Eliminating interference

[dispatcher812]

Is there a way to eliminate all the interference I am hearing on the military frequencies? Most of it is just a lot of static that you can tell isn't a transmission. I have heard it on many different bands from vhf low to 330.000 and up. I am using a mobile antenna and a 436. I look at the easier to read manual and saw the IFX option. That seemed to help. Is that what it's for?

 

[TDR-94]

Filtering and eliminating any local interference, within your residence, it about all you can do.

 

[bearcatrp]

How high is your mobile antenna? In the house or outside? If it’s inside, get it outside above the roof line.

 

[spanky15805]

Start with 100% shielded coax, 9913, LMR 240 or 400 and turn off any LED lighting, would be my starting point.

 

[Alliance01TX]

Kevin

Reducing or eliminating interference (QRM /QRN)discussions have many variables from local (in house) things (LED's as noted above, etc..) to local sources and harmonics generated by just about anything with electrical components.

Several forums are embedded with these exact discussions, and often tun into an almost religious type discussion on whats best...no perfect answer is my view, as it depends on a station-by-station view of the root cause(s) of the interference sources.

My approach has always been to try to determine if my RFI/EMI is in my house, local power systems, near my house (AC units are a big one in many cases) or more or less outside my control, like a strong AM Station overwhelming the front end of my receiver, etc...lots of folks find that a PC, Monitor, USB Hub might be the source as it was too close to an older scanner, as one example only.

In my opinion and my specific approach to my station:
-As noted above, start with very-good quality COAX and Connectors. Yes, LMR cost more, but the lower loss trade off might be worth the investment.....And COAX will last a log time, so its really an "investment"to long=term scanner enjoyment
-If available run gear via 12 VDC power supply or battery source vs 120 VAC wall warts (transformers) as they are known noise makers
- If possible place antenna(s) outside & high as reasonable & safe to expand the Line of Site (LOS)
- For MIL-AIR best reception get an antenna that covers the 225-400 range or a good Wide Band Discone as an option
- Lastly, two over options, both can be expensive at times & can be found on eBay and ScannerMaster, etc...
1. A specific coax in-line filter for 225-400 MHz for Mil-Air Only (will render other freqs almost useless unless very close)
2. If used with a filter (after you reduced noise) some use an in-line Amp to pull in more signals - I don't use amps, but its an option to ponder...

Although most scanner hobbyist do not use any :station grounding system" I actually do as already a Ham Operator, and this I run all radios via !12 VDC distribution system and a solid ground system - this cut a lot of my noise out, although I do have issues in the VHF area (146.900 range) with an newer AC unit that is known to be a noise generator ( variable motor and controllers) and that's one that is tough to reduce even with Toroids.

Any number of things can cause or contribute (multiple things) the increase your specific "noise floor" and reducing those things can take a lot of time and expense in some cases. start with good antenna (and placement) and high quality coax is always your best bet in my opinion.

Hope this gives you a few ideas and sure others have have success with other approaches as no two are exactly the same in my experience.

Bill

 

[737mech]

Be sure to set modulation to AM, try to keep your coax away from power lines, if you can use a real power supply for radios like a SEC-1223. Using the wall wart that the scanner comes with and having another item like an old monitor or computer on the same circuit is not great. Consider installing an FM trap. Putting the antenna up high and outside is the best idea.

 

[dispatcher812]

Hey guys, thanks for the replies. I should have been more specific with my situation. I apologize for not doing so. The scanner I am referring to, BCD436, is actually in my car. I have an antenna magnetically mounted on the roof and is tuned for all bands. The cable is ran directly to the scanner and the only adaptor I have is an SMA to BNC. The power is coming off a USB cord attached to an adaptor that has two Cig plugs and 2 USB ports. THAT is plugged into the car. Next to it is my other scanner, an SDS 100 also plugged into the same adaptor for power. The GPS is plugged into one of the cig plugs and I have the DB9 spilt to go to both scanners. During my commute which is 72 miles one way, I may get occasional interference that gets worse and wore the closer I get to Boston. Then almost non stop when I get off the highway. Happens on both scanners but way more so on the 436. Swapping antennas does not help.

 

[prcguy]

Have you tried running the scanner off just batteries with the USB power adapter disconnected? Many USB adapters create lots of RFI so I would rule that out before looking elsewhere. I would also disconnect everything else like GPS and its power source and all cables except for the antenna.

If there is no improvement then you have good reason to be sad. If disconnecting everything improves reception then add each cable and external device until the problem comes back and you should then know what needs more attention.

Hey guys, thanks for the replies. I should have been more specific with my situation. I apologize for not doing so. The scanner I am referring to, BCD436, is actually in my car. I have an antenna magnetically mounted on the roof and is tuned for all bands. The cable is ran directly to the scanner and the only adaptor I have is an SMA to BNC. The power is coming off a USB cord attached to an adaptor that has two Cig plugs and 2 USB ports. THAT is plugged into the car. Next to it is my other scanner, an SDS 100 also plugged into the same adaptor for power. The GPS is plugged into one of the cig plugs and I have the DB9 spilt to go to both scanners. During my commute which is 72 miles one way, I may get occasional interference that gets worse and wore the closer I get to Boston. Then almost non stop when I get off the highway. Happens on both scanners but way more so on the 436. Swapping antennas does not help.

 

[Ubbe]

There are so many electronic devices in use these days that its almost impossible to scan in a city using just the squelch and not a subtone or a trunked or digital system. All the computers in a car also makes a difference. I have found one sweet spot on the car roof where the antenna picks up the least amount of interferences from the car. My car stereo sends out interference on the VHF marine band and VHF-LO if I use a scanner antenna inside the car. When I then drive beside a brick or concrete wall or a building it also seem to reflect my own interferences up to the roof antenna. Driving into a gas pump station with all those new high tech pumps with video displays force me to turn off all scanners.

/Ubbe