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| | |-+  KTEB high pitch noise on feed?
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Author Topic: KTEB high pitch noise on feed?  (Read 2160 times)
Mark Dalforno
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« on: August 04, 2012, 01:23:19 PM »

Hello all,
Just curious if anything can be done about TEB's high pitch background noise when pilots are talking.  The feed worked amazing after it came up orginally and then developed that noise which makes it difficult to listen to.   Just curious.

Thanks!!!
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Mark Dalforno
Sacramento City College CTI program
Former Broadcaster
Norcal Approach/Oakland Center Arrivals Merced - KMCE
MikeNYC
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« Reply #1 on: August 06, 2012, 01:01:39 PM »

Mark,
That feed is one of the ones I run, in the NYC area. Also hosted there are the EWR TCA, NYC Class B/Helicopter, NYC Heli CTAF, and NY Approach/HAARP/LGA Dep/Arr.

There is intermittent radio interference at that location that's been very difficult to overcome. It seems that strong signals in neighboring bands overload the front end of the receivers, causing issues. On the EWR TCA feed, it was so bad that I swapped in a $250 airband transceiver since it had better filtering and rejection.

There are three filters before the receivers...one FM Notch and two Airband Bandpass filters, if I remember properly. They've been tried in all permutations in front of and behind the amplifier, between the amp and splitter, and in front of each receiver, and in different orders. I've also installed ferrite cores on all wiring.

The only thing I could do is run a graphical EQ to drop the volume of that pitch sound on that feed, but the feeding computer doesn't have the horsepower to do that on the fly along with the other feed it runs.

I know about the audio issue, and wish it was an easy fix. As you noted, it does come and go, but mostly it's been present. Hopefully the source of interference will disappear. The feed itself is located on the 14th floor of a building in Chelsea, right on the Hudson River with a clear view to TEB. Unfortunately it's also near the Empire State Building, with its massive transmitters, and the feed shares the building with Homeland Security, who may have radio equipment installed.

Short of a new feed location or much higher-end receivers (or installing a graphic EQ), I don't know if it's an easy fix unless someone knows more than I do.
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Feed Provider Of:
NYC Helicopter Class B/Ops
KEWR Tower (TCA/Helicopters)
NYC Helicopter CTAF
KLGA NY Approach (HAARP/Final/Dep)
KTEB Del/Gnd/Tower
NYC MilAir/MISC
InterpreDemon
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« Reply #2 on: August 06, 2012, 02:50:10 PM »

Mike, I am assuming that is an indoor antenna? It sounds to me like you have a low level interfering signal 10khz or so away on at least the ground frequency. If you are getting it on all frequencies, then we are talking about something penetrating in at the first IF frequency, which would have to be a very strong signal indeed, though it well could be a birdie from a computer or another scanner nearby or within your own setup. It is definitely a heterodyne interference and most likely in-band since you have already run the filter gauntlet. It is telling that the heterodyne increases in strength with increased on-channel signal signal strength and by the sound of it the likelihood it is an intermod product is nil, IMHO. All you have to do to rule that out is see if you can tune it in directly above or below... if you can't, it is in the IF because that is the only place it will always be present (interfering) AND that you will not be able to tune it in directly.

If it were me I would hook a little 2 or 3 element hand held "fox hunting" yagi to that radio and look for that carrier, I give it a 90% chance of being right in your building. If you are lucky it will be from a direction 90 deg off from TEB and you can null it out... while at the same time getting TEB much better. A vertical yagi is perfect for nulling out stuff on floors below and above.

On the other hand if it really is a 10.690 or 10.710 intermod product pounding in through all your tuned elements and the front end you'll have to try a helical resonator, cavity, or some strategic stubs. For example, if it is the product of two FM broadcast frequencies somewhere between 88 and 108, a 98mHz reject stub will knock the product down at least 20db one way or the other. Another stub at 155mHz would take care of the most likely sources of high-band land-mobile. I seriously doubt the latter is the problem because the heterodyne is always there and even repeaters are not always transmitting, whereas computer and electronic master clocks and broadcast stations are.

With persistence you should be able to smash down that little froggie.

As always, if you or any of your IM force are caught, killed, or just driven insane, the secretary will disavow any knowledge of your actions.

Good Luck, Mike.
« Last Edit: August 06, 2012, 02:51:49 PM by InterpreDemon » Logged

Feed Purveyor:
KJFK ARINC
KHPN ATIS
(KJFK) NY DEP Liberty East
HF CAR-A  3455/5550/6577/8846/11396
HF ARINC LDOC  6640/8933
HF NY VOLMET  6604

Complaints should be addressed to: City Hall
skyshare
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« Reply #3 on: August 20, 2012, 10:36:29 AM »

Great to have TEB back, thanks for the feed.  However, is there any chance of making it tower only as all those long drawn out clearances block out all the good stuff!
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MikeNYC
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« Reply #4 on: August 28, 2012, 11:50:53 AM »

ID - Thanks for your helpful post! The antenna is actually an outside antenna, 1/4 wave whip omni. The antenna is also shared with four other feeds, covering 127.85, 126.05, 125.25, 123.15, 128.875, 123.1, 123.075, 123.05, 123.025, 131.975, 120.8, 120.4, 134.9, 121.5, and the TEB freqs, and all coming from different directions (located about equidistant from TEB, LGA, EWR).

It's present much more strongly on some frequencies than others, and tested with a few receivers. You could be right about the product of two FM freqs. I don't have nearly enough knowledge about radio reception to properly analyze what the problem is, and unfortunately multiple directional antennas are out as the equipment has to be quite unobtrusive...it's hosted at an office I do a lot of business with. Any simple helical resonators or cavities available that I might try? And wouldn't my FM Notch filter have knocked down the FM sources you mention? Thanks for any further advice.

Skyshare - I'll remove KTEB Clearance Delivery from the scan soon per your request. I know it can block some things, but a lot of flights that operate out of KTEB are blocked on FlightAware so hearing a clearance can be the best way to actually track and match up a flight. We'll try for a bit without it and see how it goes.
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Feed Provider Of:
NYC Helicopter Class B/Ops
KEWR Tower (TCA/Helicopters)
NYC Helicopter CTAF
KLGA NY Approach (HAARP/Final/Dep)
KTEB Del/Gnd/Tower
NYC MilAir/MISC
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