[Elecraft] Blown trap?

[David Cole]

Hi Vic,

That is not surprising to me for reasons later discussed here...  When
something is rated at "1500 Watts, CW", that really means, 300 watts to
500 watts DC, or 100% duty cycle...  I wish manufactures would rate
things at 100% duty cycle.  I am pretty sure Elecraft does.

CW is taken to be about a 20% duty cycle, (for the most part), and as
such you can hammer something much harder when running CW than say when
you are running RTTY at 100% duty cycle...  That is how the 300 watt
figure came about, r=.20*1500, where r is the rating for power.  

I tend to de-rate everything 60% to 85% when I run RTTY, PSK, or any
mode that is even close to 100% duty cycle, more on the 75% side of
things.  

I would bet that 1000 watts RTTY for 10 minutes would blow another
trap...  I really dislike trap antennas for this reason, and these
reasons-- a bug gets into a trap, and you have a fire, water gets into a
trap, and you have a fire, a leaf falls on a trap, and you have a trap
fire, etc.  You get the picture...  Pretty much everything ends in "trap
fire".  

Next time try and get an antenna with no traps if possible.  I realize
you have the R8 now, and will keep it, but in the future, never forget
the lesson the MFJ antenna just taught you!  I learned my de-rating
lesson in a similar way several decades ago, running RTTY, I have NEVER
forgotten it.  If you have an antenna in a hard to get to location,
overbuild everything.

I had been considering an R8 up to now-- but the little experiment you
just performed, just convinced me to avoid that antenna.

-- 
Thanks and 73's,
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On Mon, 2014-12-15 at 19:28 +0200, Vic Rosenthal 4X6GP/K2VCO wrote:
> The good news is that I called MFJ, got a technician immediately, he 
> agreed that the 30M trap is the problem, and said he would send me a new 
> one under warranty. Elecraft-style service (so far).
> 
> The bad news is that despite the statement in the manual that it is 
> rated at "1500W CW," he told me not to exceed 800-1000 watts. Not 
> Elecraft-style design/documentation!
> 
> So if you have an R8 or similar antenna, be warned. I wasn't tuning up 
> or running RTTY -- I was calling CQ on 40M running about 1200W.
> 
> Other bands are unchanged but 30 and 40M are gone.
> 
> Thanks to everyone that responded.
> 
> On 15 Dec 2014 15:07, David Cole wrote:
> > Hi,
> >
> > No matter what happens, you will probably end up taking the antenna
> > down...  If nothing else to check to be sure it is fine...
> >
> > Grab an analyzer and connect it as close to the antenna base as
> > possible, and see if it is resonant on all bands...  Probably won't
> > anymore.  If you are lucky, it is some strange feedline thing, or a
> > connector issue, but having the antenna work on some bands, while not on
> > others reeks of blown trap.  I fear your diagnosis is in fact
> > correct...
> >
> > If you are going to "fix" it, and if it were me, I would get a trapless
> > antenna of some sort...  No traps blow.  I currently use a GAP
> > Challenger DX, (trapless), and have a band by band review of it at:
> > http://nk7z.net/review-of-the-challenger-dx-antenna-by-gap-antenna/
> >
> > The antenna takes power, and does not break, I have run 1000 Watts into
> > it on RTTY for 15 minutes with no issues.  I have had it up for at least
> > 7 years, and I think 10 or more years.  Never a problem beyond the three
> > radials coming off once...  It is a pretty good performer on 40, and 20.
> > I finally got one of the mono gaps, and it does a good job.  I do take
> > it down every few years and check things, and change out anything that
> > looks like it is going bad.
> 
>