Re: Building a Bucket Ham Repeater

The following letter is in reference to the article – “Building a Bucket Ham Repeater

Mr Rourke–

I’ve given it some thought and here’s a potential way to improve the antenna — and still meet the objective of storing it in a bucket.

To make a reasonably efficient ground plane, it doesn’t have to be “solid” — several 1/4 wave radials will make the antenna “think” is positioned above a “solid” ground plane (think of the design of commercial CB ground plane antennas) .
But they need to be electrically connected to the ground (braid) side of the feedline coax.

I checked the mfgrs description of the magnetic mount antenna you’re using and it said the antenna portion was attached to the magnetic base via a 3/8 – 24 threaded connection. That info helped considerably.

So my suggestion is this —

First — remove the paint can lid from the bucket (or start over with a new bucket lid/paint can lid)

-from an electronic store, Radio Shack, CB shop, or? — purchase a CB antenna mount that has a 3/8 -24 female threaded  on one end and a SO 239 coax connector on the other.
like this one–
http://www.amazon.com/gp/product/B0002HRBSU/ref=as_li_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B0002HRBSU&linkCode=as2&tag=msoblogarticle-20&linkId=UAQRBZSGDCI2R4UN

– Drill the required size (per the mounts directions) hole in the center of the can lid, and mount this on the can lid — with the 3/8-24 end on the side of the can lid that will be facing away from the bucket.
BUT when you mount it  you need to assemble the nylon insulating washers in a different way than the directions that came with it.  You need to keep the center terminal from touching the metal lid, but you want the large metal outside barrel of the mount just above the coax connector TO TOUCH the can lid.
This will involve using only one of the two nylon insulating washers mounted face down into the hole in the can lid.  Depending on the can lid metal thickness, you may have to use a large regular metal washer on the coax side to get a tight screwdown fit.
Using an ohmmeter or similar device, check to see that the 3/8-24 end of the mount IS NOT shorted to the can lid , and that the outer shell of the coax connector side of the mount IS electrically connected to the can lid.

how to bug in

– next make up 4-6 radials using #12 or #10  solid copper household wire (bare or insulated — it doesn’t matter).  I’d suggest starting with about 24″ length wire, as they will be trimmed to fit later. These radials have to be attached to the can lid —
The “best”‘ way would be solder (not crimp) a round holed terminal lug with 3/16 hole in it to one end of each wire.  Alternatively, you could use pliers to fashion a “round hole” by wrapping it around a 3/16 bolt.  ( if this method is used, I’d suggest care in getting a nice “round hole” for a reason that will become obvious later)

-These radials will be fastened to the can lid via short 3/16 bolts.  So lay out a spaced pattern (for 4 radials — every 90 degrees, for 6 radials — every 60 degrees ) on the can lid with each hole positioned about 1″ from the edge of the can lid — and then drill the 4 or 6 holes.

-Then mount each radial to the lid — with the bolt head on the side of the lid that will touch the bucket lid top (using “pan head” bolts will help in minimizing the amount of stand-off  from the can lid to bucket lid).  Use a washer under the nut to provide maximum clamping area to the lug or wire formed loop.  Position each radial so that the wire points directly out from the center as you tighten them down.
Tighten these bolts quite tight .

-Now to trim the radials to proper length–
with the lid-radial assembly laying on a table top (or other large flat surface), manually straighten out each radial wire so that the wire is straight and  the assembly looks a center hub with wheel spokes.
Measuring out from the center of the 3/6 – 24  antenna mount, cut each radial at 19-1/4’ (for 146mhz — the center of the 2 meter band)

– Next — prepare the bucket lid by drilling a hole in its center large enough for the coax end of the can lid antenna assy to pass thru.
Then calk the can lid to the bucket top like you originally did — I’d suggest two full circular “rings” of calk to assure water wont go under the can lid and into the bucket via the clearance hole.

– now remove the whip antenna portion from the magnetic mount by unscrewing it — and then screw the antenna whip into the 3/8 – 24 fitting in the center of the can lid.

-You will need to modify the coax feed line (or I’d suggest making a new one so you don’t destroy the mag mount)  that goes from the antenna to transceiver  —  with a PL259 on one end to mate with the new antenna assy, and whatever connector  it takes on the other end to mate with the transceiver,

In use you will have a bucket with 4 or 6 “radials” sticking out from the lid  — for storage, by using soft copper wire, each radial can be bent back on itself so that nothing protrudes from the bucket edge. And remove the antenna whip by unscrewing it and put it in the bucket as before.
For the next use — reinstall the whip, and then just straighten out the radials again.
(having a good round head  or lug on the radial end will permit this bending/straightening to happen multiple times without the connection coming loose prematurely) The radials don’t have to be perfectly horizontal when deployed — some slope is acceptable.  But they shouldn’t be sloped straight down as that would change the feedline impedance (something beyond this discussion)

——————-

Please note that having an “efficient” antenna won’t be noticeable when operating at distances/ in areas where the signal strength is strong (that’s how handi-talkie transceivers can get away with using that short stubby antenna) — where it comes into play is at extended distances/signal challenging circumstances.  In those conditions — the efficient antenna can come thru, when lesser ones won’t.

I hope this was helpful.
Radio communications, I understand — having been a ham for several decades, and an ex-Army Signal Corp Captain, but there’s a lot of this “prepping stuff” I know don’t know — so I’ve been reading your blog for a couple years now, and have learned a lot from it.
Thank you for that.

B.J.

 

Thank you B.J. for the information!

 – Rourke

 

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3 Comments

  1. actually install as many ground plane wires that you can in your case after modeling probably 32evenly spaced in a complete circle.
    Remember that 2m is line of sight and pine tree needles are notorious absorbers of those wavelengths.

  2. Thanks B.J. After the j-pole recommendation, and now yours, think I might have to get this out to the field for some testing with different antenna configurations.

  3. Thanks BJ!

    I’ve used a similar approach so I could push 5/8 wave over 5/8 wave antennas up into trees. They require a ground plane to work and give 5.5 db of gain. I’ve had great results as long as I took care with the ground plane and tuned the assembly with an antenna analyzer.
    I always do the “big two” with VHF and UHF antennas:

    1. Get it right
    2. Get it up

    It works and the range increases are pretty dramatic.

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