The transceiver and antenna tuner are in the hatch back trunk area of the Subara Crosstrek. The transceiver is powered by a Powersonic PS-12260 12V 26AH gell cell battery near the transceiver. The battery is charged from a 12 volt accessory outlet through an APT2X61S20J dual Schotky diode (75A, 200PIV, diodes in parallel) and a 50 watt 12V incandescent lamp. The lamp acts as a current limiter. When cold, its resistance is less than 0.1 ohms. When driven with 12V, it draws 4A, for a hot resistance of 3 ohms. Charging current is limited to 4A.
To get an idea of how the charging circuit is working, the following measurements were made on 20 April 2021. All battery measurements refer to the gell cell powering the radio. When the car was running, it was idling. Voltages and currents are likely to be higher with higher RPM.
| Description | Measurement |
|---|---|
| Battery voltage, radio off, car off | 12/98 V |
| Battery voltage, radio on (receive), car off | 12.87 V |
| Battery voltage, radio on (receive), car on | 12.94 V |
| Voltage across diode | 440 mV |
| Voltage across lamp | 400 mV |
| Current if diode shorted | 1.000 A |
| Current if lamp shorted | 900 mA |
| Current if diode and lamp shorted | 2.100 A |
| MFJ 336T 3 magnet mount with MFJ HamStick and Mag Daddy cable tie mounts routing coax to hatch back. The weather stripping on the hatch back is thick enough and the gap between the door and roof wide enough to not kink the coax. |
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| Rear view of Icom IC-7100 HF/VHF/UHF Tranceiver with MFJ-939I Automatic Antenna Tuner on top of it. Copper "plumber's tape" grounds the transceiver and tuner to the car chassis through a screw holding down a luggage tie-down. The tuner is held to the transceiver by adhesive Velcro. |
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| To the right is the Icom IC-7100 HF/VHF/UHF Tranceiver with MFJ-939I Automatic Antenna Tuner on top of it. To the left is the incandescent lamp charge current limiter. To the left of the lamp is the Powersonic PS-12260 12V 26AH gell cell battery. The APT2X61S20J dual Schotky 75A, 200PIV diode is held to the top of the battery with RTV silicon adhesive. The non-grounded wiring is normally covered with electrical tape. The battery is held in place with a ratchet strap to a luggage holddown. |
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| A closer view of the Powersonic PS-12260 12V 26AH gell cell battery. The APT2X61S20J dual Schotky 75A, 200PIV diode is held to the top of the battery with RTV silicon adhesive. The non-grounded wiring is normally covered with electrical tape. The battery is held in place with a ratchet strap to a luggage holddown. |
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| A plastic laundry basket is kept over the equipment to protect it. The basket is held in place by an adhesive Velcro strip. |
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| A view of the side of the car showing the through glass VHF/UHF antenna and the HamStick. |
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| The Icom IC-7100 control head is crammed into the "cubby hole" beneath the heating/AC controls and the broadcast radio. The cubby hole is wider at the top than at the bottom, so the control head is slid down until it runs into the sides. The sides and the top were then held in place with RTV silicon adhesive. I used clear adhesive, which made a pretty ugly white contrast to the surrounding black. The adhesive application was not very smooth. But, when painted black, it receives XYL approval. Below the control head you can see the warning label that the top of the HF antenna is 13 feet above ground. The microphone is to the left of the control head, held in place by adhesive backed Velcro. |
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| This is a plot of the VSWR on the 40 meter HamStick. It's pretty narrow! That's why I got the MFJ MFJ-939I Automatic Antenna Tuner. The MFJ-939I works very nicely with the Icom IC-7100. There is a Tuner button on the IC-7100 control head. Pressing that button for a couple seconds puts the MFJ-9391 into action. The control head photo above shows how it nicely centers the minimum VSWR on the transmit frequency. | |
| Here's the 20 meter HamStick VSWR sweep. It's considerably wider. | |