Help, I am new to scanning project 25 systems.
I am trying to scan York County, VA. Everything I hear is garbled. Any suggestions?
I am trying to scan York County, VA. Everything I hear is garbled. Any suggestions?
Garbled transmissions
- Thread starter budbrur
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Spitfire8520
I might be completely clueless! =)
If you're talking about James City / York / Williamsburg, then it looks like all the law enforcement is encrypted and there is nothing that can be done beside either deleting the encrypted talkgroups or locking them out. You can see if it's known to be encrypted by looking at the Mode column next to the talkgroup for an E. There's a chance that the database isn't entirely updated, so it may not accurately reflect what is encrypted and what is still in the clear.
jfhtm350
Member
If you have a good signal then its encrypted. Looks like the Fire Departments are still in the clear.
If this is the system you are trying to receive:Peninsula Site Details (James City / York / Williamsburg) it is shown as a six site simulcast system.
Simulcast systems are known for simulcast distortion on many scanners and can be dependent on where you are with respect to the sites. What you are describing is a classic symption of simulcast distortion.
A simulcast system transmits from multiple sites (in your case, 6) all on the same frequencies. Your scanner may be receiving transmissions from two or more sites. Because the transmissions are a little out of sync - data stream from site 1 is micro-seconds off from site 2, your scanner has trouble "understanding" what it receives. This is actually called "decoding". This will typically manifest itself with garbled or no audio. Unfortunately this happens, even though the signal strength meter on the scanner may show a strong signal.
A good way of confirming this is to take your scanner to within 1/4 to 1/2 mile of a site and give it a listen. If you hear clear audio, that confirms simulcast distortion. That's because the signal from that one site "overwhelms" the others.
If you can confirm clear receive by going near a site, there are some things you can try to improve the situation when you get back home:
1. Set Site Attenuation to On for the system.
2. Change the orientation of the scanner antenna, if possible.
Contrary to intuition, you are actually trying to make your scanner receive more poorly. That is so your scanner is only hearing one site.
Depending upon the model scanner you have, there may be some other things that can be adjusted. Please let us know what you have so we can make additonal suggestions if the two above are not successful.
A picture being worth a thousand words, see the image below which depicts a 3 site simulcast system. The green areas should have clear audio, yellow may have garbled audio (overlap of multiple sites) and the red area may receive no audio at all.
Simulcast systems are known for simulcast distortion on many scanners and can be dependent on where you are with respect to the sites. What you are describing is a classic symption of simulcast distortion.
A simulcast system transmits from multiple sites (in your case, 6) all on the same frequencies. Your scanner may be receiving transmissions from two or more sites. Because the transmissions are a little out of sync - data stream from site 1 is micro-seconds off from site 2, your scanner has trouble "understanding" what it receives. This is actually called "decoding". This will typically manifest itself with garbled or no audio. Unfortunately this happens, even though the signal strength meter on the scanner may show a strong signal.
A good way of confirming this is to take your scanner to within 1/4 to 1/2 mile of a site and give it a listen. If you hear clear audio, that confirms simulcast distortion. That's because the signal from that one site "overwhelms" the others.
If you can confirm clear receive by going near a site, there are some things you can try to improve the situation when you get back home:
1. Set Site Attenuation to On for the system.
2. Change the orientation of the scanner antenna, if possible.
Contrary to intuition, you are actually trying to make your scanner receive more poorly. That is so your scanner is only hearing one site.
Depending upon the model scanner you have, there may be some other things that can be adjusted. Please let us know what you have so we can make additonal suggestions if the two above are not successful.
A picture being worth a thousand words, see the image below which depicts a 3 site simulcast system. The green areas should have clear audio, yellow may have garbled audio (overlap of multiple sites) and the red area may receive no audio at all.
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ofd8001, thanks for that wonderful post! I think I'm having this same issue using a BCD996XT, the channels that I'm listening to are not Encrypted. Do you have any advice for this model scanner?
Try minimizing your antenna to one of those 1" stubby models. Also, some grounded metal shielding on one side of the radio might help. You're getting signals from too many sites at once, on the same frequency.
I find by putting my hand-held up against the side of me steel computer tower, it works best, as there are three sights that helps block.
I find by putting my hand-held up against the side of me steel computer tower, it works best, as there are three sights that helps block.
solid core or stranded wire?
Paper clip wire works good.
Thanks for the tip. I'll try it tonight.
If the antenna suggestions don't help, and I've success stories with the above suggestions, another thing to try is the P25 Adjust Mode and P25 Adjust Level.
Unfortunately these settings are system and location sensitive, so what would work good for me, may not for you. My next door neighbor uses different settings on his scanner.
The following is copied and pasted from Mark's Easier to Read Manuals:Easier to Read BCD996XT Digital Scanner Manual
"P25 Adjust Mode this is a hidden setting accessible only by turning off the radio and pressing Hold when you turn the scanner back on. This mode sets the algorithm for P25 decode.
If your firmware version is 1.06.00, set the mode to 11, which is the optimal setting for most P25 systems. Some systems are reported to decode better at a setting of 8.
If your firmware version is lower than 1.06.00, leave this setting at 3. Anything higher than 3 will just act like 3. Anything lower will have the reduced performance of previous firmware versions on the 996T. Scroll to 'P25 Adjust Mode' and press E/
Enter 3-15 and press E/
P25 Adjust Level this is a hidden setting accessible only by turning off the radio and pressing Hold when you turn the scanner back on. Sets the RSSI value below which the scanner will not attempt to make P25 fine tune adjustments. If the signal is too low, RX reliability is not high enough to make P25 adjustments correctly. The default value is 50. People have had better decoding with this value turned up. Note that for firmware version 1.06.00, Uniden specifically instructs users to reset this value back to 50 if it had been changed in the past. Scroll to 'P25 Adjust Level' and press E/
Enter 1-200 and press E/
These are "hidden" settings. To access them, turn your scanner off. Then, press and hold the Hold buttong while turning the scanner back on. You will see the screen changes colors, which is normal.
Then go to Menu>Settings and scroll down to see P25 Adjust Mode and P25 Adjust Level. From there, experiment with different combinations to see what gives you the best sound. As noted above, what works for me, may not for you, but I use 13 for P25 Adjust Mode and 175 for P25 Adjust Level.
fmalloy
Member
So what happens when a police car is in the red area? They receive nothing too?
Yep.
A properly designed simulcast system would have all the red areas outside the needed coverage areas.
The diagram above is a gross oversimplification of a real simulcast system, but serves well to illustrate what can go wrong.
This isn't an issue with actual users on the system. The radios they have are much better than scanners on dealing with simulcast systems.
As an illustration, the video from a smart phone is reasonably decent, but nothing like the broadcast quality seen in a "professional" camera such as those used by television news photographers. There are more things "under the hood" of the broadcast camera and as such there is a huge price difference.
A similar principle holds for scanners versus "real" radios on a simulcast system. There are things "under the hood" of a public safety radio that deal with simulcast issues better than a scanner will. Of course there is a similar price differential - a scanner costs around $500 where public safety radios run between $2,500 and $5,000.
Back before I retired, I had a fire department vehicle which was equipped with a mobile radio on our simulcast system, along with a Uniden 996XT scanner. There were places I would receive garbled or absent audio on the scanner but on the mobile radio, the audio was pristine.
Scanner manufacturers are in a tough spot. They probably could build a scanner having pristine audio on simulcast systems, but the cost of the scanners may put them out of reach for most folks.
fmalloy
Member
So with P25, you need expensive and complex radios to deal with digital simulcast issues, on top of the whole migration to digital costs.
Analog was much more forgiving.
I know it's a whole other topic, but still trying to understand the benefits of going digital...
kayn1n32008
ØÆSØ
Sigh, you need a receiver designed to properly receive the wave form you are trying to listen to.
Try listening to SSB with an FM receiver... SSB is not going to sound right on an FM receiver. You need a receiver designed to receive SSB.
C4FM(the wave form that P25 normally uses)can be decoded just fine with a discriminator tapped scanner, as can DMR, because DMR uses the same C4FM wave form,
This is how Uniden has designed their scanners, and for C4FMdata this is fine. The problem is that motorola simulcast systems do not transmit in C4FM, they use CQPSK. This is significant, while the subscriber radios can decode this waveform, it is because their receiver is designed much differently than scanners. The method used by scanners to get the data from the signal to the decoder is not an optimal way recover data from a CQPSK waveform. Because of this, people have difficulty with LSM simulcast systems. It is also why subscribers do not have the issues that scanners do.
It's not 'special' it is different, like SSB receivers are different than FM, than AM, than ACSB.
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fmalloy
Member
Well, I guess I'm learning. I thought when Uniden says they can receive P25 Phase II, then that's that and everything's golden. Now I hear Moto uses some different design, so it's more complicated, and there's problems.
As if a $500 receiver is not expensive enough, now I hear to properly read these systems the price would be even higher.
N8IAA
Member
Don't be misled that by using a commercial Moto radio you will be able to hear the systems easier.
To use a commercial radio to monitor the system, it must handshake with the system. Invalid radios can, and will be shut down {bricked}. And yes there are ways to program the radios, but it takes expensive software and programming cables to succeed.
Unfortunately, the scanner manufacturers have decided not to incorporate CQPSK. The defunct GRE radios and, I would believe that the Whistler versions will decode that type of system better than the Unidens.
I own both brands, and both do adequate on the systems I monitor. There are ways of tweaking the menus in the Uniden and the GRE/Whistler scanners to receive the signal better.
Larry
I think Uniden is headed in the right direction. My 396's and 996's have difficulty in decoding our local simulcast system in some areas. Unfortunately those areas with difficulty are where I spend most of my time.
I got a 536 when they first came out and there was a world of difference in the simulcast system. It isn't perfect, but is much better - less garble and fewer "no audio" spots.
Wearing my fire chief hat, I think our digital simulcast system has been the best thing to come along for our communications system in my 40 years. The coverage is much better, the audio is clearer and there are several other features that can be very valuable in certain situations. The old analog system had its issues - just about every other fire chiefs meeting, there was a complaint about something. Since we went to the digital system, nary a cross word has been said.
As a scanner listener, I've applied many bad words to it because it has been challenging to monitor. Among other things, the downside of retiring meant I no longer had a "system" radio to listen to - the scanner is all I got, other than a Broadcastify feed (which comes off a system radio).
Gone are the days of one big blowtorch of a transmitter for larger cities. To get the coverage needed in buildings like hospitals, mega-warehouses, factories, highrise buildings a very powerful transmitter would be needed. That would result in the footprint of the transmitter going well beyond the service area, thus reducing frequency availability. The FCC has began to frown upon that.
So the solution the industry came up with was to use several transmitters with lower power to achieve the coverage level needed. These transmitters use the same frequencies, which is a simulcast system.
For better or for worse, digital radio is here for a while.
I got a 536 when they first came out and there was a world of difference in the simulcast system. It isn't perfect, but is much better - less garble and fewer "no audio" spots.
Wearing my fire chief hat, I think our digital simulcast system has been the best thing to come along for our communications system in my 40 years. The coverage is much better, the audio is clearer and there are several other features that can be very valuable in certain situations. The old analog system had its issues - just about every other fire chiefs meeting, there was a complaint about something. Since we went to the digital system, nary a cross word has been said.
As a scanner listener, I've applied many bad words to it because it has been challenging to monitor. Among other things, the downside of retiring meant I no longer had a "system" radio to listen to - the scanner is all I got, other than a Broadcastify feed (which comes off a system radio).
Gone are the days of one big blowtorch of a transmitter for larger cities. To get the coverage needed in buildings like hospitals, mega-warehouses, factories, highrise buildings a very powerful transmitter would be needed. That would result in the footprint of the transmitter going well beyond the service area, thus reducing frequency availability. The FCC has began to frown upon that.
So the solution the industry came up with was to use several transmitters with lower power to achieve the coverage level needed. These transmitters use the same frequencies, which is a simulcast system.
For better or for worse, digital radio is here for a while.
Actually, it can be. If an overlap signal is delayed sufficiently, and is strong enough, it can cause problems in the demodulator of the receiver. It manifests itself as a high BER in the receiver, and to the user would be indistinguishable from any other high BER situation, unlike analog simulcast where you can hear and recognize an out of phase overlap.
C4FM and CQPSK are actually similar, enough so that the professional grade receivers will receive both with the same demodulator. The 'C' in CQPSK stands for 'compatible'. It's really a clever design.
I've ranted about the poor quality of scanner local oscillators (synthesizers) before, and I wonder if the same issue could be coming to play in P25 scanners. Unlike C4FM, which modulates only the phase of the transmitted carrier, CQPSK modulates both phase and amplitude, which is why CQPSK base station power amplifiers must be linear.
A clean LO signal in the receiver, free of excessive phase and amplitude noise is critical to demodulating a complex quadrature and amplitude modulated signal like CQPSK. I wonder if they just aren't up to the task with already marginal signals.
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