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AOR ABF128 and PAR VHFBP airband filters

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hertzian

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May 28, 2009
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Both the AOR ABF128 and PAR VHFBP filters are VHF airband passband filters, that attenuate frequencies both above and below the typical 108-136 mhz airband, while presenting a small amount of "insertion loss".

Typically they are used to prevent desense, ie the tower or atis signals on the air-band seem to be pumping, (intermittent out of band transmissions) or constantly lower in sensitivity than they should be (fm broadcast overload). They can even help with just noisy "noise-floors" from being too close to wideband noise generators - although NOTHING will cure noise that is inside in the airband itself other than changing the antenna's physical location.

In my case, both the AOR and PAR filters were tested in a very bad broadband noise area on the lunch deck on the 6th floor of an office building - well within eyesight of a local tower. Radios used were a RS Pro-106 handheld, a Uniden 396XT handheld, and an Icom R20 receiver.

Signal strengths were good, but the noise-floor was intolerable. Changing from a small duck to an extended whip raised the tower's signal strength, but the noise increased also yielding a net gain of zero - still unusable our there on the deck. The major culprits were the severe broadband hash all over the spectrum coming from INSIDE the building - even inside the airband, BUT most of the hash wash generated outside the airband.

Only the Icom R20 was usable without the filter - but that is a receiver, and not a scanner.

Both the AOR and PAR when attached to the Pro-106 and Uniden 396XT, brought the harsh noise-floor down to acceptable levels. NOW making an improvement with the antenna was worthwhile, as the noise level did not follow as much. Using either with the Uniden demands using the supplied beefy sma-bnc adapter - a common thin adapter is likely to put too much stress on the Uniden's sma connector.

Of the two units, the PAR has the better specs, and was discernable - especially in regards to FM broadcast attenuation - however, having a 3-can cavity on your handheld is definitely letting your geek-flag fly, and is not something I want to carry in my pants like the AOR filter.

Each puts enough mass above the radio to make it top-heavy, so if you topple the radio, plan on breaking something in the process. Of course each is constructed very well with high-quality connectors.

My recommendation is to use the AOR for extreme portability with handhelds, and the PAR is the one to use for fixed-station or mobile setups. No surprise there. (Or perhaps use the par for handhelds that are shelf-queens.)

Either of these filters would be very useful for those using dual-conversion scanners with 10.7 mhz first IF's, (like the RS Pro-404 / GRE PSR100/200) and are suffering from small amounts of image problems from the amateur 2-meter band. If the problem is large, then these filters only being about 10mhz or less from amateur signals might not be enough - Instead of filtering, I'd be sorely tempted to get another scanner that is at least triple-conversion.

Remember that these are passband filters, and NOT notch filters - so outside of the airband, signals are attenuated. Most will want to remove the filter when not concentrating on airband, or just use it on a dedicated airband scanner - however, if you are in a metro area, you *might* find that even with the large amount of attenuation out of band, you might be able to get away with leaving it inline - obviously each situation is different.

I used both at home, although only on the attic mounted OCFD did I notice a slight improvement in the noise floor - perhaps even wishful thinking - but on the 6th floor office terrace next to all the computers, fax machines, and what have you, both the AOR and PAR cleaned up the noise floor to make monitoring usable again.

If I could only have one, then the PAR would be for me.
 

sholt

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Oct 30, 2011
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Location
San Francisco, CA, USA
Thank you for all of your reviews - I have a feeling these things might help me get much better quality RX / less noise in my apartment block full of wireless routers in a metro area!
 

hertzian

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May 28, 2009
Messages
2,604
If you have in-band noise, no filter will take care of that. Before opening the wallet, try to identify and remove the noise source, relocate the antenna, or use an antenna with different characteristics. The frequencies the routers are on are usually not the problem, but the junk coming out from the boxes themselves, noisy switching power supplies etc are. More info on your sitation in the other thread..
 

Turbo68

Member
Joined
Dec 12, 2005
Messages
839
Location
East Devonport,Tasmania,Australia
Hi Hertzian been using the Aor-ABF125 airband filter mainly when i go to the airport with my h/h and it does do an excellent job also noticed when i used it at home with other receivers it increased the signal strength..

Regards Lino..
 
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