Wide / narrow band: Better receive signal strength on the repeater channel

[bd348]

Got my Midland MXT275 back from them (very quickly!) with new programming for wide band for the repeater channels.

I noticed that when listening to a repeater, and I compare the received signal strength between the simplex channel and the repeater channel, the repeater channel seems to have better reception and it shows as another bar or so in signal strength.

So, on a Midland 275, does channel 15, say, use narrow band reception and "15 repeater" use wide band reception, and would this account for the difference in signal strength?  I didn't notice a difference before the wide band programming update.

And if I have an FRS radio tuned to 15, and it hears a repeater, why isn't the audio overdriven?  I somewhere read an anecdote about a group where almost everyone had narrow band FRS radios but one person had GMRS wide band and his audio was horrible to the rest of them.  Perhaps repeaters receive wide band but transmit narrow?

[MichaelLAX]

I can’t wait to hear the answer to this one!

[Lscott]

3 hours ago, bd348 said:

Got my Midland MXT275 back from them (very quickly!) with new programming for wide band for the repeater channels.

I noticed that when listening to a repeater, and I compare the received signal strength between the simplex channel and the repeater channel, the repeater channel seems to have better reception and it shows as another bar or so in signal strength.

So, on a Midland 275, does channel 15, say, use narrow band reception and "15 repeater" use wide band reception, and would this account for the difference in signal strength?  I didn't notice a difference before the wide band programming update.

And if I have an FRS radio tuned to 15, and it hears a repeater, why isn't the audio overdriven?  I somewhere read an anecdote about a group where almost everyone had narrow band FRS radios but one person had GMRS wide band and his audio was horrible to the rest of them.  Perhaps repeaters receive wide band but transmit narrow?

About the signal strength difference there shouldn't be any between wide or narrow band. Many modern radios are now software calibrated, no more popping the cover and turning screws. What I suspect is something in the firmware was changed that affects the signal strength reading itself. Some calibration/scaling factor got tweaked besides the wide band narrow band setting. There might be other "tweaks" in the firmware as well to fix other issues you might not have noticed.

Your comment about the audio is that your experience or just a "hypothetical" case? It sounds like the later. If so if the repeater is programmed for wide band TX and RX and you use narrow band to TX to the repeater the RX audio level signal will be low and TX on the output as such. Now a narrow band radio monitoring the repeater's output, which now has a low deviation due to the RX audio level being low, will look like a narrow band signal to a narrow band radio. The user will hear the audio at what they are accustomed to as being "normal", no real mystery.

[marcspaz]

 

4 hours ago, bd348 said:

Got my Midland MXT275 back from them (very quickly!) with new programming for wide band for the repeater channels.

 

I sent my MXT500 in for service.  They fixed it and had it back out in the mail to me, literally on the same they they received it from me shipping it to them.  Got the radio back before the end of the next day.  In my opinion, they have fantastic service!

 

4 hours ago, bd348 said:

I noticed that when listening to a repeater, and I compare the received signal strength between the simplex channel and the repeater channel, the repeater channel seems to have better reception and it shows as another bar or so in signal strength.

So, on a Midland 275, does channel 15, say, use narrow band reception and "15 repeater" use wide band reception, and would this account for the difference in signal strength?  I didn't notice a difference before the wide band programming update.

 

As far as if any channel is set to wide or narrow, you really need to check in the menu of the radio.  Each channel is set independently and we really don't have any way of knowing what yours, specifically, is set to.

 

As far as wide or narrow and the radio's receive sensitivity, there is no relation.  I don't have an answer for you why they seem to appear different between the repeater channel and the simplex channel.  Only that the bandwidth setting isn't it.

 

4 hours ago, bd348 said:

And if I have an FRS radio tuned to 15, and it hears a repeater, why isn't the audio overdriven? 

 

Eh... it doesn't quite work that way.  Overdriven is a function of signal strength.  The bandwith doesn't have an impact on signal strength.  Non-linear demodulation by the discriminator circuit causes distortion.

 

In wide band, the radio will transmit and is configure to receive a signal that is 20 kHz wide.  In narrow band, the radio will transmit and is configure to receive a signal that is 12.5 kHz wide.  The wider the bandwidth, the more data the signal can carry.  In voice radio, that data is your voice.  So, the wider the bandwidth, the better the fidelity.

 

Without getting too far into the weeds, if a narrow band radio receives a wide band signal, not all of the audio is captured.  This causes a signal to sound like it has a little more base and louder than narrow signals.

 

If we go the other way around, and a wide band receiver hears a narrow signal, about 38% of the bandwidth the receiver is listening to has no signal.   The empty space is filled with RF noise and the discriminator circuit ends up outputting audio that is both slightly higher in tone and lower in volume.

 

 

4 hours ago, bd348 said:

I somewhere read an anecdote about a group where almost everyone had narrow band FRS radios but one person had GMRS wide band and his audio was horrible to the rest of them.  Perhaps repeaters receive wide band but transmit narrow?

 

Again, I can't really speak to this exact situation, but I don't believe a repeater was used in that case.  Anyway, same rules apply as above.  Bandwidth differences don't cause that issue.

 

[bd348]

Thanks all.  And another curiosity: why would Midland have the scan function scan through all the simplex channels then all the repeater channels?  I.e. it scans both 15 and 15 repeater.  Why not skip the simplex version of the repeater channels, if you have the repeater channels turned on?

Anyhow, things appear to be working well, and it's a nice radio which tucks away under the dash, and Midland did do a good job returning the radio quickly.  It even came back with a test report proving full power output and such.

[wayoverthere]

13 minutes ago, bd348 said:

Thanks all.  And another curiosity: why would Midland have the scan function scan through all the simplex channels then all the repeater channels?  I.e. it scans both 15 and 15 repeater.  Why not skip the simplex version of the repeater channels, if you have the repeater channels turned on?

Anyhow, things appear to be working well, and it's a nice radio which tucks away under the dash, and Midland did do a good job returning the radio quickly.  It even came back with a test report proving full power output and such.

I wonder if it's a leftover from their older firmware's/configurations that didn't allow split tones. That way, repeater 15 could have the tone filter, and simplex 15 heard everything else that didn't have the matching tone.

[Lscott]

6 hours ago, wayoverthere said:

I wonder if it's a leftover from their older firmware's/configurations that didn't allow split tones. That way, repeater 15 could have the tone filter, and simplex 15 heard everything else that didn't have the matching tone.

I guess that’s possible. You don’t have access to the firmware code so you can’t be sure exactly what they did. Maybe some more experimentation might help to figure it out.

[WRUU653]

6 hours ago, bd348 said:

Why not skip the simplex version of the repeater channels, if you have the repeater channels turned on?

I don’t know this radio but if I understand the question wouldn’t this be so it scans for everything regardless of if there’s a tone set on the output of the repeater or not? That is to say that if you’re only scanning repeater channels set with rx tones you’ll be missing transmissions with no tones either from a repeater or not. 
 

[KAF6045]

13 hours ago, bd348 said:

Thanks all.  And another curiosity: why would Midland have the scan function scan through all the simplex channels then all the repeater channels?  I.e. it scans both 15 and 15 repeater.  Why not skip the simplex version of the repeater channels, if you have the repeater channels turned on?

Hmmm... My MXT115 (NFM-only) doesn't scan the "rp" block, regardless of if the repeater block is enabled or disabled. Only 1-7/15-22 simplex get scanned.

(I pulled it in favor of a DB-20G when I discovered the 115 is only NFM; the DB-20G has per-memory N/W AND SCAN enable/disable)

[bd348]

Yea, while scanning on the 275, when you hear a repeater it may be the repeater channel or the simplex channel.  You have to make sure you move to the repeater channel before replying.

[bd348]

The mystery deepens!  When the dashboard display turns on, whether or not the engine is running, I see two bars of signal strength on the repeater channels but not the simplex channels.  Not enough to break the squelch or stop the scan.  Somehow the repeater channels are being treated differently than the simplex.  And there is still some engine RPM related noise on some of the frequencies.

Now this is all compared to before two recent changes: 20 feet of RG174, 14 of which were in a coil, have been reduced to 6 feet of RG174.  And it went in for wideband reprogramming, and came back with a test report.  Perhaps they adjusted analog gain somewhere.

Anyhow, there are a lot of digital signals running around inside modern vehicles, and the antenna cable routing or shield quality could be issues.  I can improve this by changing to 5 feet of RG58 plus one foot of RG174 and a connector going to the hood.  I can also order some ferrite beads for the antenna, microphone, and power cables.

[marcspaz]

RG174 is terrible for UHF.  There is more than 20dB of attenuation every 100 feet.  I would use as little as possible.  Even at 6 feet, you are cutting your signal by about 65%-66%.

 

The loops in the wire have zero impact on your antenna performance, nor any noise.  There has been issues with cheap cables being used for HF (no where near where GMRS lives) with people accidentally making RF traps and creating very high SWR issues by using very cheap coax and looping many, many 10's of feet of coax in about a 1 foot diameter.  With GMRS, its almost impossible to accomplish this on purpose.  Unless you are making loops that are a few centimeters in diameter with almost unshielded wire, its even less likely that it will happen by mistake.

 

Something seriously odd is happening in your Jeep.  Is there any chance you have access to another radio to test with, to see if its the radio or Jeep?

 

For what its worth, when I have the roof and doors off the JT, once I get to about 20 mph, there is a static energy that gets created and it opens my squelch only on repeater channel 19.  I have to use a TSQL instead of TN, so I don't have to hear static while I am moving.  This is only with my MXT500.  None of my other UHF radios have this issue while receiving on that frequency.

 

If I put just the roof on, just the doors on, or both the roof and doors, the issue goes away.  And it doesn't matter where the antenna is, either.  I can even take the antenna off the mount and I still have the issue.  Since the TSQL at least stops the noise, I just let it go, but it was pretty annoying. 

[bd348]

1 hour ago, marcspaz said:

 Is there any chance you have access to another radio to test with, to see if its the radio or Jeep?

Well the 2 bars of noise (repeater channels only?!?!) disappear when the dashboard display turns off.  Not when the engine turns off, but rather when the display blanks a minute later.  And the radio is mounted just below the steering wheel.  The only other radios I have are simple FRS w/o signal meters.

Anyhow, it's not a big problem, and the repeater signal levels are stronger with 14' of RG174 removed.  And they heard me when I transmitted.  These 2 bars of noise probably used to exist before I shortened the cable, it's just that it was attenuated by the longer cable at the time to something closer to 0 bars.

I'll go ahead and order some RG58 and connectors and turn it into 1' RG174 plus 5' RG58.  Better shielding near the dashboard, and more signal overall.

And I'll order some ferrite beads.  And maybe ground that hood too.

[MichaelLAX]

On 11/11/2022 at 9:48 PM, bd348 said:

Anyhow, things appear to be working well, and it's a nice radio which tucks away under the dash, and Midland did do a good job returning the radio quickly.  

Time to send the Jeep back for replacement!