[Elecraft] More KAT500

Thu Nov 15 15:00:17 EST 2012

I hope you have the ladder-line supported by fire-proof (ceramic)
insulators in the attic.

Letting ladder-line touch anything combustible can start a fire.

Amateur Radio Operator N5GE
ARRL Lifetime Member
QCWA Lifetime Member

On Thu, 15 Nov 2012 13:22:55 +0000, "hawley, charles j jr"
<c-hawley at illinois.edu> wrote:

>I use a 1:1 balun at 450 ohm ladder line to get thru the attic and then 4 inch open wire outside to the dipole.
>
>Chuck, KE9UW
>Lionel Trains, TCA, LCCA, LRRC
>aka Jack, BMW Motorcycles BMWMOA #224
>
>________________________________________
>From: elecraft-bounces at mailman.qth.net [elecraft-bounces at mailman.qth.net] on behalf of Brian Alsop [alsopb at nc.rr.com]
>Sent: Thursday, November 15, 2012 7:02 AM
>To: elecraft at mailman.qth.net
>Subject: Re: [Elecraft] More KAT500
>
>This seems so in many cases but it is very doublet length dependent.
>
>I ran one case in TLW with 45' of 450 ohm line that came out as 13 ohms.
>  With a 4:1 balun you'd probably be dropping this further.  High
>current and most likely not a match.
>
>The best suggestion is to model the antenna at height, get it's
>feedpoint impedances at bands of interest.  Then go into a program like
>TLW with the 450 ohm line length and see what impedance results at the
>shack end.
>
>Adjusting 450 ohm length or doublet length may be required for an
>adequate compromise on the bands of interest.
>
>Without some analysis (or a proven design) it will be a crap shoot.
>
>73 de Brian/K3KO
>
>On 11/15/2012 12:31, Jim Wiley wrote:
>> Ed  -
>>
>> According to Elecraft, the KAT500 can match 10:1 SWR at 500 watts, on
>> any band 80 to 10 meters.  It can also match 3:1 SWR at 1000 watts on
>> those same bands.   The 160 meter and 6 meter capabilities are a bit
>> more limited, but it will still match a fairly wide range of loads.  By
>> inference, 10:1 SWR at 500 watts between 3 and 30 MHz could result in
>> peak voltages in the range of 2250 volts and peak currents of 42 amperes
>> RF  (one or the other, not simultaneously). This is pretty impressive
>> for a box that size.
>>
>> Using those voltages as limits, that indicates that the KAT500 could
>> handle power levels of about 250 watts at a 14:1 SWR.  Any more could
>> result in damage.  I would suggest replacing the 300-ohm line on the
>> antenna with 450-ohm ladder line, and inserting a 4:1 balun between the
>> antenna and the KAT500.  I suspect that this will reduce the SWR
>> excursions, and may get you "inside the envelope" for what the KAT500
>> can handle.
>>
>> A commonly used antenna is a doublet (dipole) fed with open wire, a 4:1
>> balun, and a coupler.  Most installations use a length of RG-8 coaxial
>> cable (typically 10 to 20 feet, but no longer than necessary) to "get
>> through the wall" - or from the coupler to the balun immediately outside
>> the building, then the open wire line connects to the balun at that
>> point and continues to the antenna. 450-ohm ladder line is usually a
>> better choice because it is designed for transmitting use, where 300-ohm
>> line is usually "TV lead-in" and not particularly suited for use at
>> higher power.  Some transmitter rated 300 ohm line exists, and if you
>> have that type, it may work for you.  As with all open-wire type lines,
>> keep the line at least 8" to 12" from metal objects if possible, more is
>> better, and avoid abrupt right angle turns.
>>
>> - Jim,  KL7CC
>>
>>
>>
>>
>>
>> On 11/15/2012 2:41 AM, Goss, Ed wrote:
>>> Hi Jim,
>>>       Thanks for the info.  I am at work now and unable to post back to
>>> the group, but I appreciate the explanation. For the low bands, I use
>>> a 135 ft inv vee center fed with 300 ohm line, with a 1:1 balun near
>>> the shack. When my KAT500 starts to tune itself, I am seeing high
>>> SWRs, such as 14:1. After the auto tune cycle, it's 1:1.  Perhaps I
>>> should be concerned that even with 100 watts, there would be
>>> conditions that overstress KAT500 internal parts with this type of
>>> antenna, but I want to be very careful about not damaging the tuner.
>>> I'm not quite sure how a user would know these limits, or if the
>>> KAT500 protects itself in any way. Perhaps the KAT500 is meant to work
>>> with antennas that present a somewhat better match to start with, like
>>> a typical 80 meter dipole which is cut for CW but the user wants to
>>> use all the way up to 4.0 MHz...
>>> --Ed---
>>>
>>
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