RSGB - the Radio Society of Great Britain

• Home
• EMC Help
• Technical Help (Non EMC)
• Power Line Communications
• EMCC Minutes

EMC Filters & Ferrites

The RSGB stocks a range of filters intended to be fitted in the coaxial antenna lead of a TV set or VHF radio receiver. More information on using filters will be found in the RSGB Guide to EMC and the RSGB Yearbook. The filters listed below allow UHF TV signals to pass through but as with any filter, there is a small loss in the pass band. The HPF2 allows both VHF/FM broadcast radio (Band 2, 88-108 MHz) and UHF TV to pass through.

IIn many cases, particularly on the HF bands, amateur signals are picked up by the TV aerial downlead rather than by the TV aerial itself. If this causes breakthrough, a so-called 'braid breaker' is required. This could be part of a filter or could be a separate unit. There are several types of 'braid breaker' although some of these do not actually break the braid at DC.

The ferrite ring braid breaker.
Filters which incorporate braid breakers use several different techniques to achieve the breaking effect. For a stand alone item, by far the most popular is the simple ferrite ring choke formed by winding a length of coaxial cable on to one or more ferrite rings. This has the advantage that it introduces very little loss to the wanted UHF TV signal, and maintains the integrity of the coaxial cable screening.

• BB1 Braid breaker (RSGB order code Filter 1)
  Pass band: Most amateur bands plus FM radio broadcast (88 - 108 MHz), and UHF TV.
  Stop band: Some rejection below 10 MHz but the BB1 is primarily intended as a 'braid breaker' rather than a high pass filter.
  Braid breaking: A 1:1 transformer type braid breaker which is effective on all HF bands. Limited braid breaking up to 144 MHz.
  Remarks: A BB1 can be cascaded with other filters such as HPF2 or HPF6 which do not have any braid breaking action, although this increases the total passband loss.

• HPF 2 High pass filter (RSGB order code Filter 2).
  Pass band: FM radio broadcast (88 - 108 MHz), up to UHF TV.
  Stop band: All HF bands plus limited effect at 50MHz.
  'Braid breaking': None.

• HPF 6 High pass filter (RSGB order code Filter 8)
  Pass band: UHF TV
  Stop band: All bands 1.8 - 440 MHz
  'Braid breaking': None.
  Remarks: This is a high performance six section filter with a very sharp cut-off below 470 MHz. It provides excellent rejection of all amateur bands 1.8 - 440MHz.

• HPFS High pass filter (special) (RSGB order code Filter 3)
  Pass band: UHF TV.
  Stop band: All bands up to and including 144 MHz.
  Braid breaking: Includes 1:1 transformer type braid breaker (see BB1 above).
  Remarks: The HPFS is a BB1 combined with a high pass filter. It is a good all-round filter for all HF and VHF amateur bands but is not effective on 430-440MHz. Due to the relatively high pass-band loss, it is not suitable for areas where the TV signal strength is low. Its electrical characteristics.

•   RBF1/70 cms notch filter (RSGB order code Filter 5)
    Pass band: UHF TV
    Stop band: 430-440 MHz and all HF bands.
    Braid breaking: None.
    Remarks: The RBF1/70cms is pretuned to reject 435 MHz although an HPF6 gives greater   rejection of the 430 - 440 MHz band. The RBF1/70cms also has a high-pass action with   rejection of HF signals.

TNF2 tuned notch tilter range

These filters are designed to provide a high degree of rejection of one particular amateur band. These are for use on television aerial systems only. They are not recommended for use at the input of some types of TV distribution amplifier.

Ferrite Rings
A pack of two rings made in the USA by Fair-Rite Corporation in type 43 material, part number 2643802702. The inside diameter is 22.85 mm (0.9 inch) and the width is 12.7 mm (0.5 inch). They can accommodate 12 turns of 5mm diameter cable and are equivalent to FT140-43.

For more information on how to install filters and ferrites please click here .

Filters are available from The RSGB Bookshop

Please note: These pages are intended for members of the Radio Society of Great Britain, but are available to non-members on the understanding that any information is given in good faith and the society cannot be responsible for any misuse or misunderstanding.

©2006 Radio Society of Great Britain
Home page