Palomar Engineers RFI Filter Kit for VHF/UHF Base Radio Transceivers up to 2 GHz uses a combination of ferrite mixes useful from 1-2000 MHz. BUY THIS KIT NOW TO SOLVE YOUR RFI/EMI NEEDS! WORKS WITH MANY BRANDS OF HAM/COMMERCIAL RADIO RIGS Purpose The RFI kit is designed to be installed on your radio transceiver to reduce Radio Frequency Interference (RFI) caused by common mode current on the outside of the coax braid at the output of your radio. Additional chokes are included to reduce common mode currents on the amp relay keying line (7 pin Din), rear audio in/out for digital modes (13 pin Din), computer control line (DB-9) and the DC power cord. This kit will help reduce or eliminate: 1. “Hot mic” RFI caused by poor grounding of antennas or common mode currents from linear amps feeding unbalanced (coax fed) antennas without baluns/line isolators. 2. RFI to neighbor’s electronic devices including audio/video systems, computers, telephones, garage door openers, etc. 3. RFI to your other radios, audio/video systems, computers, telephones, etc. A side benefit is a reduction in noise floor in your receiver depending on the amount of noise being introduced by common mode currents (which are blocked/reduced by the chokes in this kit). These chokes use a special mix of ferrite core material that is effective in suppressing radio frequency interference from Ham Radio amplifiers. The split beads beads are easy to use, don’t require modification of the protected equipment and work in almost all cases, even when plug-in filters fail. This kit is designed to choke common mode currents going into or exiting from your transceiver. Chokes are supplied for the RF Out (1 antenna only), Amp Relay Cable (7 pin DIN), Computer Control Cable (DB-9), PSK31/Digital Mode Cable (13 pin Din) and DC power line. Use of the chokes often helps cure SWR problems between transceiver and a linear amp and between transceiver and antenna tuner or direct to antenna. The DC power line choke helps keep common mode current out of the power line which could cause interference to other devices connected to the same power line if not suppressed. Included are the following chokes and installation guidelines: RF Input: F240 Ring Toroid for noise reduction – 3-5 turns of RG-58/RG-8X size coax cable through center DC Input: F240 Ring Toroid – 3-7 turns of DC power cable I/O Cable 1: FSB-1/2 – multiple turns through choke – ½” diameter hole I/O Cable 2: FSB-1/2 – multiple turns through choke – ½” diameter hole I/O Cable 3: FSB-1/2 – multiple turns through choke – ½” diameter hole Also make sure you connect a good RF ground to the transceiver ground post. For additional RFI suppression, use a feed line choke at the antenna to suppress common current on the coax feed line – see our store for feed line choke alternatives for use at the antenna. If you use a linear amplifier we have RFI kits for linear amplifiers that help suppress RFI in your shack or in your neighbor’s house.
Iron powder cores are more stable than ferrites and do not saturate as easily so they are best for tuned circuits, filters, and high power inductors. They come in different “Mixes” for use at different frequencies. For best “Q” use the Mix specified for your frequency.To find the number of turns to give the desired inductance for your coil use the formula below:
Turns = 100 x 
Toroid Dimensions
To order specify core size and mix (e.g. T200A-2). Available in sizes that have µH per 100 turns shown in table.
All iron powder cores are special orders. Please allow one week for shipment after order received.
The iron powder cores shown in the above tables are primarily used for either high power feed line chokes for common mode current reduction or for 4:1 and 9;1 very high power transmission line transformers.
For high power feed line chokes, choose the inside diameter of the iron powder core closest to the transmission line outside diameter and use 6-20 cores at the junction with the antenna feed.
For 4:1 (50/200 or 75/300 ohm) transmission line transformers in the range of 1.8-30 Mhz, select the size appropriate for the power level as follows:
T200A x 2 = 1.5KW
T300A x 2 = 2.5KW
T400A x 2 = 5KW
Use Mix 2 for all the above transmission line transformers. Fully assembled and enclosed units are available for each of the power levels. Click HERE for information.
4:1 transmission line transformers using iron powder cores are typically used for ladder line to 50 ohm coax connections
For .1 – 2 Mhz wide band transformers use Mix 26 which has a higher permeability and requires less turns to achieve a given inductance. Mix 2 has almost constant permeability from 1-30 Mhz. Mix 26 has an initial permeability of 75 at .1 Mhz and gradually decreases to about 10 at 30 Mhz. For high power AM broadcast range (.5-1.7 Mhz) transformer, use Mix 26 to reduce the turn count.
Minimum order for iron powder cores is $50
Shipping on larger cores in quantity may be more than $10 – email/call for quote.