Close Call frequency picked up...

[7Seas]

Hello all,

I am using my new Uniden BC125AT and learning all the features. Lately, I've been picking up frequency 506.3125 with the 'Close Call' function, but nothing is being broadcast. It's a strong signal though. Is it possible I'm picking up a baby monitor or something?

Chris

 

[Whiskey3JMC]

Baby monitor? Not on T-band (500 MHz) Perhaps a Broadcast TV signal?

 

[KevinC]

That would probably the the pilot carrier for TV channel 20.

 

[gary123]

It is Ch 20. If its strong enough to Close Call, either your sitting right on top of something generating RFI or most probably its a TV carrier.

 

[VA3JPX]

What mode is it detecting it as? if its AM, then its a pilot TV carrier

 

[KevinC]

What mode is it detecting it as? if its AM, then its a pilot TV carrier

Close Call doesn't detect by modes, it will use whatever the band default is for that band.

 

[Tinkerwave]

Can you tell Close Call to only alert certain types of transmission, like FD and EMS? or only certain modulation, like TDMA and FDMA? And can you have it avoid a set of frequencies?

 

[Ubbe]

CloseCall are just a simple frequency counter and it doesn't use modes at all. The microprocessor in the scanner receives the frequency info from the CloseCall function and use that to set a frequency to monitor, and then it looks at the bandplan modes setting if the CC are set to auto or whatever you manually have configured in the CC setting and set that in the receiver to be able to produce any audio that will also make it possible to decode a digital signal in the same way as when you manually enter a frequency from the keypad.

As it is a frequency counter the microprocessor are set to use some limits to avoid false detects so it will have a minimum time set where it triggers and the frequency needs to be fixed within a certain bandwidth, something that's appropriate to a normal modulation level, perhaps 30KHz. When a FM broadcast station makes a pause in its 150KHz modulation for one second it will often trigger CloseCall if the FM broadcast band isn't set to be filtered out in the scanners setting. The same for a terestial analog TV signals audio carrier which is FM modulated. Digital TV signals are transmitting continous wide bandwidth datasignals so I wouldn't expect them to trigger any CC hits.

It's only logical filters in the CPU so that the frequency counter are still interfered from the RF signals and are more or less blocked to receive any other signal in that frequency band. If you use external FM trap filters you get rid of that interference and VHF aircraft and similar nearby frequencies becomes much more sensitive with a much longer CC range. You probably could also set CC to use the attenuator setting to lower the interfering broadcast signals where it doesn't block the frequency counter, but then the range will also be reduced where it gets hits at other frequencies.

/Ubbe

 

[Tinkerwave]

@Ubbe thanks for this helpful info on CC. So, when functioning as a frequency counter for Close Call, since it has demodulation, I'm a little surprised it can't be configured to first (i.e., before reporting or alerting to a detected signal):
1) determine what kind of modulation the signal used, before counting it; and
2) determine if the frequency detected is in a group/type (e.g., PD, FD, EMS, etc.); and
3) check to see if that group is to be ignored before counting.

Since no Unidens can do this type of Close Call filtering, is there a software that can? Perhaps there's one or two that could take the live serial data stream from the scanner, and do one or both of those filters?

Also, yes I plan on using an FM trap filter, as you mentioned, to help improve CC's sensitivity.

 

[Ubbe]

1) determine what kind of modulation the signal used, before counting it; and
2) determine if the frequency detected is in a group/type (e.g., PD, FD, EMS, etc.); and
3) check to see if that group is to be ignored before counting.

As todays signals are mostly digital and carry different talkgroups, it would be the next logical step for CloseCalls evolution to get more use from it. Functions to locke out systems, TG's, service types as well as compare to database and only trigger on new objects and so on. There's lots of stuff that Uniden can do to their scanners but will they get their invested money back and sell more scanners if they add new features?

/Ubbe

 

[Tinkerwave]

Good question. I don't know. I was hoping at least a software would be able to do those things. I know there's a few software that take serial data output from various types of scanners and process it, but there's very little data showing the results of those software: virtually no YouTube, webpages, screenshots, or even comments. I'm guessing you don't know of any software that can do those things?

 

[Ubbe]

The most problematic thing with these kind of projects are how to enter the different kind of filters that you would like, frequency ranges to accept or ignore, TG's to accept or ignore and so on. Would it need to use the scanners CloseCall function or could it be a SDR dongle set to a very low gain and connected to a RaspberryPie type of microcontroller that then sends commands to the scanner?

You probably would have to approach a program coder that have done something similar with the output from a scanner and ask if he could expand on the features and add the kind of functions that you and several others would appreciate to have. But first try and write down a flow diagram what should happen when the scanners output signals a CC hit on a frequency and what kind of input device are needed to program the different kinds of accept and ignore filters. If you manage to see in the flow diagram that it looks logical it will be much easier for a program coder to see exactly what you want and how much work it would take. If he already have programs that reads the data from a Uniden scanner and also sends commands to it then it is just a couple of hours work to code with fixed filters if your flow diagram looks doable. Adding ways of changing filters takes more time but I guess it could be done by reading your programming in a specific favorite list, one system with locked out frequencies and one with loacked out TG's and a system with locked out service types. It could also be whole ranges set in some innovative way. And then it could be another favorite list with accepted values and ranges. Then you could enter and change all variables in the scanners programming.

Try and design everything in a functional way with flow diagrams as it then are much easier for a programmer to follow your instructions, or he has to come up with solutions by himself that could take a lot of time if your instructions are vague.

/Ubbe