Introduction: Quarter Wave Dual Band VHF/UHF Ham Radio Antenna
A Simple & Cheap Dual band antenna will save you having two different antennas for UHF and VHF
Step 1: Step 1
You will need copper or brass welding rod cut to
3 X 19.5" length, a bit longer, eg 20" is OK if you have a SWR meter and want to cut it to tune it
3 X 6.5" length, a bit longer eg 7" is OK if you have a SWR meter and want to cut it to tune it
-You Will Also need
-Normal SO-239 4 holes chassis mount connector
-Solder & Soldering Iron
-6 X Electrical Eyelets
-4 sets of screws, nuts and washers
-2 X 6 inch black nylon cable ties
-RG-8 cable with PL-259 plug. For lightweight RG-58 cable, you need an appropriate adapter, eg. PL-259 to BNC female
-SWR meter for testing
Adjust the electrical eyelets wire grip so that it can fit the end of the copper rod
Fit snugly the end of the copper rod to the adjusted electrical eyelet.
Solder it to improve the contact but make sure you sandpapered it until shining and swab the copper and metal eyelet with methyl spirit by to clean it from grease.
-Repeat until the 6 rods have been fitted with eyelets.
-Then, solder all the eyelets to the copper rods.
-See the SO-239 socket on the right
-Take the SO-239 chassis mount connector and clamp it to a vice.
-Test fit one 6.5 " and 19.5" copper rod, putting it at the center contact of the SO-239 and bend it at the eyelets to form and angle of
approximately 60 degrees apart forming a V.
-By any means, hold the two 60 degrees angled rod so the V shape stay in place temporarily.
-Carefully solder generously the two angled rod and do not move the solder point while the solder hardened. A good soldering work
will shine like silver and not dull.
We have 2 X 19.5" and 2 X 6.5" radial rods not yet attached.
Arrange the radial rods, making sure the 19.5" VHF rod is in between the 2 X 19.5" radial rods and the 6.5" UHF rod is in between the 2 X 6" radial rods
Attach the 4 radial rods with screws and nuts, putting in washers in between. Before tightening the screws, align the 4 radial rods so that they are 45 degrees of each other horizontally
-Attach the antenna assembly in a 1" diameter heavy duty PVC pipe. The length depends on your planned setup.
-The SO-239 will not be tight fit but you can think of a way to do it. One option is holding it using a thick, black cable tie and threading
it through 2 holes drilled at opposite sides of the PVC pipe.
-Carefully angled the 4 radial rods 45 degree vertically
-Connect a RG8 cable with a PL-259 connector. Use an adapter if you want to connect to a RG59 cable.
-Test using a SWR meter, making sure the SWR readings is between 1 to 1.5 . Testing procedure will be in the next step.
-You can cut the rod end little by little, about 1/8" at a time to adjust the SWR but too much it will be unadjustable
Step 8: SWR Testing Procedures
-To tune the antenna to my country, Malaysia amateur VHF band 144-148 Mhz, I set the radio frequency to the center frequency of 146
Mhz so it can generally covers the whole VHF amateur band.
-Connect a SWR meter to the antenna and to the radio, making sure you attached it to the right connector posts
-Take a SWR reading, and if it is beyond 1.5, cut the 19.5" VHF element rod 1/8" at a time until the readings is in between 1-1.5. -
-Theoretically , a reading of 1 is the best but rarely achieved. If you try to achieve it, you may cut a bit too much until the antenna is
unadjustable and you have to replace the elements to a longer one, back to square one :-)
- The amateur UHF band of Malaysia (ITU Region 3) is 430-440 Mhz set the radio frequency to the center frequency of 435 Mhz
so it can generally covers the whole VHF amateur band.
- Repeat the VHF tuning procedures but this time you must cut the 6.5" UHF element rod 1/8" at a time.
Step 9: Weatherproofing
-Tie the rods with black cable ties and cover the soldering point with silicone sealant for weatherproofing.
-Happy transmitting !
-73 from 9W2WDX Asni ( QTH: Bandar Baru Bangi,Malaysia)
-View my other activities at think2bgood.blogspot.com and kakipedal.blogspot.com
Step 10: My Other Project
Dont miss the opportunity to see my other exciting video on hardware coding for small kids at https://youtu.be/yCF2LiYm1WA
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