various other external
antennas (such as externally supported wire dipoles, etc).
5. An MFJ-907 impedance transformer to help match various antennas to the linear amplifier.
6. Remote sensor for the AMW-35H remote power/SWR display module
7. Band-pass filter (for use whenever one is necessary).
8. Power distribution strip with multiple fused outputs.
9. Numerous ferrite cores installed everywhere.
The driver’s seat operating position includes the IC-7000 remote control module and hand mike
along with an iPad with Wi-Fi and cellular 4G capability mounted on the windshield pillar. This
iPad is the one that I use daily and is installed in the van only when I’m on the road. The iPad
and IC-7000 remote control module are supported using a RAM mounting system which provides
excellent adjustability and stability. Since the remote controller and iPad occupy the space
between outside mirror and the windshield, they do not block the drivers view at any time. A
floor mounted foot switch is on the drivers left side and an earphone headset is hung behind
the driver’s headrest for easy access.
The large 10 inch iPad Retina display screen is bright and easy to read under all lighting
conditions. The iPad is used for TomTom GPS navigation, station logging, hot spot location
and band condition information, QRZ information, Wi-Fi and Cellular internet access, e mail
and a number of additional functions. The iPad is easily removed from it’s holder for answering
emails, watching movies, birding, flower identification, navigation while hiking, etc.
|DRIVER'S SEAT OPERATING CONTROLS
In addition to the basic station installation, a “movable” remote control console has been
designed and fabricated that is connected to the basic station by an 18 foot long plug-in
umbilical cable. This controller can be used to control the station in a wide variety of different
operating situations. For example, the remote control module can be paced onto the van’s
pull-out kitchen table inside the van, which, when combined with the reversed passenger’s
seat, creates a very comfortable operating location in the front area of the van. This remote
control module can also be moved outside of the van onto an outdoor table (under a shady
tree or canopy) for camping, field day, special event or emergency operation.
Unless the counter space is needed for some other purpose, such as cooking, I like to leave
this remote console on the corner of the kitchen counter. This way, it can be quickly and easily
moved to the kitchen pull-out table for use whenever the van is parked. Control is easily and
quickly reassigned to the driver’s seat or to the remote controller location by a simple exchange
of the IC-7000 control head interconnect cable that comes from the IC-7000 remote
This remote control console includes the following:
1. Remote control head for the IC-7000 transceiver.
2. Remote control head for the ALS-500M linear amplifier.
3. Remote read-out module for the AWM-35H power / SWR unit.
4. Screwdriver antenna tuning switch.
5. Clock (12 or 24 hour), temperature and battery voltage metering unit.
6. Video monitor for the IC-7000 display (7 inch LCD)
7. Hand microphone on a clip mount
|REMOVABLE REMOTE CONTROL CONSOLE
|MOBILE ANTENNA SELECTION PROCESS
Before starting to narrow down the antenna types that will be considered as candidates for this
mobile, I gathered as much information as possible from various antenna handbooks, magazine
publications as well as from the internet. In addition I compared all of the 75 meter “shootout”
information that I could locate starting in the late 70s through the present. A simplified summary of
these shootout results is as follows:
1 .High end screwdriver antennas with capacity top hats (mounted in middle of pickup bed) 0db
2. High end screwdriver antennas without capacity hats (mounted in middle of pickup bed) -2db
3. High end screwdriver with 6 foot whips (without capacity hat) mounted on right rear fender .-3db
4. Hustler resonator based antennas (mounted on right rear fender) -6db
5. Hamstick (mounted on right rear fender) -9db
6. Whip mounted on right rear fender using an auto-tuner at the base -12db
There also seems to be at least a 3db variation in each antenna category depending upon the
details of that particular installation. For example, trailer hitch mounted antennas are often less
efficient while the result from a high end screwdriver antenna with a long active radiator section
below the coil and the total length of the coil above the vehicle’s roof line can be very effective.
Also, Hustler based antennas using the heavy duty coil located high above the vehicle’s roofline
can provide a significant improvement in performance. A hamstick or a “short” screwdriver mounted
in the center of vehicle roof can improve the results for these antennas by several db. Finally, the
mounting position that is chosen can cause as much as a 6db variation (maybe much more) in
different directions relationship to the mobile’s heading.
After reviewing the various types of antennas that might be applied to this mobile, two different
pathways to an efficient and flexible mobile antenna system for this installation were given serious
First, if mobile operation is intended to be mainly on the high frequency bands and if band hopping
is to be relatively infrequent, simple ¼ wave whips would be a very efficient, very low cost option.
These antennas can perform very efficiently on the bands from 6 to 17 meters where the tip height
of a bumper mounted ¼ wave whip should not exceed a reasonable tip height of 14.5 feet or so.
Operation on 20 meters would only require a small “resonator” coil to keep the antenna height
sufficiently short for highway cruising. If separate whips are used for each band, this style of
antenna system can provide low SWR, broad bandwidth and maximum efficiency. For the lower
bands, i.e. 40 and 75 meters, a high efficiency Hustler Super or similar “resonator” loading coil and
whip section attached to the top of a 54 inch base section can do a reasonably good job at a very
low cost. A complete set of whip and coil pieces would be very economical and can be purchased
for a couple hundred dollars. All that is required to change bands is to get out of the vehicle and
attach a different antenna element. Frequency agility within the “wider” bands would typically requires
either some manual adjustment of the antenna’s tuning section to achieve resonance, or better yet,
would employ a tuner between the transceiver and the antenna (my preference if I was going to be
using this type of antenna system). The use of a tuner would typically produce an antenna that is a
slightly less efficient compared to a “resonant” antenna and the cost of adding a good high power
tuner to the system can be expected to bring the total cost to near that of a screwdriver style antenna.
Ham Stick types of antennas were not given serious consideration for this mobile station. While they
are very inexpensive, they are very inefficient, particularly when used on the 40 and 80 meter bands
where their performance is reported to be typically 6 db or more below that of a screwdriver antenna.
This is not to say that they are not applicable in cases where they meet all of the expectations for a
particular mobile setup, just not for this one.
The second antenna choice that was seriously considered was a “screwdriver” style antenna, so
called because in earlier days the loading coil was adjusted to resonance using a screwdriver
motor that selected the correct number of coil turns in the antenna tuning coil. The highest practical
efficiency for this type of antenna is usually achieved by the antenna’s designer by positioning the
loading coil as high up the antenna’s length as practical. The coil should also be of a high Q design
featuring a large winding diameter with appropriate turn spacing, should be wound with large gauge
wire and should be free of Q spoiling metal end caps. A mounting location on the vehicle that keeps
the entire length of the coil above the top of the vehicle’s metalwork is also very helpful since a
significant amount of the antenna’s radiation comes from along the length of the coil particularly
when operating on the 40, 80 and 160 meter bands.
After due consideration of these two options, a screwdriver type antenna was selected for this
mobile based partly on the fact that this antenna, with a relatively short 6 foot whip, can be used
on all bands from 10 to 80 meters without going outside the van. In addition, by attaching different
length of “band specific” whip elements to the top of the coil, the antenna can be resonated on the
bands 10, 12, 15, 17 and 20 meter bands without using any of the screwdriver turns (except for
tuning the antenna to the low frequency end of the wider bands). Of course, using these longer
whips may not be practical for use except when the mobile is “parked”.
There are a number of good screwdriver antennas on the market that meet the general criteria
described. However, I have chosen the Scorpion SA-680 antenna that is personally hand crafted by
master machinist Ron Douglass (NI7J). This antenna is expensive but is truly a work-of-art that will
handle full legal limit power levels and can be expected to last forever.
The coil of the SA-680 is 3 inches in diameter, is about 18 inches long and is wound using 10 gauge
copper wire. There is no metal end cap at the top of the coil that would lower the Q of this antenna
coil. An additional, and very important, reason for choosing the Scorpion was that the 30 inch long,
3 inch diameter support structure below the coil is an active radiator rather than just a grounded
support structure. Several credible antenna analyses have indicated that this portion of a screwdriver
antenna, below the coil, can contribute as much as 1 db per foot of length to the far field signal
strength. The end result is that this antenna, with its heavy gauge wire and radiating support
structure, is reported to have as much as a 3 db advantage over many other designs. This is
equivalent to doubling the transmitter’s power - as well as improving the receiving characteristics
by a similar amount. Even if the improvement provided is by some lesser amount, it is still
worthwhile, especially for mobile operation where we need all the help that we can get.
In the end, this screwdriver antenna can provide acceptably efficient all-band coverage which is
controllable from inside the van. By using different whip configurations a screwdriver antenna
can also provide a base for very efficient individualized antennas that are each tailored and
optimized for a specific band.
|SCREWDRIVER ANTENNA INSTALLATION
Originally, I had considered mounting the antenna on the roof of the van at the center of the
vehicle. As everyone agrees, this would be the perfect location for optimum radiation efficiency
and radiation pattern symmetry (around the van). The antenna would have been pivoted from
vertical (when being used) to horizontal (when not being used or when navigating low overhang
stretches of roadway, filling stations, etc) using an electrically or pneumatically operated actuator
mechanism. However, with a rooftop height for the van of around 8 feet, the overall antenna
height including the mounting base, coil and whip would be limited to about 6 feet if an overall
height of 14 to 15 feet of height was not to be exceeded. Several short screwdriver antennas
were identified where the whip length and “spring” combination that would have worked.
Although the efficiency of these compact screwdriver antennas is reported to be in the range
of 3 db or so below that of a full size screwdriver antenna, the prime location could have
compensated for most, if not all, of this deficiency. If I had gone with this mounting location, I
would have chosen one of the short screwdriver antennas that have the sliding contact
mechanism inside of the coil so that the antenna length does not change as the bands are
changed. This would have kept the overall length in the 14 to15 foot height range for all
operating conditions. However, in the end I decided that I would always be worrying about
hitting something that would seriously damage the antenna or some overhead structure.
Therefore, I compromised and went with my second choice which was to mount the antenna at
the rear of the van. Here, the base of the antenna could be mounted fairly high and the antenna
could remain in place while driving. With a 14.5 foot tip height, there would be only minimal
concern about damage to the antenna or surroundings while motoring along the roads and
highways. In order to mount the screwdriver antenna as high as practical at the rear of the van,
so the full length of the coil would be above the top of the van, the base of the screwdriver
antenna is supported 6 feet above the road surface by a five foot long 3 x 3 inch square
aluminum bar that is attached to the rear of the spare tire carrier. This bar easily supports
the 15 pound weight of the antenna plus the associated drag on the antenna at highway
speeds. The resulting tip height when using a 6 foot whip is 14 ¼ feet above the roadway
when the antenna coil is fully retracted and about 14 ½ feet when the antenna is tuned to 20
meters. This height is ok for freeway driving but is a little high for some city streets. A
significant benefit of this location is that the base of the coil is at least 22 inches distance
from the van’s body and that all of the coil’s length is always higher than the top of the van.
Please note that, depending on what I learn on future antenna tests, I may choose to revisit
the center rooftop location for the main antenna at some future date.
Mounting the antenna on the left rear of the van has the advantage that it minimizes collisions
between the antenna and low hanging tree branches and telephone wires that are common
along many city streets. However, this mounting location causes the antenna’s radiator to be
somewhat non-symmetrical as well as causes the system to be susceptible to SWR surges
when a large vehicle passes on the driver’s side. This is only a problem if the SWR goes
above 2:1 which can cause the amplifier to trip off. However, this seldom happens since the
SWR is typically 1.1:1 to 1.5:1 for most bands and, if it is necessary, I can overcome this
situation by pausing transmission while I am being passed by an 18 wheeler.
The overall height of the particular screwdriver antenna that is installed increases by a foot or
so when operating on the 75 meter phone band. If mobile operation on this band becomes a
normal routine, it might be necessary to lower the base height of the antenna by a foot or so at
some later date.
The isolation chokes, for both the coaxial feed line and the motor drive power, are packaged
inside of a 5 x 5 x 5 inch plastic weatherproof box which is mounted immediately at the base
of the antenna. The shunt coil will be located in this box (in the final version) in order to keep it
out of the weather and to keep it from being struck by things that might be flying by. This shunt
coil is required so that the SWR will be sufficiently low level on the 40 and 80 meter bands.
This coil is not needed on the higher bands but does not do any harm. Until a better option is
worked out, this coil must be disconnected when the antenna is used in the 160 meter band
configuration in order to achieve an acceptable SWR. A removable “link” on the exterior of the
box would allow this to be accomplished without too much fuss.
A 25 foot length of RG8x coaxial cable feeds the antenna. This coaxial cable, as well as the
wire that carries power to the antenna’s motor, are shielded from the antenna’s near field
radiation by running these lines inside of a length of ½ inch steel conduit that is attached to the
side of the aluminum support. At the base of the support bar, the leads are further shielded by
routing them inside of the hollow spare tire support tubing until they can exit underneath the
The base of the antenna is connected to the van’s bodywork using a 22 inch long length of 1
inch wide heavy duty tinned copper flat braid (with equivalent conductivity to a 6 gauge copper
wire). Although the ground return strap is a little longer than desirable, this setup tunes to the
10 meter band with the 6 foot long whip that is normally attached. A shorter 3 foot long whip is
used when 6 meter operation is desired. However, unless the sun influence changes for the better,
6 meter operation is not much of an issue. If the 6 meter band does go crazy, I will be
very happy to stop and replace the longer whip with one that is shorter (which I normally carry
in the space under the back seat).
Some mobile antenna websites on the internet have stated that this lead must be a wide solid
copper strap. As a test, I have substituted a 2 inch wide 0.014 inch thick copper strap for the
22 inch long braid that normally connects the base of the antenna to the van’s metalwork. This
substitution results in no noticeable change in the antenna’s resonance point, SWR, power
meter reading or signal strength on received signals. Although, this is contrary to the
information that is published on many of the mobile antenna sites, it is what I have found for
this particular antenna setup.
The antenna ground return connection and pathway are very important in order to achieve
high radiation efficiency and reliably predictable antenna performance. This is where we are
entering a grey area that is subject to endless argument and debate. For example, is the
body metalwork a counterpoise or does it simply represent a capacitance to ground.
Also, what kind of a signal return path does a vehicle body offer, what is the frequency
dependence of these effects and does the orientation of the vehicle body direct or block the
radiated signal, etc,etc, etc? It is obvious from the initial data collected for this van and it’s
screwdriver antenna system that the vehicle’s body acts as something of a director, especially
on the high frequency bands. On the plus side, this phenomenon may produce significant and
real gain on the higher bands the “preferred” direction, acting much like a multi-element beam.
This may be an advantage when operating from a fixed location – as long as the preferred
direction is known. I will have some more thoughts about this topic later, after making a few
more calculations and some additional measurements on this specific antenna system.
|A FEW ADDITIONAL MOBILE OPERATION TOPICS
For best antenna results the coil for a screwdriver antenna (which produces much of the
radiation on the lower bands) should be higher than the top of the vehicle and should be as
far as possible from the metal body components (by at least 24 inches if possible). The
longest whip length should be used that does not exceed a safe maximum height. The
maximum tip height for highway driving is generally considered to be around 14.5 feet.
For city streets, overhead phone lines will often be much lower than this. Lowering the tip
height and adding a good spring at the base of the whip will help here. The height of the tip
of the antenna can be further lowered and the antenna efficiency significantly increased by
attaching a “capacity hat” type of device to the whip at a point that is a few feet above the top
of the coil. A lot of useful information about achieving good mobile antenna efficiency can be
found on numerous mobile antenna web sites
When parked, the “normal” 6 foot long whip that I use is often replaced with a 13 foot long whip
that is attached to the top of the coil. This setup resonates at 20 meters without requiring that
any of the loading coil is engaged thereby maximizing the efficiency on 20 meters and
substantially improved performance on both 40 and 80 meters. This caused the antenna
height to exceed the 14.5 foot maximum height limitation so that the long whip must be
removed and replaced with the shorter whip before hitting the road. I tape a note to the
steering wheel to remind me to do this before driving off. So far that has worked.
Hustler model QD-2 quick whip disconnects are used to facilitate quick and easy whip changes.
This disconnect hardware has been attached to the ends of all whips, extension sections and
“resonators” building block elements that are used to assemble band specific antennas.
A hitch mounted 30 foot push-up mast can also be used when parked. Four antenna
configurations are generally used for this antenna, one for 160 meters, a second for 75
meters and a third for 40 meters. As the fourth configuration, the mast is used to support a
horizontal dipole antenna that can be tuned from 2 to 20 meters using telescoping elements.
Long wire antennas can be attached to the top of the screwdriver coil (or better yet to the tip
of the whip or the push-up mast) when parked at a camp site. The variable coil of the
screwdriver antenna then has the potential to be used to “tune” various wire antennas. This
can be expected to substantially increase the efficiency of this antenna on the lower bands of
40, 60, 80 and 160 meters. However, this typically lowers the resulting antennas feed point
impedance and raises the resulting SWR to high levels that cannot be tuned by the
IC-7000 or the ALS-500M amplifier. This means that either a impedance step-up transformer
or a switchable shunt capacitor must be used or that a tuner must be added to transform the
impedance to an acceptable level. The improvements in radiated efficiency versus complexity
and cost will be evaluated before proceeding. In the meantime, long wire horizontal dipoles
hung from trees or push-up pole(s) will be used to cover the 40 meter through 160 meter bands.
160 meter operation is not considered to be necessary while the mobile is in motion. However,
since I occasionally like to contact a local net on that band when I’m camping in the desert or
mountains, I need a good antenna for that purpose. While there are “factory made” coils
available from several screwdriver manufacturers that can be installed above the regular
screwdriver coil to convert an 80 meter screwdriver antenna into a 160 meter vertical antenna,
they are relatively expensive. Therefore, I designed my own 160 meter antenna setup by
adding a 54 inch Hustler base extension (which I had on hand) to the top of the Scorpion coil,
then added an 80 meter Hustler Super resonator (which I also had on hand) along with a six
foot whip and DX Engineering capacity hat above that. This combinations performs very well
and has an SWR of just under 2:1 wherever it is tuned within the 160 meter band (by adjusting
the turns on the screwdriver’s coil). A 2:1 impedance transformer could be used to lower the
SWR if desired.
There is always a question about what the isometric radiation pattern looks like for a mobile
antenna installation that is not symmetrical. The radiation pattern for this screwdriver antenna,
when attached to the back left hand corner of my van, has been measured on three bands, 12
meters, 40 meters and 75 meters. These data were collected using two different methods with
very similar results. The first set of data was collected by monitoring the signal arriving from my
home station which was at a distance of 10 miles from the test site. The signal strength was
monitored using the mobile’s 7 inch monitor as the s-meter display. The mobile was located in
the middle of a very large flat parking lot and the signal strength was collected each 45 degrees
while the van and it’s antenna was rotated about a fixed spot on the parking lot. Several laps of
data were recorded on each band and the signal strength measured. The data collected varied
less than +/- 1 db for each data pass, and was averaged to get the final result.
A second set of data was collected using an Elecraft XG3 RF signal source. The output power
from the signal source was set at one milliwatt and the unit’s antenna was held vertically at the
top of a 20 foot fiberglass pole. The signal source was placed at a distance of 500 feet from the
mobile’s location across the length of a large flat and unobstructed parking lot. The results
collected by this second method matched the initial data run by 2 db or less.
In addition, the relative antenna gain for different antenna whip lengths (on 75 meters) was
measured. Signal strength measurements were made for a 6 foot whip (which is the one that
is normally attached to the screwdriver antenna and was used to collect the polar radiation
pattern described previously), for an 8.5 foot whip, for a 13.5 foot whip and for the 13.5 foot
whip with a DX Engineering Hot Rodz Model DXE-HR-1P capacity hat (with six 24 inch radials
placed at 54 inches above the top of the coil). Compared with the results when using the 6 foot
whip, the signal improvement was 1.5 db for the 8.5 foot whip, almost 3 db for the 13.5 foot
whip and about 5 db for the 13.5 foot whip when the capacity hat was added. These
measurements were made with the rear of the van pointed toward the signal source and
polar plots were not collected at this time. This last whip arrangement is the one that is most
often used when camping and produces a little extra punch when operating on 75 meter AM.
When combined with the amplifier, this produces a solid 2 S-units of improve over the
barefoot IC-7000 using it’s normal whip.
For camping, field day and special event operation, a 30 foot tall self- supporting fiberglass
push-up antenna is supported from an aluminum plate that is captured under the van’s front tire.
This mast is most often topped with a half wave dipole on one of the bands from 6 to 20 meters
(17 meters is my favorite). Although the direction is easily change using an Armstrong rotor,
the position at our San Diego location is usually set at about 45 degrees. If desired, the mast
can also be configured as a vertical (using the van body as the “return” connection) or as the
support for various types of wire antennas (such as inverted Vs, dipoles, etc). This mast
can be easily installed and raised by one person in 15 minutes or less.
A supplemental grounding scheme might be of benefit, particularly on the low frequency bands.
If you believe that this is true, you can attach some radials to the vehicle body or run some
radials directly to the screws at the base of the screwdriver antenna which have been provided
for that purpose. You might also drive some stakes into the ground and connect them to the
vehicle’s body – however you might want to calculate the soil’s skin depth and evaluate the
resistivity of the soil over which you are parked before you do this.
|PERFORMANCE WHEN OPERATING ON BATTERY POWER
The house battery consists of two parallel connected Trojan T 105 batteries that provide a total
capacity of 185 to 225 amp-hours (depending on the peak current being drawn). In addition a
third battery (type 27F) can be added in parallel with the house batteries on a temporary basis.
This third battery adds an addition 95 amp-hours of storage capacity for a total of about 300
amp-hours for the battery system. For best battery life these batteries are usually not discharged
below 50% of their fully charged capacity for an available useable capacity of at least 150 amp-
hours. In an emergency, the battery reserve of 150 amp-hours can also be used. However, it
is more likely that the van's on board generator would be used to supply the additional power.
The steady state drain for the mobile system including the IC-7000, control, monitoring
components and amplifier is only about two amps which would provide a stand by time or at
least 75 hours. When operating at 400 watts output, for an advantage of 6 db over the IC-7000
alone, the peak current drawn from the batteries during sideband phone transmission is about
70 amps. For normal voice waveforms, and when taking into account the spacing between
words, etc, the average current is reduced to an average of closer to 30 amps. Considering a
50% talk time duty for a normal QSO this would result in an average QSO current requirement
of around 15 amps. If the house batteries are not to be discharged below about 50%, this will
allow operation, using the amplifier at 400 watts peak output, for around 10 hours. Fact is, that
when the typical listening time between QSOs is factored in, the effective time is even greater.
If that is not enough operating time, the current drain for the entire station at an output of 85
watts, when using the IC-7000 alone at normal QSO duty cycle, would be at least 30 hours
based on the same battery capacity.
Note that the output is not a full 100 watts for the IC-7000 because the IC-7000 output is limited
to this lower figure of about 85 watts when it is operating from a no load battery voltage of 12.5
volts. Full 100 watt output would require that either the engine’s alternator or the house ac
generator is operated (which would then maintain the house battery voltage at around 13.5
volts). Also, the amplifier will produce up to 500 watts when the alternator or generator is
running. Both of these output power increases are hardly noticeable in the grand scheme of
|VHF/UHF DUAL BAND MOBILE TRANSCEIVER
Although the mobile’s ICOM IC-7000 main transceiver covers both the 144 MHz and 440 MHz
bands, I decided that I would like to be able to monitor and communicate on both of these two
bands while simultaneously operating on the HF bands. Therefore, a Kenwood TM-V71A was
added to the mix. This rig can provide both simplex and repeater operation on one or both
bands at the same time as well as monitors any two frequencies at once. The Kenwood’s
controller has been remotely mounted on the van’s dash using a RAM ball mount with a short
6 inch extension. This mount positions this controller within easy reach of the driver and allows
a fully adjustable height and viewing angle.
The main transceiver box is mounted out of the way under the driver’s seat. The controller
interconnecting cable dressed out of sight under the van’s carpet and inside of the center
console for a wire free look. Snap on ferrite cores have been placed on the mike cable, on the
controller cable (at both ends of this interconnecting cable) and on the dc power supply input
leads. This was done to insure that the HF transmitter will not interfere with the VHF/UHF rig.
The microphone is attached to the side of the seat base and is within easy reach of the driver.
It is positioned next to the rocker switch (that is used to tune the HF screwdriver antenna from
the driver’s location).
The antenna is a Comet SBB1NMO dual band “rubber ducky” mounted on the roof of the van.
This 16 inch long antenna is rated at 60 watts and has a claimed gain of 1.5 dBi on 144 MHz
and 2.15 dBi on 440 MHz. The antenna’s interconnecting coaxial cable has been dressed
inside of the van’s head liner for a clean wire free look.
This setup has been found to be very easy to program using the factory KRS-V71-USB
software and USB cable. The rig is very easy to use, has been reliable and provides
|THE MOBILE FEATURES THAT I LIKE THE BEST
Some of the features that I like the most about this mobile station are:
1. I can escape the S9+ noise level at my home QTH that occurs in the early evening when
people arrive home from work and start to turn on their flat screen TVs and LED lighting. There
are many locations nearby that typically have only an S2 level for the man-made noise.
2. I can park at the top of a hill, even in town, which increases my antenna height by as much
as 400 feet above the surrounding landscape. As a bonus, some of these locations even have
a sharp drop off in the direction of interest.
3. I can choose the different types of the ground plane material beneath the van. Sometime I
park on the beach at an island in the middle of the San Diego Mission Bay with damp sand
under the van. I am not sure that I believe in this one yet, but I am convinced that it doesn’t hurt
4. I can take this mobile anywhere with confidence that it is adaptable to any operating situation.
5. I can run this mobile at high power for a full day of QSO’s without using all of the power in the
6. This mobile provides me with a great test bed for trying out numerous types of antennas for
both mobile and fixed operation.
In the end, I believe that I now have a mobile station that is almost as
good as my home station whether I am operating mobile or set up at a
remote location. It is extremely versatile and a lot of fun to operate. I am
looking forward to operating mobile for many years to come.
FINALLY, THIS MOBILE IS STILL
A WORK IN PROGRESS AND
PROBABLY ALWAYS WILL BE!!!
Please come back and visit again.