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Author Topic: Fishing pole. Short one for 20meters band  (Read 5448 times)
IZ8FFC
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Posts: 11




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« on: February 01, 2014, 07:21:37 PM »

Hello everybody.
My intentions are to build a short vertical antenna (fishing pole) for 20 meters band. Lenght approx 3 meters. Loading coil in the middle.
Could you recommend me a website where can I calculate this?
any suggestion?

73 de IZ8FFC
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WB6BYU
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Posts: 12980




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« Reply #1 on: February 02, 2014, 11:52:35 AM »

You can try the free demo version of EZNEC:   www.eznec.com

A quick model suggests around 7uH should be a good starting point, which, with zero
losses would have an input impedance around 17 ohms.

This coil calculator will help you calculate the physical dimensions:
http://hamwaves.com/antennas/inductance.html

With a small diameter coil wound on the fishing rod itself, and depending on your
ground system, you may have enough loss to get a low SWR with no other matching.
If you can keep the loss resistance down to 11 ohms you'd have a 2 : 1 SWR, which
could be matched using a shunt coil across the feedpoint - the exact details will depend
on the Q of your coil and the details of your radial system.
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NO9E
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Posts: 381




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« Reply #2 on: February 21, 2014, 10:36:48 AM »

Why 3 meters? They are very lightweight fishing poles up to 7 meters. 5 meters with 5 meter radials will get you close to 50 ohm and higher efficiency than 3m. Shorter radials and higher pole may give even higher efficiency but require an antenna tuner. With the tuner you will have many bands covered.
Ignacy, NO9E
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KV7W
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Posts: 136




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« Reply #3 on: May 31, 2014, 06:48:14 AM »

I came up with a cool little capacitance hat for crappy poles a few years ago. Longest anodized aluminum knitting needles I could find only cost a few bucks. They are solid and after cutting the steel end off, thread well. The ring they thread into, if I remember right, is a piece I cut off an aluminum spacer for a car alternator. The vertical shaft is about 3" of aluminum arrow. Fits and sits right over the tip of the crappy poles and is light enough to not bend them over. The weight of the antenna wire holds them down.

Drill and tap the collar with 4 holes for the needles and one smaller for the #6 screw to hold the antenna wire ring connector. Thread the needles with appropriate die, (I had to go a little large, but it doesn't take much thread to grab). Thread these into the collar to hold the arrow shaft. I capped the arrow shaft with epoxy putty on one end. I use a lot of 20 gauge teflon wire for my experiments, but if you wanted to use 12 gauge, I'd probably use a longer piece of arrow shaft to act as strain relief for the pole.

Isn't the end all be all for short verts, but anything you can do add capacitance helps. 10 foot vert for 20m is pretty short.



 
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K1DA
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Posts: 460




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« Reply #4 on: June 09, 2014, 09:32:17 AM »

Why not buy a mobile antenna.  They can be painted, flat black can make one hard to see.
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W1AJO
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Posts: 107




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« Reply #5 on: July 04, 2014, 05:58:20 AM »

For Field Day this year I used a vertical 20m mobile hamstick type antenna.  I added four 16.5 foot radials and built a stand for it.  The base was up about 15 feet.  I tuned the antenna stinger to 14.200 mHz.

From Newnan GA (30 miles south of Atlanta) with 5 watts I made QSOs with western MA, Minnesota, Los Angeles, Santa Barbara CA, and Halifax NS Canada.  Use the fishing pole to get a Hamstick up into the air.
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KB1GMX
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Posts: 699




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« Reply #6 on: July 06, 2014, 05:54:12 AM »

with a 5M pole the antenna can be a end fed half wave and would be very efficient as a
vertical.  while some counterpoise is needed the required length is less the 1m.

If you load or shorten it as a 1/4 wave monopole then the requirement for a 5M radial(s)
to work against is important.

At 3M tall Jetstream, MFJ and ,many other make loaded mobile whips  at best these are
less than 50% efficient and they do require a good counterpoise to work against.

All cases spoken of will require some form of matching network.


Allison
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W1AJO
Member

Posts: 107




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« Reply #7 on: July 09, 2014, 08:52:52 AM »

........

All cases spoken of will require some form of matching network.


Allison

Yes, I used an LDG Z11 tuner with the 20m hamstick.
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