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

donate to eham
   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Kenwood 281a restarts when keyed  (Read 448 times)
KJ4RWH
Member

Posts: 246


WWW

Ignore
« on: July 10, 2019, 06:06:54 AM »

I have an on & off problem that has returned and would like your input. I installed a TM-281a in my Ford Van. I ran a 8awg power drop from the battery post to a barrier strip behind the driver's seat and then ran 12awg up and over to the radio. Grounds are made through the sheet metal with self tapping screw and star washers. The radio is attached to a Tram base loaded antenna which shows a beautiful match thru-out the 2 meter band (MFJ-259b). It worked like this for over 2 years. I have High power selected for most all the memorized channels.
Recently when I key the radio it resets the power as if the 12v was lost for an instant. Low power does not cause this problem. I've been told that it could be RF coming in the power leads so I added 2 snap on chokes with the power leads looped through twice. This worked for a couple of minutes and the problem returned 100% of the time
I once had the same model of radio inside as a base unit and had to add B+ chokes for the same thing. What do you think?
Logged
K0UA
Member

Posts: 4800




Ignore
« Reply #1 on: July 10, 2019, 06:41:38 AM »

My first thought is you have a high resistance joint in either the power lead or the ground.  For starters I never rely on sheet metal for a ground lead. I always rely on the same size black wire as the red wire. What is likely happening is since you have a resistance in the power lead, when you draw more current with the selection of high power the resistance in the power system causes a voltage drop that drops below the threshold that the radio will tolerate and the cpu in the radio reboots.  On low power the drop is not enough to reset the cpu. You can measure the voltage drop with an analog meter placed on the power leads.  The use of 8 gauge wire seems like overkill for the + lead for such a small radio, but the use of the car body for the negative lead seems like a problem to me.  You could also use a "dummy" power load on your power distribution system say for instance the correct sized resistor or an automobile headlamp as a load to test the drop in voltage with an equivalent load of current like the 281 would pull.
Logged

73  James K0UA
ARRL Missouri Technical Specialist
K0UA
Member

Posts: 4800




Ignore
« Reply #2 on: July 10, 2019, 06:45:17 AM »

Also you could prove or disprove your RFI getting into the power leads and causing the cpu reset by using an RF dummy load for your transceiver instead of the antenna. If you still have the problem with a dummy load for an antenna, you would know that this RFI theory is not the correct one.  A good dummy load should be the second piece of test equipment that a ham should own after purchasing their multimeter. Smiley
Logged

73  James K0UA
ARRL Missouri Technical Specialist
KJ4RWH
Member

Posts: 246


WWW

Ignore
« Reply #3 on: July 10, 2019, 07:27:53 AM »

Your explanation makes sense regarding the voltage drop. There are additional items in the van that require the 40A feed, hence the #8 wire. I will install ground cabling for the radios as soon as I can.  Cheesy
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!