KBOS feed pictures

[dave]

Inside the KBOS feed setup - latest pictures.

-dave

[Lezam]

Some equipment you got there... nice! 

[PIT]

What is the big metal box?, i see that y ou use a AMP on youre feed. i tryied that on the PIT feed but the powered amp makes it worse, but just the round tube makes it sound better?? idk??

[PIT]

about how far do you live from logan? just curios

[dave]

What is the big metal box?, i see that y ou use a AMP on youre feed. i tryied that on the PIT feed but the powered amp makes it worse, but just the round tube makes it sound better?? idk??

The big metal box is a custom bandpass filter designed for the aviation band.  It is what we call a helical bandpass filter because the filter elements are made out of helical coils.  Its frequency response looks something like:

http://dcidig.sasktelwebhosting.com/html_commercial/graph_118-18-8_wo322.htm

The amp is used primarily to provide a small gain stage ahead of the bandpass filter, which does have a little bit of signal loss.  The power divider on the output side of the filter is an active power divider which has its own small gain stages to overcome splitting losses.  SO the whole system is pretty much lossless, except for the small loss in the 50-60' of Belden 9913 coaxial cable.

If your amplifier works better without being powered, that's a new one on me.  Without power it is, at best, a lossy passthrough.  At worst, it's an attenuator.  Perhaps you have some powerful transmitters very close somewhere in the FM radio broadcast band or close to it.  Those preamps are broadband in nature (i.e., they cover a wide frequency range) and a strong signal will saturate it, causing some of the problem you mentioned.  I do have an additional filter right after the tubular amplifier (which I got from Radio Shack) - an FM trap filter to attenuate FM radio stations.  Then the big airband filter knocks down any signal that is not in the 118-136 MHz band.

-Dave

[PIT]

"At worst, it's an attenuator.  Perhaps you have some powerful transmitters very close somewhere in the FM radio broadcast band or close to it."


When i tune to PIT ATIS i hear a radio station. I think it also has to do with my antenna. When i move it the radio station doesnt come in as clear but, when its in its normal place on my roof the station comes in really really strong. I am looking into buying another antenna so that each feed has its own but, i dont know what antenna to buy, or maybe if i should buy a filter first or something.

[dave]

Google for "AB-125 filter."  They are less than $50 and will work magic for your situation.

[nxradio]

Very interesting, Dave. Thanks for showing us your radio station.
How about a photo of your antenna?

Jerrold and Winegard make some good products, I would think much improved over Radio Shack stuff, but RS is easier to buy, eh?

Your bandpass filter is definitely saving your bacon. These days, it's almost a necessity. These FM broadcast transmitters have drove me nuts also. I even had to put a choke and bypass caps across the speaker terminals (to ground) on my stereo amp. The suckers even got into my audio system, if you can imagine. TV stations don't seem to be so bad, but the FM are real bad.

joe  Howell county missouri