Towertalk
[Top] [All Lists]

Re: [TowerTalk] Fair rite materials for choke baluns

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Fair rite materials for choke baluns
From: "Roger (K8RI) on TT" <K8RI-on-TowerTalk@tm.net>
Date: Tue, 5 Jul 2016 02:40:24 -0400
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
It's my understanding that a choke of (theoretical) infinite Z does not disconnect the antenna. It would reduce the current flowing on the outside of the coax (common mode) to zero at that point. It has no effect on the interior currents

The choke does nothing to the balance of the antenna. It just stops (more correctly reduces) the CM current caused by a reasonable imbalance such as a sloping dipole, or that caused by nearby objects. The greater the imbalance the greater the power dissipated in the core material. The difference between sloping, center fed dipoles on 80 Vs 40 is very pronounced
Different core materials will likely have different dissipation values.

OTOH it does not prevent that same exterior shield from picking up signals if long enough, or of the right (or wrong) length. Then a second and possibly third choke of smaller values might be advisable making the shield appear as if it were broken up with insulators.

Unless referring to a specific antenna, I'd not expect Z to be relatively important. For a specific type of antenna Z & R vary with height, particularly on 160 and 75. Sometimes by large amounts.

73

Roger (K8RI)


On 7/4/2016 Monday 2:08 AM, Jim Thomson wrote:
Date: Sun, 3 Jul 2016 11:23:10 -0700
From: "Richard (Rick) Karlquist" <richard@karlquist.com>
To: Steve Hunt <steve@karinya.net>, Reflector -tower
<towertalk@contesting.com>
Subject: Re: [TowerTalk] Fair rite materials for choke baluns


On 7/3/2016 10:05 AM, Steve Hunt wrote:
Rudy,
http://www.karinya.net/g3txq/temp/52_mix.png

It achieves Rs>5000 Ohms from 10Mhz thru 28MHz, and Rs>8000 Ohms from
12MHz thru 21MHz.

Steve G3TXQ

It is more useful to think about Rp than Rs.  Rp determines the
power dissipation for a given voltage.  Although Z is a figure
of merit for how well the antenna works, Rp is a figure of merit
for how much power can be handled.  On the G3TXQ curves, note
that where Z=Rs, it is also true that Z=Rp.  Away from that
frequency, the general trend is that Rp monotonically increases
with frequency, at least up to resonance.


It's nice to brag about extremely high Z values, but even if
Z=infinity, all you have accomplished is that you have
disconnected the feedline from the antenna.  It doesn't
guarantee there will be no feedline currents.  Also, it merely
PERMITS the antenna to be balanced, if there is no external
conductor otherwise perturbing it.  It does not guarantee
balance.

Rick N6RK

##  Ok, Im lost.   I thought  we wanted  Z >  RS > XS .
Put another way, RS ideally should be the same as Z... or as close as
you can get to Z.   And  RS  should definitely be >  than XS.

What is RP  ??

Jim   VE7RF



_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk


--

73

Roger (K8RI)


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus


_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk

<Prev in Thread] Current Thread [Next in Thread>