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: Can I use a ZM-2 QRP antenna tuner to tune a 1/4 wavelength loop?  (Read 4436 times)
KC9YKI
Member

Posts: 6




Ignore
« on: April 30, 2013, 05:29:54 PM »

I'm intrigued by what I've read about the MFJ Loop Antenna Tuner and wonder if I can use my Emtech ZM-2 QRP antenna tuner in a similar fashion into a quarter-wavelength loop (40 meters? 30 meters?).  Still working on my CW skills, so not on the air yet.  Is there any reason I couldn't use this tuner for such a loop?  Severely restricted on anntenna possibilities here.  Wondering if I should give this a try.

Thanks for any input. 

Jim Carpenter
Logged
K3VV
Member

Posts: 13




Ignore
« Reply #1 on: May 01, 2013, 07:01:49 PM »

Looking at the ZM-2 schematic, you have a polyvaricon capacitor (C1) in series with the loop.  Any capacitor in that location needs to have high Q and a high voltage rating  A polyvaricon has neither, unfortunately.

Look at the loop calculator here:

http://www.66pacific.com/calculators/small_tx_loop_calc.aspx

Plug in your desired length, frequency, and transmitter power.  Run the calculation and look what happens to the capacitor voltage.   Depending on band and loop size, it can be hundreds of volts even for a 1-watt transmitter.

I would say using the ZM-2 as a small loop tuner can't be recommended.

Logged
KC9YKI
Member

Posts: 6




Ignore
« Reply #2 on: May 01, 2013, 07:16:13 PM »

aha! Just as I suspected/feared.  You've probably saved me the cost of a new tuner, and for that I at least owe you a beer.  If you're ever in Milwaukee... Smiley



Logged
N3LCW
Member

Posts: 151




Ignore
« Reply #3 on: May 02, 2013, 09:11:47 AM »

Jim,

You could build a very simple and effective 1/4 wave loop with little cost:

http://g0cwt.co.uk/magloops/new_page_2.htm
 
and

http://g0cwt.co.uk/magloops/new_page_6.htm

It took me less than 2 hours to build and tune my first loop and its results were very exceptional for its size.
You can use a type 43 ferrite toroid if you don't have those ferrite tubes as Ben suggests.  I use both.

I also built an 80M version, 10ft vertical by 22ft horizontal.  It was the most effective way for me to get on 80M from a postage stamp size yard.

You won't need a vacuum variable capacitor at QRP, but something better than a polyvaricon.

73...

Andy
N3LCW



aha! Just as I suspected/feared.  You've probably saved me the cost of a new tuner, and for that I at least owe you a beer.  If you're ever in Milwaukee... Smiley




Logged
KC9YKI
Member

Posts: 6




Ignore
« Reply #4 on: May 02, 2013, 06:39:59 PM »

Thanks Andy...

Clearly, I shouldn't have thrown away the dozens of variable capacitors I accumulated as a kid 50 years ago. Smiley

This is neat stuff. 

Thanks to you both.

Jim
Logged
JAHAM2BE
Member

Posts: 277


WWW

Ignore
« Reply #5 on: May 06, 2013, 04:18:35 AM »

You can build a small loop tuner yourself fairly easily:

http://homepage.ntlworld.com/g4kki.william/army_loop_tuner.htm

Note that this kind of tuner may have problems with common mode currents:

http://www.eham.net/ehamforum/smf/index.php?topic=87076.0
Logged

AA4PB
Member

Posts: 12896




Ignore
« Reply #6 on: May 06, 2013, 10:09:32 AM »

One source of loss (due to the high currents) is the wiper contact on the capacitor rotor. MFJ uses a split stator variable so that no wiper contact is required to carry current. Current flow is from one fixed stator, through the rotor, to the other fixed stator.

The ZM2 is definately not a reasonable candidate for a small loop tuner.

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!