On 8/9/2010 1:06 AM, Charles Harpole wrote:
> Roger, have u thot of applying for membership in SOC ?
SOC?
>
> Meanwhile, all I can say is hook all this stuff up with the convient
> lengths of coax and forget trying for perfection.
That was what got me to the point of the amp kicking off due to high SWR
>
> BUT, your coax switch may leak enuf RF into your antanna analyzer to
> burn it out... if it is the MFJ one I think of.
That part I feel safe about, even if I had it on the output of the amp,
but it's on the input side and it's a good mechanical coax switch with
good isolation.
>
> Also, have u thot of a resonant antenna? 73,
They are, but unfortunately only over a narrow range, particularly on
160 and 75.
Even then, I still need to tune the amp and I'd prefer to do that into a
dummy load. So, yes I can often dispense with using the AT5K except to
switch from the antenna to the dummy load and I can bypass each coax
directly to the respective antenna.
73
Roger (K8RI)
>
> Charles Harpole k4vud@hotmail.com
>
>
>
> > Date: Mon, 9 Aug 2010 00:52:43 -0400
> > From: sub1@rogerhalstead.com
> > To: Amps@contesting.com
> > Subject: [Amps] Dummy load, tuner, antennas, amps, coax length...
> >
> > Not sure which reflector this one should go to as it includes coax
> > length, antenna tuner, dummy load, and antenna.
> > I'm going to try TT and AMPS, but not cross posted. I hate cross
> posting
> > to other reflectors with a passion, particulaly when I'm not subscribed
> > to the other one with the same e-mail address.
> >
> > At-any-rate, when I tune up the amp or match the exciter to an antenna,
> > I have a coax switch between the exciter and amp on relatively short
> > sections of RG8-X. The allows me to switch between the exciter and the
> > antenna analyzer. Between the amp and tuner is a minimum length of
> > LMR400UF as well as between the AUX connector and DL5K. So the thought
> > is I can tune the antenna with the Palstar AT5K, then switch and tune
> > the amp into the DL5K dummy load by going to the aux position which
> is a
> > straight through to the dummy load. Of course there are lead lengths
> > inside the AT5K and it's not a small tuner. Tuner to DL is only about
> > 8". It's about a foot from the amp to the tuner, and from the exciter
> > to amp (through that switch) is about 2'. The idea is to go on the air
> > without ever tuning on the air. This has worked very well on the lower
> > bands up through about 20, but I ran into two problems. The first is
> the
> > R and X vary from 50 to about 30 ohms and the X goes from 0 to over 60
> > ohms. It appears this is a function of the total distance between the
> > exciter and the dummy load through the antenna tuner including all coax
> > which above calculates out to about a minimum of 44" plus the distance
> > inside the tuner. It *appears* I can ignore the distance inside the
> DL5K
> > as it's coax that is compensated and does not appear to enter into the
> > equation with the analyzer hooked directly to the input. Hooking the
> > antenna analyzer to the dummy load confirms this with a virtually flat
> > SWR of 1.1:1 from 1.8 through 30 MHz with R remaining 47 ohms across
> the
> > range. Not quite perfect as I was aiming for 1.0:1, but it'll do. With
> > the normal equipment configuration and leads as short as possible, the
> > best I can get at 30 MHz is a tad over 3:1. I don't normally use the
> > amp on 10, but still, I'd like the option without having to tune up on
> > the air. I can match the coax lengths so the distance from the analyzer
> > is the same as the exciter.
> >
> > I did have one resistor in the DL5K apparently change value a bit which
> > was attributed to overheating, but as the most I can put into the DL5K
> > is 2KW when pushing for tilt and then a slight back off of the drive,
> > that puts me very close to the continuous ratings of the DL5K which BTW
> > is a fan cooled, dry load.
> > So as I try to keep the key down time limited, it's close to the
> > continuous ratings with the max I can get out being 2KW or a bit less
> > than a single 8877, I doubt it was overheated. Cooling is via a pair of
> > fans that don't have quite enough power to move the DL5K off the desk
> > when in high gear<:-)) They move a LOT of air!
> >
> > So, I'm trying to figure out how to get the DL5K to represent R=52 and
> > X=0 across the HF bands and even 6 meters without having to hunt for
> > specific coax lengths for everything from 20 on up through six.
> >
> > Any thoughts and suggestions? I could tune up on the air like most do,
> > but I'd prefer to avoid that and can at present.
> >
> > 73
> >
> > Roger (K8RI)
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
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