eHam Forums => Antennas and Towers and more => Topic started by: KA2ZEY on March 05, 2013, 11:41:23 AM

Title: Alex Loop and SWR
Post by: KA2ZEY on March 05, 2013, 11:41:23 AM
I just picked up a used Alex Loop antenna and KX3. I've only scratched the surface of this combo, having tried it out in the living room of my 'RF challenged' apartment last night. I'm wondering if there are any Alexloop users who have luck with getting a low SWR. I would tune the loop til I heard the noise level come up and then try to fine tune with the SWR meter on the KX3. I wasn't able to get it below 3:1 and sometimes not even 7:1, causing the rig to lock up. Does this have to do with operating inside?


Title: RE: Alex Loop and SWR
Post by: KB8LOG on March 05, 2013, 06:14:05 PM
I have an Alexloop as well and haven't had any SWR issues.

Do you have yours near any metal objects? Both the Alexloop and my homebrew loop are very sensitive to metal stuff that is nearby. Just to give you an example, moving either of those loops a foot closer to a metal pole lamp in my apartment will raise SWR from at or below 1.5:1 to nearly 3:1.

What else do you have connected between the KX3 and the loop?

Title: RE: Alex Loop and SWR
Post by: PY1AHD on March 06, 2013, 05:06:51 PM

Hi, here is Alex PY1AHD

I think that is only a matter of a litlle practice to get used with the tuning knob

I will recommend you to improve your AlexLoop irradiation balance to:

a) Keep the small top excited loop on the same plane with the outter coaxial cable loop and the tuning box.

b) After mounting procedures, hand mold the coax loop to be as a perfect circle as possible.

c) Certify yourself that the loop connecctors are firmlly atached to the tuning box.

This a and b recommendation needs only a simple visual check to be OK.

Thank you very much.


Title: RE: Alex Loop and SWR
Post by: WB6BYU on March 07, 2013, 08:58:40 AM
Quote from: KA2ZEY

...Does this have to do with operating inside?

Yes.  Or at least, very probably.

The tuning control only adjusts the resonant frequency.  The impedance
at resonance (and hence the SWR) depends on the design of the loop.
If it is coupled to any metal (which is very likely due to the wiring, ducting,
etc. in a modern apartment) the impedance will change, and you won't be
able to get a low SWR by just adjusting the tuning capacitor.  You may be
able to modify the loop feed coupling to adjust accordingly, but the value
will change when the loop is moved or rotated.

Title: RE: Alex Loop and SWR
Post by: KA2ZEY on March 07, 2013, 09:18:38 AM
I really appreciate the feedback and Alex, thank you for such a wonderful product. I realize that operating my KX3 from an AC Walwart might be part of the problem too. I bought it used and am awaiting the power chord (separate shipment) to use with my Jetstream PS. Using this AC adapter was send rf back into the radio and probably made SWR screwy.