How To Cut Down On AirBand Interference?

[Rt169Radio]

Hello all, I been listening to the airbands for a little more then a year now and one thing I have noticed that I can't seem to get rid of is the random noise and interference.

I have a Uniden BCT15 hooked up to a Diamond DJ130J outside that is 25 feet of the ground with 50 feet of RG8X coax.

What happens is I can't listen to the airband without my squelch being closed all the way, and even then I still get some random noise and interference. It will be enough to break the squelch and I end up temporary locking out the offending frequency. I have a FM radio station transmitter six miles away from me and a AM radio station transmitter two miles and a half away from me. What the noise sounds like can be either quick and short loud bursts of static or the noise that is present when you open the squelch all the way on a frequency.

I been looking at this filter that is listed below, but I'm not sure it is what I need.

BPF-AIR Air Band Band Pass Filter | Scanner Master

BPF-AIR Air Band Band Pass Filter

www.scannermaster.com

 

[Ubbe]

It's the sum of all signals that pass thru the scanners bandpass filter that can create problem. It sounds as if the FM broadcast transmitter are creating a lifted noise floor in the scanner and it could also be some strong signals in the VHF band, perhaps a pager transmitter in the 155MHz band or NOAA. If you do not need to monitor any frequencies other than VHF AIR then that BPF-AIR filter should work to reduce offending signals enough to not create interferences.

If you monitor other frequency bands then something like the HPN-30118 will allow VHF AIR to be monitored but block FM broadcast and signals below 30MHz. But if that FM transmitter are high power you will probably need a FM trap filter that attenuates a lot more. Look in the FM trapfilter thread. You also have this filter: FM Notch Filter 88-108MHz; 85dB Rejection; Bandstop; 9th order SMA-M + SMA-F | eBay

/Ubbe

 

[BinaryMode]

There is also an FM broadcast band stop filter that the RTL-SDR blog makes that can be used as well. But, I'm wondering if using two filters would reduce the db for air?

Do tunable notch filters exist withen consumer price ranges? I see nothing but microwave stuff.

 

[dispatchgeek]

Try an FM filter and see where that gets you. It was day and night for me with an FM about 1/4 mile away.

 

[G7RUX]

The sources of your woes are difficult to determine and you will likely need to have a bit of a scan around and experiment with a few things. Most scanners don’t do all that well when hit with multiple strong signals although they might be ok with one or two. The most common sources of problems are vhf pagers, nearby broadcast FM radio and occasionally strong nearby comms systems, especially digital ones, all of which tend towards producing intermodulation distortion in a wideband receiver. Indeed, even a MF or HF station nearby can cause issues.

One way to tell if it is intermodulation distortion is to pop an attenuator in front of the receiver input (use a hardware one and not one that might be built into your receiver) since it’s usually a third-order product; reducing the interferer by say 6dB will likely reduce any intermods due to it by something like three times that much. This might be enough to avoid the issue in the meantime, although it will obviously reduce your system sensitivity a little for the duration.

if you are only listening to VHF airband then making your own filters is not too much of an issue and can be very instructive, there being lots of useful information out on the web, or there are filters available to do the job reasonably well. Using the receiver more widely might mean you need to look at a notch filter to take out a good chunk of the most problematic signal(s) and there are lots of sources for this style of filter, made from coax, on the internet.

Do let us know how you get on!

 

[xms3200]

I have the same interference issues, but only when it is hot, like around noon, and at nightime and early morning, it is clear. Will a filter help solve my issue. I thought VHF air did not get affected unlike HF

 

[wtp]

if it is a near continuous signal.
set up a custom search for 25 to 1300,
take the antenna off,
and let it scan.
you should find birdies, internally generated signals, and any local transmitters.
since the radio covers the FM band you should find that local one.
when you find the real interference ones, give us a list.
you might find it in a spot no one thought of.

 

[Rt169Radio]

Thanks for all the responses, I will have to do some checking around for interference.

 

[G7RUX]

Thanks for all the responses, I will have to do some checking around for interference.

It probably won’t look like interference, just reasonably strong signals.

 

[wtp]

my county has some stuff in the 217, 453 and 458 telemetry.

 

[G7RUX]

my county has some stuff in the 217, 453 and 458 telemetry.

That would be a good point to start, especially since the original issue was digital noise breaking the squelch.

 

[Rt169Radio]

So what I have done so far is take my antenna connection of my scanner and open my squelch almost to full open to look for any birdies, internal signals, or any local transmitters on the Aircraft band.

Unfortunately or maybe in this case fortunately I get nothing at all, its just when I hook my antenna back up is when I start getting noise on random freqs again.

 

[G7RUX]

It is unlikely the frequencies of interest are random since the relationships which generate intermodulation products can be rather complex.

 

[wtp]

that video lets you hear a birdie. it just sounds like an open mic.
you would not have to open the squelch, it will come through it.
have you tried it with just the back of the set (stock) antenna as too much signal does not help.

 

[Rt169Radio]

So far I haven't been able to figure out where any interference is coming from, but I did notice one weird thing. On my trash pickup days I noticed that the trash truck for some reason causes immediate interference to the air band.

I found that out by noticing when the truck pulls up to my next door neighbor house I get immediate noise on the airband, and by the time it goes by my other next door neighbor house it immediately disappears.

I think my next step is to get a handheld scanner and go around my house with the antenna off and see if I can track down any interference.

 

[wtp]

you can also call the truck the big reflector...
we are about to have some nice mirrored windows installed, that should cut down on my reception.

 

[G7RUX]

Having had a bit of a look around at available filters for receiving airband, both Temwell and MiniCirCuits can supply decent performance filters for sensible money. They are components and not connector used so a little work will be required to hook them up but none of it will be terrible if you’re old with a bit of small soldering.

 

[dlwtrunked]

Having had a bit of a look around at available filters for receiving airband, both Temwell and MiniCirCuits can supply decent performance filters for sensible money. They are components and not connector used so a little work will be required to hook them up but none of it will be terrible if you’re old with a bit of small soldering.

I have looked at many of them and made measurements. Cheap ones for cable TV are terrible as they block out low end of VHF aircraft (down to 118 MHz) and so do all the ones sold for scanner users (as most do not listen to VHF aer). The best, essentially only good one, that I found was the ZBSF-95-N+. I consider anything else, for the people listening to VHF aero, to be a waster of money. Not cheap ~$125 and Mini-circuits only shows 7 in stock.

 

[Ubbe]

Most filters have been measured in the FM trap filter thread so it's easy to see which filters that leave VHF air unaffected. But then the FM 108MHz frequencies are not attenuated a lot and it will depend of where your local FM transmitter are in the FM band if you can use a filter with low attenuation.

/Ubbe

 

[MiCon]

"So what I have done so far is take my antenna connection of my scanner and open my squelch almost to full open to look for any birdies, internal signals, or any local transmitters on the Aircraft band.
Unfortunately or maybe in this case fortunately I get nothing at all, its just when I hook my antenna back up is when I start getting noise on random freqs again."

This caught my attention. It's possible the problem is your antenna, antenna cable, cable connectors, or a combination of any of these.

Have you tried a different antenna and feed? It doesn't have to be on the roof, just hook something different up to your radio and see if you still get the interference.

<>< Mike