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Author Topic: Money's Tight, but 2 meters is inviting  (Read 1509 times)
KJ4ANC
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Posts: 5




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« on: March 14, 2012, 10:09:52 PM »

Received my General in 2007, bought a used Kenwood TW4000a 2meter/70cm, then built a J-pole antenna for the 2 meter band.
Got on the Air one time in 2007 and enjoyed the experience.

Time has a way of slipping by and it has been an interesting five years of adventures.

It is now 2012 and I want to get back into 2 meters
Still have the Kenwood, but need an antenna.
I have a brand new Shakespeare 5246 Marine antenna. (Bottom loaded coil with a 36" Stainless steel whip)
Instead of buying another antenna I am planning on cutting a longer stainless steel whip. (Already have the longer whip)
36" vs 50" whip

The radio is rated at 25 watts, the antenna is rated at 50 watts.
Here is my problem.

I do not know how long to cut the new whip.
Just want to get it in the ball park before I start tuning..

Anyone wanting to make an educated guess?   
Seems easier than building one from scratch...

Don't hammer me too hard, times are tough and I have everything sitting on the table...

 Roll Eyes
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AC4RD
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Posts: 1236




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« Reply #1 on: March 15, 2012, 04:04:05 AM »

I'm sorry, I don't know anything about modifying that marine antenna.  But I did want to mention that you can *easily* put together a 2-meter groundplane, with nothing more than an antenna connector (SO-239) and some wire.  Coat hangers are often used for this.  Google "two meter ground plane" and you'll find a bunch of places with diagrams and instructions.  Cheap, and they work just fine!  :-)  GL!
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WB6BYU
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Posts: 13152




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« Reply #2 on: March 15, 2012, 05:42:19 AM »

First, there might not be a simple answer to your question, because that round thing
at the base of the antenna probably isn't just a loading coil, but a tuned circuit.
Without being able to adjust it, you might not get the antenna to work.

But I'd also take the pragmatic side:  First, try it as is and see how it works.
If there is a set screw at the base of the whip, pull it out as far as it goes and
try that.

Then grab a foot or so of bare wire (something like the diameter of the top of
your whip is a good starting point.)  I think I have some #22 tinned solid copper,
but stripping the insulation off anything handy will do the job.  Twist the wire
around the existing whip until it holds fairly tightly, leaving about 6" sticking off
the end.  Now you should be able to slide the added wire up and down to find a
good match.  I'm going to guess that you'll end up with about an extra 2" beyond
the top of the existing whip.

Then, if that seems to work, before cutting your whip take a longer piece of bare
wire and use that to replace the existing whip.  It won't stand up to mobile use,
of course, bit it will give you a chance to confirm the required length before you
cut the new whip too short.  It's much easier to trim a piece of copper wire, then
throw it away and try a new one when you trim too much.  Once you find a length
that works, cut your whip a bit longer to account for the taper on the whip.

That antenna is an end-fed half-wave.  A half wave on 2m is 38" rather than 36".
(Well, close enough.)  But the actual length depends on the matching network in
the base, and there is no guarantee that it actually will work on 2m.


Beyond that, building a ground plane antenna using copper wire on a coax connector
will work as well, and may be easier.  There are lots of other cheap and simple
antennas you can build, including beams of various sorts.

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KJ4ANC
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Posts: 5




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« Reply #3 on: March 15, 2012, 11:27:10 AM »

WB6BYU, Thank you very much for your detailed and informative response.
You have given me the answer and the education to figure this out without wasting materials, time and effort..

Simple and well thought out...  I am glad I asked and even happier with the responses I received. 

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MDNITERDER
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Posts: 146




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« Reply #4 on: March 15, 2012, 11:38:01 AM »

 I built for a buddy a 2m 5/8 wave for dirt cheep using a few UHF connectors 1"pvc #12 copper wire for the loading coil and the whip off an old cb antenna. he had a 1.1 to 1.2 match, You could also use a chassis mount so-239 a plexiglass rod and bolt it to a flat tin sheet. This design was in the old 198x's ARRL book, also my 1994 Antenna book for a 5/8 wave antenna.

Ill see if I can get the instructions for you
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WB4AUW
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Posts: 40




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« Reply #5 on: March 15, 2012, 12:00:56 PM »

Is there any activity on two meters these days? Last time I listened, you could go days without any traffic.
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KJ4ANC
Member

Posts: 5




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« Reply #6 on: March 15, 2012, 01:01:34 PM »

Traffic may be slow, but we have several 2 meter nets that are interesting to listen to. I need the experience, so I am excited about joining in. (Right now I listen in with a scanner).

The great thing is I have all the equipment to join in, I just have to hook up and join in.

So far I ahve received a lot of great responses and in the near future I will try my hand at building another J-pole. The first one worked well and was not difficult to assemble. The suggestions everyone has offered will help me learn more about wave propagation, so I will be trying my hand @ a few of them..
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MDNITERDER
Member

Posts: 146




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« Reply #7 on: March 15, 2012, 01:19:09 PM »

Also try the 5/8 wave like I said, they are easy to build. In my ride home I hear a lot on 2m excluding 147.435
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KG4NEL
Member

Posts: 373




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« Reply #8 on: March 15, 2012, 01:49:37 PM »

Is there any activity on two meters these days? Last time I listened, you could go days without any traffic.

Can you reach the PCRN machine on 147.255? That one seems pretty popular, at least from when I've listened.
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WX7G
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Posts: 5977




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« Reply #9 on: March 15, 2012, 02:36:39 PM »

Money's tight, times are hard, put a ground plane in your yard.
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MDNITERDER
Member

Posts: 146




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« Reply #10 on: March 15, 2012, 03:08:22 PM »

my 1/4 wave on gmrs with doing around 40 watts 2ft from the ground gets aprox 45miles Not to shabby
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KE6WNH
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Posts: 126




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« Reply #11 on: March 16, 2012, 07:27:21 PM »

While cleaning my garage a couple of months ago, I found an old 2m Isopole vertical I bought new about 25 years ago. It's still in good working condition but needs ground radials. I'd be willing to part with it since I put up my Diamond a couple of years ago.  Wink
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WB6BYU
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Posts: 13152




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« Reply #12 on: March 16, 2012, 08:38:37 PM »

Quote from: KE6WNH
...I found an old 2m Isopole vertical I bought new about 25 years ago. It's still in good working condition but needs ground radials...


I have two IsoPoles  and they don't need radials at all - unless you mean that the two cones
are missing.  (In which case you can use a hose clamp and some strips of aluminum instead.)
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KJ4ANC
Member

Posts: 5




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« Reply #13 on: March 17, 2012, 03:45:24 PM »

KE6WNH,

That is a very generous offer, but shipping from California and the fact that it would take at least a hour of your time to pack and ship leads me to believe you should offer this to your local club. If in fact you would like to ship this antenna to Florida (32548) e-mail me and let me know the price.. 

FerrariMX5@gmail.com
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