TRX-1: FM vs NFM performance?

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kc5igh

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Has anyone ever noticed a reception/performance difference between FM and NFM modulation settings on the TRX-1 . . . or any other commercial scanners for that matter?

As an experiment, I reset all the FM channels in my TRX-1 to NFM. It may have been my imagination (or a slow night for radio communications), but it seemed that I received fewer signals after that change, with the exception of digital signals, which continued to come in loud and clear.

I know that Uniden's BCD436HP is supposed to have "true narrow band filters," but I can't help but wonder if the FM/NFM modulation choice on most commercial scanners might be cosmetic.

RadioReference database information for my listening region (northern New Mexico) has a mix of both modulation types, even though everyone was supposed to have transitioned to narrowband after the 2013 FCC order.

Thanks!
 

RFI-EMI-GUY

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Has anyone ever noticed a reception/performance difference between FM and NFM modulation settings on the TRX-1 . . . or any other commercial scanners for that matter?

As an experiment, I reset all the FM channels in my TRX-1 to NFM. It may have been my imagination (or a slow night for radio communications), but it seemed that I received fewer signals after that change, with the exception of digital signals, which continued to come in loud and clear.

I know that Uniden's BCD436HP is supposed to have "true narrow band filters," but I can't help but wonder if the FM/NFM modulation choice on most commercial scanners might be cosmetic.

RadioReference database information for my listening region (northern New Mexico) has a mix of both modulation types, even though everyone was supposed to have transitioned to narrowband after the 2013 FCC order.

Thanks!
Going to NBFM has a penalty in analog mode. Digital has a benefit.

Though, I would have predicted you would have better reception of EXISTING NBFM systems by switching your receiver from WBFM (25 KHz) to NBFM (12.5 KHz). Are these Part 90 frequencies you are scanning in NBFM?

See the tables and maps on this link:

LEIKHIM AND ASSOCIATES LLC - VHF-UHF Narrowbanding
 

ecps92

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Because, unless someone actual makes a DB Submission it won't change. :cool:

RRDB is User Supported, there is no assumption that users actually did Narrowband.
ie: T-Band was originally part of the plan, then exempted, Yet many agencies did NB.

If you find missing or wrong data, make a submission to have the FM changed to NFM

RadioReference database information for my listening region (northern New Mexico) has a mix of both modulation types, even though everyone was supposed to have transitioned to narrowband after the 2013 FCC order.

Thanks!
 

kc5igh

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Going to NBFM has a penalty in analog mode. Digital has a benefit.

Though, I would have predicted you would have better reception of EXISTING NBFM systems by switching your receiver from WBFM (25 KHz) to NBFM (12.5 KHz). Are these Part 90 frequencies you are scanning in NBFM?

See the tables and maps on this link:

LEIKHIM AND ASSOCIATES LLC - VHF-UHF Narrowbanding

Based on my brief experiment, it seems that there might have been an overall decline in analog reception when I switched over to NFM (hard to confirm without more work). I left the digital channels in their original modulation modes (P25 = NFM, DMR, NXDN), and they didn't seem to be impacted.

At this time, I can't confirm which analog frequencies are actually coming from NBFM systems, but I certainly didn't notice any improvement in analog signal reception during the switchover. I've now converted all the analog channels to "WB"FM to see what happens, and if anything, they seem to be somewhat louder . . . go figure. I think I'll try switching back to NFM for government channels that I'm pretty sure made the transition to NFM to see if I can hear a difference.

All this is what got me to wondering if the FM/NFM modulation settings on this radio makes any real difference.

Thanks for responding! I'll study the information in the link more carefully when I get a chance.
 

kc5igh

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Because, unless someone actual makes a DB Submission it won't change. :cool:

RRDB is User Supported, there is no assumption that users actually did Narrowband.
ie: T-Band was originally part of the plan, then exempted, Yet many agencies did NB.

If you find missing or wrong data, make a submission to have the FM changed to NFM
That was my assumption, too.

I've noticed an overall decline in signal strength from many agencies out here that I attributed to the FCC narrowband mandate, but my basic question is whether or not the FM/NFM modulation settings on most commercial scanners make any real difference in reception quality.

Thanks for the feedback!
 

RFI-EMI-GUY

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Because, unless someone actual makes a DB Submission it won't change. :cool:

RRDB is User Supported, there is no assumption that users actually did Narrowband.
ie: T-Band was originally part of the plan, then exempted, Yet many agencies did NB.

If you find missing or wrong data, make a submission to have the FM changed to NFM

You would think everyone made the transition already. Easy enough to check, switch the mode to NBFM and if the audio starts sounding more distorted. the licensee probably never made the switch.

Also this is a good time for the scanner owner to check and see if the scanner is still receiving on frequency. I know how I would do it, since I have a systems analyzer.

1) Select a channel, say 450.000 MHz, calculate the local oscillator frequency by subtracting or adding the first IF frequency (low side or high side injection depending upon design) and then sniff it on the analyzer with a short wire antenna probe.
2) Calculate how many PPM it is off.

3) If you have only a frequency counter, you need to find the TCXO and probe it directly with a high Z probe.

4) Adjustment is another story, some radios you tune a capacitor, others require software adjustment.
 

RFI-EMI-GUY

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That was my assumption, too.

I've noticed an overall decline in signal strength from many agencies out here that I attributed to the FCC narrowband mandate, but my basic question is whether or not the FM/NFM modulation settings on most commercial scanners make any real difference in reception quality.

Thanks for the feedback!
It all depends upon the manufacturer's de$ign philo$ophy. I was surprised to find that a well known model of ham 2 meter mobile did not have a separate NBFM filter in the receiver, probably figuring that adjacent channel interference on ham bands was not a huge problem. Switching from WB to NB in that radio only reduced TX deviation to +/- 2.5 KHz and increased RX audio level by 6 dB. So the listener was not getting the benefit of improved SNR of a NB receiver.

You can try to find schematics, carefully compare advertised specs or better yet, pop off the covers and look at the filters and try to look them up on DigiKey or manufacturers website. If you have two sets of second IF filters, the receiver is probably a true NBFM receiver.
 

ecps92

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Yes, but how many Casual listeners would even know what to do or even notice the difference. IMHO it's just experiment with what works for you and then settle back and enjoy the monitoring

I've seen so many complaints about Low audio and blaming it on NB, yet it was actually the Tech's not spending enough time aligning the system. Not the Scanner settings
ie: Car too Loud and Dispatch too Soft/Quiet


You would think everyone made the transition already. Easy enough to check, switch the mode to NBFM and if the audio starts sounding more distorted. the licensee probably never made the switch.

Also this is a good time for the scanner owner to check and see if the scanner is still receiving on frequency. I know how I would do it, since I have a systems analyzer.

1) Select a channel, say 450.000 MHz, calculate the local oscillator frequency by subtracting or adding the first IF frequency (low side or high side injection depending upon design) and then sniff it on the analyzer with a short wire antenna probe.
2) Calculate how many PPM it is off.

3) If you have only a frequency counter, you need to find the TCXO and probe it directly with a high Z probe.

4) Adjustment is another story, some radios you tune a capacitor, others require software adjustment.
 

RFI-EMI-GUY

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Joined
Dec 22, 2013
Messages
3,290
Yes, but how many Casual listeners would even know what to do or even notice the difference. IMHO it's just experiment with what works for you and then settle back and enjoy the monitoring

I've seen so many complaints about Low audio and blaming it on NB, yet it was actually the Tech's not spending enough time aligning the system. Not the Scanner settings
ie: Car too Loud and Dispatch too Soft/Quiet
I was involved in a $6 million upgrade of a public safety system. Along with the new infrastructure and consoles I made sure brand new headsets were supplied. On the cutover night, the field units were complaining of scratchy audio from dispatch. "It sounds no better than the old system". I checked and the dispatchers had not bothered to put on the new headsets, they simply moved to the old headsets to the new jack.

Who would have thought we could have saved the city $6 million by simply providing a few new Plantronics headsets?
 

AggieCon

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Almost everything you hear theses days, especially in public safety, will be narrow band.

I, too, think the FM/NFM setting in EZ Scan is merely cosmetic. I can't tell a difference. If anything, I think it might artificially boost the volume gain if you set it to NFM, but I don't think the scanner is using a different filter or anything like that. This way, though, your pretty scanner matches what the RR DB says.

I think 700 & 800 bands are about the only think still wideband these days, but most of the activity up there is digital trunked systems.
 
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