http://elecraft.85.s1.nabble.com/135ft-flat-top-with-K2-KAT2-BL2-and-450-ohm-feedline-tp394239p394241.html
The feedline is actually 65 ft long. It happened to be the perfect
the middle if needed. I'd just have to make the feedline take a less
direct path through the attic. What would you suggest as a good
sure if the 65 ft would be a problem on 80m. In one of the first tables
ohms, but I didn't do any calculations. I guess I was a bit anxious to
Stephen W. Kercel wrote:
> Zac:
>
> I'm guessing that the configuration that you propose could run you into
> all sorts of trouble on 80 M. The problem is that the 135 ft flat top
> would have low impedance, about 50 Ohms. The transmission line is
> disturbingly close to a quarter wavelength. A 450 Ohm line with an exact
> electrical quarter wavelength and a 50 Ohm load would have 4050 Ohms
> impedance at the transmitter end, and the KAT-2 would see it as an SWR
> of about 80:1. Even if your line is not an exact quarter wavelength, if
> it is within a few feet either way, the impedance that your KAT2 will
> see is very high.
>
> You need to do a bit of studying with EZNEC and a Smith Chart. You need
> to find out the feedpoint impedances that the flat top will give you on
> all the bands on which you want to operate, and then find a length of
> 450 Ohm line that presents acceptable impedances to your KAT2/BL2 setup.
> This same set of calculations would tell you whether you are better off
> with a 1:1 or 4:1 balun (or it might show you that you need one balun
> for some bands, and the other balun for other bands). You may discover
> that no single length of feedline works for all bands 80-20 M. In that
> case you need to get a very big DPDT knife switch (Military surplus
> outlets carry them) so that you can switch an alternate section in or
> out to change the length of your line for different bands.
>
> 73,
>
> Steve Kercel
> AA4AK
>
>
> At 12:18 PM 10/1/2006, Zac Brown wrote:
>> Fellow Elecrafters,
>>
>> I am putting up a 135 ft flat-top at my QTH. I'll be feeding it with
>> about 60 ft. of 450 ohm ladder line, connecting the feedline to the
>> BL2, and tuning it with the KAT2.
>>
>> I was wondering if anyone on the list has tried this arrangement and
>> could comment on whether the KAT2 will have any problems tuning this
>> setup from 80 - 20m. I'm also curious about which bands work better
>> with the balun set to 1:1 vs. 4:1 with this setup.
>>
>> Thanks,
>>
>> Zac Brown
>> KD5IEF
>> K2# 4907
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