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eHam Forums => Antennas and Towers and more => Topic started by: KC2MWJ on November 27, 2012, 07:44:08 AM



Title: I-Max 2000 tuning ring adjustments
Post by: KC2MWJ on November 27, 2012, 07:44:08 AM
  I just purchased an I-Max 2000 vertical antenna. I read all of the reviews here, but am unsure of how the tuning rings should be adjusted. I want to use this antenna for 10 thru 15 meter use. I am getting ready to mount it on a 20 ft mast, without radials or the radial kit. Some say the tuning rings should be all the way up, and others say all the way down. A few say to leave them as they were adjusted at the factory. What are your thoughts on this? 
Thanks,
Tony


Title: RE: I-Max 2000 tuning ring adjustments
Post by: SWMAN on November 27, 2012, 09:21:17 AM
 Tony,
I have the radial kit on mine. I have tried it with the rings at the top and at the bottom and I dont see any difference at all. Weird I know. I even tried it with one rind up and one down, still no difference in SWR. I really dont see how moving the rings up or down 3 inches or so would be able to make any difference anyway by the way the antenna is designed.  The aluminum rings just move past the internal coil at the base ??? To me it looks like a sales gimmic, the same for the A 99. The antenna is great though for me on 10 and 15 with no tuner. Also a good SWL receive antenna.  But for the rings, mine are still on the bottom.      73 Jim  W5JJG


Title: RE: I-Max 2000 tuning ring adjustments
Post by: W4OP on November 27, 2012, 09:22:24 AM
While I have never owned the antenna, it certainly seems they should be adjusted for lowest VSWR.
Be aware though that an antenna of this type without radials will have lots of common mode current on the outside of the coax- so the coax  also becomes part of the antenna. Change the coax length or how it is routed and the VSWR changes.

Dale W4OP


Title: RE: I-Max 2000 tuning ring adjustments
Post by: KE5JPP on November 27, 2012, 09:26:19 AM
While I have never owned the antenna, it certainly seems they should be adjusted for lowest VSWR.
Be aware though that an antenna of this type without radials will have lots of common mode current on the outside of the coax- so the coax  also becomes part of the antenna. Change the coax length or how it is routed and the VSWR changes.

Dale W4OP

The radial kits for these antenna are also ineffective and will do nothing to limit common mode current on the coax.  They are nothing more than end fed verticals and common mode current on the coax is to be expected.

Gene


Title: RE: I-Max 2000 tuning ring adjustments
Post by: W5WSS on November 27, 2012, 11:33:34 AM
Try adding 4 full size tuned 1/4 wave radials made of #14 wire.

Attach the radials directly to the outer PL 259 ( shield) with a SS hose clamp for a temporary look at the differences that proper radials make.

Route the 4 radials opposite each other and slope downwards.at 45 degrees or so

The effective sloping radials will change the feed point Rr and the rings may be adjusted accordingly along with the radials if easier than adjusting the vertical length.

And:

The effective sloping radials will reduce common mode current substantially because the antenna is now approaching better balance since it is no longer an end fed antenna but rather a dipole where the 4 radials are representing a single second leg split into 4 symmetrical parts and positioned opposite each other the antenna is now much improved with respect to common mode traveling along the outer shield towards the station equipment.

The end fed vertical benefits allot from tuned sloped radials re tune and enjoy.


Title: RE: I-Max 2000 tuning ring adjustments
Post by: N5TMC on November 27, 2012, 11:56:06 AM
I belive this is the same antenna as the antron 99. I have one up right now and all i did is cut one inch off of the top for ten mtrs.


Title: RE: I-Max 2000 tuning ring adjustments
Post by: K2TL on December 03, 2012, 10:43:00 AM
I have mine without the radials, but I do have a ferrite line isolator at the feedpoint.  Absolutely no RFI issues.  I did find that the height above the roof line makes a big difference in where the antenna resonates.  Under my roof there are a lot of conducting materials, like HVAC ducts, plumbing, electrical wiring, and stuff like that.  This antenna seems to be affected by close proximity to counterpoise material.  Adjusting the tuning rings does nothing but screw things up.  Leave them alone.
BTW, this antenna performs quite well on 10 through 15 with an autotuner at the feedpoint, not in the shack.  Don't bother with it lower than 15 meters.  This antenna has a matching network that will look like a dead short at frequencies below 15 meters.  The tuner will give you a nice match, but your RF is going mostly to ground.
I have no regrets with this antenna.  Just understand its limits.