Two Tone Detect capturing wrong tones.

[JMR3865]

Hi all,
I dont think this is the correct forum to put this in but not sure exactly where to put it. It's not really scanner related either but I figured someone may be able to help me here.

We are using Two Tone Detect from Iamresponding for recorded audio pages notifications to our phones. My problem is, TTD is picking up another squad's tones that are close to ours and it initiates notifications for ours. We looked over the coding and found where their tones are being captured. We tighted the software but it still does this.

The kicker is, it doesnt do this 100% of the time, I believe its only on one of the dispatch center's consoles.

We have been in contact with IAR and did not get any solid solutions.

Thanks for any suggestions.

 

[902]

Modern console-based encoders are microprocessor controlled and should be able to generate tones well within tolerances. The other place that's falsing your tones may have an older Plectron encoder that's not so precise. They used wire wound around cores and capacitors to get into the ballpark. Back in the day, when those were new, they were usually pretty tight and a technician could tune them with a Lissajous pattern, but they probably haven't been touched in years and may be "good enough" to activate their own devices, but may be out of tolerance enough to false yours. Maybe. And maybe not. You need to do more legwork on exactly when you are getting falsed and what the circumstances are through which you are falsed. For all anyone knows, everything could be completely microprocessor driven, and the alerting tone sequence could be heterodyning with a CTCSS tone from one base station in a multi-site arrangement that might be a higher level than the other stations and creating a mix that's on your tone frequency. It could get complicated. A competent local technician can help you with that.

The company you talked to might not have a solution because in their eyes, their stuff probably works fine. That might also be amplified by the sampling rate they use, which might expand that window of tolerances even more.

What you have now is a delicate situation of politics and persuasion. You have to ask the powers that be to check their equipment, and having as many details as possible will help you, especially when identifying which console the transmission came from. Remember, if their stuff is working, they don't "have to" anything, so a cordial approach is everything.

Your ultimate solution might be to change tone frequencies to something that's not so close.

 

[KC2NNS]

A suggestion -

A directional antenna pointed at your dispatch and away from the interfering station (if that's possible from your location) may be a good "outside the box" fix without worrying about the tones themselves.

Good luck!

 

[902]

A suggestion -

A directional antenna pointed at your dispatch and away from the interfering station (if that's possible from your location) may be a good "outside the box" fix without worrying about the tones themselves.

Good luck!

There's a way to make a cardioid antenna pattern using an omnidirectional antenna with a Yagi and feeding them out of phase so the Yagi cancels the signal from the omni in the direction it's pointed at. It would need to be a pretty sharp directive pattern on the Yagi, the Yagi would have to have just enough gain to match the other signal, but not so much as to overpower it and be the dominant signal received, and it would need to be designed with precision. It would take a lot of math, sophistication, and some equipment like a spectrum analyzer to set it up. I've only seen that once and the guy who built it was a WW-II radioman (he's gone now) and had to be a Zen master.

 

[JMR3865]

I dont believe that changing the direction of the antenna will help as It is coming from the same communication center. It seems to depend on the console they use (which is weird because I believe it's all computer based). Sometimes we get it, sometimes we dont.

Thanks