Re: KX1 + Tuner + Norcal Doublet

Posted by Dave-7 on Jun 03, 2011; 9:16pm
URL: http://elecraft.85.s1.nabble.com/KX1-Tuner-Norcal-Doublet-tp6436432p6436976.html


For a center fed wire 44' long (the dimensions of the Norcal Doublet)
EZNEC shows an antenna feedpoint Z of 23-j570 ohms.

If fed with 28' of 300 ohm line the feed line losses are approx. 2.4
dB. Somewhat high but may be acceptable. The losses in the proposed
stranded computer cable (and speaker wire) are probably higher, but
are unknown.

Again assuming 28' of 300 ohm line, the Z at the line input would be
approx. 11+j155 ohms. It would not be a good idea to run this through
a 4:1 balun and come out with ~3+j39. That would make matching more
difficult and losses worse instead of better.

Generally a multiband dipole should be a minimum of about 3/8 wl on
the lowest band of interest. If one uses 300 ohm or 450 line to feed
it the losses are usually acceptable. If using a resonant antenna as a
multiband wire, on the higher bands the Z at the center of the wire
will become quite high and this is not a particularly good idea.
Better to make the wire non-resonant on all bands and avoid the high
impedances.

The problem here is likely the limited matching range of the KXAT1
tuner. Have to get a wider range tuner . . .

BTW, when you post an antenna question it is a really good idea to
give the dimensions of the wire. Not everyone knows what a Norcal
Doublet is.


73 de dave
ab9ca/4

>
>> I constructed a Norcal Doublet using some speaker wire.  It seems to
>> tune up fine on 20 meters using the internal KX1 tuner - but on 40
>> meters I could not get the SWR under 4.
>>
>> Would a 4:1 balun help with this?
>>
>> Any links on how to build a simple balun using an aircore and not a
>> torroid?
>>
>> Thanks a bunch!
>>
>> Burke Jones
>> N0HYD
>> Olathe, KS
>> http://www.n0hyd.com

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