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: DK3 Screwdriver Antenna HELP!  (Read 652 times)
KU4GW
Member

Posts: 8


WWW

Ignore
« on: August 10, 2001, 06:33:35 PM »

Hi fellow amateurs,
                  I have a friend running a DK3 Screwdriver mobile on his Volvo tractor-trailer. He says he is having problems with the SWR fluctuating up & down. We confirmed he has a good ground with a continuity check and he replaced his coax with new coax, but still has this problem on all HF bands. Was hoping someone out there may have experienced the same problem before and have a possible cure. Any suggestions would be much appreciated. The antenna is a new one just purchased 3 weeks ago from NU4W David.
                                    73,
                                   Cliff KU4GW
                                   ku4gw@arrl.net
Logged
N3PJ
Member

Posts: 2




Ignore
« Reply #1 on: August 10, 2001, 07:52:21 PM »

Hi Cliff, Please give detail on where antenna is mounted ,near muffler shroud ,near trailer,etc . I will help me or others to help you out.
Logged
AC5E
Member

Posts: 3585




Ignore
« Reply #2 on: August 10, 2001, 08:08:29 PM »

  Hi Cliff: I hate to say it - but an ohmmeter is not suitable for checking for a suitable RF ground. Particularly on a Freightshaker, AKA White/Volvo.

  I think the first thing I would try would be the shortest battery cable with an eye on each end that will fit between the antenna and a CLEAN spot on the frame. USE the biggest bolts that will fit the holes, and BIG fender washers between the frame and the cable.  And then I would make sure the body, muffler heat shield, and anything else I could find, is solidly bolted to something that is solidly bolted to the frame.

   I hope this helps, because this can be a first class pain in the drivers seat to cure.

   73  Pete Allen  AC5E
Logged
W7DJM
Member

Posts: 1




Ignore
« Reply #3 on: August 11, 2001, 11:17:32 PM »

The thing is, the "frame" is not necessarily rf ground, here.   You may have several parts of the truck, including one or both fenders, the hood, parts of the cab, and even the doors providing an intermittent poor ground in relation to each other.  The "tractor" as a whole is forming your ground plane, and depending on its configuration, so is the trailer.  

First, how much is the whip "whipping"   in the wind?

This itself can cause a large change.  Maybe try temporary guys from fishline or even heavy cord.  


If that checks out, maybe try bonding various parts of the truck together, and to the fram, with short lengths of cable.  If the hood and so on is glass, it still may have a radiator grill or some such that is intermittently making contact, or not.  

I formerly had a mobile in a small pickup, and it does change swr some as you drive, and also as you pass others, especially vans, pickups with boats/campers, and trucks.  

How MUCH is it changing?  You may actually have nothing to worry about.
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!