[TowerTalk] Fwd: Modeling antenna traps

[Hans Hammarquist]

Don't underestimate MFJ. A coil on the their analyser works great. I have used that many times very successfully. I didn't bother using their "GD" coil but instead used a simple coil connected to the port. The dip is very visible on the SWR meter.


Hans - N2JFS



-----Original Message-----
From: Gary Schafer <garyschafer at largeriver.net>
To: 'Timothy Holmes' <taholmes160 at gmail.com>; towertalk <towertalk at contesting.com>
Sent: Mon, Jun 6, 2016 2:00 pm
Subject: Re: [TowerTalk] Modeling antenna traps

I don't think that you will have much luck with the MFJ used as a grid dip
meter. You will need a decent grid dip meter.

73
Gary  K4FMX

> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of
> Timothy Holmes
> Sent: Sunday, June 05, 2016 5:40 PM
> To: jim at audiosystemsgroup.com; towertalk at contesting.com
> Subject: Re: [TowerTalk] Modeling antenna traps
> 
> Hi Jim
> 
> I guess that goes to the crux of my question, how do I go about
> measuring
> those parameters, and, once I have done so, how do I then model them.
> This
> is turning into quite an interesting discussion.  I should mention that
> I
> have an MFJ antenna analyzer with the grid dip coils if that will help,
> as
> well as a multimeter
> 
> TIM
> W8TAH
> 
> On Sun, Jun 5, 2016, 6:33 PM Jim Brown <jim at audiosystemsgroup.com>
> wrote:
> 
> > On Sun,6/5/2016 1:20 PM, Timothy Holmes wrote:
> > > I would like to model them so that I can properly adjust them to see
> if
> > it
> > > is even worth my time, and what the performance will roughly look
> like
> >
> > To model the antenna, you will first need to measure the traps to find
> > their complete equivalent circuit. A trap is fundamentally an inductor
> > with series resistance in parallel with a capacitor with parallel
> > resistance. Near resonance, they simplify to parallel R, L, and C, but
> > above and below resonance, we need to know the R in series with L,
> > because these values affect performance on bands below the resonance
> of
> > the trap. And, of course, both Rs vary with frequency, thanks to skin
> > effect.
> >
> > 73, Jim K9YC
> >
> >
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