This is the latest and greatest transformer design for End Fed Half Wave (EFHW) antennas. Researched and 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 is integral 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 author's CQ article
|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