PA3DUV Mobile HF Station

Mobile amateur radio is FUN. It turns your wasted time behind the wheel into an exiting activity. The traffic jam just means another nice QSO. Spending an annual 70 000 km on the road it sure has revived the amateur radio hobby for me. Consequently, I spend less time in the shack. To put out a competitive mobile HF signal think big! Of course the antenna is the MOST important part of the system.

The Antenna

My checklist for the antenna:

    Multiband capability 80 - 10 meter band
    Highest efficiency possible (why wasting your precious HF power to heat up that loading coil?)
    Remote tunable, tuning while rolling
    Capable of coping with the harsh environment on the European roads
    Proven performance
    Sleek design, good looking
    Able to handle 1 kW PEP effortless
    Quick release systems for the antenna system

Long research and a lot of reading made me decide to purchase the HiQ 4-80 motorized vertical from HiQ Antennas, Wildomar, California.  There is a distinct feature of this antenna which sets it apart from all other so called screwdriver antenna's: The Non Moving Coil Design! This gives the antenna unique features and allows the designer to optimize coil specifications resulting in a superior working grade of this multiband mobile vertical antenna. After one year of very succesfull operation with the HiQ 4-80 I decided to upgrade to the HiQ 5-80. The 5 inch loading coil gives my mobile signal an edge on the low bands. The 1100 watt signal on 80 is now comparable with a 100 watt flat top antenna station. The HiQ 5-80 really rocks the low bands with a solid signal, to my knowledge it is the only remote tunable HF mobile vertical with a 5" loading coil.  Check out the HiQ Antennas Web Site
The HiQ 5-80 is mounted on a stainless steel mount, without any additional guying or undermast support. A recent business trip into Germany proved that the HiQ 5-80 is a highway star, the antenna easily deals with speeds up to 200 km/h on the German Autobahn, using the Giant Quick Disconnect to fix the antenna to the mount. See picture.

The Amplifier

The physical restrictions in a mobile set up allow for an antenna length of 3.5 meter. If you cannot accommodate capacative loading, the only way to improve your signal is an amplifier. Lucklily I could get my hands on the last Henry SS750 solid state HF amplifier. With 30 watts of drive and the actual board voltage this amp loafs at 500 watts all day long, 100 watt drive gives a stiff 1100 watt out on 160, 80- and 40 meters, reducing to 550 watt on 20 and up. The Henry SS750 is well engineered, beautifully build  and a real powerhouse. Two big fans channel air through the heatsink fins, providing adequate cooling. The amp is equipped with a temperature shutoff protection and a rather fast acting 100 amp breaker.
The safety devices in the Henry SS750 are adequate but a bit primitive. There is no high SWR trip circuit which I feel is a real omission. However, high SWR results in a high collector current which will result in a breaker trip. This will be a point of future modification. I will build a SWR trip circuit around the Palstar WM150 remote directional coupler in order to get a more civilized way of protecting the amp against transmitting into a bad load. My previous amp, a SG-500 is more sophisticated when is comes to the protection circuitry. Soon I will try to use two of these SG-500 amps together, feeding a 2 kilowatt combiner. Reports on that project will follow later.

An important consideration when running an amplifier in a car is wether to monitor the output power and VSWR or not.  I choose to use a Palstar WM150M mobile peak power/VSWR meter with a remote directional coupler. The control head sits in the front. VSWR and output power are shown on the cross needle meter.


The power supply

To operate an amplifier this size the power supply is of eminent importance.
Rule 1: put one ore even better two batteries close to the amp.
Rule 2: use heavy high quality wire and hardware for the power supply connections.

Powering a kilowatt amp in a motorcar means: mo' is betta! Don't save on DC cables, use adequate size (read: "massive") cable lugs and breakers. The Powerwerx high power DC connectors, cabling and circuit breakers were used to connect the transceiver and amplifier to the DC source.

Don't save money on low quality fuse holders and hardware. I did and the voltage drop was huge, approx. 1.8 volt. That made me change my mind and I changed all the power cabling from the remote batteries to the amp for 25 mm² copper wire.  Powerwerx is a good source for high current fuse holders, switches, connectors and cable.  The cabling  from the alternator to the remote batteries is 70 mm² neoprene insulated welding cable. Under test conditions, transmitting a one minute long 1100 watt carrier into the Palstar DL5K dummy load the voltage dropped from 13.4 to 12.5 Volt, measured on the amplifier terminals

Since I use the 2  batteries inside my car the use of a gell cell battery is obligatory. No gassing and the resulting premature destruction of the car and its passengers.

The Rig

I did not choose a rig specially for mobile ham radio. I had a IC 706MKIIG collecting dust as a back up rig and decided to give that nice little rig a job to do. An important consideration when choosing a mobile rig is the ergonomically design. All small mobile rigs today have these multi functional menu buttons. This makes is difficult to operate the rig. So far the 706MKIIG has filled my bill since the primary functions: tuning, band, IF shift and LF controls are easy accessible AND it has a detachable front.
I am not impressed by the AF DSP unit from ICOM, that gap was filled with the ClearSpeech DSP speaker, now available from Bob Heil. This is a remarkable product and very useful in a mobile enviroment!

Rig: IC 706MKIIG
Amplifier: Henry SS 750, 1100 w@3600 kHz
Antenna: HiQ 5-80  from HiQ Antennas
Power supply: Exide Gell Cell Battery
Headset: Heil HS 706
DSP Speaker: Heil ClearSpeech Speaker
Pactor Controller: SCS PTCII Pro
Computer: HP NC 4010 running Windows XP-pro + Airmail for Pactor II

Operating position                The Trunk                  The Antenna