50:450 ohm (9:1) Balun or Unun Core Kit, 1.8-30 MHz, 250 watts PEP, end fed, T2FD antenna

Name: 50:450 ohm (9:1) Balun or Unun Core Kit, 1.8-30 MHz, 250 watts PEP, end fed, T2FD antenna
Brand: Palomar Engineers
SKU: BA-9-250
Price: 21.95 USD
Availability: InStock

Store/Antenna Products/CUBE Impedance Transformers (<1:1, 1:1, >1:1)/50:450 ohm (9:1) Transformers

SKU BA-9-250

$21.95

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50:450 ohm (9:1) Balun or Unun Core Kit, 1.8-30 MHz, 250 watts PEP, end fed, T2FD antenna

Store/Antenna Products/CUBE Impedance Transformers (<1:1, 1:1, >1:1)/50:450 ohm (9:1) Transformers

Product Details

Input ohms/Output ohms: 50 in, 450 out

Frequency Range < 2:1 SWR (MHz): 1-31

PEP Power Rating (watts): 250

Model BA-9-250 is a 9:1 balun/unun kit (assembly from parts supplied required) used to translate a 50 ohm input up to 450 ohms at RF power levels up to 250 watts PEP when used with a matched load. With a matched 450 ohm load the SWR over the frequency range 1.8 to 30 MHz is shown in the following table measured with an AIM 4170 network analyzer. Notice that the conversion from 450 to 50 ohms is very consistent from 1-31 MHz and SWR is less than 2:1 over most of the range allowing easy tuning by most radio internal antenna tuners or an external tuner. Graph is for a 9:1 unun often used with long wire or end fed antennas.

Radio Club idea:

Buy 10 for a club do it yourself construction project - you can learn something about winding impedance transformers and also build an end fed antenna (just add wire).

Typical SWR curve for this project:

When considering solutions for AM broadcast (550 Khz – 1.8 Mhz) you should consider Mix 77 ferrites available in a variety of shapes and sizes. Choose a size to give the maximum number of turns of the affected wire or cable.

AM broadcast transmits on a low frequency with large antennas. Consequently it takes a large antenna to receive the signals. Typical “antennas” are AC house wiring, phone lines, long satellite or cable TV cables, DSL/CAT5 lines running between rooms, etc. The device wires that connect to these “antennas” need to be choked with as many turns through the ferrite as possible. Some installation examples are shown below on this page.

For AC/ DC power cords and coax cables the F240-77 (2.4″ OD, 1.4″ ID) “Donut” toroid is the most popular. Also available are smaller toroid donuts and Mix 77 beads. Shown below is a graph with 8, 10, and 12 turns through the toroid – obviously more turns has higher choking impedance. Mix 77 toroid products are HERE and Mix 77 small beads (for small wires) are HERE

F240 77 Turns Comparison 1024x648 - AM Broadcast RFI Kits

F240-77 Turns Comparison from .1 – 8.1 Mhz

Shown below is a graph of frequency response verses choking magnitude for a F240-77 in the AM Broadcast band for a 12 turn coil around the toroid. (Same info as above but different frequency range).