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Bruce H. McIntosh scotsman@afn.org Visit my work homepage Last revised Jan 04, 2021 |
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Stretched WA5VJB Cheap Yagi for 2 Meters with PVC Boom
Design considerations
As described in the original 10 element Yagi article,I had neglected to weatherproof the boom on the 2 meter antenna,and suffered the expected consequences. With the approach of yet another VHF contest it was time once again to take down the 6 element beam and put up something heftier.
I decided that since I had such good results with my stretched WA5VJB Cheap Yagi article design I'd go with the same basic design:
| Element | Length | Position |
|---|---|---|
| Reflector | 40.5" | 0" |
| Driven Element | 38.5"x1" | 7.5" | Director 1 | 37.5" | 16.5" | Director 2 | 36.5" | 34" | Director 3 | 36.5" | 52" | Director 4 | 36.5" | 70" | Director 5 | 36.5" | 88" | Director 6 | 36.5" | 106" | Director 7 | 36.5" | 124" | Director 8 | 32.75" | 142" |
This time,however,I decided to go with 1/2" PVC pipe,which will be immune to the sort of weather related damage that consumed the 1x2 boom of the previous iteration of the antenna. The only trouble is,1/2" pvc is not the most ridgid material on God's green earth. The solution to the floppy pipes is something I came up with for a hypothesized but never built 6 meter 4 element quad - two parallel runs of pipe tied together in a "ladder" structure.
Construction
Again,in the WA5VJB Cheap Yagi spirit,I went with inexpensive materials. The driven element and feed were recycled from the dead antenna. New elements were cut from straightened out coat hangers (10 for a couple bucks at WallyWorld).
Here's what I came up with for a boom design. I figured everything from location of the driven element; its J shape dictated using a tee fitting so there would be space to drill two holes. Each piece was cut long enough to allow for the ends being inserted into the tees and cross fittings. The front end of the boom is about 4' long,which I figured is the most the PVC would take without appreciable sag.
The first bit to go together was the back of the boom,with the tee for the driven element.
The center section came next. I cut 1" stubs of pipe to tie the top and bottom runs together. The vertical stubs are the mount points for attaching the antenna to the boom. More on that later.
Here's the whole boom put together.
The driven element,reflector and some of the directors have been glued to the boom.
Assembled at last! Now to get it out the sliding glass door without snagging on the chandelier,and get it up on the mast!
Sixty five pounds of counterweight make it easy for me to tip the tiltover tower down without assistance,though having my father in law on hand to unsnarl the feedlines from the holly (and catch the mast when the stop tether proved to be a tad bit too long!) was nice.
With the tower down,it was just a matter of a few minutes to pull the 6 element beam off the mast and attach the new antenna. The two vertical stubs were tied to the mast with stainless steel hose clamps. I've used this scheme for years with my portable antennas,with great success.
Another couple of minutes and everything is back up in the air,ready to take on the world. Time to head back indoors and get back into the VHF QSO Party!