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  #1 (permalink)  
Old 10-24-2013, 8:52 AM
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Default XPR4550 Choppy other radios clear?

What would cause an XPR 4550 (in analog) to receive choppy audio while other (lower quality) radios have a clear signal.

The problem started after norrowbanding.

The radio was bench tested and is working perfectly.

The signal is a provided by the state for Ambulance/Hospital communications and the state engineers are also trying to figure it out?

We are all scratching our heads?

Thanks!

Last edited by noloflash; 10-24-2013 at 9:07 AM..
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Old 10-24-2013, 11:09 AM
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Could be either the transmitter or the radio are not actually narrowbanded. Could be an audio processing filter or Comression/Compandering setting on the tx or rx radios. Different vendors radios (even different Tier radios by the same manf) do not play well. together. Can you tell make and model of the other radios? How about the repeaters? TT
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Old 10-24-2013, 11:22 AM
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it's repeater directly to the XPR4550....the problem is consistent with all seven of the XPR4550s in service.
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Old 10-24-2013, 11:24 AM
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Quote:
Originally Posted by noloflash View Post
What would cause an XPR 4550 (in analog) to receive choppy audio while other (lower quality) radios have a clear signal.

The problem started after norrowbanding.

The radio was bench tested and is working perfectly.

The signal is a provided by the state for Ambulance/Hospital communications and the state engineers are also trying to figure it out?

We are all scratching our heads?

Thanks!
A service monitor on the transmitter will tell what is going on.

By saying the audio is choppy, doesn't provide enough details. My first guess is that when (maybe if) the base or repeater was narrow banded, did the tech ever measure both the voice and CTCSS deviation. In many cases, they just went into the software, made the changes, wrote it back to the radio and packed their bags. If the CTCSS tone level is low, it will cause decode issues in the receive end. If it's carrier squelch, then the audio deviation is set too high.
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Old 10-24-2013, 11:57 AM
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I set the receiving radios to CSQ and the problem remained.
Forwarded your message to the state engineers. Open to any suggestions.

Last edited by noloflash; 10-24-2013 at 12:25 PM..
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Old 10-25-2013, 12:21 AM
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Have you checked the 4550 on a service monitor to see if the reference oscillator is aligned properly? (Is radio "on frequency"?)

On narrowband, being off-frequency is much more noticeable due to the narrower receive window.

Same deal applies to the radios/repeater you're receiving, if they're over-deviated. It could cause RX clipping, as the signal would be too wide -- even if by a few hundred Hz.

What firmware version are the 4550s running at? Make sure you're using the latest CPS (R9.0) and current firmware. You can grab the firmware from our file download site at P25.ca: https://www.p25.ca/threads/4681-MOTO...-North-America CPS must be obtained from Motorola.

Last edited by Mars_P25; 10-25-2013 at 12:26 AM..
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Old 10-25-2013, 12:52 AM
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Another thought: Are you using scan? If so, are you using PRIORITY scanning? This will cause the audio on your RX to be choppy as it searches for activity on your other higher-priority scanlist members.
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Old 10-25-2013, 8:47 AM
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Thanks...it sounds like the infrastructure may be 'over-deviated'. Scan is not in use. Would this typically be something addressed by a firmware upgrade? I'm looking for a workaround to get it to work until the infrastructure is repaired. Would you recommend changing deviation setting on the XPRs?
Thanks!

Last edited by noloflash; 10-25-2013 at 9:01 AM..
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Old 10-25-2013, 2:29 PM
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You are stuck...

Nothing you can do to your XPR unless you have the entitlement to set the RX side to the good old bandwidth, Leave the transmit alone.
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Old 10-27-2013, 12:34 AM
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Default Narrowband deviation adjusted?

That's what I was thinking. Reprogram the frequency to narrowband does not legally make it narrowband. The deviation has to be reduced to 2.5kHz instead of 5kHz. Then the compression setting has to be changed. Everything has to match.
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Originally Posted by noloflash View Post
Thanks...it sounds like the infrastructure may be 'over-deviated'. Scan is not in use. Would this typically be something addressed by a firmware upgrade? I'm looking for a workaround to get it to work until the infrastructure is repaired. Would you recommend changing deviation setting on the XPRs?
Thanks!
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Old 10-28-2013, 10:41 AM
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Default Problem solved

The infrastructure was never changed to narrowband.....they're fixing it!
Thanks!
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Old 10-29-2013, 10:01 AM
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I would be a little concerned that some of my supposed narrowband radios hear a wideband signal just fine. That doesn't say much for the receiver bandwidth in those radios.
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Old 12-02-2013, 9:15 AM
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Default XPR4550 Choppy other radios clear?

Our EMS channels are all wideband. Funding for NB was declined by admin


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Old 12-02-2013, 11:17 AM
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Not sure that excuse will fly with the FCC. The FCC told the last agency that used that excuse they had 10 years to get the funding. There are a couple of excuses that will buy some time but that isn't one of them.
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Old 12-02-2013, 11:35 AM
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Default XPR4550 Choppy other radios clear?

You don't know my boss. The radio stays until it's unrepairable then it won't be replaced. That happened to our UHF station in the ER we had to take down the ambulance to hospital tower and make sure it couldn't be seen from the ground. He's against any radios even cellphones are banned from the property


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Old 12-03-2013, 6:31 AM
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I wish I could say your situation was unique. In the 15 or so years I have been doing this, that mindset has showed its head a few times. It usually ended up in someone being hurt or resulting in poor care being delivered to the patient (read that as liability). We are seeing an increase in JCAHO and AHCA inspections scrutinizing radio/RF as life safety critical components. TT


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You don't know my boss. The radio stays until it's unrepairable then it won't be replaced. That happened to our UHF station in the ER we had to take down the ambulance to hospital tower and make sure it couldn't be seen from the ground. He's against any radios even cellphones are banned from the property


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Old 12-03-2013, 9:50 AM
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Had the same problem with a trbo repeater, they do not like wideband any thing over 5khz dev will clip, even though you can set them wideband. Sounds like there are some programming mistakes, IMO.
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Old 12-03-2013, 10:18 PM
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All wide/narrow band radios built in the past 10 years during the transition period have wide band receivers. They have the same type "mechanical" component window filters they have always had to create their 25 KHz window. There are 2 common methods used to switch the receiver from wide to narrow (sometimes on a per channel basis). One method is to add a second stage narrow filter that is turned on for narrow channels. The narrow filter also reduces received signal strength which contributes to the range reduction we've all experienced after narrowbanding. This type of receiver is truly narrow when the second filter is active and will distort or clip a wide signal outside its narrow bandwidth.

Some radios just have the wide filter and use DSP to "track" the received bandwidth. DSP does not effect the signal strength and are more transition friendly because these radios will receive both wide & narrow in either mode without clipping the audio, however a wide transmission will always sound stronger than a narrow transmission. DSP radios are more prone to interference from a strong nearby transmitter than radios with the extra narrow filter.

Both methods have their advantages & disadvantages and I don't think one method makes a radio better than another. TDMA capable radios are very sensitive to adjacent channel interference, especially from another TDMA radio which cause adjacent channel interference (ask the license coordinators about that) so it only makes sense that those radios would have very tight narrow band filters.
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