Newbie, Airband interference issue help!

[Rod1989]

Hello guys, im Rod, new in the forum and in the scanning world, im an aviation enthusiast and love to listen to the airband.
I have some issues that hope more experienced people can help me.
First i use a Uniden Bct15x and a Diamond D777 dedicated airband antenna with 75ft of lmr400 coax. I can hear my local airport thats like 6 miles away with almost no issues except for one thing: Im getting a lot of hiss backround noise mainly in a 118 range tower freq, the other ones higher than 121 have less noise, the strangest thing is that all the hiss noise goes away during the nights and on saturday afternoons and on sundays, times where common office hours are off. During this time i get the comms as clear as if i was living in the airport itself, i can even pick up another airport thats 20 miles away with a big hill in between.
Does anyone knows what could be the issue here?
I really appreciate all the help.
Thanks.

 

[RadioFreq]

Hello guys, im Rod, new in the forum and in the scanning world, im an aviation enthusiast and love to listen to the airband.
I have some issues that hope more experienced people can help me.
First i use a Uniden Bct15x and a Diamond D777 dedicated airband antenna with 75ft of lmr400 coax. I can hear my local airport thats like 6 miles away with almost no issues except for one thing: Im getting a lot of hiss backround noise mainly in a 118 range tower freq, the other ones higher than 121 have less noise, the strangest thing is that all the hiss noise goes away during the nights and on saturday afternoons and on sundays, times where common office hours are off. During this time i get the comms as clear as if i was living in the airport itself, i can even pick up another airport thats 20 miles away with a big hill in between.
Does anyone knows what could be the issue here?
I really appreciate all the help.
Thanks.

It could be interference generated from computer equipment, a television or other electrical device running during those hours.
For example: I have an FM radio in a nearby room that routinely causes the same couple of channels in the Mil Air band radio to lock up.
I turn the FM radio off, and the interference goes away. I would suggest an experiment within your home or office to see if you can isolate the source. Good luck.

 

[iMONITOR]

You might need a FM Notch Filter if you have strong FM broadcast stations in your area.

Receive Filters

 

[dkcorlfla]

A neat trick to help find some of the sources of interference is to use a portable AM radio, tune it between stations so it only has static and walk around and see if the "hiss" gets louder. Turning the radio 90 degrees will null the signal (the AM radio with have the most gain broadside)

I have used this many times to find the source of interference on ham HF bands. Wall warts, SMPS (Switching Mode Power Supplies] are often the source. Note - I have not tried this on VHF AM but it's worth a try.

 

[GROL]

Hello guys, im Rod, new in the forum and in the scanning world, im an aviation enthusiast and love to listen to the airband.
I have some issues that hope more experienced people can help me.
First i use a Uniden Bct15x and a Diamond D777 dedicated airband antenna with 75ft of lmr400 coax. I can hear my local airport thats like 6 miles away with almost no issues except for one thing: Im getting a lot of hiss backround noise mainly in a 118 range tower freq, the other ones higher than 121 have less noise, the strangest thing is that all the hiss noise goes away during the nights and on saturday afternoons and on sundays, times where common office hours are off. During this time i get the comms as clear as if i was living in the airport itself, i can even pick up another airport thats 20 miles away with a big hill in between.
Does anyone knows what could be the issue here?
I really appreciate all the help.
Thanks.

What airport do you monitor? I was just going to see what else is in the area. I would not consider FM broadcast since they are 24/7. Does the interference come and go during the hours you encounter it, or is it continuous? By the way, the BCT15X is excellent for VHF and UHF air bands. I use one extensively. I would think of things around your house as the source of interference. Modern electronics emit a herendous amount of EMF. Now we also have to contend with LED light bulbs as well. If you use the telescopic antenna on the back of the scanner inside the house do you still encounter the interference?

 

[RadioFreq]

You might need a FM Notch Filter if you have strong FM broadcast stations in your area.

Receive Filters

Thanks, iMonitor.

 

[Rod1989]

Hi guys, thank you for your replies, ive managed to find the source, its an office building thats right next to my house, its an administrative office of a local super market. Noise goes away when they dont work, i tried it with a portable went very close to them and the signal bar got all crazy, went again when they were off and all quiet. Anyone knows which type of equipment they might be using? I can see they have those big air conditioners, but maybe its something else. I do suffer from broadcast fm issues but i have already filters in and have solved that part.
Hope you could point me out what can i do.
Rod.

 

[iMONITOR]

Hi guys, thank you for your replies, ive managed to find the source, its an office building thats right next to my house, its an administrative office of a local super market. Noise goes away when they dont work, i tried it with a portable went very close to them and the signal bar got all crazy, went again when they were off and all quiet. Anyone knows which type of equipment they might be using? I can see they have those big air conditioners, but maybe its something else. I do suffer from broadcast fm issues but i have already filters in and have solved that part.
Hope you could point me out what can i do.
Rod.

Is it a newer recently built building or a very old building? It could be cause by the type of lighting they use. Other than just a normal office environment could they have another type of equipment in the building? Maybe if you could post a sound byte or describe the sound in more detail?

 

[tvengr]

AM is very susceptible to noise. LED and fluorescent lighting can generate a lot of noise. USB power supplies are notorious for wideband interference. The computer equipment in an office can also be another offender. The AC wiring in the building could be acting as a transmitting antenna for any equipment plugged into it. Do you still receive the interference with the antenna removed? If so, it could be coming in from the AC wiring in your house. You may need to work with the people in the building doing things like turning lights on and off as well as other equipment to isolate the source of the interference. You could power your BCT15X from a battery and walk around through the building to find a hotspot for the interference. An AM broadcast receiver may also work.

 

[bearcatrp]

There are tweaks to the P25. Make sure you change one at a time, do it in small increments. Try shutting off all services except police. How high is your discone? Is it above your roof?

 

[tvengr]

There are tweaks to the P25. Make sure you change one at a time, do it in small increments. Try shutting off all services except police.

OP is having problems receiving aircraft. Aircraft do not use P25. They are AM.

 

[dkcorlfla]

OP is having problems receiving aircraft. Aircraft do not use P25. They are AM.

Here is a little trivia question - why do Aircraft use AM? I was studying for the ham extra exam and one of the questions covered this. It has to do with FM capture. Can't have capture when flying an airplane, even the weaker signals need to be heard. I thought that was interesting and just wanted to share.

 

[wtp]

could the building or something nearby have solar panels ?

 

[tvengr]

could the building or something nearby have solar panels ?

That's a possibility since they would stop generating power once the sun goes down.

 

[iMONITOR]

Hello guys, im Rod, new in the forum and in the scanning world, im an aviation enthusiast and love to listen to the airband.
I have some issues that hope more experienced people can help me.
First i use a Uniden Bct15x and a Diamond D777 dedicated airband antenna with 75ft of lmr400 coax.

I'd be interested in your results if you disconnect your antenna system and try it with just the stock back-of-set telescoping whip antenna.

 

[dkcorlfla]

I'd be interested in your results if you disconnect your antenna system and try it with just the stock back-of-set telescoping whip antenna.

The Diamond D777 looks like a very good antenna and the extra gain may well be adding to the RFI problem. I could not tell from the picture I pulled up as to what connection is used to connect the coax. It might be worth trying a choke near the base to cut off any common mode current that may be coming down the outside of the coax. Perhaps try making an ugly balun from some pvc tube and a short section of RG8X.

 

[CrabbyMilton]

Here is a little trivia question - why do Aircraft use AM? I was studying for the ham extra exam and one of the questions covered this. It has to do with FM capture. Can't have capture when flying an airplane, even the weaker signals need to be heard. I thought that was interesting and just wanted to share.

AM has the advantage of longer range.

 

[prcguy]

AM has the advantage of longer range.

Why do you say that?

 

[CrabbyMilton]

For the reason that commercial AM radio can be heard many miles away from the market where it originates where FM would fade long before that. If aircraft went to FM, there would have to be a complex and expensive network of repeaters.

 

[wtp]

or...
WABC in NYC has 50,000 watts output
my local NOAA has, as do many, 1000 watts.
ABC covers 38 states, my noaa guy barely makes it here at 20 miles.
OR it could be frequency related.
lower freqs go around the world
higher act like light and go straight.

the AM thing for planes is that a mayday can be heard through another plane transmitting.