15 watt QRP HF L-match for portable operations. Peter VK3YE published a QRP 7 MHz to 52 MHz (40m to 6m) L-network ATU project and circuit diagram in VK’s Amateur Radio magazine , Edition 5, May 2017. I have constructed the L-match ATU and added a 5th inductor L5 4uH for matching on 3.6 MHz (80m).
All credits to VK3YE and Amateur Radio magazine, Edition 5, May 2017.
VK3YE 40m L-match ATU circuit diagram
I am using the QRP L-match with an 80m EFHW mounted as an inverted V for SOTA activations. My version of the 80m EFHW antenna is a 40.4 metre length of silicon insulated 18 AWG multi-strand copper wire supported by a 9 metre telescopic pole. The antenna matches on all HF bands 80m through to 10m. On 80m the antenna’s propagation is NVIS. Coincidently with all switches closed and variable capacitor in the minimum position the inverted V matches on 6m. My counterpoise is three random lengths of 22 AWG insulated wire.
Five inductor 80m to 6m L-match ATU. Inductor values in order are 0.5, 1, 2, 4 and 4 uH. Inductors are bypassed when the switches are in the closed position. All components are mounted in a small jiffy box.
If you find you need additional capacitance for tuning on 80m, simply add a 500 volt 220pf silver mica across the output terminals in parallel to the variable capacitor. Mount the fixed value capacitor on a piece of copper circuit board which slots behind the banana screw terminals. Cut an insulator line in the copper board to create to pads. Solder the legs of the 220pf capacitor to each pad.
Toroids – L1, L2 L3 and L4 T50-6. L5 is two T50-2 mounted side-by-side wound with 21 turns of 22 AWG enamelled copper wire.
Did you know this homebrew QRP L-match ATU offers the same match result as an Elecraft T1 L-network ATU? It does and without the need for a interface cable, tune button, chatter of relays and batteries to power the unit. 🙂
In the event of RF feedback on the coax feedline, I have a hombrew 50 ohm 1:1 current choke which connects between the transceiver and L-match.
Enjoy building your very own L-match ATU 🙂
QRP L-match users: Roman DL3TU, see Roman’s post here.