AOR ABF128 FILTER

FILTERING FOR AIRBAND

As you can see above, I live very close to a major transmitter (Winter Hill, 1500ft ASL) which pumps out around 500kW of signals to feed TV and Radio to the North West viewers and listeners. Generally speaking, I don't suffer massively from the close proximity to Winter Hill, but nonetheless, it does have an impact.

And listening to anything on a wideband receiver adds to any problems, so when I saw the ABF128 AirBand Filter from AOR, I thought it might be worth a punt. I bought the BNC version and now I wish I'd gone for the SMA model instead.

At £55, it's not cheap, but then again, many other filters for your radios are even more expensive. Rather than me trying to explain the technicalities of the device, I'll reprint what I found on Waters & Stanton's website where I bought it from and then I'll post a little video so that you can see and hear the difference .

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The AOR ABF128 is a receive bandpass filter especially designed for serious VHF airband listeners. This filter improves the strong signal handling characteristics of scanners and wideband receivers for VHF commercial Airband listening. The ABF128 is suitable for connection to most scanners and wideband receivers on the market, regardless of brand. The addition of this filter to the antenna's signal path provides additional selectivity which enables the receiver's circuitry to better cope with strong interfering signals that can leak into the 108-136 MHz VHF air band.

The ABF128 provides additional selectivity to any receiver's front-end by reducing a multitude of unwanted strong signals from reaching and saturating the receiver's first mixer stage. This results is less interference and improved reception. The ABF125 offers excellent out-of-band attenuation typically of 25 dB from 0.3 to 75 MHz and 20 dB from 190 to 400 MHz. This makes the ABF128 suitable for connection to both external antennas and for connection directly under the whip aerial of a hand-held receiver. A BNC socket (female) is fitted to the top of the ABF128 and a BNC plug (male) to the other making connection to an aerial easy and straight forward.

The ABF128 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 ABF128 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 4 dB.

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I made this recording using the Yaesu FT3D and I wish I'd used my Kenwood TH-D74 instead because the D74 has infinitely better sounding audio! Ah well.

I tuned into Manchester's (EGCC) ATIS frequency of 128.175MHz. The airport is 20 miles away from me and is not a particularly strong signal, so it's perfect for this test.

NO CHANGES WERE MADE

TO THE RECEIVER

BETWEEN RECORDINGS

Click To Watch Video

So there you have it - much clearer signal with the ABF128 fitted. The filter does a fabulous job and I'm now much more inclined to invest in similar filters - say for 2M portable work, where you can come across all sorts of noise problems when out and about.

Oh, nearly forgot! If you're scanning banks which contain frequencies outside the AirBand, you're obviously going to struggle to hear them while the filter is attached, so be sure to have a dedicated VHF bank setup for your airband listening.

Thanks for visiting.

73, Tom, M7MCQ.