Not good reception in specific frqs excellent in others, why?

kbantikos

Member
Joined
Apr 11, 2012
Messages
20
ok, guys thank you sooooo much for your interest (y)(y)(y) due to the covid pandemic the package has made a looooong time to reach my house. This is the reason it took me so much time to reply. So long story short DEFINITELY i had an improvement BUT something to the experiments seems to go wrong after a day or two of experiments and tests, the signal sometimes was lost and sometimes was coming strong and I just could not figure out why until..... well you saw the picture.
I have the impression that in the first one or two days I had not this problem so most probably the filter broke after these days and in that period the background noise was completely silenced especially in 118.625 frq which is one of the tower's frequencies and it was quite more subtle in some other frequencies.
Also, I saw an improvement when I used both the FM filter and the airband filter, better than using only the FM filter which makes sense cause the airband filter was silencing some noise, slightly, but it did.
Unfortunately, I don't know if it came broken and just it became worse after one day or two of experiments, it was quite a fake filter so i believe the tension from the cable and the airband filter combined was too much for it.
Why I am so unlucky?
here are two videos one with the broken filter (when it came really broken) and one without just to take an idea I'll have to purchase another one :mad::mad::cry::cry: i am so unlucky.
My thoughts are that with a good FM filter I would have had some quite impressive results but who can really tell....
But I'll go for it .....
 

Attachments

ATCTech

Active Member
Joined
Aug 13, 2002
Messages
1,512
Hey, great to hear back from you! Do you have access to or know somebody that can solder the connector back on for you? If the board isn't cracked that should take care of it, but definitely create some sort of structural support for that chain of cable adapters and filters, they're never meant to take that kind of physical loading on the connectors or solder joints. Maybe put them on a little wooden backboard and use cable ties through holes drilled in the backboard to hold them securely to the wood? Arrange then so there's no tension or lateral force being applied to any of the connectors or the bodies of the filters. They should last decades that way.
 

spanky15805

Newbie
Joined
Sep 18, 2004
Messages
217
You have enough connectors there to almost qualify as a RCAG site(humor). But to what ATCTech mentioned. The mechanical strain with all that weight hanging off the back of the radio is not good. Try a quick experiment, as you're listening to what ever airband frequnecy, slowly lift from the cable end and listen for the change. If nothing changes, remove everything and plug the cable directly into the radio. It better improve! If it doesn't, means you broke the trace in the radio.
 

KB2GOM

Member
Joined
Jun 1, 2020
Messages
191
Location
upstate New York
Taking a very quick look I see the tower frequency shows full strength noise on your S-meter when no-one is transmitting. You'll have to find the reason for that as the radio looks like it's swamped with RF in that part of the band. Switch the radio to different modes - FM, WFM etc and see if there's any intelligence in that noise, music, voices, data and go on and search from there.

Second, the ATC transmitters may not be at the airport for the approach/departure frequencies. They may be at a remote radio site much higher up and/or closer to you. This would make sense if the same ATC frequencies are used for multiple airport terminal control activity. There are even mutiple sites at the SAME airport in many cases. We do that to separate main and standby radio from being affected by power or landline failures. Tower and ground frequencies may be running at lower RF power than IFR frequencies as well, but I can't say that's the case there obviously. Of course that would have no impact on how you hear the aircraft, that's strictly a distance, terrain, altitude and noise background related. 25km is quite a stretch for ground to ground reception with that terrain but it is possible - I have a similar situation here and can pretty much hear things at an airport about 25km south of me with a 120m rise in terrain not 4km away from me. The airport sits in a bit of a depression in the terrain atop that hill and is certainly not line of site for me in any way.

Your first task is to slowly (manually) run through the air band (and both sides of it) and watch the signal meter on the radio when there are no transmissions. If you have broadband noise that covers most of the band, especially the low end, then continue down the dial, as far as you can go, and see if there are and real hot spots in signal level. Do this WITHOUT any filters or preamps or other devices between the antenna and radio. You don't want that stuff influencing the result initially. If you see something curious it may be time to start powering off devices in your home (LED/CLF lights, dimmers, wireless devices of ANY type and anything that has a CPU of any type in it including telephones, routers, TV sets, cable/satellite boxes and so forth to start with). If you could a great starting point would be to power you radio from 12V DC battery and kill the power to your entire house. Then, if that changes nothing, take the radio mobile and scouring the area of a source. It could be very local to you and relatively low power, it could be industrial or even broadcast related. I've been involved with similar situations at work where factory machinery that uses RF energy loses it's shielding in a factory miles away which results in lumps of RF energy at differenet places in the spectrum. It doesn't take much, these radios are VERY sensitive. Once that's sorted the noise floor drops.

Keep me updated! My entire career was centered in part to almost exactly what you're chasing.

Cheers.
I agree entirely. To quote a famous detective: “Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.” - Sherlock Homes”

Weird stuff can happen with radios. I have a scanner that locks up on a particular frequency when I turn on a nearby shortwave radio.

Follow ATCtech's advice and "eliminate the impossible."
 
Top