DB-212 Folded Dipole

WA1ZYX / KA1QFA

DB-212 Folded Dipole

Mods By:

Joel Huntley - WA1ZYX
Home Page
E-Mail

This page describes what needs to be done to modify a DB Products DB-212 folded dipole antenna only, not the cable harness if there is one. These antennas were a favorite among the paging industry for their lo-band operations, primarily in the 43 Mhz range. This mod will only cover the conversion to the 50 Mhz band.
With all the changes over to higher frequencies, these antennas are now finding their way into the surplus market and we hams love 'em for 6 meter work. They're rugged, reliable, and more than likely FREE just for the asking. As long as you know who to ask - but please, don't ask me!

Diagram of DB212

The antenna itself is constructed of 3 different diameters of aluminum tubing, one sliding into the next, tuned to the paging company frequency and then riveted and "dimpled" in place. The largest diameter tubing on the side furthest from the mounting structure, that extends from the center mount is actually one solid piece strictly for physical strength. It will be screwed (mounted) to the center mount.
We will be working with the smallest diameter tubing that makes up the trombone end of the antenna.

Drill out the rivets that are about 4 inches from where the smallest diameter and the next section of tubing join. Also drill out the dimples very close to the end of the tubing near the rivets. There will probably be 3 dimples at each junction. Do this at all 4 junctions. (4 rivets and 12 dimples)

At this point, the trombone should slide. If it doesn't, you may need to loosen the plastic spacer near the largest diameter and the middle diameter tubing. Also a little penetrating or cutting oil might not hurt to break up the oxidation.

Once the trombone will slide, remove it - pull it right out. Now use a hacksaw and cut a slit lengthwise in the tubing where you drilled out the dimples about 2 inches deep. I usually make the cut go through the holes left by where the dimples were.

You will need some stainless steel hose clamps to re-secure the trombone after you re-insert it into the slotted end of the tubing. Remember to slide the hose clamps over the tubing BEFORE you re-insert the trombone!

Now to determine the length. Using the standard formula: 468 / freq in Mhz, will give you the length in feet. Multiply your result by 12 and you will now have a pretty good beginning point in inches for the length of each element as measured from the center (mount) to the end of the trombone.
You will need to make final adjustments using Mr. Bird - or some other type of SWR measuring device or analyzer. However you will now be in the ball park.

Use the link below for a very handy page to do all the math for you. Just remember the results will be in FEET and you need INCHES.
Frequency to length Conversion page written by W4RLD.

WebMaster WA1ZYX

If these pages don't look right, you're not using:

Download it now!

Back Home

DISCLAIMER:
Modifications made to any equipment based on the information contained on this or any ZedYX pages are AT YOUR OWN RISK!

September 10, 2007