Centereach FD repeater on public frequencies? - need help

[SeldenRadio]

Good morning everyone. Been a long time searcher of frequencies but never created an account until now.

Below is a serious question for all you Gurus out there!

I need some help from all of you. The company that programmed Centereach FD (Intergrated Wireless) is blowing it off as "intermod"
I can't imaging 2 years of "Intermod"!!?? Are your serious? (

Centereach FD is on a listening frequency of 476.8625 dcs132, does anyone know what the input frequency is for their repeater? Your reply and this question technically shouldn't be answered, however I have tracked their input on a public GMRS frequency. They should be on the T-band business band and to where near GMRS. I have contacted Centereach dispatch and he said he has had interference since it has been changed 2 years ago, and so has Selden Radio. So without giving any details away of their input frequency, I need someone neutral to confirm my outcome.

The listening frequency is: 476.8625 DCS132, the T-Band is a 3MHZ shift, in this case a positive shift. So, their input "should be" 479.8625 with a DCS132 tone.

I cant hear anything on that input, however I can hear everything on the GMRS band clear as day.

As a courtesy, my club tones are private, please keep it that way. I know you will find them, but please dont post them.

For the past 2 years we have been having a ton of interference, and since it is GMRS and public we blew it off as being weather related QRM/Intermod conditions.
This is a huge problem as my club is following the FCC guidelines for input and output frequencies. I can not be responsible for interference if they programmed the repeater and radio's wrong.

Looking forward to your findings and answers.

 

[62Truck]

RF can do some strange things especially when singles mix and what not. What repeater are you using? Where is it located in relation to the transmitter on the 476 frequency? I know you have mentioned you have listened to the 479 frequency and haven't heard anything. You mentioned you hear everything on the GMRS frequency. What are you exactly hearing? Can you provide any audio recordings?

Years ago, on a RadioShack bubble back radio I had, I used to hear the local private ambulance company pretty clear on one of the GMRS channels, but they were indeed operating on 462.975.

Again, a number of years ago, when the local Sheriff's office here would do a mult-select to transmit from different base stations on different frequencies at the same time it would actually key up one of the local ham repeaters.

One would assume that a professional radio shop would do things the right way, but then again, I've seen some of the shops in my area do some questionable things.

 

[gatekeep]

Centereach FD is FCC lic WQCT243 which provides the T-Band freqs:

• Output 476.8625 as the FB2 (repeater output), they actually apparently have 2 transmit locations on their license
• Input is 479.8625 as the MO (repeater input)

There is literally no harm in knowing or posting this information as it is publically available from the FCC anyway. The last time I monitored them they were indeed using 479.8625 on both the rig mobiles and portable radios as the input into their repeater.

EDIT: I will also point out (and I might be thinking of a different department) they were using split DCS, and not using DCS 132 on the input due to harmful interference, this was a few years back though.

 

[mastr]

...For the past 2 years we have been having a ton of interference...This is a huge problem as my club is following the FCC guidelines for input and output frequencies...

With all due respect, there is much more to designing a repeater site than "following FCC guidelines...".

...I can not be responsible for interference if they programmed the repeater and radio's wrong...

Again, with all due respect, it is unlikely that "they" made a programming error that causes your interference.

Questions-

(1) has anyone actually done an intermod study, or did they just say 'its probably intermod" and call it done?

(2) are you co-located with or nearby other stations?

(3) do you know what a circulator is?

(4) what is the make/model of your GMRS repeater, duplexer and antenna?

 

[GTR8000]

Perhaps you should stop being so cagey and provide the details of what you think is happening here. Are you suggesting that Centereach FD is transmitting on an input of 467.725 and that's keying up your GMRS repeater on 462.725? Or are you suggesting that they're using 462.725 as their input?

Also, nothing that goes out over clear air is "private", including the input tone to your repeater.

 

[pro106import]

Centerreach FD input IS 479.8625 with the same DCS as their output. I can confirm it because I hear the input fine from my location. And your input is 467.725 with a DCS of xx1 (I won't publicize it on your behalf) . I have never seen in all of my years of experience an RF signal that can interfere with that combination. Even if your input was DCS 132, and your duplexer was terribly tuned or whatever, it is still a stretch. I think you are barking up the wrong tree. I'll try to monitor the input here and there and see if I catch anything abnormal. I do know that Gateway Terminal in New Haven uses 467.725 but with a DCS of 351, low power portables.

Edit... just heard 2 people talking on your input using DCS 432. Sounds like they were 2 mobiles talking to each other. Still, that shouldn't interfere. Maybe you can temporarily try changing your input DCS to see if that helps.
Bob

 

[W1KNE]

Centerreach FD input IS 479.8625 with the same DCS as their output. I can confirm it because I hear the input fine from my location. And your input is 467.725 with a DCS of xx1 (I won't publicize it on your behalf) . I have never seen in all of my years of experience an RF signal that can interfere with that combination. Even if your input was DCS 132, and your duplexer was terribly tuned or whatever, it is still a stretch. I think you are barking up the wrong tree. I'll try to monitor the input here and there and see if I catch anything abnormal. I do know that Gateway Terminal in New Haven uses 467.725 but with a DCS of 351, low power portables.

Edit... just heard 2 people talking on your input using DCS 432. Sounds like they were 2 mobiles talking to each other. Still, that shouldn't interfere. Maybe you can temporarily try changing your input DCS to see if that helps.
Bob

What is the third frequency adding to the mix factor that is making his receiver hear input communications on an odd frequency. They're not even a harmonic apart. So he's clearly having an overloading mix issue in his "receiver". (Which he doesn't list here. It could be anything from a Baofeng to something more.)

 

[SeldenRadio]

With all due respect, there is much more to designing a repeater site than "following FCC guidelines...".

Again, with all due respect, it is unlikely that "they" made a programming error that causes your interference.

Questions-

(1) has anyone actually done an intermod study, or did they just say 'its probably intermod" and call it done?

(2) are you co-located with or nearby other stations?

(3) do you know what a circulator is?

(4) what is the make/model of your GMRS repeater, duplexer and antenna?

No Duplexer, MTR2000, I can't tell you antenna make, but its 10.5dB gain.

 

[SeldenRadio]

What is the third frequency adding to the mix factor that is making his receiver hear input communications on an odd frequency. They're not even a harmonic apart. So he's clearly having an overloading mix issue in his "receiver". (Which he doesn't list here. It could be anything from a Baofeng to something more.)

Using simple formulas (2a+b and 2a-b) from your previous email we calculate the intermodulation.
For the input frequency Intermod
2(f1−f2) 2×467.725−479.8625 = 935.45−479.8625 = 455.5875 MHz
2(f2−f1) 2 × 479.8625 − 467.725 = 959.725 − 467.725 = 491.8625 MHz
While this should be sufficient, as these are the inputs of CFD and Selden Radio repeaters as you can clearly see that Intermod is NOT the issue, I will do the listening frequencies too.

2(f1 − f2)

2×462.725 − 476.8625 = 924.4125 − 476.8625 = 447.550 MHz

2(f2 − f1)

2 × 476.8625 − 462.725 = 953.725 − 462.725 = 491.000 MHz

Just to cover all bases, I did my input and output frequencies to prove a point.

2(f1 − f2)

2 × 462.725 − 467.725 = 925.45 − 467.725 = 457.725 Mhz

2(f2 − f1)

2 × 467.725 − 462.725 = 935.45 − 462.725 = 472.725 Mhz

As well as CFD input and output frequencies.

2(f1 − f2)

2 × 476.8625 − 479.8625 = 953.725 − 479.8625 = 473.8625 MHz

2(f2 − f1)

2 × 479.8625 − 476.8625 = 959.725 − 476.8625 = 482.8625 Mhz

 

[SeldenRadio]

Intermod should not be 100% clear communications with a readable DCS tone.

Video proof: Centereach FD on GMRS 22 Repeater input.mp4

 

[mmckenna]

Simple question here, so bear with me...

How confident are you that someone isn't rebroadcasting the fire channel on GMRS? There are some firebuff/whacker types that would do something like this to make it easier to hear the traffic, or purposely to cause interference.

While I've seen some radio shops do some stupid stuff, this is on a different level. The signal level is nice and consistent, which would not always be the case if this was their input channel.

 

[GTR8000]

There are no shortage of buffs/whackers on the island. Wouldn't surprise me in the least if someone is rebroadcasting them on GMRS.

 

[rr60]

There are no shortage of buffs/whackers on the island. Wouldn't surprise me in the least if someone is rebroadcasting them on GMRS.

Exactly. Re-Distribute signal for just about any convoluted reason. This is the most likely explanation.

Hypothetical: I can’t hear department in the location I work or live. Someone may want to listen reliably in that building. Simple effort to set up a simplex relay on top of building. RX 476.xxx TX GMRS Simplex. Deploy cheap CCP radio to listen on GMRS.

@SeldenRadio have you or others considered RDF of this signal. Determine the who, you may understand why.

GMRS is like the wild west, has been, likely always will be. Tough RF space.

 

[SeldenRadio]

Simple question here, so bear with me...

How confident are you that someone isn't rebroadcasting the fire channel on GMRS? There are some firebuff/whacker types that would do something like this to make it easier to hear the traffic, or purposely to cause interference.

While I've seen some radio shops do some stupid stuff, this is on a different level. The signal level is nice and consistent, which would not always be the case if this was their input channel.

100%, if they were to rebroadcast on my repeater, it would be also on my tone as well to trigger my repeater. Selden radio is about 6 times higher in elevation than Centereach FD. I have narrowed it down to just one of their repeaters being on the wrong input. They have 4.

 

[SeldenRadio]

There are no shortage of buffs/whackers on the island. Wouldn't surprise me in the least if someone is rebroadcasting them on GMRS.

Its not being rebroadcasted, its not triggering my repeaters input. its causing interference. When we transmit, CFD is having receiving problems because we are fighting for RF input control. different tone, same input frequency, from an improper repeater configuration .

 

[SeldenRadio]

Centerreach FD input IS 479.8625 with the same DCS as their output. I can confirm it because I hear the input fine from my location. And your input is 467.725 with a DCS of xx1 (I won't publicize it on your behalf) . I have never seen in all of my years of experience an RF signal that can interfere with that combination. Even if your input was DCS 132, and your duplexer was terribly tuned or whatever, it is still a stretch. I think you are barking up the wrong tree. I'll try to monitor the input here and there and see if I catch anything abnormal. I do know that Gateway Terminal in New Haven uses 467.725 but with a DCS of 351, low power portables.

Edit... just heard 2 people talking on your input using DCS 432. Sounds like they were 2 mobiles talking to each other. Still, that shouldn't interfere. Maybe you can temporarily try changing your input DCS to see if that helps.
Bob

add into your scanner 467.725 and search for tone. Leave out 479.8625. I have another video to post that shows both inputs being hit at the same time.. This is how I found it was only one repeater mis-configured.

 

[SeldenRadio]

Here is the smoking gun...

CFD on GMRS.mp4

drive.google.com

 

[rr60]

Since you absolutely are sure, verify your belief. Go to the sites and verify using what RDF tools you may have.

What you believe may or may not be true. This is the way forward. Good luck.Out.

 

[gatekeep]

Here is the smoking gun...

CFD on GMRS.mp4

drive.google.com

I will assume your scanner test setup is using the same or similar antenna's to capture the traffic. Based on your video, I'm gonna wager its not intermod or a image, and its not rebroadcasting.

If it were an intermod or image, unless you were sitting on top of the transmitting unit there would be some noticeable signal degredation. Additionally, based on your monitoring of both their authorized input and the GMRS 467.725 input, if *I* were in your position without further information, I would say yes, some combination of field units and the repeater are incorrectly or sloppily programmed by whatever contractor did the work for Centereach.

My only suggestion would be to capture another series of events with *clear* traffic on 467.725, *AND* the repeated output on the 476.8625 repeater output.

 

[mmckenna]

100%, if they were to rebroadcast on my repeater, it would be also on my tone as well to trigger my repeater. Selden radio is about 6 times higher in elevation than Centereach FD. I have narrowed it down to just one of their repeaters being on the wrong input. They have 4.

Then I'd try another radio than a scanner. Get a real UHF LMR radio and program it up. Get closer to their system and see how it behaves.

If you are sure this is what is happening, then contact the FCC and ask for assistance.

https://www.fcc.gov/enforcement/divisions-offices/ofd

No, the FCC is not going to respond like this is a 911 call, but if you have done all your homework, and documented everything, they should be willing to assist.