[Elecraft] KX2

Thu Jul 14 20:38:56 EDT 2016

I totally agree. End-fed half waves are tweaky. One terminal is the antenna wire and the other terminal must be something. The RF will find something to drive as the other “pole” of the antenna. There are no monopole antennas.

It could be the outside of the coax, it could be a “counterpoise” (not fond of that term), or it could be your hand on the key. Ouch.

I was using “ground reference” as the negative side of what you measure RF voltage against. Whatever that is.

There might be an antenna topic with more voodoo than end-fed antennas, but I don’t know what it is. The EC-130J flies a long wire out behind it and broadcasts on medium wave. I guess the other pole of that antenna is the airplane itself. http://www.af.mil/AboutUs/FactSheets/Display/tabid/224/Article/104535/ec-130j-commando-solo.aspx <http://www.af.mil/AboutUs/FactSheets/Display/tabid/224/Article/104535/ec-130j-commando-solo.aspx>

wunder
K6WRU
Walter Underwood
CM87wj
http://observer.wunderwood.org/ (my blog)

> On Jul 14, 2016, at 5:14 PM, David Gilbert <xdavid at cis-broadband.com> wrote:
> 
> OK, I can buy that ... except that the term "ground reference" as used by you and Don doesn't really apply.  The counterpoise is simply providing some minimal balance to the high impedance at the end of the EFHW, and it doesn't need to have anything to do with "ground".
> 
> If the counterpoise is located at the rig (as I inadvertently thought Don was suggesting) instead of at the end of the antenna then indeed the feedline would radiate, and if located at the rig the impedance transformation effect of the transmission line (depending upon it's length) could easily put a low impedance there ... rendering a short counterpoise essentially ineffective.
> 
> For the record, I know how electricity works.
> 
> Dave   AB7E
> 
> 
> On 7/14/2016 3:42 PM, Walter Underwood wrote:
>> The transmitter needs to drive into two terminals. That is how electricity works. If you do not provide a ground or a capacitive RF ground (counterpoise), the ground is the chassis of the transmitter. In a big grounded shack, that might be a stable reference. Otherwise, you need to provide a ground reference. Without that, the feed impedance changes every time you touch the rig.
>> 
>> The ground reference does not need to handle much RF current, because of the high impedance feed (around 10 kOhms). Even a little capacitance to ground will stabilize the feedpoint impedance.
>> 
>> A minimum length of coax feedline would reduce the SWR due to losses, but it would also provide an RF ground reference with currents on the outside of the shield. Currents on the inside of the shield are balanced, of course.
>> 
>> Walter Underwood
>> wunder at wunderwood.org
>> http://observer.wunderwood.org/  (my blog)
>> 
>> 
>>> On Jul 14, 2016, at 2:40 PM, David Gilbert <xdavid at cis-broadband.com> wrote:
>>> 
>>> 
>>> I'm confused why an EFHW should need a counterpoise.  If it needs a counterpoise it isn't actually acting like an EFHW.  If it needs a counterpoise that means there isn't enough choking impedance at the feedpoint, and it means that the feedline is radiating with the counterpoise acting as ... well, a counterpoise.
>>> 
>>> Manufacturers state a minimum length feedline simply to have the feedline losses help swamp out SWR variations along the line, and of course to marginally lower the SWR.
>>> 
>>> Dave
>>> AB7E
>>> 
>>> 
>>> On 7/14/2016 1:03 PM, Don Wilhelm wrote:
>>>> Andy,
>>>> 
>>>> What happens if you connect to a dummy load?  Does the KX2 tune it properly?
>>>> If so, then you know the KX2 is operating into a 50 ohm load OK.
>>>> 
>>>> Do you have an antenna analyzer?  If so, then connect it to the antenna feedline and look at the impedance - both real and reactive - as well as the SWR.
>>>> That will tell you whether the antenna is troublesome.
>>>> 
>>>> You specifically said an EFHW - that should be a resonant antenna.  If instead you have a random length wire (not a halfwave), and what is the matching device?
>>>> Many EFHW antennas need a counterpoise to work - that is why many manufacturers state a *minimum* length feedline.
>>>> 
>>>> If the problem is *not* the antenna, contact Elecraft support.
>>>> 
>>>> 73,
>>>> Don W3FPR
>>>> 
>>>> On 7/14/2016 2:40 PM, Andy Clift wrote:
>>>>> Just received my KX2, but unable to get it to tune an EFHW wire. I’ve tried a home made one and then tried a SOTABEAMS MultiBander that I’ve used successfully with an FT-857. I’ve checked the continuity in the wire and also the continuity in the KX2 between the BNC connector and where the wire connects inside the KX2 (as I removed this to fit the end panels). Battery is at over 11v. Any ideas please?
>>>>> 
>>>>> ______________________________________________________________
>>>>> Elecraft mailing list
>>>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>>>> Help: http://mailman.qth.net/mmfaq.htm
>>>>> Post: mailto:Elecraft at mailman.qth.net
>>>>> 
>>>>> This list hosted by: http://www.qsl.net
>>>>> Please help support this email list: http://www.qsl.net/donate.html
>>>>> Message delivered to donwilh at embarqmail.com
>>>> ______________________________________________________________
>>>> Elecraft mailing list
>>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>>> Help: http://mailman.qth.net/mmfaq.htm
>>>> Post: mailto:Elecraft at mailman.qth.net
>>>> 
>>>> This list hosted by: http://www.qsl.net
>>>> Please help support this email list: http://www.qsl.net/donate.html
>>>> Message delivered to xdavid at cis-broadband.com
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:Elecraft at mailman.qth.net
>>> 
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>> Message delivered to wunder at wunderwood.org
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Elecraft at mailman.qth.net
>> 
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to xdavid at cis-broadband.com
> 
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to wunder at wunderwood.org