Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Force 12 Flagpole  (Read 4798 times)
K9OF
Member

Posts: 29




Ignore
« on: May 11, 2010, 03:46:14 PM »

Does anyone know what actually comprises the 21' F12 flagpole antenna? Is it just a 20' metal pole with a lanyard and external tuning/loading at the bottom? Or perhaps something more clever/efficient?

K9OF
Logged
WX7G
Member

Posts: 6213




Ignore
« Reply #1 on: May 11, 2010, 03:52:17 PM »

It includes no tuner. You supply that. Either a base mounted remote tuner or a tuner at the shack.
Logged
KG4RUL
Member

Posts: 2749


WWW

Ignore
« Reply #2 on: May 11, 2010, 04:14:13 PM »

And you will need RADIALS!  As many as you can lay down.
Logged
K9OF
Member

Posts: 29




Ignore
« Reply #3 on: May 11, 2010, 05:36:15 PM »

So its really just a flagpole!
Logged
KH6DAN
Member

Posts: 2




Ignore
« Reply #4 on: May 12, 2010, 11:18:30 AM »



Yes ...  it's a flagpole and an antenna. It's made of aluminum pipe. This is a compromise antenna. It's designed for people who can get a permit for a flagpole but not for an antenna.   

It comes 16 feet, but you can order additional 4 foot sections (mine is 20 feet high). Force 12 says the 16 foot antenna resonates on 20m (not really true). I use the antenna on 20, 17,15, 12 10 and 6 with a tuner. Works pretty good on 20 and 10. Will tune 6 but don't expect too much. I use a 1:1 choke balun right at the feed point. I have 4 radials but I also have an 8 foot ground rod next to the antenna and the antenna is very quiet (one day I'm going to add more radials as 4 is not really doing much).

When conditions are good I can work to world on 20 (200 watts). I have gotten good results on 10 when the band is open.  I have experimented to use this on 40 with poor results. Force 12 offers a "40 meter" coil and 80 but I do not use them (save your money). I've tried a 4:1 unun but the antenna is just too short. I get much better results on 40M feeding a 29 foot wire, fed at the end with the unun. Don't think you can use it for bands lower than 20. Considering my situation I'm very happy with it. Maybe one day I'll try the Zero Five flagpole as everyone raves about the quality.   Just my 2 cents.

Cheers 73
KH6DAN
Logged
K9OF
Member

Posts: 29




Ignore
« Reply #5 on: May 17, 2010, 07:51:34 PM »

Tnx, OM, for a good summary of how this item works on different freqs. Very helpful.

Does it come with a insulating base mount? 20' is the max ht I will be allowed, so no prob there.

To make it work better on 40, my present thoughts include putting a matching network in a fake doghouse next to the flagpole and running a linear loading wire out of the doghouse, up and down a 6' plastic fence post and to the base feed point.

Wish me luck....

K9OF
Logged
N3OX
Member

Posts: 8847


WWW

Ignore
« Reply #6 on: May 17, 2010, 08:13:12 PM »

To make it work better on 40, my present thoughts include putting a matching network in a fake doghouse next to the flagpole and running a linear loading wire out of the doghouse, up and down a 6' plastic fence post and to the base feed point.

Don't mess with linear loading.

Linear loading is antenna marketing BS.  You need the same amount of inductive reactance no matter what, and a small coil uses less wire and will have higher Q than the amount of linear loading you'll need.  And it will fit inside your fake doghouse.

http://www.w8ji.com/loading_inductors.htm

Here are some coils inside my fake doghouse:

http://n3ox.net/projects/lowbandvert/networks_lg.jpg

 Smiley

Mine's not "stealth" so I've since switched things up and don't use that house anymore, but I needed an enclosure and a tiny homebrew house fit the bill:

http://n3ox.net/projects/lowbandvert/vertical_view_lg.jpg

If you want help calculating the right inductor I can take a stab at it for you.  I won't get it "just right" but I'll get it close enough to give you an idea.  It will be pretty easy to determine experimentally though.  Bare, solid copper wire on a low loss form or space wound, with about 1 wire diameter between turns are good "rules of thumb" that will result in a very good inductor even if you don't dial it in just right, and you don't need the "best of all inductors" because you probably won't put in the ultimate ground system.

A fat-pipe 20 foot vertical with a good loading coil  and decent radials will work very well on 40m... it's possible to make it work practically as well as a full-size vertical, aside from somewhat narrow bandwidth.  It would be easy to switch between two different coil taps on the inductor using a good relay to more easily cover CW and SSB, or if you're planning on a wide range autotuner or whatever in the doghouse, you could just use that to stretch the bandwidth.  I would take your loading coil out of line when you want to use the other bands (that would apply to linear loading wire too... )

73
Dan


Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
WX7G
Member

Posts: 6213




Ignore
« Reply #7 on: May 18, 2010, 07:28:42 AM »

To resonate a 20', 1.5" diameter flag pole at 7.15 MHz requires 5 uH of base loading inductance. Given a 20 ohm ground loss resistance it easily covers the 40 meter band with a VSWR of less than 2:1. The minimum VSWR will be 1.5:1 or higher.

A suitable inductor can be close wound on PVC pipe. Using a 1.5" OD pipe and #14 THHN (house wire) wind 13 turns. I'd wind a few extra turns and remove them one-half turn at a time to tune the antenna. Each 1/2 turn removed will raise the antenna resonant frequency by 100 kHz.
Logged
K3PRN
Member

Posts: 25




Ignore
« Reply #8 on: May 18, 2010, 08:35:55 AM »

Hi:

I used a Force 12 Flagpole antenna for four years. I ordered the extra 4' section and the antenna is comprised of 20' of 2" aluminum pipe, a fiberglass insulator section, and the ground mount pole.
The top of the unit has a cap in which thin nylon rope goes through to a tie off about 1' from the ground. I ran the flag (you must purchase flag separately) for a month. Radials are essential for vertical antennas. See the vertical antenna article in past QST. Also use an Alpha Delta lightning arrestor at the base of the antenna to a 8' ground rod (Do Not use 4' ground rods!). Ground rods can not be substituted for radials!

As to how well the flagpole works? A very difficult question to answer as there are so many variables to consider. I got my PSK31 WAS with it and have worked about 50 countries with PSK31.

Secondly, tell no one that you are a ham! As they say in the Navy "Loose Lips Sink Ships!"

Also see the S9 vertical sold for $75 in kit form. This antenna is very difficult to see and may work in your area.

Unfortunately I can not use my flagpole at my new qth, and am using a 20 meter delta loop in the attic.

If you have any further questions, just e-mail me at druokonen@hotmail.com.

73,

Don K3PRN
Logged
N3LCW
Member

Posts: 152




Ignore
« Reply #9 on: May 18, 2010, 08:53:14 PM »

Linear loading keeps getting a bad rap but I still haven't seen any convincing real world data why this method of loading an antenna is significantly inferior.  Compared to the same physical length antenna using a loading coil in its most optimum location just how many db's worth of difference is there compared to its linear loaded counterpart?   I've used both methods and have had equally satisfying results.    A linear loaded antenna can be built and tuned in a short time out of simple parts like a length of 450ohm windowed ladderline.   In less than 30 minutes I cut, mounted, and trimmed to resonance an 18ft length of ladder line for 40M yielding excellent signal reports.   

When it comes to loaded short antennas, you are mitigating losses, and the lower the loss the better.  The counerpoise/radial field is an area you can make an immediate positive impact, the more radials the better.  Even here you will run into the law of diminishing returns.

In the case of the Force 12 flag pole, extend the length as much as possible and use an autotuner with a good radial field.  8 - 16 as long as the flagpole itself as a minimum.  As time permits, double that amount.  Bottom line: put something up and get on the air and have fun.

Andrew
N3LCW





To make it work better on 40, my present thoughts include putting a matching network in a fake doghouse next to the flagpole and running a linear loading wire out of the doghouse, up and down a 6' plastic fence post and to the base feed point.

Don't mess with linear loading.

Linear loading is antenna marketing BS.  You need the same amount of inductive reactance no matter what, and a small coil uses less wire and will have higher Q than the amount of linear loading you'll need.  And it will fit inside your fake doghouse.

http://www.w8ji.com/loading_inductors.htm


Logged
N3OX
Member

Posts: 8847


WWW

Ignore
« Reply #10 on: May 19, 2010, 08:17:00 AM »

Linear loading keeps getting a bad rap but I still haven't seen any convincing real world data why this method of loading an antenna is significantly inferior.  Compared to the same physical length antenna using a loading coil in its most optimum location just how many db's worth of difference is there compared to its linear loaded counterpart? 

Not much at all for this antenna.  Ground system loss will almost certainly dominate whatever you do with a 20 foot high stealth vertical loaded on 40m.

A 20 foot high, 2 inch diameter vertical has an impedance over a "perfect" ground system of about 10-j200 ohms.  A ~10 foot shorted stub of Wireman 551 open wire line could be used as a linear loading "inductor," with an input impedance of about 1.5+j200.  That 1.5 ohms, unless the ground system really IS nearly perfect, won't matter much, and the equivalent inductor Q is Q = 200/1.5 = 133.

That's not a very good Q, but it's sufficient for the task at hand.  And probably your 18 feet, with a Q of 115 was also enough.    Loading loss only matters  a great deal when it's the significantly dominant loss, or when the loss in the component is sufficient to burn it up.      I'll grant you that.  The reason why linear loading should get a bad rap is because it is always possible to build a smaller loading device that has higher Q.  The Q might not matter in the application.  But then we can consider the other advantages.

Your point about getting on the air quickly is a good one..  But if more hams with websites would take the time to wind inductors to load antennas instead of using linear loading, it would be EQUALLY easy for homebrewers to use a nearly optimum form factor inductor.    I don't like linear loading mostly because it seems that ham homebrew projects are very unlikely to use a simple compact loading coil even though it's always better... people use linear loading and helical distributed loading because they can't find good examples quickly of what inductor to use, or how to estimate it.

You don't really have to calculate anything... all you really need is a ballpark estimate for size and number of turns and then you can add or subtract from the coil as necessary.  No harder than a linear loading stub.   It's often the case that coil loss is down in the "diminishing returns" area, but there are other advantages to using coils, like stealth.  And it is possible, for VERY short antennas with decent grounds (or ground independent antennas like short dipoles) for the linear loading to add significant loss with respect to better form factor antennas.  But when you NEED it, there aren't very many  examples because everyone likes linear loading so much.  Plus, the physically extended nature of linear loading makes people think it radiates.  In fact, KLM says that in the manual of their 40m linear loaded beam, and that is pure BS. 

Can you give me a good argument for the advantage of linear loading if  it were easy for hams to design or estimate the needed loading coil in a few moments? 

I dislike linear loading because it steers people away from posting easy ways to design and build coils, and homebrewers then have a hard time finding information on simple use of loading coils in their antennas.

73
Dan
Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!