New Series - Building Low Budget Antennas - 2m Oblong (rectangular loop) Antenna - Project 3

 Reminder:  

I continue with the series of low budget antenna "builds".   In the series I will be looking into building antennas that is:

• Highly Portable
• Cheap to Build
• Easy to build (Novice and Experienced builders)
• Use readily available material from the local hardware store
• Needs minimal tools to construct
• Needs only a SWR Meter to do some final tuning and adjustments.  However if you do have an antenna analyzer, that will be a bonus.
• Highly affective and has gain.
• Light weight and easy to install or to dismantle
• Fun to build and play around with.            

Please note that none of the antennas that I will be constructing is my personal designs.  Credit will be given and links provided where you can find more information about the antennas.

I trust that new, novice and experienced radio amateurs that will be building some of these antennas  will find them of great use and enjoyment.  Isn't this what amateur radio is all about?

 (Click on image for larger view.)

The 2m Oblong (rectangular loop) Antenna 

Center frequency: 145.000 Mhz

Frequency Span:  144.200 - 146.500 Mhz

Modes: SSB, CW and Digital Modes (Can also be use on FM ( Local repeaters and simplex))

Polarity:  Horizontal  (Note: Repeaters use vertical polarization.)

Antenna Impedance:  50 Ohm or very close to 50 Ohm

Gain: Some gain but could not find any proof

In a previous article available HERE I constructed a 2 Element 2m Square Quad Loop Antenna. It is a good antenna and has performed well during the testing of the antenna.  You can feed it at the bottom center for horizontal polarization or in the middle of either side for vertical polarization.

Something that makes its construction slightly difficult is its 100-120 ohm feed point impedance. Unlike a half wavelength dipole (especially the inverted-V variety) it can't be fed directly with 50 ohm coaxial cable.  Instead you need to make a transmission line transformer (using 1/4 electrical wavelength of 75ohm coax) to reduce ~100 ohm to ~50 ohm.  Another issue with a square loop is height.  You need a decent portable or fixed mast at least 10 m height for the square quad.

 

One solution to the above is the (Oblong) rectangular loop. It's still a wavelength around but its no longer square. That reduces its feed point impedance to 50 ohm with certain dimensions.  I ran into the websites and videos of Peter VK3YE and Andrew VK1AD who published information on a 2m rectangular loop antenna that I needed to try.  The rest is history.  Enough said let's start building the 2m Oblong Antenna.. 

Materials I used:

2 x 420 mm length of 16 mm dowel (top and bottom arm)

2 x 420 mm PVC (20mm) pipe length of 16 mm dowel (cover the 2 x 16mm dowels)

2.2 m length of insulated 1.5 mm multi-strand insulated copper wire.

BNC panel mount with solder tab

2 x 30mm bolts, washers and nuts

4 x S/S Self-tapping Screws ( To adhere PVC end caps to dowels and PVC pipe)

4 x PVC End Caps

1 x 500mm long Nylon Rope

1 x 50 mm x 50 mm piece of Single Sided PCB

Odds and Sods:

Cable Ties

Hot Glue Sticks

Insulation Tape

Solder

Solder Paste

Coax Cable (RG58CU Mil Spec) 50 ohm

Self Amalgamating Electrical Tape

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

Tools:

Metal Punch

Drill

Drill Bits 4mm + 3mm

Hack Saw or PVC Pipe Cutter

Hot Glue Gun

Soldering Iron

Screw Driver (Small flat)

 

Test Equipment:

 

VHF SWR Meter

Antenna Analyzer (If you have one but not compulsory) 

VHF Radio 

Coax Patch Leads

Mast (Non conductive)

Coax feed line cable  5 - 10m  RG58CU 50 ohm

Power Supply for Radio 

Building the Antenna:

I am not going to go into detail how I constructed my version of the antenna. I used PVC pipe to cover the dowels and added PVC end caps and nylon rope to fix the antenna to my link stick mast.  Cosmetic durable or weather protected .... who cares?  It looks a bit more snazzy though but rest assure it does not work better than those built by VK3EY and VK1AD.

More information on the build and use of the antenna available at:

Website Peter VK3YE (Click to view website)

Website Andrew VK1AD (Click to view website)

Video: Oblong loop antenna for 144 MHz SSB and WSPR by Peter VK3YE

 

 Video:  Comparing various simple antennas on 2 meters by Peter VK3YE

 

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 (144.300 - 145-900 Mhz)  I could also trigger all the local repeaters in the George / Mossel Bay area with two watt output.  Remember this antenna is horizontally polarized while the repeaters are all vertical polarized.  Once the weather improves I will do some more tests and hopefully hookup with somebody on SSB and the Digital Modes.  More on this in a future posting.

Conclusion:

This antenna will be great for HOTA, SOTA, POTA and even Emergency Communications.  Although it does not have gain like a Yagi or a Quad antenna it is ideal for a cheap, quick and minimal setup.

Images:  (Click on images for larger view.)