Antenna: Portable Dual Band (70cm & 2m) Radio Antenna

AntennaOne of the reasons I got into the Ham radio scene was to increase the effectiveness of handheld radios.  In my day job I use handheld radios a lot and they are critical to our wildland firefighting mission.  At work I can talk on a handheld for hundreds of miles across six counties.  I wanted similar capabilities in private life during emergencies, disasters or especially during “grid-down” when it comes.Desert

So I built a repeater using a Yaesu FT-8800r dual band mobile radio.  You can read more about the Yaesu FT-8800r <click here>.  Or, you can read about the cross-band repeater I built <click here>.  Along with a great repeater is a need for a great antenna.  And that antenna has to be proven reliable, sturdy, portable and something you can depend your life on.  So that was my next challenge, build an antenna to meet the repeater need but go beyond that as well.  This article covers that quest.  So let’s get going…

Mission –

General – To allow maximum performance on 70cm & 2m frequencies in the field via a highly portable, easily set-up, and sturdy antenna.

Primary – Use in conjunction with a Yaesu FT-8800R as a portable cross-band repeater (70cm & 2m).

Summary –

This portable dual-band antenna allows a user to attach the antenna to a handheld (via adapter cable) or directly to a mobile Ham radio. The antenna itself is a purchased wire antenna which is then mounted internally in ¾” PVC pipe. That section is then configurable with or without two (2) additional sections of 3” PVC pipe to vary the antenna height from 5’ – 15’ from the base.

Materials List –
DBJ-1 Designed by Dr. Ed Fong WB6IQN of UC Berkeley

DBJ-1 Antenna

  • The antenna, DBJ-1 J-Pole dual-band, designed by Dr. Ed Fong WB6IQN of UC Berkeley.
  • 1 section (10’) of Class 200 3” PVC pipe
  • 1 section (5’) of Class 200 ¾” PVC pipe
  • 1 3” threaded Class 200 PVC clean-out adapter, the inside diameter of the non-threaded end is 3”. See the picture in Step #7 for a better idea.
  • 1 threaded cap for the Class 200 PVC clean-out adapter. See Step #2 for a better idea.
  • 1  2” x 1-1/4” Class 200 PVC bushing. The 2” is male; the 1-1/4” is female.
  • 1   3” x 2” Class 200 PVC reducer. Both ends are female.
  • 3 or 4 swivel bales. See Step #15 for a better idea.
  • 30   1-1/4” wood screws with washers.
  • 1   ¼” carriage bolt, star lock washer, nut.
  • 2   2’ x 2’ pieces of ¾” marine plywood.
DBJ-1 Antenna Info –

SWR:  Less than 1.3 to 1 on both bands.
Gain:   +6dB over a rubber duck antenna

Steps –

Step #1 – The base is cut from 3/4″ marine plywood.  You want two pieces 24″ x 24″.

Step #2 – Take your 3” threaded drain clean-out plug. Cut square hole in the center of one piece of base material. It should look something like this…

Antenna-DBJ1build1

Step #3 – Place cap through hole so it looks like this…

Antenna-DBJ1build2Looks like this from the backside…Antenna-DBJ1build3

Step #4 – Now line it up and chisel out a small indent in the second board for the cap to sit in. Do not cut the hole all of the way through. Using the indent for the cap to sit in will give the base added strength and prevent the cap from turning. It should look something like this…

Antenna-DBJ1build4Step #5 –  Line the two boards up, make sure everything lines up correctly, put a generous amount of construction grade adhesive (i.e. Liquid Nails) between boards, clamp, then using outdoor screws screw boards together.

Step #6 –  Using wood screws and washers secure the cap to the board. I used 1-1/4” wood screws. It is a good idea to pre-drill the cap where the wood screws will pass through to avoid accidental cracking of the plastic cap. The washers ensure that the screws, when tightened, will not crack the plastic cap.

Antenna-DBJ1build5Step #7 –  When the boards are securely “sandwiched” then use a ¼” bolt (I used a carriage bolt), star lock washer, and locknut. Drill a hole for the bolt through the cap bottom (centered) and through the lower board. Install bolt from the bottom through the boards, through the cap and secure with lock washer and nut. Be careful to not tighten the bolt/nut too much; you don’t want to chance breaking/cracking the plastic cap.

Step #8 –  Now you have the base ready for priming and panting. I suggest a high quality primer and then multiple coats of a high quality paint to seal the wood against moisture. I suggest you tape off the threads with painter’s tape prior to painting.

Step #9 – Using the 10’ section of Class 200 PVC pipe, cut the 3” PVC pipe in half. Cement a double-female joint to each section of pipe. Use a plastic primer spray paint; paint the pipe any color you wish. It is not necessary to paint the pipe, I just think it looks cooler painted. Allow for the paint to fully dry before installing the swivel bales.

Step #10 – In the 5’ section of ¾” Class 200 PVC pipe install the wire DBJ-1 antenna according to the instructions included with the antenna.

Step #11 –  Using the 3” x 2” PVC reducer connection cut a ¾” hole in the side of the reducer as shown.

Antenna-DBJ1build6Step #12 –  Using the 2” x 1-1/4” PVC bushing cement the antenna cap (with the PL-259 connector installed) into the 1-1/4” opening in the bushing. Then cement the 2” end of the PVC bushing into the 2” opening on the 3” x 2” PVC reducer. (When ready to use the cap will fit over the male end of the PVC base.)

Step #13 –  Paint the 5’ antenna section any color you wish. Painting is not necessary but it looks cooler if it is painted. Make sure you use a plastic primer prior to painting with the finish coat.

Step #14 –  After the paint is dry on the 3” x 5’ sections of PVC pipe secure 3 or 4 of the swivel bales to one section. You will install the swivel bales on the end that does not have the joint installed. Make sure you are sufficiently lower from the end of the pipe to allow the 5’ antenna section to fit securely and snugly onto this section.

Antenna-DBJ1build6Step #15 – Allow all painted surfaces to completely dry prior to initial use.

Installation Options –

You have three installation options:

Starting with the base…

Antenna-DBJ1build7

Option #1 – Install the 5’ antenna section directly onto the base.

Antenna-DBJ1build8Option #2 – Install the 5’ antenna section on one of the 3” x 5’ sections, and then install the 3” x 5’ section on to the base.

Antenna-DBJ1build9Option #3 – Install the 5’ antenna section onto the 3” x 5’ section with the swivel bales, and then that section on the remaining 3” x 5’ section. Then install the entire configured pipe/antenna onto the base.

Antenna-DBJ1build10Note #1: If you are going to be securing the antenna with Para cord, tie the Para cord onto the swivel bales prior to raising the pipes and installing onto the base.

Note #2: If you are concerned about the unit’s stability you can place sandbags or large rocks on the base to improve stability.

Note #3: I painted my antenna a combination of colors and textures that will help it blend in with the desert environment where I will be using it.

Yaesu FT- 8800R ham radio

 

Yaesu FT-8800r Dual Band Ham Radio review.  Click for more information ->

 

Yaesu FT-8800r based cross-band repeater.

Easy to build Cross-Band (UHF/VHF) Repeater  Click for more information ->

 

 

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2 thoughts on “Antenna: Portable Dual Band (70cm & 2m) Radio Antenna

  1. Pingback: Communications | One Planet Thriving

  2. Sir; Regarding the DBJ-1 antenna base, is it necessary for all pvc parts to be 200psi or just the antenna tube? I really like this project, ideal for me. Schedule 200 is difficult to find in my area. thanks Mike

    Like

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