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Author Topic: Antenna using fiream cleaning rods  (Read 3194 times)
W0TLP
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Posts: 83




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« on: October 17, 2010, 12:46:22 PM »

I'm pretty new to ham radio and am getting very interested in portability for location operations.

I'd like to build a few highly portable antennas, starting with 2 meter, the only band I am currently operating. I think I can build a 1/2 wave vertical antenna with sections of firearm cleaning rods, in either brass or aluminum. I want 1/2 wave since it does not require a ground plane.

I'm trying to figure out what I can use to screw the antenna into that will then allow me to add the appropriate feed line. I'd like the base to mount to a 1/4-20 screw thread to attach it to a compact photo light stand.

The only option I can think of now is to solder a 1/4-20 nut to a sheet of metal, possibly a round electrical box cover, and then mount a mag-mount base to it, provided I can screw the cleaning rods into the base. The tip section of the rod will be cut to provide the appropriate total length for 1/2 wave.

I should add that I have considered using an MFJ 332 mag mount with an MFJ 1714 telescopic antenna, but I need something that will handle the 35 watts from my amp. I don't think the 1714 will take 35 watts. Besides, I though it would be more fun to create this myself.  Smiley

Any thoughts?

Thanks in advance for your consideration and ideas.

KD0KVV
« Last Edit: October 17, 2010, 01:02:49 PM by Teak » Logged
WB6BYU
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Posts: 13288




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« Reply #1 on: October 17, 2010, 01:37:36 PM »

Any sort of conductor will work as the radiator.  What size are the cleaning rods and do they have threaded
ends that connect them together?

You need some sort of matching circuit for an end-fed half wave, whether it is a transmission line stub (like
a J-pole) or a parallel-tuned or "L" network circuit.  I've had good results using the bases from CB mobile
antennas for this (since some of them use 36" radiators that are a half wave on 2m already.)  In that case
I disassemble the base and remove the existing coil, replacing it with about 4 or 5 turns of wire, tapped
about 1/2 to 3/4 turn from the bottom.  A variable capacitor across the coil tunes it to resonance, and
the position of the tap on the coil sets the 50 ohm point.  The mounts typically have some sort of
threaded rod sticking out the top that the antenna whip screws into, so you'd just need a matching
thread on the whip.  I built one base using a screw through a PVC pipe cap that fit on a short length
of pipe that slipped into the top of my packframe - made a great antenna for hiking, though it did
tend to knock the dew off the overhanging branches, making for wet morning hikes.  (Half wave
antennas do want some sort of ground or counterpoise - the packframe served in this case.)

One approach is to get a threaded metal standoff (preferably nickel-plated brass) with the desired
thread and solder the antenna element into one end (making sure the solder doesn't plug up the
other end.)

The first step, however, is to decide what sort of antenna will best suit your operating needs and
what supports you will have available.  If you will be around trees, one of the roll-up J-poles are
a quick and simple way to get an antenna up in the air.  For fixed operation, the mast height makes
more difference than the antenna design:  you may be be better off focusing on some sort of
portable support and using a simple quarter wave ground plane built on a coax connector - that will
work as well as any other half wave antenna (J-pole or end-fed half wave.)

Most of the discussion regarding half wave antennas requiring minimal ground planes is for HF, where
ground-mounted verticals can require a significant radial system for good efficiency.  At VHF most
hams aren't going to mount their antennas on the ground, and quarter wave radials are much shorter
(19" or so for 2m) so it really isn't an issue.  Perhaps the only time the ground would be a problem
at VHF is if you are using a mag mount with a thick insulator, non-metalic car body, etc.

So start by describing what sort of operation you are planning, then we can choose a suitable
antenna design and figure out how to build it with cleaning rods if that is the way you want to
do it.


I regularly travel overseas with a 3-element yagi for 2m in my carry-on luggage, so portability need not
be a problem.
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W0TLP
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Posts: 83




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« Reply #2 on: October 17, 2010, 03:44:37 PM »

Thank you for the feedback.

I would like to have a portable antenna to mount on a lightstand tripod that collapses very small (25") and raises to about 7 feet. This would be the mast for whatever antenna I use, whether a vertical, roll-up j-pole or eventually a yagi. It can support 3.5 lbs, so everything needs to be light weight.

The idea is to have a compact package that includes the tripod mast and maybe a couple antenna options. This kit can be easily stashed in my truck and thrown in luggage or a backpack for operation almost anywhere, even when trees are an option.

I started with a simple MFJ 1/4 wave mini-mag mount antenna (sometimes called the Hersey's Kiss mount). To make a ground plane, I cut a 19" X 19" metal screen and covered the edges with aluminum tape. I placed the antenna on top and put a small piece of steel underneath to connect with the magnet. I put this on top of a wood fence post. I got a signal out but reports were that I had considerable white noise at repeaters 35 miles out from the top of a high bluff. The noise may have been more a matter of distance than an inefficient antenna. I used the screen because it will roll up into a PVC tube. This set up would be easier to deal with if I did not have to do a ground plane.

I will use this primarily with an a VHF HT boosted by a 35-watt amplifier (it's the Mirage B-34), which will be powered by a sealed battery. I may have a solar panel for it eventually. The radio gear will be in a Pelican or similar case.

The concept of the rods came to mind as a solution for a take-down antenna. They are threaded, although I don't know the tread size right now.

I'm willing to consider buying a a commercial antenna but would enjoy home-brew more.

I hope this helps.

Thanks

KD0KVV
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WB6BYU
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Posts: 13288




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« Reply #3 on: October 17, 2010, 05:15:45 PM »

No need for the screen - four radials of #14 wire are quite adequate for an elevated mount, are lighter and
cheaper, and can be bent to fit in the truck as needed.

If you have a reasonably clear line of sight to the repeater it doesn't take much of an antenna:  I'm using
an omni with 3dB gain over a dipole and hit repeaters 100 miles away.  On 2 watts or less.  Of course,
range is more limited when there are intervening hills.

My usual recommendations for those planning to provide portable 2m communications are:

(1) portable mast 12' to 20' feet tall that breaks down to a convenient length for you to carry.  Some
folks use telescoping painter's poles or pool cleaning poles (from Lowe's?).  I've got telescoping
squeegee pole that is nearly 12', and a bundle of aluminum tent poles that I found at Goodwill that
I can combine in various ways to get to 15'.  (I've also got a bunch of the 4' military mast sections -
they are great for Field Day and portable antennas, but a bit heavier and bulkier than some of the
other options.)

(2) ground plane or equivalent 1/2 wave antenna (dipole, J-pole, etc.)  Yes, you can get omni antennas
with more gain than this, but you still have to get them up in the air to take advantage of it.  For example
here is a simple ground plane antenna you can build:  http://www.hamuniverse.com/2metergp.html
(I use different dimensions and connect the radial wires to the coax connector differently, but the
principle is the same.  With brazing rod (stiffer) for the vertical part and #14 copper house wire for the
radials, the whole thing takes virtually no space to store if I bend the radials down flat.)  Some folks
prefer J-poles, either the roll-up type, copper pipe, or whatever.  (You could use screw-on elements
to allow the J-pole to collapse into a 20" bag for transport, or arrange for the radiator and radials
of a ground plane antenna to screw on.)

(3) sufficient coax - you can use RG-58 up to 25' or so, but RG-8X is better, and RG-213 is the best
choice for longer distances.  (I would normally carry about 25' of coax for my portable antenna, with
a barrel connector and 50' of RG-213 (or more) in case I have to place the antenna further from the
radio.)

(4) for difficult paths, some sort of directional gain antenna.  A reasonable 3-element yagi will have about
6dB gain over a dipole, equivalent to 4 times the power.  A well-designed 2-element quad is 1dB less. 
A boom length less than 5' will give you a couple more dB.  I use aluminum ground wire (from Radio Shack)
stuck through holes in a 3/4" PVC boom and the antennas are very light.  For transport I pull out the
elements and slip them inside the boom.  Depending on the length of your threaded cleaning rods you may
be able to put a threaded rod through the boom (with a couple nuts to hold it in place) and screw the
elements onto each end of it.  I'm experimenting with some fibreglass rod with similar threaded ends and
wire elements running along it.

Many of my 2m yagis are made using measuring tape for the elements, but then I have a particular
application:  I use them for radio direction-finding while running through the woods.  The elements bend
when they hit a branch, then snap back into place.  A 3-element version is less than a pound using
1/2" thinwall PVC and fittings.  I have another 3-element 2m antenna using copper wire stuck through
a wood boom and it is 8 ounces - the elements fold down against the boom by simply bending the
wires, then straightening them when I use it.

But the limit on your support won't be weight as much as it will be wind loading:  you can make a very
light 6-element using aluminum wire elements, but the force of the wind blowing against it will cause
more problems with the tripod than the weight itself.

As a practical note, I find some way for all of my antennas and masts to mate with 3/4 PVC slip connectors.
It might be a piece of PVC that slips over the top of the mast, or is taped to the bottom of the antenna,
but that gives me a common mounting interface so any antenna can be mounted on any mast if needed.

Also, for masts, I find that the easiest way to put them up is from the BOTTOM.  That is, I put the
antenna on the top section, raise it up in the air, and slip the next mast section on underneath.  With
a telescoping mast I push up the sections one at a time starting with the TOP, while holding the mast
and antenna vertical.  This is much easier than trying to assemble the antenna on a complete mast
and tilting it up into place.  (I was going to put the HF triband yagi up by myself this way for Field
Day, but someone insisted on helping.  However the two of us didn't have any problems, or even
have to work hard to get the antenna up to 24'.)


So my suggestion would be to start with a ground plane and see how it works over the paths that
you want to cover.  Remember that height makes the biggest difference for signal strength, so even
you might try some temporary masts (perhaps wood or PVC pipe) to see if that works any better
than what you have now.  The next step might be to try a yagi:  here is a simple construction method
that is easy and inexpensive to build and works well:  http://wa5vjb.com/yagi-pdf/cheapyagi.pdf
(we can adjust the element lengths a bit if you are going to be operating near the top end of the band.)
Once you find what type of antenna meets your needs, we can look at how to build a more durable
version using the materials you have handy.
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KG4YMC
Member

Posts: 297




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« Reply #4 on: October 18, 2010, 10:18:20 PM »

ok, I have to say it , if you use a muzzle loader ramrod for antenna . Load the muzzleloader , attach coax to ramrod , fire muzzleloader  skyward. You give new meaning to " launching a signal. Ok its late and I'm going to bed, had to get that corney joke off  chest feel better now . Seriously should work fine  tho . good luck kg4ymc
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AD6KA
Member

Posts: 2237




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« Reply #5 on: October 21, 2010, 05:11:25 PM »

If you've got a good back, a great portable
(but a bit heavy) mast base mount is one
of those concrete "Patio Umbrella Bases".
They are about 24" in daimter and have an
8" long 1 1/2" or 2" inner diameter thick walled
metal pipe, and one or two wing nuts.
And they're cheap, too.

I use them with telescoping fiberglass
masts, and sometimes even thin walled metal masts
when out operating portable (fun!). They'll
hold up a 10-15' mast without guys easily,
but I am usually in a windy area (top of mountain)
so I have to guy it...and go to 20' or more, depending
on your antenna type. If it gets REALLY windy,
you can always pile boulders or cinderblocks
on the base too.
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WM9V
Member

Posts: 106




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« Reply #6 on: October 30, 2010, 06:10:25 AM »

I'd like to build a few highly portable antennas, starting with 2 meter, the only band I am currently operating. I think I can build a 1/2 wave vertical antenna with sections of firearm cleaning rods, in either brass or aluminum. I want 1/2 wave since it does not require a ground plane.

In an  Obamanation....

The Chicago city council banned the sale and purchase of any firearms or ammunition
and associated accesories including cleaning kits.

By decree all amateur radios which are painted black would be considered assault radios.

All cleaning rod antennas would be required to have a warning label stating their dangers in use around power lines.

Posession of cleaning rod antennas would be a class 3 felony only in the state of Illinois.

Posession of cleaning rod antennas shorter than 16 inches would be a violation of BATF rules which also apply to sawed off long guns.

When two meter FM radios are banned only criminals will have 2 meter fm radios.
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N1DVJ
Member

Posts: 491




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« Reply #7 on: November 01, 2010, 10:20:31 AM »

Well, also consider arrows.  They have threaded inserts at both ends.

And also telescoping whips.  A lot of them are available with threaded inserts in the bases.

Finally, consider tape measures.  When it comes to a collapsible antenna, building one out of tape measure tape is hard to beat.

By the way, is anyone else seeing a lot of issues with eHam lately?  It seems to 'miss' capital letters.  And it still has a problem when you do more than a screen in the window.
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W0FM
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Posts: 2055




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« Reply #8 on: November 04, 2010, 01:37:13 PM »

Some interesting suggestions here.  Whatever you decide to go with, I applaud your enthusiasm for wanting to build it yourself.  Stealth and portable antennas have been my "hobby within a hobby" for many years.  Ain't it great?

Let the creative juices flow!

73,

Terry, WØFM
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KE3WD
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Posts: 5689




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« Reply #9 on: November 05, 2010, 06:22:05 PM »

The common and readily available aluminum cleaning rods break very easily when encountering stresses from the side...

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