BCT15X: SIGNAL TO NOISE RATIO on AM VHF/UHF AIR BANDS?

[iMONITOR]

I'm using a Uniden BCT15X exclusively for reception of AM VHF/UHF aircraft. I'm using a diamond D130J N discone antenna mounted on a 9' tripod inside my home office. Almost without exception I get full 5 signal strength bars every time the scanner breaks squelch. The odd thing is about half the transmissions are very clear with very little noise, almost full quieting but the rest are accompanied by static. Is this due to weak audio modulation from the transmitter or something else? I'm considering trying a preamp but if the signal is good, would it help or make the noise worse?

I should mention I'm also using a Stridsberg FM notch filter. The frequency does not appear to matter.

Thanks!

 

[ka3jjz]

I would first check the antenna connection at the scanner, and then at the antenna. Sounds a lot like a flaky connection at either or both Water in the coax isn't out of consideration here, either.

The constant 5 bars of signal also indicates something amiss. You may be experiencing intermod not from a FM station, but something else - MW or TV is not completely out of the question. You might also be getting clobbered by someone's appliance, or maybe even a crappy power transformer. This isn't the time to add a preamp until this is resolved.

Time to do some homework

Mike

 

[900mhz]

I would first check the antenna connection at the scanner, and then at the antenna. Sounds a lot like a flaky connection at either or both Water in the coax isn't out of consideration here, either.

The constant 5 bars of signal also indicates something amiss. You may be experiencing intermod not from a FM station, but something else - MW or TV is not completely out of the question. You might also be getting clobbered by someone's appliance, or maybe even a crappy power transformer. This isn't the time to add a preamp until this is resolved.

Time to do some homework

Mike

A very good point. I, myself experienced issues with aircraft and VHF-hi reception. Extremely bad reception until I realized that there is a TV transmitter less that 2 miles from my location broadcasting on channel 10. It is line of sight to my antennas. I built a band reject filter (over 6 MHz wide) to notch out the offending DTV transmitter over 90 dB. End of problems.

 

[ka3jjz]

Once you get this resolved, get that antenna up in the air. The way you have it now, you're really limiting what your discone can 'see'. Get it up, above obstructions, use a good grade of coax....do all of this BEFORE you think of a preamp

Mike

 

[iMONITOR]

I would first check the antenna connection at the scanner, and then at the antenna. Sounds a lot like a flaky connection at either or both Water in the coax isn't out of consideration here, either.

The constant 5 bars of signal also indicates something amiss. You may be experiencing intermod not from a FM station, but something else - MW or TV is not completely out of the question. You might also be getting clobbered by someone's appliance, or maybe even a crappy power transformer. This isn't the time to add a preamp until this is resolved.

Time to do some homework

Mike

Thanks Mike. The antenna connectors are professionally installed using Amphenol connectors. The scanner is brand new. The antenna and 18' of coax is all indoors so no weather/water related problems. The 5 bars is not constant, only as squelch breaks on an actual aircraft signal. Power related issues have been eliminated by trying a 12V Gel-Cell.

 

[iMONITOR]

Once you get this resolved, get that antenna up in the air. The way you have it now, you're really limiting what your discone can 'see'. Get it up, above obstructions, use a good grade of coax....do all of this BEFORE you think of a preamp

Mike

I don't need the antenna outdoors or higher. I'm hearing everything I want to hear (two airports withing 10 miles of home, and again with a full solid signal, just poor audio and static sometimes. Maybe just the nature of AM? I don't have any tall structures anywhere near my home for 20+ miles.

 

[n1chu]

I got a CREATE directional antenna I use with a rotator. I’m on the very edge of reception so that’s why I tried a directional antenna with some gain. I was told the aviation band favors vertical polarization so I mounted the antenna with the radials pointing up and down. I never tried a horizontal polarization so I havent any comparison but I’ve been assured vertical plays better. The coax is Belden 9913. Preamps do work somewhat but it must be noted they amplify not only the signal but any noise that’s there with it. My experience with preamps is for the little improvement I may see it’s not worth the expense of buying a decent amp.

 

[n1chu]

If it’s audio quality you seek, take a look at some of the aftermarket ham radio external speakers. Hams work in the AM Mode all the time. Some offer variable tone settings and noise blankers. They aren’t cheap but they work.

 

[Ubbe]

about half the transmissions are very clear with very little noise, almost full quieting but the rest are accompanied by static...I should mention I'm also using a Stridsberg FM notch filter.

Do you see any difference without the filter? If it gets much worse it could be some sort of overload problem from something not FM broadcast. The FLT201A have a 20dB attenuation at 118MHz and still 3dB at 135MHz. It's over 140MHz where it has less than 1dB.

If you believe its the traffic controller that gets static it could mean that they switch between different transmit towers and some of them are too far away.

/Ubbe

 

[ko6jw_2]

AM will always have more noise than FM. The signal to noise ratio is actually signal+noise to noise. AM does not have "quieting" nor does it "capture" like FM. A discone is a good choice for air monitoring. It has a higher angle of radiation (aircraft are up in the air) and unity gain because you almost always have line of sight to a plane. Discones are wideband which is good given the bandwidth of air bands.

An amplifier will also amplify noise and interference. Generally a waste. Antenna height and good feed line are more important.

Aircraft are vertically polarized.

A good external speaker may be helpful. One with built in DSP may be good.

Don't obsess over signal strength readings on scanners. They are not calibrated accurately. Even real S meters are not lab grade instruments. Can you hear the signal? Yes? Don't worry about the reading.

 

[ka3jjz]

Any possibility of common mode issues here? As the run of coax is totally indoors, if it happens to pass too close to a microwave, plasma TV, etc. I could see this causing noise issues.

Oh and learn how to solder a PL259 or a BNC correctly. Heck if a klutz like me can do it anyone can. I don't doubt that there are any number of YouTube videos on this subject.

Mike

 

[iMONITOR]

If it’s audio quality you seek, take a look at some of the aftermarket ham radio external speakers. Hams work in the AM Mode all the time. Some offer variable tone settings and noise blankers. They aren’t cheap but they work.

I did. I'm using a Yaesu SP-9000

 

[vagrant]

@iMONITOR There is a paging system near me that has four sites, two are within five miles and one of which is a mile away. They all TX simultaneously on the same frequency with a maximum ERP of 350 watts. They are intermittently transmitting, which mimics the issue you have of not always hearing the static. I have tested with a discone indoors and out, as well as my vehicle. The RFI is nasty. I pulled it up on an SDR and I would see my whole noise floor shift when looking hundreds of MHz away from the paging signal which is around 152 MHz when it would transmit.

A nearby paging system may not be the cause of your issue. It could be a wonky transformer/wall wart inside your home, or something else. Still, for me I now use two paging filters inline from Dale Parfitt tuned to the offending signal for my system at home that uses an outdoor antenna. (Yeah, so bad I need to use two) I also use one with the scanner in my vehicle and I use one inline with my amateur mobile radio. The filters work very well.

If you have an SDR, look for a strong frequency that intermittently transmits. Turn down the volume on the SDR and watch the waterfall. If you hear the noise during transmit...time for a filter.

I am unsure if you are in the U.S.A., but one could use the FCC website to search and identify the offending site and it's location.

License Search - Geographic Search

 

[iMONITOR]

Any possibility of common mode issues here? As the run of coax is totally indoors, if it happens to pass too close to a microwave, plasma TV, etc. I could see this causing noise issues.

Oh and learn how to solder a PL259 or a BNC correctly. Heck if a klutz like me can do it anyone can. I don't doubt that there are any number of YouTube videos on this subject.

Mike

I appreciated the suggestions from you Mike, and others, but I'm stumped. There are no PL259's involved. Type N connector on the antenna side and BNC on the scanner side. The cable was factory made. I've also tried other cables with no difference. I would think it that was the cause of the problem the problem would be consistent. I momentarily killed the main breaker shutting down all electrical interference in my home.

 

[iMONITOR]

Do you see any difference without the filter? If it gets much worse it could be some sort of overload problem from something not FM broadcast. The FLT201A have a 20dB attenuation at 118MHz and still 3dB at 135MHz. It's over 140MHz where it has less than 1dB.

If you believe its the traffic controller that gets static it could mean that they switch between different transmit towers and some of them are too far away.

/Ubbe

I ran "Close Call" with no results of other strong offending signals. Ham radio/CB/FRS-GMRS are almost non existent near me.

 

[iMONITOR]

Most of the aircraft signals will break the squelch even when sit at 18, so the signals are not the problem. The noise must be coming in on the transmission itself.

 

[n1chu]

I did. I'm using a Yaesu SP-9000


View attachment 109423View attachment 109426
View attachment 109425

Awesome.

 

[Ubbe]

I ran "Close Call" with no results of other strong offending signals. Ham radio/CB/FRS-GMRS are almost non existent near me.

Close Call needs one single frequency to be much stronger than anything else, that seldom happens.

Best tool would be a SDR dongle and SDR# and look as wide as possible at the spectrum display and note if the noise floor moves up when you hear the noise in the air transmission. Then it's a strong signal in another band that interfere. Then move the SDR# spectrum to 140-150Mhz and lock for a big spike when the noise are heard. Then move further up to 160Mhz and so on.

Try setting the attenuator on for the VHF airband. If the noise are gone then for sure it's an interference from another frequency. It's the opposite test compared to removing the FM filter and see if it gets worse, but gives the same result of a possible out of band interference.

Some air channels are often interconnected and one channels reception are relayed to another frequency's transmit frequency. If it receives a weak aircraft transmission it will retransmit that bad audio at full signal strength on another frequency.

/Ubbe

 

[iMONITOR]

Awesome.

Thanks! It is very awesome, only exceeded by it's insane price!

I have my BCT15X on top with protective rubber feet, and my BCD996P2 on top of the BCT15X, also with rubber feet. This puts them at an ideal viewing height without the need to tilt them. This thing is huge, 9.7w x 6.5h x 17.2d inches. There is a lot of unused space in the enclosure, giving some ideas about putting something else inside, possibly a 12V power supply. It shouldn't cause noise as the speaker is not amplified.

 

[iMONITOR]

I'm now logging the RSSI of all signal hits using Proscan.