Do You Have RF Getting Back Into The Shack?

Do You Get Bad Audio Reports Because Of RF Getting Into Your Mic?

Does Your Rig Act Strange When You Increase Your Transmitter Power?

Do You Get “Bit” By Your Mic When Keying The Rig?

Then CHOKE-KIT!

 

CHOKE-KIT! is a simple and effective way to reduce or eliminate unwanted RF from being conducted back into the
shack when installed either near the antenna feedpoint or near the rig, or both.  CHOKE-KIT! is a quality pre-assembled
high power current balun* which provides approximately 24 microhenries of “common-mode” inductive reactance.  
“Common-mode” means  CHOKE-KIT! will only attenuate or” choke” unwanted RF power present on the coaxial
feedline and not affect the RF power you want to deliver to the antenna.  It is perfect for dipoles, G5RV’s, loops and other
installations where the unbalanced coaxial feedline interfaces with the balanced portion of the antenna.  It will also reduce
RF introduced on the feedline due to close proximity to other radiating sources such as power line noise or other adjacent
HF transmitting antennas.

Applications include:

  • Feeding dipoles, loops, or other similarly balanced antennas with unbalanced feedlines (coax)
  • Reducing unwanted RF due to feedline proximity to antenna elements (low height dipoles, etc).
  • Reducing man-made noise (computers, lamp dimmers, etc) conducted from the shack to the antenna by the feedline.
  • Great for emergency “Go” kits when deploying less-than-optimal antenna installations (no counterpoises, poor grounding).

The secret behind CHOKE-KIT! is the premium ferrite material which will not saturate under high power and high VSWR.  Seven

ferrite cores provide inductance equal to over 28 feet of RG-8 coax wound in a nine-turn coil.  This means less wind loading when

used at the antenna feedpoint and less clutter when used at the rig.  CHOKE-KIT! will not couple RF into other nearby objects when

properly installed.

The use of high performance materials allows CHOKE-KIT! to provide reasonable attenuation of unwanted RF on coaxial feedlines

well into the VHF bands with a minimum of power loss.  Installing  CHOKE-KIT! is easy, since both male and female UHF style

connectors are supplied.  Every effort has been made to ensure years of trouble free operation, however there are a couple things to

remember:

  • Be sure to use adequate coaxial waterproofing sealant when using outdoors.  UHF connectors are not waterproof by themselves.
  • Do not drop on a hard surface.  The ferrite cores are like any other ceramic material and will crack if handled roughly.
  • Do not use this device to support wire or cable weighing in excess of 10 pounds without a strain relief or the connectors may pull off the cable.

If you want a CHOKE-KIT! with more inductance (more ferrite cores), or with “N” type connectors, or if you want to purchase the

cores separately for DC power line filtering and other uses, please ask.

 

Specifications

Frequency:  1.8 – 60 MHz

Through-line impedance:  50 ohms (nominal)

Insertion loss: less than 0.2 dB at 60 MHz

Common mode inductance: 24 uH (nominal)

Power handling: 2kW continuous duty

Load mismatch tolerance:  greater than 5:1 VSWR at 2kw

Connectors:  PL-259 and SO-239

Ferrite material:  seven Fair-Rite P/N 2643102002 (850 Initial Perm, 2900 gauss at 10 oersteds, nickel-zinc)

Specifications subject to change without notice

24 microhenries provides an inductive impedance of 270 ohms at a frequency of 1.8 MHz.

(multiply Inductance in microhenries by Frequency in megahertz by 6.28 to get Inductive Impedance in ohms)

*For a full explanation on how a balun works, see Chapter 9 of ŇTransmission Line Transformers” by Jerry Sevick, ISBN 1-884932-18-5.