SOTA – 23cm from Mt Coree

VK1AD SOTA shack at Mt Coree VK1/AC-023 @ 1421 metres ASL, Namadgi National Park VKFF-0377, Grid QF44JQ

Australia’s Capital Territory (ACT) is experiencing 4 days of heatwave conditions with daytime temperatures up to 39 degrees C (102 F). To take a break from the early morning heat my wife and I headed for the summit of Mt Coree where the ambient temperature is 10 degrees cooler than the landscape below.

In the picture below, an early morning (7:30 am) inversion layer has trapped smoke from bushfires north of Braidwood in NSW.

Photos: © Copyright 2018 Andrew VK1AD

view east – Inversion layer trapping smoke from nearby brushfires. Today’s top temperature is 39C.

In close the fire watch tower, on the horizon a view north over a blanket of cloud. The summit is 1421 m above seal level

View west – Brindabella National Park. To the right of the picture is Dingi Dingi Ridge VK2/ST-004 and Webbs Ridge VK2/ST-005

Extract of VK1AD SOTA Activator Log: 20 November 2017 Mt Coree

Today’s QSO of the day on 23 cm (1296.150 MHz) was with Michael VK2FLR in Sydney Grid (QF56OD). The 23cm signal path is 268 km, my antenna is a homebrew 12el yagi.

On 23 cm I did hear Trevor VK3VG confirming a QSO with Rob VK1KW. I called Trevor two or three times without luck. Distance to Trevor’s location QF42UK from Mt Coree is 263 km.

Bands worked 2m, 6m and 23cm.

Time Call Band Mode Notes
21:24z VK1AI 144MHz SSB Greg s58 r55 144.2
21:27z VK1DJA 144MHz SSB Dave s59 r58 144.2
21:30z VK2UH 1240MHz SSB %QRA%QF45LD% Andrew s58 r56 49 km 1296
21:32z VK1KW 144MHz SSB Rob s59 r59 144.2
21:33z VK1MT 144MHz SSB Matt s59 r57 144.2
21:34z VK1BG 144MHz SSB Ian s59 r59 144.2
21:35z VK1RX 144MHz SSB Al s59 r59 144.2
21:36z VK1FWBD 144MHz SSB Wade s59 r59 144.2
21:38z VK1KW 1240MHz SSB %QRA%QF44MT% Rob s59 r59 20 km 1296
21:39z VK1MT 1240MHz SSB %QRA%QF44NM% Matt s58 r58 33 km 1296
21:43z VK1BG 1240MHz SSB %QRA%QF44MS% Ian s59 r59 18 km 1296
21:52z VK2FLR 1240MHz SSB %QRA%QF56OD% Michael s51 r31 268 km 1296
22:09z VK1CT 144MHz FM Chris s59 r57 146.5
22:13z VK1RX 50MHz SSB Al s59 r59 50.160
22:16z VK1CT 144MHz SSB Chris s58 r59 144.2
22:21z VK1DI 144MHz SSB Ian s59 r59 144.2
22:37z VK1RZ 50MHz SSB Roald s59 r59 50.160
22:44z VK1MA 50MHz SSB Matt s59 r59 50.160
22:48z VK1WX 50MHz SSB Amanda s59 r59 50.160

VK1AD SOTA shack at Mt Coree VK1/AC-023 at 1421 metres ASL

3el 2m yagi and a 23cm Bi-Quad

Mt Coree Trig Station. The telescopic pole is supporting a 6m 1/2 wave coaxial dipole


23cm Transverter – Tripod Platform and Bi-Quad Antenna Mount

At VK1AD Bi-Quad antenna construction I’ve had a hoot-of-a-time building 23cm antennas for SOTA and portable field ops. 🙂

“It’s time to cut my signal losses..”

For sometime I have used a 1 metre length of LMR195 coax feed line between the 2.5 watt 23cm transverter and my choice of antennas. Due to the feed line length this option introduces losses in both transmit and receive signals. Weak or marginal 23cm received signals are attenuated by feed line losses. In the picture below you can clearly see the feed line length, yes you are right it’s too long! (Mt Gillamatong 19 Nov 17)

VK1AD SOTA shack at Mt Gillamatong 19 Nov 17

It’s time to cut my signal ‘losses’ and move the transverter to the top of the tripod. This option permits the full extension of the tripod to a height of 1.4 metres above ground level, every millimetre gained helps.

Sunday 31 December 2017…its New Years Eve and I have nothing on my plate!  Starting with a tripod mount for the 23cm Bi-Quad antenna, also known as a double-quad antenna, I have also spent the afternoon fabricating a small platform for my SG-Lab 23cm transverter.

First let’s look at the the Bi-Quad antenna mount

Camera top plate – I purchased two standard top plates on eBay. Remove the 1/4 inch screw from the center of the plate.

Tripod head – top plate receptor in the vertical position

Mount the spare top plate to the rear of the 23cm Bi-Quad antenna. Do you like my nifty teeny-tiny G clamp?

rear surface of the Bi-Quad antenna

outline of the top plate

Top plate secure at the rear of the Bi-Quad by two 3 mm screws, washers and nuts

top plate secured to the rear surface area

Bi-Quad antenna fitted to the tripod head – it’s a neat fit.

Construction of a Transverter Platform

In the picture below you can see the tripod head locking knob has space behind the knob flange – Let’s be clever and make use of the space behind the knob and the flat surface of the head. 🙂


Homebrew double-sided copper clad PCB platform – I love fabricating stuff, useful or otherwise! You are not restricted to using double-sided PCB, you may have other materials on hand such as sheet aluminium. Go ahead explore the junk box.

Transverter platform secured by the tripod head locking knob – cool 😉

23cm Transverter and 6el Yagi antenna – LMR195 feed line is now 50% shorter at 500 mm

23cm Transverter and Bi-Quad antenna – For now ignore the feed line length, I will make up a 200 length of RG58 Cell Foil.

That’s my ‘New Years Eve’ afternoon of fun playing amateur radio antenna construction! I will test the B-Quad tomorrow from South Black Range, 40 km south-east of Canberra.

Post update: 6 February 2018

Construction and assembly of a new 200 mm feedline between the transverter RF output socket and the Bi-Quad antenna socket.

200 mm length of 50 ohm ‘Cell Foil’ terminated in male sma connectors

23cm transverter – 200 mm 50 ohm RG58 Cell Foil feedline

You have my permission to copy the design and build your own. 😉

Happy New Year to all and have a safe time playing SOTA in 2018 🙂

73, Andrew VK1AD

Published: 31 December 2017
Last Update: 12 March 2018