NXDN Bleed-over on several frequencies

[Tim]

Greetings,

I recently purchased a SDS-200 radio from Scanner Master. I purchased it with the upgrade for DMR/NXDN. I am receiving NXDN bleed-over on a number of UHF frequencies. It would be similar to what you get when you try to scan in a downtown environment. The problem is that I am a good 10 miles from downtown. My previous base radio (BCD536) didn't have bleed-over like this at all. To my knowledge, there is no NXDN tower in my immediate area. I am just wondering if there is some sort of setting that could be messed up? The only settings I could think of was the "Global Auto Filter", but i tried is as "Normal" & "Auto" with no luck.

Any thoughts as to what else I can do?

Tim

 

[jonwienke]

It is entirely possible a new transmitter has been installed near you recently. NXDN is fairly commonly used by businesses, as well as railroads, and by some government and public safety agencies as well.

 

[Saint]

Greetings,

I recently purchased a SDS-200 radio from Scanner Master. I purchased it with the upgrade for DMR/NXDN. I am receiving NXDN bleed-over on a number of UHF frequencies. It would be similar to what you get when you try to scan in a downtown environment. The problem is that I am a good 10 miles from downtown. My previous base radio (BCD536) didn't have bleed-over like this at all. To my knowledge, there is no NXDN tower in my immediate area. I am just wondering if there is some sort of setting that could be messed up? The only settings I could think of was the "Global Auto Filter", but i tried is as "Normal" & "Auto" with no luck.

Any thoughts as to what else I can do?

Tim

I have the same problem with the 436HP scanner, I get terrible bleed over of dmr and nxdn systems in the military band, also had terrible bleed over with the SDS100 scanner in the 118-136 AM aircraft band.

 

[Ubbe]

I am receiving NXDN bleed-over on a number of UHF frequencies.

Are you only hearing a datasignal that sounds like NXDN or are the scanner decoding the signal and says it's NXDN and show RAN and TG?

It doesn't need to be a NXDN site causing the overload issue, it can be any strong transmitter that makes the scanner receiver a mix of all kinds of frequencies. What does the dBm signal strength say and Noise and D-error? There are two kinds of Auto settings you can try in the filter. Also when you receive a bleed over on a channel, try activating IFX on that channel and try the filter settings again.

If all signals you receive are strong, it shows -80dBm or stronger like -70dBm, then you can activate the attenuator setting and see if that helps.

/Ubbe

 

[bmendez]

Quick question whast the best rrsi supposed to be

 

[jonwienke]

RSSI is a negative number, so -100dBm is worse than -70dBm.

 

[Tim]

There are no RAN or TG's that come up when I am hearing this. Listening to the radio this evening there is not much bleed-over going on. I am sure that coincides with the fact that most local NXDN users are daytime businesses. I will have to check out the dBm strength tomorrow. At least this post gives me a few more things to look for.

I will say that occasionally the BCD-536 would get bleed-over on the airband from the nearby airports ATIS. I am roughly 2 miles west of KMKE airport, but would hear the airport's ATIS bleeding over on a few non-airport used frequencies at times.

Tim

 

[Ubbe]

I will say that occasionally the BCD-536 would get bleed-over on the airband from the nearby airports ATIS. I am roughly 2 miles west of KMKE airport

Those ATIS transmitters are usually low power, something like 10watt. The airport has a radiosystem of its own for mainantance and gate personel and all people involved in the daily work at the airport. That system are probably using higher power than 10watt to give good coverage.

It could be a bit of a problem being that close to several multifrequency radiosystems. It's probably when the tower transmits, or a nearby aircraft, that mix together with the constant ATIS transmitter that creates that intermod or overload issue. Also Uniden scanner have a bandpass filter for VHF air that pass 108-137MHz and it's not that it stops all signals at 100MHz. It will still pass those broadcast transmitters signal at a high level. Maybe a more effecient FM trap filter could help. It is the sum of all signals that are passed to the receiver that could create a problem. Reducing the level of one of the signals might be enough to give a trouble free reception.

The 400MHz bleedover are more difficult to solve as the bandpass filter in the scanner pass the whole 320-510MHz range. But as the BCD536 seems to cope with it without issues it migth be fixable in the SDS200 with all the settings that are available. Especially if you do not do weak signal monitoring and can take a loss in reception range.

/Ubbe

 

[JoeBearcat]

Try using IFX. It may be a frequency mix ending up on the IF frequency of the scanner.

 

[bmendez]

What does the attenuator

 

[ratboy]

What antenna are you using on the SDS200? I found that at home, I can't really use anything but the stock whip or I have problems with static bursts in the railband and even some UHF frequencies. At work, I can run a mag mount mobile antenna stuck to the top of my steel cabinets and it works quite well, as long as I avoid a few frequencies I don't really care all that much about. Mobile, it all depends where I'm at. If I am sitting where I normally watch trains, I get a of desensing period, due to a nearby FM station and WX transmitter. My other handheld radios work much better there. If I go about 4 miles or so west, all is well, and I can use a mag mount antenna with no real problems.