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: Yaesu FT-890AT Transmit cycling over 40 watts  (Read 397 times)
KG4ONJ
Member

Posts: 50




Ignore
« on: October 27, 2005, 04:08:11 PM »

Hello!  I have a Yeasu FT-890AT HF rig running a five element "stacked" dipole.  I can tune and transmit fine up to about 40 watts but when I push the power past that, the transmit "cycles" - shuts off and resumes, about every 2 seconds.  This happens whether I am using SSB or a carrier.  This happens regardless of which band I'm operating on.  

I have grounded the rig to a 4 ft. ground rod buried just outside the shack.  Then I tried grounding to a cold water pipe in the celing above the shack (shack is in the basement).  No change with either method.

I am guessing that RF is getting back in to the rig and causing it to stop transmitting.  Or there is a grounding issue.  I made several good contacts below 40 watts so I know that the system is basically working.

Any suggestions?

Thanks & 73's!

Michael
KG4ONJ
Logged
KC8VWM
Member

Posts: 3124




Ignore
« Reply #1 on: October 27, 2005, 04:16:24 PM »

Ok this might sound dumb, but you didn't mention anything about your SWR reading.

What is it?

73 Charles - KC8VWM

Logged
WB6BYU
Member

Posts: 13149




Ignore
« Reply #2 on: October 27, 2005, 04:40:10 PM »

More important than the SWR, can describe your antenna
a bit better?  Is it fed with coax cable?  How far is it
from the rig?

Although the SWR may be a useful indicator if there is a
broken shield at one of the coax connectors...
Logged
W2AEW
Member

Posts: 638


WWW

Ignore
« Reply #3 on: October 27, 2005, 04:51:10 PM »

...also be sure to take a look at the power supply voltage *at* the rig.  Maybe you've got a supply voltage drop that becomes critical at/above 40W.  Does the same problem exist when tx'ing into a dummy load?
Logged

------------------------------------------------------
My YouTube channel...
...ham radio, basic electronics tutorials, etc.
http://www.youtube.com/w2aew
N6AJR
Member

Posts: 9914




Ignore
« Reply #4 on: October 27, 2005, 05:11:57 PM »

if you have a high swr, the rig will go into autoprotect mode and cut down on power out,

also if you are using a power supply it has to be an honest 13.8 volts, if the leads are too small or too long you loose voltage and current capacity, you want 20 or better 25 amps if this a 12 volt rig , or does it plug in the wall on 110..

I am not familar with a stacked dipole.. can you explain the antenna better...
Logged
KG4ONJ
Member

Posts: 50




Ignore
« Reply #5 on: October 27, 2005, 06:59:16 PM »

Thanks for the replies..  Sorry I didn't give enough information to begin with!

The antenna is homebrew and is basically a "fan" dipole with the elements stacked on top of each other instead of fanning out from the center.  It is five dipoles all hooked to the same center and I have plastic rods serving as "spreaders" to keep the elements equal distance apart all the way down the length of the antenna.  All the wires run parallel to each other on both planes (looks like a music staff suspended in the air).  It is center-fed with RG-8X.  I made a "dirty" balun by coiling about 21 feet of the feedline around a piece of 3" PVC pipe.

As for SWR, I can get it down to about 1:1.3-1.6 on each band with the external tuner (and the internal one for that matter).  But again, only at around 40 watts or less.  My power supply is the same one that I have always run the rig with, an Astron 20 amp.  Nothing about my setup is different than at any time in the past, only the antenna.  Unfortunately I cannot test with a dummy load because I cannot find it after our move!  I fear that it's been left behind.

Hope this helps to clear things up..  Thanks again!

Michael
KG4ONJ
Logged
N6AJR
Member

Posts: 9914




Ignore
« Reply #6 on: October 27, 2005, 08:06:44 PM »

are all 5 elements cut for the same length or are they like a true fan dipole and all have different length.. it kind of sounds like rf getting back into the radio, but the coax choke should help.  is this 40 watts on ssb, or cw or am.. if it is on am it will be knocked down in the radio due to the duty cycle.. more info please..
Logged
KC8VWM
Member

Posts: 3124




Ignore
« Reply #7 on: October 27, 2005, 08:15:54 PM »

Ok the radio draws 13.7 vdc 14.9 amps at 100w output.

Does the radio exhibit the same problems when connected to a fully charged car or marine battery?

(Ruling out the power supply as the cause)

73 Charles - KC8VWM
Logged
K0BG
Member

Posts: 9867


WWW

Ignore
« Reply #8 on: October 28, 2005, 05:45:14 AM »

This is a classic example of fold back current protection in a linear power supply. Check the voltage with a known good meter while you increase the power out.

Alan, KØBG
www.k0bg.com
Logged

K7JBQ
Member

Posts: 80




Ignore
« Reply #9 on: May 07, 2006, 02:47:38 PM »

I agree; it's the power supply. Or at least, that's where the solution lies.

It happens that I have exactly the same set-up: FT-890AT and Astron 20A. A couple of weeks ago I got two reports of a "warbling" CW note - the kind you hear in the last hours of Field Day when the batteries are going soft. Hooking up a meter, I found the voltage dropping at keydown.

Astron being local, I took the supply down to Fred, the service guy. He put it on the bench, hooked it up to the scope and said it was fine. Sure enough, it was -- on the scope.

Just to be sure though, he replaced one capacitor and added another. At, I should mention, no charge, since this was only a 23 year old Astron. I took it home and...

Clean CW note.

File under "Go figure."

73,
Bill
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!