I continue with the series "Building Low Budget Antennas" for Radio Amateurs. Nothing fancy or with high gain.... no just simple low budget antennas!
In this article I will be looking into building a 1/4 Wave Ground Plane Antenna for 2 Meters. Now I know there are thousands of ways to construct this antenna, but how cheap can you build one? R10, R20 or R50. You decide how much such an antenna will cost.
General Specifications:
Resonant Frequency: 145.550 Mhz
Frequency Span: 145.000 - 145.800 Mhz
Modes: FM ( Local repeaters and simplex)
Polarity: Vertical (Note: Repeaters use vertical polarization.)
Antenna Impedance: 50 Ohm or very close to 50 Ohm
Gain: Approximately 2 - 3 dBd
I found a very useful quarter wave calculator if you want to change the measurements to suite your needs. This calculator is used to determine the length of each element of the antenna. That includes the vertical monopole radiating element and the 4 radials.
The calculator is available HERE
Enough said let's start building the 1/4 Wave Antenna.
Materials I used:
3d Printed Ground Plane Support Parts (3 items) Available HERE (Note you do not need these parts. I will explain later how to build the antenna without these parts.)
1 x PL239 Socket Connector (Not ideal rather use BNC or N-Type Connectors but I used what I had on hand)
1 x 1 meter 25mm Electrical Conduit pipe
1 x brass 5A Electrical Connector Block ("Chocolate" Block)
1 x 1.5 Meter (2.5 mm) Copper Wire (Ideal would be brazing rod but I used what I had on hand. Brazing rod is far sturdier but more expensive.)
Odds and Sods:
Cable Ties
Silicon Sealant
Insulation Tape
Solder
Solder Paste
5 -10 m Coax Cable (RG58CU Mil Spec) 50 ohm with 2 x Connectors (Feeding line to radio)
Self Amalgamating Electrical Tape
Tools:
Hack Saw or PVC Pipe Cutter
Soldering Iron
Sharp Utility Knife
Screw Driver (Small flat)
Test Equipment:
VHF SWR Meter
Antenna Analyzer (If you have one but not compulsory)
VHF/UHF Radio
Coax Patch Leads
Mast (Non conductive)
Power Supply or Battery for Radio
Building the Antenna:
I am not going to go into detail how I constructed my version of the antenna as there is more than enough info via the links and images how to construct this antenna. A word on the 3d Printed parts. You can use the SO239 without the 3D printed parts. Just fit the bottom threaded part of the SO239 and the PL259 in the one end of the 25mm electrical conduit pipe. To make it fit tightly you can use self amalgamating tape around the connectors and then push it into the pipe. Hot-glue can also be used to hold the connectors tight in the pipe. Improvise is the answer here. You can also make an aluminum L bracket and secure the SO239 to the bracket.
Testing the Antenna:
I ran a quick test on the antenna with my HT just to see what the SWR was like. Well the images speak for themself. SWR was 1: 1 between 145.000 - 145.800 Mhz. With the antenna just above the roof, I can work the 145.750 Mhz Aasvoelkop- and all the other repeaters in the area. I did some more tests with the VNA Antenna Analyzer. See the images below.
Side Notes:
I found that the antenna works just as well on 70 cm's. SWR 1.2:1 on 70cm. Unfortunately I did not do any measurements with the VNA on 70 cm's .
Conclusion:
This antenna will be good to download SSTV images from the ISS. It is lightweight and easy to setup/install. To the new radio amateurs this antenna is an ideal first time antenna project.
I am very happy with the performance of this 1/4 wave antenna on 2m and 70 cm's. Well worth spending my time on building this antenna.
Final cost to build this antenna: R45.00 ($2.5 US)
Images: Click on images for larger view.
