Reception Mystery - Help!

[emsflyer84]

FM is the mode the scanner is receiving. Has nothing to do with the interference. Yes, a scanner will drastically degrade with strong FM or TV broadcasts nearby. Try a cheap FM broadcast notch filter from radio shack or even Lowes if they carry them. I have a cheapy and it was effective.

Thanks. Does the filter need to be installed at the antenna? Or is at the scanner OK. I already have a custom notch filter at the scanner for some strong pager data interference I was getting on weaker signals.

 

[vagrant]

Install the filter at the scanner along with the PAR filter you have. Just as the pager signal was causing you problems, so is the FM broadcast station, or stations, that are nearby.

 

[Btruitt95]

Hey all, I've posted several times on the forums looking for help or advice to extend the range of my home scanner setup. I have a Whistler TRX-2 and a folded dipole antenna tuned to my scanning range, high VHF. In between is about 75' of low loss RG6 coax. For the past few months I've played around with different antennas, even buying and installing a Larsen tri-band whip antenna installed on a ground plane kit which was highly recommended for my situation. I still felt like I wasn't getting the range I should be. The reason being is that I was getting almost the same reception with a handheld scanner and rubber duck antenna while driving around in my car. Finally today I did an experiment. I took my folded dipole off the roof and ran a 3' jumper cable directly to my handheld scanner. I stood in my driveway and the reception was dramatically better then when the antenna was on the roof. I did the same test with the Larsen tri-band. Again, super performance, and the antenna was laying on it's side in my trunk. Still better reception then either antenna on the roof. Perfect! My feed line in the problem. Maybe water intrusion, maybe it's because I have two sections pieced together to make up the 75' run. So back on the roof I went to put my dipole back up. Just for fun I took the handheld scanner and 3' section of cable on the roof with me. I was shocked to find the reception was garbage again! The same setup that works amazingly well 30' lower in my driveway, now had junk reception. It seemed only SLIGHLY better while I was holding the antenna in my hand vs. when it was mounted on the metal mast I have on my roof. To make a long story longer, there is something about the physical location on the roof that is killing the reception. My house sits on a bit of a hill, with great line of sight for miles in all directions. I should have phenomenal reception on the roof. There are no other antennas, the electrical feed line from the street is on the other side of the house... I even took my wifi weather station down and turned it off with no change in reception. This part of my roof is above the master bedroom, and there is no electronics in that room by a tv and cable box. I've been chasing this issue for months thinking it was my equipment so it's frustrating to find out it's the location (which I cannot easily change).

Any thoughts at all about this? It's a total mystery to me. I'm glad it's not the equipment that's the problem and at least I'm getting somewhere here, but frustrating at the same time. Thanks again.

most antennas always work bit better in vehicles cause of metal ground. Sound to me you're no grounded your antennae. Even tho I am no expert that usually cut your receive by 90-95% unless they are close.

 

[emsflyer84]

Thanks all, ordered a cheapo FM notch filter to start and see what happens. If it seems like it’s working ill have PAR make me one for the specific FM frequency.

Side note: PAR Electronics is excellent to deal with and makes excellent products.

 

[vagrant]

You are not alone. Many are not familiar with the affect a strong transmitter nearby will have on their monitoring whether watching broadcast TV, scanning, etc. Someone tells us, we figure it out, or we don’t. FM transmitters use significant power versus whatever power that pager transmitter was causing you grief. I also use filters in my vehicle to reduce the interference ranging from AM, FM, 152, and 162 MHz because of the improved antenna exterior to my vehicle. 152 MHz is so bad for me, I use a filter on my VHF/UHF amateur radio line, thanks Dale.

Also, to answer your question, yes.

Thanks. I guess I’m just not familiar with the effects of FM and AM transmissions on scanner antennas. So it is possible that these close transmitters are killing my reception, not just making it sound like there is interference?

 

[emsflyer84]

Thanks, I’ll give the filter a shot. It’s strange though, it seems like this problem just arose, or at least got worse in the past few months. I can’t think of anything that would have changed in that time.

 

[RFI-EMI-GUY]

Thanks, I’ll give the filter a shot. It’s strange though, it seems like this problem just arose, or at least got worse in the past few months. I can’t think of anything that would have changed in that time.

1) Make sure the transmitter your paging filter is designed for is still on same frequency where is was.
2) Foliage dropping increases signal levels, especially UHF and 700/800 frequencies. Your receiver is seeing an aggregate of many frequencies in its front end and the powers add up.

 

[emsflyer84]

1) Make sure the transmitter your paging filter is designed for is still on same frequency where is was.
2) Foliage dropping increases signal levels, especially UHF and 700/800 frequencies. Your receiver is seeing an aggregate of many frequencies in its front end and the powers add up.

Thanks, lots to think about. I think the notch filter I have now is still doing its thing. When I take it out of the line the pager interference is very strong on many of the weaker frequencies. Boy it would be nice if the FM filter solves this issue. We’ll see...

 

[emsflyer84]

1) Make sure the transmitter your paging filter is designed for is still on same frequency where is was.
2) Foliage dropping increases signal levels, especially UHF and 700/800 frequencies. Your receiver is seeing an aggregate of many frequencies in its front end and the powers add up.

Since the same tower houses an AM transmitter, is it possible I’ll need an AM filter as well? Does AM typically not interfere as bad as FM?

 

[kruser]

After you get the FM trap, run your coax tests again with the antenna still on the roof. A coax problem may still exist and be responsible for the worsening conditions you think you have noticed.
A coax problem may be masked by the strong signal from the FM station but may show up after you have the filter inline with your portable for the short 3' coax jumper test.
Hopefully the FM trap will do the job!

I'm very near ( a couple miles) from several tall hospitals in almost all directions around me. Every one of these hospitals have 152 MHz paging transmitters on their rooftops! A 152 MHz paging filter from PAR was a must for me for all older scanners and then all ages of GRE designs except the Pr0-2004 thru 2006 models GRE made for RadioShack. Those were triple conversion models and apparently also had better filtering so the local paging transmitters did not bother them.
The other GRE designs including the TRX models all suffered badly from the paging signals.
I'm also several miles away for the group of FM radio station towers in town. I did not thing they were affecting my reception until I noticed a hissing like background noise in all the GRE designs. It turned out to be noise from the FM stations even though they were at least 12 to 15 miles away.
So I bought another PAR filter but this time it was their FM Trap.
That thing worked wonders and immediately helped my GRE designed radios pull in signals they never heard before. The FM stations were actually responsible for desensitizing the front ends of the GRE based models so their AGC circuits would basically shut down the front end to the point you heard near nothing. That's called desense. The paging filter cured intermod problems mostly but it also helped with desense issues when our states new statewide P25 system came online using several paging band frequencies only a hundred or so kHz away from the worst paging signal.
I could not hear the states P25 system with any GRE based model. That one was tricky as the PAR paging notch filter also notched out the states frequencies being so close together. I had to play with filters and custom attenuaters in order to kill enough paging signal but leave enough P25 signal in order to hear the new statewide system.
I guess the good think I learned from it all was the fact that the Uniden models did not suffer from the same problems and I can run them without any filters at all. Same goes for the expensive comms receivers I own made by Icom. They are fairly bulletproof when it comes to strong in and out of band signals.

Good luck with the new filter when it comes in and I truly hope it works well for you. I have a feeling it will as the advice you've been given by the others in this thread is all spot on good advice!

 

[kruser]

Since the same tower houses an AM transmitter, is it possible I’ll need an AM filter as well? Does AM typically not interfere as bad as FM?

All the troubles I've had similar to yours have never needed an AM band filter.
Some of my HF radios were helped by an AM filter but I think most scanners provide pretty good AM broadcast band filtering from the factory. The AM band is so far away from a scanners reception range that out of band filtering should be commonplace in probably all scanners to prevent AM band issues.
If you do suspect AM issues, that cheap HPN-30118 filter linked earlier by @vagrant that scannermaster sells does a pretty decent job with the AM band but it's FM portion can eat into the lower part of the civil AIR band if you monitor aircraft at all. I've used the exact filter for the AM problems I had and they worked well. That filter also did a decent job at reducing the signal levels from the FM stations I mentioned in my other post to the point that desense was not really an issue any longer but I then became more involved in air band monitoring so now that little HPN filter sits in my HF antenna feed if needed.

 

[RFI-EMI-GUY]

Since the same tower houses an AM transmitter, is it possible I’ll need an AM filter as well? Does AM typically not interfere as bad as FM?

You should not normally need an AM band filter for your VHF/UHF receiver as the antenna is a small fraction of the MW AM wavelength. If this were a shortwave radio receiver and wire antenna, yes most likely.

But your coax cable and house wiring are a significant wavelength and the outside of the coax and your house wiring itself, may have common mode AM interference that would need to be stopped by grounding them or toroidial chokes installed.

 

[WB9YBM]

Finally today I did an experiment. I took my folded dipole off the roof and ran a 3' jumper cable directly to my handheld scanner. I stood in my driveway and the reception was dramatically better then when the antenna was on the roof. I did the same test with the Larsen tri-band. Again, super performance, and the antenna was laying on it's side in my trunk. Still better reception then either antenna on the roof. So back on the roof I went to put my dipole back up. Just for fun I took the handheld scanner and 3' section of cable on the roof with me. I was shocked to find the reception was garbage again! The same setup that works amazingly well 30' lower in my driveway, now had junk reception.

When a problem "mysteriously" appears and disappears, it's usually because of an intermittent somewhere--intermittent open or short. Have someone wiggle the connectors, antenna, etc. while you listen to the scanner and where ever that someone is when you hear signals appear and disappear, that's where the problem is (and hopefully it's only in one spot!).

 

[emsflyer84]

All the troubles I've had similar to yours have never needed an AM band filter.
Some of my HF radios were helped by an AM filter but I think most scanners provide pretty good AM broadcast band filtering from the factory. The AM band is so far away from a scanners reception range that out of band filtering should be commonplace in probably all scanners to prevent AM band issues.
If you do suspect AM issues, that cheap HPN-30118 filter linked earlier by @vagrant that scannermaster sells does a pretty decent job with the AM band but it's FM portion can eat into the lower part of the civil AIR band if you monitor aircraft at all. I've used the exact filter for the AM problems I had and they worked well. That filter also did a decent job at reducing the signal levels from the FM stations I mentioned in my other post to the point that desense was not really an issue any longer but I then became more involved in air band monitoring so now that little HPN filter sits in my HF antenna feed if needed.

Just thinking about these issues some more, it makes sense that I’m getting outside interference, like FM signal. That would explain why both antenna’s, the dipole and the Larsen tri band have almost identical performance when mounted in the same spot, even though they are very different antennas. If the FM signal is effecting the scanner, it wouldn’t matter what kind of antenna was connected to it...

 

[dlwtrunked]

Well I would start on that because most scanners have little rejection of the FM broadcast band. You will need a filter to block that. If you are using 75 ohm cable you can get a FM broadcast band filter from you local Radio Shack (LOL).

Concur. EVERY scanner owner should have and FM broadcast filter to test when things like this happens and often it is best left in the feedline. FM broadcast de-sensing is devious. It often leaves *no* identify characteristic other than weakened reception of other signals. If one does not think they have this problem, there is a good chance they do if there is a nearby FM broadcast station.