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2 Meter Flower Pot Antenna: DIY Amateur Radio VHF Antenna Tuning Guides
Quick Answer: A 2 meter flower pot antenna is a vertical dipole made from RG-58 coax. It covers 144 to 148 MHz with a typical SWR of 1.3 to 1.5 after trimming. Build the top radiator long at 490 mm and cut it in small steps while testing with an SWR meter or NanoVNA.
The flower pot antenna is a common first build for amateur radio operators in apartments and small houses. It does not need a ground plane. It is easy to hide on a balcony. This guide gives you the cutting dimensions, assembly steps, and tuning method for the 2 meter VHF band. In practice, most builders finish this project in one afternoon.
How the 2 Meter Flower Pot Antenna Works
The antenna is a half wave vertical dipole. The top half uses the center conductor of a coax cable. The bottom half uses the braid folded back over the outer jacket. A choke coil below the feed point stops RF from flowing on the outside of the feed line. That keeps the radiation pattern stable and reduces noise.
Because the antenna is a dipole, it does not require a metal ground plane. You can mount it on a PVC pipe or fishing pole. The main tuning variables are the top conductor length, the folded braid length, and the choke coil position.
Materials and Starting Dimensions
You need 2.2 m of RG-58 coax, a 25 mm PVC pipe, heat shrink tubing, cable ties, and a BNC or SO-239 connector. Do not use RG-174 for the antenna section. It has high loss at VHF.
Cut the top section at 490 mm for a target frequency of 146.000 MHz. Fold the braid back for 480 mm below that point. These lengths are slightly long on purpose. You can trim but you cannot add material back. The velocity factor of the insulation and the folded braid varies between cable brands. Start long and test.
Step by Step Assembly
Measure 490 mm from the top end of the coax. Remove the outer jacket and the braid from that top section. Leave the center conductor and its dielectric insulation intact. Do not strip the dielectric off the center conductor. That changes the velocity factor and moves the resonant frequency.
Fold the exposed braid down over the outer jacket for 480 mm. Slide heat shrink over the folded braid to keep it even. Below that folded section, wind 5 turns of the RG-58 around a 25 mm PVC former. That forms the RF choke. Keep the coil near the bottom of the folded braid but outside the radiating section. Secure the coil with cable ties. Install the connector at the bottom of the coax.
Tuning the Antenna for Low SWR
Connect the antenna to an SWR meter or NanoVNA. Use low power, 5 watts is enough. Sweep from 144.000 MHz to 148.000 MHz. Find the frequency where the SWR is lowest. If the lowest SWR is below 145.000 MHz, the antenna is too long. Trim 5 mm from the top conductor and test again. In practice, a 5 mm trim moves the resonant frequency up about 300 kHz on the 2 meter band.
If the lowest SWR is above 147.000 MHz, the antenna is too short. You may need to start
Test the antenna in its final mounting position. Metal objects within 1.5 m can shift the resonance. A builder in Surabaya in Indonesia could not get below 2.0 SWR until he moved the antenna away from a metal railing. No trimming was needed after that change.
Common Mistakes on First Builds
Many builders remove the dielectric from the top center conductor. The antenna then resonates too high in frequency. Leave the insulation in place. Some skip the choke coil and then see RF on the feed line and erratic SWR. Others mount the antenna too close to air conditioning units or metal window frames. Always test in the final location.
Where the 2 Meter Flower Pot Antenna Works Well
This antenna suits portable operations, apartment balconies, rental units, and emergency go kits. It is light and cheap. Replacing it takes a few minutes. It performs best outdoors at 3 m or higher. Indoor use can work near a window but avoid concrete with heavy rebar.
FAQ: 2 Meter Flower Pot Antenna Tuning
What is the best coax for a 2 meter flower pot antenna?
Use RG-58 for the antenna section. For feed lines longer than 10 m, RG-8X or RG-213 has lower loss. A solid polyethylene dielectric is easier to work with than foam. Foam can deform when you solder the connector.
How long should the top section be for 146.000 MHz?
Start at 490 mm. Test the SWR. Trim in 5 mm steps until the dip lands on 146.000 MHz. Some cable brands need 465 mm to 475 mm because the insulation velocity factor is different.
Why is my SWR stuck above 2.0?
Check the choke coil first. It should be 5 turns on a 25 mm former and placed just below the folded braid. Check for metal objects nearby. Also confirm that the braid is folded evenly and not touching the top center conductor.
Can I use this antenna indoors?
Yes, but performance will be lower. Place it in a window or attic. Keep it away from metal frames, rebar, and electrical wiring. Outdoor mounting at 3 m or higher gives the best range.
Does a flower pot antenna need a ground plane?
No. It is a vertical dipole. The folded braid is the second half of the antenna. The choke coil keeps RF from the feed line. A ground plane is not required.
About Silver Automation Instruments
This antenna guide is for radio builders. Silver Automation Instruments supplies industrial flow meters and process instruments, not antenna parts. We help plants in oil and gas, water and wastewater, chemical, food and beverage, and marine industries. If you need a Coriolis mass flow meter, electromagnetic flow meter, ultrasonic flow meter, vortex flow meter, oval gear flow meter, thermal mass flow meter, pressure transmitter, or paperless recorder, send us your pressure in bar, temperature in deg C, pipe size in DN, and flow range. Tel: +86-25-68650347. Whatsapp: +86-25-52155837. WeChat: +86 15365082610.