Saturday, April 12, 2014

And here I thought it was me!

To say it is a beautiful day in New Jersey today is in understatement.  The sun is shining, and the temperatures are in the upper 60s (20C).  The breeze (if there is any) is so gentle that you don't even notice it.  So I decided that after grocery shopping, but before other chores, that I would sneak off to the park and try out the EARCHI antenna.  I built the 9:1 UNUN late last Autumn and didn't get a chance to try it out.

The antenna line launcher worked perfectly, once again.  First shot, I cleared a 50 foot tree with ease. The end fed EARCHI was up in record time.  I used a 33 foot piece of wire attached to the UNUN, and ran a 20 foot piece of coax from the UNUN to the KX3.  My results with tuning it via the KX3's autotuner were so-so.  The KX3 loved the antenna on 30, 20, 18 and 12 Meters. On 40, 15 and 10 Meters, I got a decent match, but the KX3's tuner clacked around noticeably longer finding a match on these bands.  I think I am going to have to experiment with different radiator lengths to see what ends up working best as an "all around" antenna length.

But even with decent matches, the bands seemed dead!  I did end up working W1AW/KP4 on 20 Meters, but other than them, I did not hear much.  I hear much more activity during the workweek from the Jeep than I heard today. Naturally, the first thing the Ham suspects is that it's the antenna - especially when it's a new one. Actually, my first reaction was that I screwed up something when I built the UNUN. I came home after only a short time out, a bit dejected.

Then when I got home, I got on the computer to order some wire and rope from The Wireman.  For the heck of it, I also decided to check out Facebook.  A lot of my Ham friends had posted about how lousy the band conditions are today. In fact, one commented that he went outside to make sure his antennas were still in the air!

Courtesy of Facebook

So it ends up that today was not the day to base a critical performance review on,  I will have to wait for another weekend with decent weather and better band conditions for another test. In the meantime, I will also browse the Internet to see if I can garner more information on optimal radiator lengths for use with a 9:1 UNUN.

72 de Larry W2LJ
QRP - When you care to send the very least!

3 comments:

David said...

Larry, this is guesswork and not based on
experiment. If the UnUn is doing a good job and if
the antenna impedance is high (say several
thousand ohms) then after going through the
UnUn it should be several hundred ohms. At that
point I would try using as short a length of coax as
possibly (ideally none at all) and letting the KX3's
internal tuner handle it. The KX3 tuner cannot
handle a really high impedance load, but the 9:1
UnUn should take care of that. So you'd want an
integral number of half waves in the anterna, easy
to do for 40, 20, 15, and 10 all at once but that
leaves 30, 17, and 12 out.

The reason suppliers of UnUns recommend a
longer coax lead is to provide a counterpoise.
There are other ways to do that, and the higher the
antenna impedance, the less stressed the
counterpoise becomes. Another argument for half
wave or multiple thereof, in the antenna.

Several hundred ohms into 50 ohm coax is
however not a recipe for low loss which is why I
say keep the coax short, or non-existent.

One other thing you could try would be to have
separte winding not tied together on the UnUn.
Wind things quadrailar instead of trifilar, hook
three sets of turns in series for the antenna, use
the other set of turns for the low impedance side,
and do NOT tie the ground end of the high
impedance side to the ground end of the low
impedance side. Instead, connect the ground end
of the high impedance side to a counterpoise.

David, VE7EZM and AF7BZ

Richard Quick said...

Hi Larry, Rich - W4RQ here,
I did the 9:1 Balun End Fed thing too.
I am much happier with a KE4PT End fed Center fed antenna that is non-resonant on all the Bands.
The feed point impedance is relatively low on all bands, and the KX-3 ATU loves it.
A simple antenna to make, and a good performer, it consists of 30 ft of 18 to 24 ga wire and 11 1/2 ft of RG-174. Google the KE4PT EFOCFD antenna.
Kai Dreamed this one up and it's a winner in my Go Bag.

Anonymous said...

Suggested lengths with a 9:1 from Balun Designs:
http://www.balundesigns.com/servlet/the-102/QRP-9-cln-1-Unun-1.5/Detail