[Elecraft] (K3) Alexloop Antenna

[Fred Jensen]

I've had an Alex Loop for about 2 years now, it replaced my Buddipole 
[about the same cost].  You can build your own mag loop for a lot less 
than the Alex but I wanted the cool carry case and had the $$ from the 
BP sale. :-))  I use the loop when activating a SOTA summit and general 
field operating, usually with my K2/10.

My Alex easily works as well or discernibly better than the BP ever did. 
  It is very narrow BW, and tuning it on 40 requires a steady hand and 
care.  It's less touchy on 30 and just fine on 20 and up.

I have mine on a light-weight tripod I found at Home Depot with a Rain 
Bird sprinkler on top.  I cut 9 inch piece of 1/2" gray PVC nipple with 
threads on one end and screw it into the tripod.  The hollow Alex handle 
fits down over the PVC.  I finally filed some shallow slots in the PVC 
to keep things stable in wind.

I set up next to the tripod and can reach up and tune the loop with one 
hand.  There is one gotcha with loops like this:  It is a resonant 
transformer.  At resonance, your SWR will be 1:1 and you'll make Q's. 
If you "get it close" with the knob and then let the ATU [if you have 
it] match it, you will have created a very well shielded dummy load and 
you'll make no Q's.  So, bypass the ATU and get 1:1 with the little knob 
on the capacitor.  You can't QSY more than maybe 5 KHz on 40 without 
tweaking the capacitor.  BW gets larger on 20 and up.

It is mildly bi-directional in the plane of the loop but the lobes are 
quite broad.  There are two very sharp, fairly deep nulls orthogonal to 
the loop plane which can sometimes help reduce noise or QRM.  It is 
essentially insensitive to ground, and doesn't really care how high it 
is, a tremendous advantage in the field over E-field antennas.

Pay attention to the power limits.  Because it is resonant and small in 
terms of electrical degrees, RF voltages can get quite high.  It's 
definitely a QRP antenna.

Hope this helps,

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 50th Running of the Cal QSO Party 3-4 Oct 2015
- www.cqp.org

On 1/30/2015 12:47 PM, David Guernsey via Elecraft wrote:
> I live in a condo with pretty strict rules re antennas, etc.  I am
> considering an Alexloop on a tripod on my balcony, Does anybody have
> any experience with this antenna? Any comments. I have a K3/10 that I
> operate at 5-10 watts PEP onSSB.Thanks 73 de Dave KJ6CBS