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Author Topic: Help rebuilding a 6 meter yagi.  (Read 922 times)
K9ZF
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Posts: 76


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« on: April 04, 2014, 10:37:32 AM »

I recently bought a Cushcraft A50-6S.  At least that is what it was advertised as.  What I have appears to be a homebrew 6 element beam that may have been patterned after the Cushcraft, but it doesn’t match the antenna in the Cushcraft manual, or the descriptions I have heard of the old style A50-6.  So I am guessing homebrew…

The boom is two pieces.  I didn’t count the sleeve over the center where the boom to mast plate is located.  The two boom sections telescope into one another, and are roughly 1.5” Al tubing.  One section is 11’ long, the other is 10’, with one foot of overlap, this ends up being a 20’ boom.  Each element is made from a single piece of 1/2” Al tubing.  It is fed by a gamma match.

Here are the element lengths:
Ref:      117 1/8”
Driven:   110 ¼”
Dir. #1:   105”
Dir. #2:   104 1/8”
Dir. #3:   103”
Dir. #4:   101 ½”

The element to boom mounting uses a U-bolt and saddle like the Cushcraft, although a few have been replaced with muffler clamps.  I didn’t write down the element spacing because I’m guessing I may change it.

My plan is to refurbish this yagi and put it up this spring.  Right now it just needs a good cleaning and a few of the clamps replaced.

Would anyone care to model or offer suggestions on improvements to this antenna?  Element spacing is easily adjustable, since it just clamps around the boom.  Elements are easily trimmed, if needed.  Making them longer is a bit more of a challenge, but I could get a size smaller tubing to slide into the existing tubing if needed.

It will be used exclusively for the weak signal portion of the 6 meter band.  For example, 50.000 to 50.300...

All comments appreciated!

73
Dan

--
K9ZF
Amateur Radio Emergency Service, Clark County Indiana. EM78el
The once and future K9ZF /R no budget Rover
 ***QRP-l #1269
Check out the Rover Resource Page at:
<http://www.qsl.net/n9rla>
List Administrator for: InHam+grid-loc+ham-books
Ask me how to join the Indiana Ham Mailing list!
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--
K9ZF
Amateur Radio Emergency Service, Clark County Indiana. EM78el
The once and future K9ZF /R no budget Rover
 ***QRP-l #1269
Check out the Rover Resource Page at:
<http://www.qsl.net/n9rla>
List Administrator for: InHam+grid-loc+ham-books
Ask me how to join the Indiana Ham Maili
KM3F
Member

Posts: 497




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« Reply #1 on: April 04, 2014, 10:40:44 PM »

My 6m beam is all home brew at 5 elements and uses muffler clamps.
If yours has adjustable element spacing, use wide element spacing for best gain and directivity as found in an Antenna handbook.
The wide spacing will be out beyond about 20 feet+.
If gamma matched, face it straight up in the air and match it down with an analyzer or noise bridge as the quickest way..
Do a frequency run, then raise it up and see what change you need to make if the match is to far out.
.
I first done a 5 element close spacing and soon learned it's pattern was wide as barn door and little F/B ratio.
The same elements wide spaced made  a nice pattern with no detectable side 'lobes'.
I built another 3 element for another use as a wide space, and it to works well but by size is not as high a gain but still no side lobes and the driven element is a dipole design no less with all elements isolated off the boom and a coax choke at the feed point.
Just used it with a Linear amplifier operating 6m AM local net and the amp likes the match as nearly flat over a wider frequency than a Gamma match.
It is a 3 element so the beam width is not so tight I can't hear stations off the side a bit in front of the beam.
It's a pain with very high gains and narrow beam widths running the rotor all the time finding the other stations. It  breaks coax at the rotor after while and the rotor needs service if your wiling to accept these things as a price for DX and long haul.
Lesson learned is to use coax  guides that minimize the coax stress  at the turning mast above the tower and at the tower so there is free movement, no wrap or snag at the tower and no hot weather droop of the coax.
Good luck..
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K9ZF
Member

Posts: 76


WWW

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« Reply #2 on: April 05, 2014, 05:49:27 PM »

KM3F,
Thanks for your input!

Yeah, I figure I will go with something like an OWA design, but haven't got that far yet.  Just thought I would put it on the forum and look for tips and comments.

73
Dan

--
K9ZF
Amateur Radio Emergency Service, Clark County Indiana. EM78el
The once and future K9ZF /R no budget Rover
 ***QRP-l #1269
Check out the Rover Resource Page at:
<http://www.qsl.net/n9rla>
List Administrator for: InHam+grid-loc+ham-books
Ask me how to join the Indiana Ham Mailing list!
Logged

--
K9ZF
Amateur Radio Emergency Service, Clark County Indiana. EM78el
The once and future K9ZF /R no budget Rover
 ***QRP-l #1269
Check out the Rover Resource Page at:
<http://www.qsl.net/n9rla>
List Administrator for: InHam+grid-loc+ham-books
Ask me how to join the Indiana Ham Maili
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