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: 12-Meter Question  (Read 2540 times)
K3CXG
Member

Posts: 27




Ignore
« on: November 03, 2010, 06:54:06 AM »

I recently picked up an IC-706 MK II.  I have an old unmodified Rat Shack mobile CB antenna that I use for 10 and 6.  It's base loaded, with a whip that's about three feet long.  My question is, can I add a few inches of wire to the top to use it as a quick-and-dirty 12 meter antenna, and if so, how many inches?  I don't currently own or have access to an SWR meter or antenna analyzer, so if anyone has a reasonable guess, I'd love to see it here.  I'll be getting an actual 12-meter whip at some point, but I'd like to get on now, if I can.

Thanks

73,
Mike K3CXG
Logged
K0BG
Member

Posts: 9862


WWW

Ignore
« Reply #1 on: November 03, 2010, 07:04:16 AM »

To answer the question you'd have to know a bit more than you do. Like the reactance of the inductor. You could calculate it, and perhaps come close. But in the end, it is still going to be a cut and try.
Logged

W5DXP
Member

Posts: 3552


WWW

Ignore
« Reply #2 on: November 03, 2010, 08:18:30 AM »

... can I add a few inches of wire to the top to use it as a quick-and-dirty 12 meter antenna, and if so, how many inches?

A quick and dirty simulation with EZNEC says that adding ~7 inches should shift the resonant frequency from 27 MHz to 25 MHz assuming the base-loading coil is a constant inductance.
--
73, Cecil, w5dxp.com
« Last Edit: November 04, 2010, 11:04:42 AM by Cecil A. Moore » Logged

73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
K3CXG
Member

Posts: 27




Ignore
« Reply #3 on: November 03, 2010, 11:29:18 AM »

Alan and Cecil, thank you very much for your input.  I'll try seven inches; if that's not it, I'll try slightly longer and/or shorter to see what may develop.

73,

Mike K3CXG
Logged
W5DXP
Member

Posts: 3552


WWW

Ignore
« Reply #4 on: November 04, 2010, 04:31:28 AM »

Alan and Cecil, thank you very much for your input.  I'll try seven inches; if that's not it, I'll try slightly longer and/or shorter to see what may develop.

The seven inch estimate is based on the base-loaded three foot whip being resonant on 27 MHz.
--
73, Cecil, w5dxp.com
Logged

73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
K8KAS
Member

Posts: 569




Ignore
« Reply #5 on: November 09, 2010, 09:06:32 AM »

I have never seen a IC706 without a SWR bridge , its under M3--"meter"  and just punch up SWR and you will see it displayed. It should be simple to add or whatever to your old CB antenna. You can use a small hose clamp to add the needed wire, I would think 3 to 5 inches would do it.

Denny K8KAS 73
Logged
KD4LLA
Member

Posts: 454




Ignore
« Reply #6 on: November 09, 2010, 03:40:42 PM »

Call me stupid, but I would never trust the SWR meter in my IC-706 trying out an adjusted old CB antenna.  I am not saying I wouldn't use the antenna, I would just find a meter or analyzer first.  After the radio, the next most important thing is the antenna.
Logged
W5WSS
Member

Posts: 1683




Ignore
« Reply #7 on: November 12, 2010, 12:25:05 PM »

One can add a small hub of spokes and attach with a SS hose clamp. The empirical method is satisfactory since pre modeling is not perfect yet. I have used several different methods of adding length to a mobile antenna to serve a temporary need. I used an electrical barrel splice crimped and soldered the the copper wire spokes sloped downward, and stripped the insulation off then SS hose clamped it to the tip of the mobile whip it required a little tweaking but alas tuned nicely. I suggest the crimp and soldering after the final adjustments are made have fun.
Logged
WB6BYU
Member

Posts: 13127




Ignore
« Reply #8 on: November 12, 2010, 03:35:06 PM »

I've also added a temporary horizontal extension wire (single spoke) with an alligator clip.  In fact for one
antenna the alligator clip alone was all I needed to get it to tune.  At least it makes it easy to get started.
Logged
KC9QPF
Member

Posts: 1




Ignore
« Reply #9 on: November 30, 2010, 02:25:28 PM »

K3CXG: If you have an unmodified CB antenna, how are you using it on 6M and 10M? How do you know what your SWR is on those bands if you don't have an SWR meter? I'd bet that it's far out of an acceptable range.
Logged
WX7G
Member

Posts: 5962




Ignore
« Reply #10 on: November 30, 2010, 03:08:41 PM »

A 12 meter Hamstick ($30.95 at HRO) is a good and inexpensive 12 meter mobile antenna.
Logged
K3CXG
Member

Posts: 27




Ignore
« Reply #11 on: December 02, 2010, 08:43:37 AM »

KC9QPF:  You're right.  I misspoke - I use the CB antenna on 10; however, I use the 5/8-wave 2M antenna on 6, as it approximates a 1/4 wave on 6. My bad.  I typically have both antennas on the car, hence the momentary confusion. 
 
WX7G:  I am indeed planning to get a hamstick.  Just wanted something to tide me over until I get there.

Thanks again to all who have offered their help!

73, Mike K3CXG
Logged
NK5G
Member

Posts: 102




Ignore
« Reply #12 on: December 03, 2010, 12:35:53 PM »

I use the Hustler coils with the MO-4 mount. Works FB.
Logged
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!