Model 36131 - 36:1 for EFHW, 800 watts

Calculated at Checkout
  • Model 36131 - 36:1 for EFHW, 800 watts
  • Model 36131 - 36:1 for EFHW, 800 watts
  • Model 36131 - 36:1 for EFHW, 800 watts
  • Model 36131 - 36:1 for EFHW, 800 watts


After much research and testing, a new transformer design for End Fed Half Wave (EFHW) antennas has been achieved. Developed by Bob Glorioso, W1lS and Bob Rose KC1DSQ, they discovered that most transformers for EFHW antennas used higher impedance transformations than necessary and were wound in a way that limits the high frequency response of the transformer. By utilizing their capacitive loading technique developed for OCF antennas, they found it created an EFHW antenna with low SWR on all bands 80-10m. In addition to their capacitive loading, the "Bobs" also found the most important thing to make EFHW antennas work consistently on all bands was the need for a properly sized counterpoise as shown in the diagrams above.

For proper operation with this EFHW design, a quality 1:1 choke balun with a minimum of 30db suppression is essential to the overall performance. Depending on your decision for which counterpoise option you will use, the choke balun is installed either immediately behind the EFHW transformer or at the end of the coax length recommended for the use of your coax shield.  An air wound coax choke (aka Ugly balun) will NOT provide enough choking for proper operation of this unit.

We are offering the transformer either by itself, with just the excellent surface mount capacitive load or with both the load and the model 1115u choke/suppression balun.

Complete design and installation recommendations are available using the link below to view the authors' CQ article.  Please be sure to carefully follow the Installation Notes when installing the choke balun.

Installation Notes


  Core Material   Medium mix permeability toroid by Fair Rite Products for maximum bandwidth.
  Winding Type   Stacked cores with winding configured as 36:1 auto transformer
  Downward impedance transformation by factor of 36.
  Winding Material   14 gauge Superior Essex Heavy build polyamideimide Allex 240 Winding Wire
  Windings are inserted into Teflon tubes increasing total breakdown to 10,000+ volts.  
  Power Rating   3 to 31 MHz - up to 1kW intermittent (50% duty cycle)
  Useable Frequency   3 to 31 MHz
  Insertion Loss
  0.3 to 1.65 db based on frequency
  Connectors   SO-239 connectors are silver plated with Teflon insulation.
  Studs and eyebolts are 1/4 inch stainless steel.
  Alternate connectors and Mounting Options are available in the Accessories section.
  Hardware   All Stainless Steel
  Enclosure Type
  NEMA rated 4x marine grade junction box for outdoor installations.
  Cover utilizes integral neoprene gasket for weatherproof integrity.
 Dimensions  4x4x2 inches for main body of unit
 Dimensional Drawing of Standard Enclosure
View AllClose