Antenna Project – 2.4 GHz 13cm Bi-Quad for SOTA

I recently purchased a 2.4 GHz transverter from SG-Lab in Sofia, Bulgaria. To get you on air the transverter is shipped with a 2.3 GHz 4el HB9CV PCB yagi which at 2.4 GHz has a VSWR 1.7:1, that’s easy to fix. 🙂

In addition to using the supplied HB9CV PCB yagi, I will construct a 22el yagi (in progress) and the Bi-Quad directional antenna mentioned in this post.

You may recall I’ve had good results on 23cm 1296 MHz with a Bi-Quad antenna, also known as a double-quad antenna, so I hope to repeat similar results on 13cm 2.4 GHz. This post describes how I constructed a 2.4 GHz Bi-Quad directional antenna. The VK 2.4 GHz narrow band SSB call frequency is 2403.150 MHz.

13cm Bi-Quad Antenna

For dimensions see: Changpuak Bi-Quad online calculator

2.4 GHz Bi-Quad Antenna Dimensions – courtesy of changpuak.ch

Materials

  • Double-sided copper clad PCB 130 * 85 mm (I had this piece on hand)
  • 50 mm length of semi-rigid 50 ohm RG402 (mini kits)
  • Female SMA socket to RG402 (solder type)
  • 300 mm length of 2 mm copper wire (junk box)
  • 2 * 15.2 mm stand-off insulators. I used 7 mm diameter plastic sprinkler riser tube
  • 2 * Cable ties
  • PCB enamel

Prepare a double-sided copper clad board 130 mm * 85 mm. Drill the center of the board staring with a pilot drill 1.5 mm followed by a 3 mm drill bit. Use a taper ream to finish the hole.

Debur the hole and edges of the board.

Prepare a 1/2 wave length (43 mm) of 50 ohm RG-402 and a female SMA. RG-402 has a velocity factor of 69.5%.

Assemble connector to RG402 feedline

Prepare the Bi-Quad driven element, 30 mm per side.

2.4 GHz Bi-Quad antenna parts – reflector, RG402 feedline and driven element

Assemble driven element and feedline

preparation for soldering driven element to RG402 feedline

preparation for soldering the driven element to RG402 feedline

Center of the driven element is soldered to the RG402 inner conductor. The two open ends are soldered to the RG402 copper shield

Bi-Quad driven element held in place for soldering

Almost finished – adjust the spacing between the reflector and driven element for a 1:1 VSWR. In this case to achieve a 1:1 VSWR the spacing is 15.2 mm, a small variation (0.4 mm) to the calculator dimensions table.

2.4 GHz Bi-Quad Antenna

2.4 GHz Bi-Quad Directional Antenna

Spacers – 15.2 mm length of 7 mm plastic riser tube, measured with a vernier caliper. Solder the RG402 shield to the PCB front and rear.

RG402 passes through the reflector. Spacing is 15.2 mm

Assembly finished, 9dB gain Bi-Quad antenna

Rear of the reflector – RG402 feedline and female SMA connector

Enjoy building your own 2.4 GHz Bi-Quad. 🙂

To finish off, below is a picture of the supplied 2.3 GHz 4el HB9CV Yagi. This antenna is designed for 2.3 GHz, at 2.403 GHz the VSWR is 1.7:1. To change the antenna’s resonant frequency to the VK SSB call frequency (2403 MHz) I trimmed 2 mm off each side of the two active elements (copper tracks). I left the director elements untouched.

2.3 GHz 4el HB9CV Yagi

20180225_102206

2mm trimmed from each side of the active elements.

First published: 19 February 2018
Last Update: 25 February 2018

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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. 🙂

Platform

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