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[N1AUP]

Any suggestions on how to attach elements to an aluminum boom when making a 900 mhz quagi?

Do you have to insulate the elements from the boom?

[WB6BYU]

You can insulate them or mount them in any
number of ways - but the element lengths will
change with the mounting method.

If you have a particular design you want to copy,
best to copy the mounting method as well.

I recommend GM3SEK Long Yagi Workshop for
details on element length corrections - far better
than I could try to explain it.


Especially with an aluminum boom, passing
elements through holes in the boom and trying
to make a reliable connection isn’t always easy.

Depending on the element size, using an
insulator of some sort may be more reliable.
Various types of plastic pieces (like expansion
anchors forcuse in wallboard) have been used.

If you want to mount it above the boom, the
various sorts of conduit or pipe mounting clips
or brackets may be useful.  I found some bags
of plastic clips for PEX pipe used for underfloor
heating that will snap onto a 1/2” boom, but
the conventional U-shaped clamps will work if
the ends are bent to hold the element.  They
might need an extra sheet metal screw to hold
them in place.

But again, all of these may require different
corrections to the element length.

[AC6LA]

I recommend GM3SEK Long Yagi Workshop for
details on element length corrections - far better
than I could try to explain it.

Another good resource: DG7YBN / Boom Correction

Dan, AC6LA

[N1AUP]

The plans I'm using called for a wooden boom, but I ordered aluminum.  Maybe that was a mistake.

[WB6BYU]

Not necessarily a mistake, depending on the
physical properties required.

It just may require some adjustments.

I often use thin-wall PVC or even PEX pipe
for shorter yagis and/or quick prototypes,
as it doesn’t require a correction to the
element lengths.  Fiberglass electric fence
posts are another option.

But for longer booms and/or more permanent
installations, aluminum has advantages.

All depends on the antenna you are trying to
build and how you plan to use it.

[AI5BC]

The plans I'm using called for a wooden boom, but I ordered aluminum.  Maybe that was a mistake.

Then throw away the plans and start over is what you decided to do. So now what?

[W1VT]

33cm will require a boom correction if you go from a wood to metallic boom.
I'd suggest using a wood boom at 33cm. 
I use aluminum with Delrin insulators and push nuts but I think that may be too much work in this application.  I scaled a K1FO 22 element Yagi to 903!
I know someone who has a friend that TIG welds his  aluminum elements to the aluminum boom.  He brought a sample.  Very nice work!

Zak W1VT

[WA3SKN]

There is a difference between insolated and metallic booms that will need to be adjusted.
Now how long a boom do you plan to use?
How much lightning is in the planned area of usage?

-Mike.

[N1AUP]

Here is one article that I found.

I'm in Mass, so lightning is moderate.

https://www.qsl.net/n9zia/wireless/pics/900quagi.gif

[WB6BYU]

More info (and history) of the quagi on N6NB's web page.

Note that the loop dimensions will depend on whether
the wire is bare or insulated.  The original design used
the standard TW insulated house wire of the time.  Now
house wire uses THHN insulation, which requires about
a 1% change in dimensions from the original due to the
different electrical characteristics.

For a 3' boom, I'd go with a non-conductor, like wood,
fiberglass, or plastic pipe.  The elements are small enough
that there won't be a lot of wind loading.  Wooden dowel
(or a replacement broom handle) should be available if
you don't have a small strip of plywood or 1x2 handy.

Meanwhile, WA5VJB's "Cheap Yagi" designs would be another option.

[WV4L]

https://www.amazon.com/Hydraulic-SENRISE-Plastic-Standard-Diameter/dp/B0841K171Q/ref=sr_1_2?crid=1OPLLR73IG1P0&keywords=hydraulic%2Btube%2Bclamps%2B3%2F4&qid=1674517750&sprefix=hydrolic%2Btube%2Bclamps%2B3%2F4%2Caps%2C66&sr=8-2&th=1

Will these work for you?

[N0GV]

The element lengths will depend upon the attachment, material and dimensions of the boom.

Design the antenna in free space, mount an element on the boom and take a VNA and lightly couple the VNA port to the element using a very short probe parallel to the element about 3mm away from the element end and find the resonant dip frequency.  The change from the designed free space resonant frequency of the element taken as a ratio is then used to multiply each element's length as a correction factor and you will be close to where you want to be for each element. If you need more precision you will need to do this for each element separately.  If all elements are the same length then once and done is fine....

Grover

[VE7RF]

33cm will require a boom correction if you go from a wood to metallic boom.
I'd suggest using a wood boom at 33cm. 
I use aluminum with Delrin insulators and push nuts but I think that may be too much work in this application.  I scaled a K1FO 22 element Yagi to 903!
I know someone who has a friend that TIG welds his  aluminum elements to the aluminum boom.  He brought a sample.  Very nice work!

Zak W1VT

At the telco I worked at, a long boom commercial yagi was installed at a remote mtn top...way down Douglas channel, abt 400 miles north of me.  Think the yagi was made by Larsen, but not sure, since it was eons ago.

Think the freq was around 400 mhz.   The solid rod 6061-T6 elements went right through the solid rod 6061-T6 boom.... then heliarc welded on both sides of the boom.   Folded DE, with N connector.   Yagi in a huge box, no assy required.  Designed to take ice, wet snow,  extreme high winds, lightning, and anything else you could throw at it.  That location was helicopter only access.  In the early 80's, the Bell jet ranger helicopter was $350.00 per hr, and the clock started ticking from the time they took off from the airport 40 miles north west of the main CO...and the remote site was 40 miles south of main office.  160 mile round trip for the chopper...plus the time he sat idling, while work being done at the remote site.

So the cost of the yagi becomes a moot point.  I was there when we opened up one end of the box..and slid it out.  Think the ele's were  3/8" solid, or bigger.   Boom was aprx 1 5/8" also solid.  The welds were pristine.

[WB8PFZ]

If you have an aluminum boom I would build a loop yagi.