New Series - Building Low Budget Antennas - "Flower Pot" Antenna 70 cm - Project 5

This is a 70cm antenna using a short piece of white 25mm electrical conduit, 2 end caps and coax cable - to build the antenna.

I decided to build this antenna as part of the New Series - Building Low Budget Antennas.  Here is my version of the "naked" 70 cm Flower Pot Antenna:

General Specifications:

Resonant Frequency: 433.100 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: Some gain but could not find any scientific proof

I found a very useful Flower Pot Antenna 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 flower pot antenna. That includes the upper radiator, lower radiator, also the length of the cable that will be wound on the PVC pipe.

The calculator is available HERE

Enough said let's start building the Flower Pot Antenna.

Materials I used: 

1.5 meter of 50 ohm RG58CU Mil Spec coax

1 x PL259 Connector (Not ideal rather use BNC or N-Type Connectors but I used what I had on hand)

1 x 80cm 25mm Electrical Conduit pipe

2 x 25 mm PVC End Cap (The Co-Op is your friend here)

1 x 50mm length of 6.5 mm heat shrink tubing to fit over the coax cable

1 x 50mm length of 5mm heat shrink tubing to fit over the inner coax cable

1 x 100mm of fishing line

1 x plastic sucker sweat stick (Blue in photo)

1 x brass chocolate block connector to hold top radiator upright.

1 x 160 mm x 1.5 mm solid insulated copper wire for the Top Radiator Element.  ( I use this instead of the normal fine stranded inner wire of the coax.)

 

Odds and Sods:

Cable Ties

Hot Glue Sticks

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
PVC Cement ("Glue") (Permanent gluing of the PVC caps.)

Tools:

Metal Punch
Drill
Drill Bits 6 mm + 3mm
Hack Saw or PVC Pipe Cutter
Hot Glue Gun
Soldering Iron
Sharp Utility Knife
Screw Driver (Small flat)
 
Test Equipment:
 
UHF SWR Meter
Antenna Analyzer (If you have one but not compulsory)
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 on the Internet how to construct the antenna.   However for more information on the build and how this antenna works, click HERE to view my article on the 2 m/70 cm Flower Pot Antenna I constructed.

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 low over a very broad spectrum.  Although the antenna functions as it should I would prefer to have a antenna analyzer to obtain more useful information on testing the antenna. I will do some more tests once I invest in a VNA Antenna Analyzer, hopefully early next year.  More on this in a future posting.

Conclusion:

This antenna will be great for HOTA, SOTA, POTA and even Emergency Communications.  It is lightweight and easy to setup/install.  I do not intend to install the antenna in a 25mm PVC tube.  This one will stay just the way it currently is.  

 

I am happy with the first impressions of the 70 cm Flower Pot antenna, however the proof on effectiveness and performance will be out in the field.  Update to follow once I tested the antenna in the field. 

Images:  Click on images for larger view.