[TowerTalk] Fwd: Modeling antenna traps

[Jim Hargrave]

I do not use the MFJ coils with my MFJ-269. I fabricated  simple 2-3
turn link coils of varying diameter  attached to a short coax..
The dip will vary depending on the link coupling and circuit Q.

73, Jim - w5ifp at gvtc.com


>> -----Original Message-----
>> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On
>> Behalf Of Hans Hammarquist via TowerTalk
>> Sent: Monday, June 6, 2016 9:03 PM
>> To: towertalk at contesting.com
>> Subject: [TowerTalk] Fwd: Modeling antenna traps
>> 
>> 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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