Construction of a QRP 23cm HB9CV antenna

Homebrew 23cm (1296 MHz) HB9CV yagi antenna for SOTA

To get the 23cm amateur started, SG-Lab’s 23cm 1296 MHz transverter is supplied with a PCB 23cm 2el HB9CV antenna.    I am very happy with the performance of the PCB version, having worked Rod VK2TWR in Nimmitabel from Mt Taylor in Canberra, that’s a 130 km path with just 2.5 watts.  I have seen 2m and 6m versions of the HB9CV antenna so I was keen to make my own 23cm version using brass for the boom and radiating elements.  Inspiration for this project can be traced to Ernest PA3HCM for his post on a 23cm HB9CV used to access a 23cm amateur television (ATV) repeater.

This is my take on the 23cm HB9CV 2el yagi:

Materials:

• 2 * 3 mm dia brass rod 120 mm long
• 6 mm square brass bar 300 mm
• Piston trimmer capacitor 3.5 pf
• Short length of 1.5 mm copper wire
• SMA elbow panel to PCB mount
• Plastic project box 129 x 78 x 43 mm (minimum size)
• Solder

My starting point for dimensions see: Changpuak HB9CV online calculator

23cm HB9CV dimensions courtesy of changpuak.ch

***Note*** the materials I have on hand are 6.3 mm square brass bar and 3 mm brass rods.  This doesn’t match the online calculator.  How is a 1 mm radiating element going to survive?  I used the calculator for element lengths and the gamma match dimensions.  I cannot validate the boom diameter of 2 mm as the calculator outputs 2 mm for a frequency input range of 900 MHz to 1400 MHz.   You should also note the calculator doesn’t have a provision for element length correction on boom size or element diameter.

It’s up to you if you decide to follow the online calculator.  What I can confirm is that after constructing the antenna it works as expected.

Construction

Prepare two elements as per the dimensions above for 1296 MHz.  Next mark out the boom element spacings, drill two 1.5 mm pilot holes followed with a 3 mm drill bit. Next chamfer each hole then place the elements into the boom.  Take care to center each element then solder the elements in place.

Reflector and D1 elements soldered in place (both elements are driven)

Other components

gamma match and feed point components

Gamma match

gamma match connecting the reflector and D1

position the gamma match ready for soldering

gamma match soldered in place

Piston trimmer capacitor range – 0.42 to 3.82 pf

piston trimmer minimum reading (pf)

piston trimmer maximum reading (pf)

Piston trimmer is soldered to the gamma bar corner nearest to the reflector (longest element)

piston trimmer capacitor

HB9CV gamma match complete

SMA connector

place the SMA connector center pin to align with the trimmer capacitor pin

Solder the SMA connector to the boom.

SMA connector soldered to the boom

Cut the brass boom 5 mm behind the SMA connector.  Retain the brass bar for the next homebrew antenna.

remove excess boom material

Adjust the piston trimmer capacitor for a low VSWR reading.

Cleaned up 23cm HB9CV antenna ready for mounting in a plastic project box 129 x 78 x 43 mm.

23cm HB9CV yagi antenna finished

23cm HB9CV enclosed in a plastic project box

23cm HB9CV enclosed in a plastic project box.

23cm HB9CV

23cm HB9CV

23cm HB9CV

23cm HB9CV

If you got this far well done!

My actual antenna dimensions, measured with a vernier calliper are:

• L1
• L2
• Etc to be completed later today

Next antenna construction project is a 23cm Bi-Quad   😉

Thanks for reading this post. Good luck with your antenna construction  🙂

Published: 12 November 2017
Last Update:  9 September 2023