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KX1 + Tuner + Norcal Doublet

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Burke Jones

KX1 + Tuner + Norcal Doublet

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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Steve Ellington

Re: KX1 + Tuner + Norcal Doublet

That's a bad design for 40m because the input resistance is only about 3
ohms. The designer was concerned about the radiation pattern resembling a
dipole on higher frequencies with little regard to matching.

Using a 4:1 balun would do the opposite of what you want to accomplish. 5
ohms is difficult for any tuner to match and can cause a lot of power loss
in the circuit and with higher power, burn up a torroid coil! That balun
would drop the impedance to an insane value.

Generally a multiband doublet should be 1/2 wavelength on the lowest band.
That's about 65 feet for 40m cw. Also that feedline that the author used no
doubt has a rather low impedance which further complicates things. I'de
guess it is about 100 ohms. Using 300 tv twin lead would help raise the Z
for your tuner to about 15 ohms on 40m even with the 44' flat top. Try that
first.

If all else fails, tie the feeders together and feed it like a long wire
against a counterpoise.

Steve
N4LQ
----- Original Message -----
From: "Burke Jones" <[hidden email]>
To: <[hidden email]>
Sent: Friday, June 03, 2011 2:44 PM
Subject: [Elecraft] KX1 + Tuner + Norcal Doublet

>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
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

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Dave-7

Re: KX1 + Tuner + Norcal Doublet

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

John Harper AE5X

Re: KX1 + Tuner + Norcal Doublet

In reply to this post by Steve Ellington

Steve N4LQ said:
>Using a 4:1 balun would do the opposite of what you want to accomplish. 5
>ohms is difficult for any tuner to match and can cause a lot of power loss
>in the circuit and with higher power, burn up a torroid coil! That balun
>would drop the impedance to an insane value.

Thanks Steve - you've inadvertantly answered my question/problem as well...I think:
http://www.ae5x.com/blog/2011/06/03/problem-possible-solution-question/

John AE5X

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Moe

Re: KX1 + Tuner + Norcal Doublet

Buddipole has a Triple Ratio Switched Balun that will match a 50 ohm feed line to 50, 25, or 12 ohm antenna impedance. You could use a Pomona 1296 BNC male to banana plug/binding post adapter with your existing antenna.

http://www.buddipole.com/trraswbat.html

Regardless of what their on-line store says, they DO have it in stock. Call them.
--
Moe - AB8XA
Elecraft KX1 #2484, Fists #13020, SKCC #7460,
FPQRP #2617, NAQCC #5352, QRP-ARCI #14326

On Jun 3, 2011, at 5:57 PM, John Harper wrote:

> Steve N4LQ said:
>> Using a 4:1 balun would do the opposite of what you want to accomplish. 5
>> ohms is difficult for any tuner to match and can cause a lot of power loss
>> in the circuit and with higher power, burn up a torroid coil! That balun
>> would drop the impedance to an insane value.
>
> Thanks Steve - you've inadvertantly answered my question/problem as well...I think:
> http://www.ae5x.com/blog/2011/06/03/problem-possible-solution-question/
>
> John AE5X
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html