AOR ABF125 User guide

ABF~125

VHF Air Band Filter for better strong

signal performance...

The ABF125 is a receive bandpass filter especially designed to improve the strong signal handling characteristics of
receivers for VHF commercial Airband listening. The ABF125 is suitable for connection to most airband and wide range
receivers on the market, it is not designed just for AOR branded products. The addition of this filter to the aerial signal path
will provide additional selectivity which will enable the receiver's circuitry to cope much more easily with strong interfering
signals such as Band-2 Stereo or Shortwave broadcast transmissions which can be manifest in many ways such as ‘hissing’,
mixing of many signals together, music breakthrough and desensitisation of the receiver.

The ABF125 will provide useful additional selectivity (in many situations) to any receiver's ‘front end’ by
reducing the multitude of unwanted strong signals from reaching and saturating the receiver's first mixer
stage... this results is less interference and improved reception.

Of course ‘stub filters’ can provide a degree of rejection to unwanted signals but tend to be bulky being
suitable for base station applications and usually have to be hand-made. The ABF125 on the other hand is
ready made and very compact measuring only 73.5mm and weighing a mere 52g yet offers excellent out of
band attenuation typically of 25dB from 0.3 ~ 75 MHz and 20dB from 190 ~ 400 MHz. This makes the
ABF125 suitable for connection to both external aerials and for connection directly under the whip aerial of
a hand-held receiver. A BNC socket (female) is fitted to the top of the ABF125 and a BNC plug (male) to
the other making connection to an aerial easy and straight forward.

The ABF125 is not an amplifier so will not ‘boost’ signals, however the additional selectivity offered can
significantly improve reception in many situations by removing unwanted strong signals which may
overload the receiver and reduce it's effectiveness. When any connection is fitted to the aerial signal path
some reduction of signal is resulted (attenuation) however the ABF125 in band attenuation level is very
small due to the excellent in band V.S.W.R. of 2:1 resulting in a loss of only about 4dB.

Note: Remember to remove the ABF125 from the aerial when monitoring signals other

than VHF Airband or signal strength will be dramatically reduced.

Specification

Model... ABF125
Bandpass Coverage... 108 ~ 136 MHz
Nominal Impedance... 50 OHM
Through Attenuation
In Band... 4dB
Attenuation typically

0.3 ~ 75 MHz... 25dB minimum
Attenuation typically
190 ~ 400 MHz... 20 dB minimum
V.S.W.R. in band... 2:1
Aerial input... BNC socket (J)
Aerial output... BNC plug (P)
Size (length)... 73.5mm
Weight... 52g

ABF125

shown

to scale

* Specifications subject to change without

notice due to continuous development

of the product. E&OE.

AOR Ltd., 2-6-4 Misuji, Taito-Ku, Tokyo 111. Japan. Tel: [phone]