QRP in the Front, Barefoot+ in the Back

K0BAK’s vehicle portable station with IC-705 radio plus amplifier

Radio Upgrade

My first 100w radio bought as a baby ham in 2014, the Icom IC-7100 (HF/VHF/UHF, all modes, remote head) has served me wonderfully in countless contests as a winning mobile in state QSO parties, roving in VHF contests, and hundreds of park activations in POTA and predecessor programs. Time moves on though, and its technology has been left behind by self-contained software-defined radios (SDRs) having eye-popping performance compared to inexpensive analog radios of just a few years ago.

I’m also spoiled by the graphical signal display I have at my home station, so I wished I could have that display in a small radio in my vehicle-portable operations. (I had a high-performance SDR in my now-sold TV van station, but the Flex 6500 is too unwieldy for my small SUV and not self-contained.)

IC-705

The Icom IC-705 caught my eye due to its small size, graphical signal display, and direct conversion SDR technology (below 25MHz). I was also used to the general menu topology and touch-screen interface similar to the IC-7100’s. As with the 7100, the 705 covers HF/VHF/UHF on all modes. While I was intending to use the 705 mostly for HF vehicle portable operations, the inclusion of 2m and 70cm SSB/CW would also allow me to use it directly in VHF contests and as the IF driver radio for microwave transverters on the 33cm to 3cm bands.

The only big downside? The IC-705 is only 10w max RF out. But we could “fix” that …

Mobile Amplification

My very first mobile contest was the 2014 PA QSO Party. I was absolutely hooked on contesting as a mobile/rover/portable from that first experience (winning the first time helped too). But I noticed pretty quickly during that contest that quite a few stations I could hear clearly could not hear me. The easy but expensive solution was to boost my TX power, and by the following year I operated contests with a 12vdc “500 watt” amplifier, the Ameritron 500M that I typically ran at 350-400w out.

While the 500M probably enabled thousands of contacts I wouldn’t have gotten without it, its reliability is less than I would have wanted with a couple hard failures, sticky RX/TX relays I had to replace, and random soft hiccups. It was also an old design even when I bought it new, and its power transistors became unobtanium for a while.

I decided to upgrade to a modern though lower-powered amplifier, the RM Italy model HLA 305. Built to be driven by QRP radios, it’s rated at 250w out though I operate it with 5-8w in and 200w out. While the RF output power is about 3db less than the 500M, it actually performs more amplification due to lower input power. One big advantage of the HLA 305 is automatic band switching, avoiding error-prone manual band switching under contest conditions or the complication of extra components for automatic switching driven by radio band information.

I also like that the entire case is a heat sink and has two large external fans: Based on my experience with similar heat management in my VHF+ amplifiers, I suspect I will be able to run 100w out on FT8 with no overheating. On my first try at 100w FT8 for about an hour, the amplifier only gained a few degrees C, though operating it in a longer session in the summer will be the real test.

Initial Breakage Disappointment

One of the best features of my old IC-7100 is the wired remote head, making it easy to place the small remote head in the front of the car, with the guts of the radio in the back with all the other heavy components like the amplifier and high current distribution components. Like most radios, the IC-705 is self-contained (though it can be operated remotely via a network connection). I ran an LMR-240 coax from the 705 in the front to the amplifier in the back, along with the radio’s PTT signal (the “send” signal in Icom parlance).

In the 2022 PA QSO Party, the arrangement worked well and I was thrilled to be able to see signals displayed to let me quickly find an opening in the band to call CQ. However, at one of my final stops, the fragile 2.5mm(!) TRRS connector for the microphone + transmit button broke off inside the radio when I was trying to change another connection. At home, I started disassembling the radio to get to the socket, but after a couple of layers I lost confidence because of the not-surprisingly intricate construction. I had to send the unit to Icom for repair. I scrambled like crazy to get my old station components installed for the next week’s NY QSO Party.

With the following year dominated by work on my “TV van” large VHF rover vehicle, I continued to use the old station in my Subaru Forester for HF. In April 2024, partial recovery from a six-month health issue and a PAARC-sponsored POTA event coincided to motivate me to go back to the IC-705 + HLA 305 system.

Front Operating Position

In the front passenger seat is a plastic and wooden “desk” that takes up the entire seat and is built to be secured with the passenger seat belt. There is one large and three small vertical holes next to the wooden desktop; I use the larger hole to hold my laptop case / steering wheel holder. That the desktop is wood allowed me to add my own bolted-down wood top, with the idea that I could make attachments for equipment in different scenarios without permanently ruining the native wooden desktop.

Facing the desk from the driver’s seat from where I operate, there is a large cubby hole available which I use to carry accessories for special purposes. Someday I want to install a mini-PC and related equipment in the cubby hole for a dedicated better-integrated station computer that doesn’t require a separate laptop.

While operating, my laptop case doubles as a mini desk that hangs on the steering wheel. After the laptop case is placed on the steering wheel using a “pocket” in the back of the case, I open the case where the laptop sits horizontally and I can open the laptop to use it’s keyboard and screen.

Optionally I can connect a well-choked USB cable from radio to laptop to support two-way N1MM logger integration and WSJT modes like FT4 or FT8, but often I don’t bother for quick POTA activations. Note that the 705 also offers wireless network connectivity for the integration normally provided by that physical USB connection, but I haven't tried it yet—mostly because it requires more software on the laptop (more software = more configurations to get right = more fragility).

Securing the 705

To secure the IC-705 to the desktop while allowing easy removal, I wanted to use hook-and-loop strips. But I also didn’t want the strips directly on the 705 which would inevitably leave adhesive mess behind when they’re eventually removed. To meet both requirements, I cut a rectangle of thin aluminum stock from a hobby shop to create “wings” wide enough for the hook-and-loop strips, and drilled holes to allow M4 screws to secure the plate to the AMPS pattern screw holes on the 705. The extra length of aluminum on both sides was also used for adhesive tie-downs for the fragile cables plugged into the sides of the radio.

Microphone Adapter Adaptation

To allow me to quickly log contacts and keep a good rate after a pileup is established, it’s important to keep both hands on my computer keyboard. In turn, this requires a headset (headphone + attached microphone), plus a footswitch to put the radio into transmit mode. Another mini build adapted my existing Heil headset and generic footswitch to the IC-705:

To save time, I bought the only commercial adapter I could find for the IC-705’s tiny 2.5mm TRRS socket for microphone audio + microphone condenser power + transmit switch. The Heil adapter had a 3.5mm microphone socket output as expected, but disappointingly used a pushbutton for transmit. (Come on Heil, why not provide a standard ¼” footswitch socket that would work with standard footswitches, and anyone who wanted a pushbutton instead could connect one. Like the ones I’ve bought in the past for my IC-7100 and Flex radios. Sheesh.)

I did the obvious modification by cutting off the pushbutton and installing a ¼” footswitch socket. The challenge for this untalented builder was creating a physically robust adapter out of the surprisingly thin wires provided by the native Heil adapter. With lots of shrink wrap I built a pretty stiff combination that I hoped could be mounted with enough stability to avoid a repeat of my earlier broken jack disaster.

Other Desktop Components and Cables

The IC-705 is famously easy to damage its output PTT signal circuit (called the “send” signal by Icom) by drawing too much current to ground. Probably my new amplifier would not have been a risk, but I didn’t want to take a chance. An isolation or relay circuit would have been easy even for me, but again to save time I bought a unit from eBay that provided the active circuit in a convenient package with a more-standard RCA connector output and the 3.5mm cable needed for the send/ALC output of the 705.

The other components were reused from the old station: 

• Remote RF power meter to monitor power and SWR at the output of the amplifier in the back.

• Simple up/down switch for the screwdriver antenna.

• Compact unfused PowerPole distribution for the low current 12vdc power used in the front. 

Only five cables are needed from front to back, allowing for relatively fast removal of the passenger desk unit for human use of the front seat:

• LMR-240 coax from the radio’s BNC output to the SO-239 amplifier input in the back.

• 12 gauge red/black power cable from the back PowerPole distribution to the front.

• Screwdriver motor control cable to the up/down switch in the front.

• RCA “audio” cable from the PTT isolation box in the front to the amplifier in the back.

• CAT8 shielded ethernet cable (not carrying network traffic) from the RF sensor in the back to the remote RF power meter in the front.

Back Station Components

The DC and RF power components in the back (trunk?) of the SUV were carried over from the old station, with the major exception of the RF amplifier. The rack shelf on which the amplifier and DC power distribution is mounted has been reused at least four times since originally being installed in my large “TV van” VHF rover station, which gives that build its haphazard look. Connecting the battery to the rack shelf DC distribution are two 4-gauge flexible welding cables, which are reused from a higher current application in the “TV van”. 

DC Battery Power

Originally bought to power my Ameritron 500M and its stated 80A peak DC current draw, my Bioenno 100Ah LiFePO4 battery is now larger than necessary for my new RM Italy amplifier’s 40A peak current. Of course, better to have bought too large than too small originally. The Bioenno is installed in a trolling motor battery case, bought in 2013 for my original AGM station battery. The case protects the raw battery, provides handles for carrying, has insulated wing nuts for screw-down output connections, and includes a 60-amp circuit breaker.

A Bioenno 20A charger charges the battery at home or in hotel rooms on the road. But I also carry a 5A charger and inverter connected to a 10A cigarette outlet in the back. The smaller charger allows me to charge the battery a little while on long drives between operation locations, in effect extending the useful life of the battery’s charge before giving it a proper full charge. This is less necessary with the lower energy need of the new amplifier, but I’ll still connect the road charger if I’m driving over an hour to the next operation.

Rack Shelf DC Distribution

The RF amplifier and high current DC distribution are mounted together on a 2-foot-long spanning rack shelf originally installed in my “TV van”. The old 500M amplifier was oriented with its long axis parallel to the long axis of the rack shelf, but the new HLA 305 amplifier is too long for that orientation but luckily just barely fits in the other orientation.

Quarter-inch binding posts are the input to the DC distribution, which first goes to chrome distribution blocks. (Those blocks are from the high-powered car audio enthusiasts’ world; better distribution blocks for ham use are available today.) The plus side block has spaces for up to four bolt-down MIDI fuses, of which I only use two: One 40A fuse for amplifier power, the other 40A fuse for the rest of the station.

That second 40A circuit is the input to a boost regulator that used to be sitting on the floor but is now mounted securely to the rack shelf. The idea behind the booster is to keep station power (ex-amplifier) at a steady 14 volts, especially for the radio, as the current demands of the amplifier can tend to otherwise sag voltage seen by other components. First purchased to support my older lead acid battery stations, I probably would not have bought it for a lithium battery station, but I already had it so I might as well incorporate the booster.

The output of the boost regulator is the input to a fused Powerpole distribution. Again, this component was reused from the TV van, and now includes many more output circuits than needed in the Forester station. Only two outputs are used currently: one to power the remote RF power sensor in the back, and the other for the power cable running to the front operating position distribution.

RF Circuit

The new amplifier has two inputs: The RF input (accepting up to 10 watts) is connected to the IC-705 radio’s output via LMR-240 coax, and the PTT input is connected to the IC-705’s PTT output via a buffer box described earlier. The amplifier’s RF output is connected via a short jumper to the input of an MFJ inline power sensor, which sends analog forward and reverse power level signals to the remote RF power meter in the front. Another short jumper from the output of the RF sensor is connected to a high-power choke unun. The other side of the unun is connected to the screwdriver antenna input via another LMR-240 coax chosen for its small diameter and flexibility. That coax is snaked past the spare tire under the trunk floor and through a native drain hole in the bottom of the spare tire well.

The screwdriver antenna system is my reliable Tarheel model 200, bought in 2015 and only replaced in 2019 due to a parking lot accident. This model is rated for 1500 watts from 80m to 6m (with proper whip). I use a bottom-mounted capacity “hat” to reduce the coil windings needed for low bands, and a 17-foot telescoping whip. The whip is at full extension for 80m and 40m, but has to be shortened for bands 20m and above where the screwdriver coil is not used for loading. Note that I originally bought the screwdriver to allow vehicle portable operation on 80m & 40m & 20m, where all the action was in the mid-2010s. Now with higher bands available in the favorable part of the sunspot cycle, the screwdriver would be an unnecessary complication and expense today.

I did no RF “bonding” to the vehicle for the shield side of the antenna. Instead, I use two dual radial wires made from “lamp cord” usually used for AC power. The overall length of each dual radial is 50 feet, with one of the two zipped wires cut back to 25 feet for higher bands. The lengths were chosen to be non-resonant, long enough to be effective, but short enough to quickly install in most open operation locations. The antenna end of the wires has crimped ring terminals, which are attached to the body of the antenna mount on a threaded post and quickly secured with a wing nut (which is why I carry extra wing nuts because they’re easy to drop into tall grass). Both radial wires are stored on a spinning reel, which allows fast deployment and reasonably quick wrapping when done.

Ready for Operation

At the time of writing this article, recurring health issues were preventing me from using this vehicle-portable station. When I get better, I’m looking forward to taking the all-wheel-drive Forester into the many Pennsylvania POTA sites I haven’t activated yet. Most of those sites are PA Game Lands with primitive access roads, which was a top consideration when I bought the AWD Forester.