SO YOUR RADIO DOES NOT SEEM TO WORKThis is paper is a set of different topics related to why your radio does not seem to work. While it is directed to the CS800D, the advice in here relates to all radios.

Various Papers:

1. IT'S NOT ALWAYS YOUR RADIO

2. SENSITIVITY OF THE CS800D

3. HANDHELD WORKS MOBILE DOES NOT

4. EFFECT OF BAUD RATE ACCURACY ON DMR RADIOS

5. EFFECT OF BROADCAST STATIONS ON DMR RADIOS

6. EFFECT OF MODULATION AND FREQUENCY ACCURACY

7. EFFECT OF THE INTERNET ON DMR RADIOS

IT'S NOT ALWAYS YOUR RADIO

I just had a problem with a customer trying to get his DMR radio to work. I had him try various things and nothing seemed to work. Just as I was about to give up on him and have him send back the radio to have us look at it, he E-Mailed and said his repeater was down.

We get a lot of calls where the customer blames the radio. Some of the problems are the radios fault but a good percentage of the problems are not the radio. We have found problems relating to the power supply in a base station mobile radio, problems with the antenna, and of course problems with the radio.

SENSITIVITY OF THE CS800D

We have about 95% of the people using the CS800D happy with the sensitivity of the radio and 5% who are not. This paper explores why that 5% are having problems. The people who think they are having problems made that determination by comparing the CS800D to another radio in their car. It might be a mobile and then they think they did an apple to apple comparison or it might be a handheld and the handheld worked but the mobile did not. If good engineering practices are adhered to, we would expect that more than 99% of the people would be happy with the sensitivity.

Why other analog mobiles seem to be more sensitive than the CS800D mobile

There are many different mobiles available and many different designs. Each of the designs have a trade-off that will be explained below.

Most of the multi-band radios use relays for switching between Tx and Rx as well as switching in the different bands. The reason for using relays for high powered mobiles is because it gives great performance compared to the other choices and it is less expensive than then the other choices. The disadvantages of the relay based design is the increased power requirements to drive the relays and reliability. The increased power requirements can be eliminated by using latching relays but at an increased cost. The integrated circuit solution is the second best solution except it is not available except in low power portables. If you could make a 50 watt solid state integrated circuit, the part would probably melt without having a large heat-sink.

The Connect Systems CS800 and CS800D uses a discrete design and I would estimate has between .5 db and 1 db loss for each stage. As the products sold were designed for the commercial marketplace, reliability with reasonable performance was the most important criteria.

If you take a look at the chart below, you can see the trade-off in performance between the different approaches.

RF switch loss in db

Technology VHF 144 MHz UHF 900 MHzRelay 0.03 0.12 Power Integrated Circuit 0.40 0.50Solid State Discrete 0.50 to 1.00 0.50 to 1.00Note: Relay is: Potter & Brumfield 1462051-1 IC is: RFSW8000 and rated at 5 watts Discrete: CS800D design and is estimate

The Japanese radios will start out with a 1 to 2 db performance advantage over the CS800 and CS800D mobile radios because they use relays.

However, the CS800 and CS800D has a dual conversion superhetrodyne design with front end varactor tuning and a Low Noise R.F. Preamplifier to give the ultimate in performance in bad RF environments.

The CS800D dual band DMR and Analog radio have an extra set of switches to switch between the VHF and UHF frequencies compared to the CS800/CS801 single band DMR and Analog radio. This extra set of switches will account for between .5 db and 1 db loss of sensitivity. If

the CS800 has a sensitivity of .1 uV, the CS800D will have a sensitivity of about .12 uV.

The chart below gives the approximate sensitivity of the different radios.

Radio Estimated SensitivityCS580 .07 microvoltJapanese Radios .08 microvoltCS800 .10 microvoltCS800D .12 microvoltAT-D868UV .20 microvolt

These numbers above are estimates only and is determined by the quality of the components used and various other factors. Some of the Japanese radios might have less sensitivity because of their inherent design. The CS580, CS800, CS800D, and At-D868UV readings are measured.

PL259 to Type N Adapters

When comparing your Japanese Mobile radio to the CS800D in what you are hoping is an Apple to Apple comparison might actually be an Apple to Orange comparison. The reason is because your adapter to allow you to do the test might have a significant loss. Some of those adapters have a loss of as much as 3 db. However, a quality adapter probably has a loss of a lot less than .5 db. Those adapters range in price from about $3 to about $30 dollars. You normally get what you pay for.

Squelch Settings

The next problem you have with doing an Apple to Apple comparison is the squelch settings of the two radios you are testing. There is no standard the different manufactures use to define their squelch settings. As an example, the CS800D might not open up with squelch setting 1 until it sees a .15 microvolt signal but the Japanese radio might set squelch setting 1 to .12 microvolt. The radios have a means to adjust the level but the equipment necessary to do it is usually beyond the means of most Amateurs. If the radio is too sensitive, then the lower squelch settings are going to be continually triggered in some locations because of noise.

Even the settings within the same brand might be slightly different. This could be the difference between receiving signals and not receiving signals.

Conclusion

Some but not all of the Japanese radios might be a little more sensitive than the CS800D or CS800/CS801 in the Analog mode but getting an apple to apple comparison is very difficult. The increased sensitivity might be at the expense of higher squelch noise when there is no signals as well as reduced performance when there are adjacent channels in use.

Because the CS800/CS801 is slightly more sensitive than the CS800D, there might be cases where the CS800/CS801 is picking up a signal and the CS800D might not.

As of right now, there are no Japanese DMR radios for the Amateur market that we can compare against.

Why your Handheld might work when your mobile might not

Coax Cables

When you attach you mobile to your antenna, you are normally doing it through a coax cable. The quality of the cable can make a significant difference. The chart below shows the attenuation for a 20 foot coax cable. Your installation might be a little less or a lot more.

Coax cable Loss in db for a 20 feet run in the car:

Cable Type VHF 144 MHz UHF 450 MHzRG58 1.24 2.12RG-8X 0.94 1.72LMR-240 0.60 1.06RG-213/214 0.56 1.049913 0.32 0.56LMR-400 0.30 0.543/8" LDF 0.26 0.46LMR-600 0.192 0.341/2" LDF 0.17 0.307/8" LDF 0.11 0.17

At the 70 cm band, your coax loss might be at least 2.12 db. Because your handheld antenna is directly connected to the radio the loss is effectively 0.

PL259 to Type N Adapters

If you got lazy, you might have kept the PL259 on your antenna cable and got a PL259 to Type N adapter. You might also have used a cheap PL259 to Type N adapter with a loss of as much as 3 db.

Antenna Characteristics

The antennas attached to the handhelds normally match the radio. Some aftermarket antennas are better than the antenna that came with the radio. The antenna you got for the car might not match the frequencies in the radio you are using and can easily exceed a SWR of 6:1. This alone can take an excellent radio and make it unusable for all but the strongest signals nearby. Under ideal conditions, a dual band antenna is not as good as a single band antenna.

Conclusion

The mobile might not be working as good as you hoped because of bad engineering practices with the installation in your vehicle. The chart below shows the possible losses.

Reason For Loss Minimum Loss Maximum LossCoax Cable 0.1 db 6 dbAdapter 0.2 db 3 dbAntenna 1.0 db 20 db

So when you compare your mobile to a handheld radio where the manufacturer was able to minimize all losses, your mobile might come in a far second. Your radiated power from your mobile might actually be less than your handheld and the receiver sensitivity might be far less.

When good engineering practices are adhered to, we would expect the radios to satisfy at least 99 percent of the customers rather than the 95% we are getting now. When you consider a DMR radio for the

amateur market, the CS800D radio is still far better than all our current competitors.

HANDHELD WORKS MOBILE DOES NOT

Coax Cables

When you attach you mobile to your antenna, you are normally doing it through a coax cable. The quality of the cable can make a significant difference. The chart below shows the attenuation for a 20 foot coax cable. Your installation might be a little less or a lot more.

Coax cable Loss in db for a 20 feet run in the car:

Cable Type VHF 144 MHz UHF 450 MHzRG58 1.24 2.12RG-8X 0.94 1.72LMR-240 0.60 1.06RG-213/214 0.56 1.049913 0.32 0.56LMR-400 0.30 0.543/8" LDF 0.26 0.46LMR-600 0.192 0.341/2" LDF 0.17 0.307/8" LDF 0.11 0.17

At the 70 cm band, your coax loss might be at least 2.12 db. Because your handheld antenna is directly connected to the radio the loss is effectively 0.

PL259 to Type N Adapters

If you got lazy, you might have kept the PL259 on your antenna cable and got a PL259 to Type N adapter. You might also have used a cheap PL259 to Type N adapter with a loss of as much as 3 db.

Antenna Characteristics

The antennas attached to the handhelds normally match the radio. Some aftermarket antennas are better than the antenna that came with the radio. The antenna you got for the car might not match the frequencies in the radio you are using and can easily exceed a SWR of 6:1. This alone can take an excellent radio and make it unusable for all but the strongest signals nearby. Under ideal conditions, a dual band antenna is not as good as a single band antenna.

Conclusion

The mobile might not be working as good as you hoped because of bad engineering practices with the installation in your vehicle. The chart below shows the possible losses.

Reason For Loss Minimum Loss Maximum LossCoax Cable 0.1 db 6 dbAdapter 0.2 db 3 dbAntenna 1.0 db 20 db

So when you compare your mobile to a handheld radio where the manufacturer was able to minimize all losses, your mobile might come in a far second. Your radiated power from your mobile might actually be less than your handheld and the receiver sensitivity might be far less.

When good engineering practices are adhered to, we would expect the radios to satisfy at least 99 percent of the customers rather than the 95% we are getting now. When you consider a DMR radio for the amateur market, the CS800D radio is still far better than all our current competitors.

EFFECT OF BAUD RATE ACCURACY ON DMR RADIOS

If you do the math, over a 27.5 millisecond period, you have 264 bits which means each bit is 27.5 ms/264 = 104.166 microseconds

Being that DMR has a slot 1 and a slot 2, this is what the bit structure looks like for a single frame.

This is what a voice superframe looks like. What you should notice is that there is a sync every 330 milliseconds. So if you loose sync, it will take up to 330 milliseconds before you can synchronize the radio and recover the voice data again. Also, every 330 milliseconds, you have to decode about 330,000/104.166 = 3,168 bits else you will loose the voice.

So if the timing of the product is off even a little bit, by the time you get to the 3,000th bit, you might be looking at bit 2,999 or bit 3,001. The ETSI standard quantifies what accuracy is needed for a DMR product as shown in the next page.

What this chart from the ETSI standard is saying is the BS (abbreviation for Base Station) must have an accuracy of 1 ppm or about 440 Hz at UHF and about 288 Hz at VHF

What this statement from the ETSI standard is saying is that the crystal accuracy that controls the generation of the packets must have an accuracy of 2 ppm or better. The following page is the specification of the TXCO that is used in the CS800 and CS750 product lines from connect systems. Note that the accuracy is 1.5 ppm and is temperature compensated.

EFFECT OF BROADCAST STATIONS ON DMR RADIOS

If you remember from your basic radio theory, a mixer, is a nonlinear electrical circuit that creates new frequencies from two signals applied to it. Mixers are also used to modulate a carrier signal in radio transmitters and up or down convert in a superhetrodyne receiver.

An example or a non linear device is a diode. An example of a diode is the old cat whisker type of diode. A cat whisker diode is formed by the contact of two dissimilar metals.

This type of diode can be formed by accident. Say you have an old barbed wire metal fence in contact with some other conductor. This will then form a diode and any radio signals in the vicinity can be mixed to form other frequencies.

So now you have two radio stations not on the same frequency as your DMR radio but mixing and forming a radio frequency exactly on your frequency. While this is not a common problem, is very hard to find and correct.

Another possible problem with the broadcast station is harmonics. While most radio stations are very good at suppressing harmonics, they are not perfect. If you start out at 50,000 watts at about 108 MHz, the fourth harmonic being in the 70 cm band can be quite strong if the station is nearby.

EFFECT OF MODULATION AND FREQUENCY ACCURACY

Discriminator in a FM Radio

All FM radios have either a discriminator or the equivalent of a discriminator. A discriminator is simply a device that converts frequency to voltage. The Chart below show what it looks like.

DMR uses a FM modulation technique called 4FSK. What this means is that the signal can take on four discrete values. The chart on the next page is from the ETSI standards.

This could be represented on the chart as follows:

If the frequency was off, the same chart would look like the following:

If you notice, the frequency shift only caused a linear offset compared to the correct frequency. If the frequency is off too far, then the discriminator output will be limited by the range of the output. Within reason, the radio could compensate for a little frequency drift.

If the modulation did not meet the standards as shown per table 10.3 on the previous page, you might get a chart that looks as follows:

The problem with this chart is the voltage between the different frequencies is not enough and due to noise, it might not be possible to reliably tell the difference between the frequencies.

Summary of Problems

If you are using one of our radios you can be assured that the radio meets the ETSI standard of frequency accuracy of 1 ppm for UHF and 2 ppm for VHF and the radio will be able to reliably decode a DMR signal compliant with the ETSI standard.

However, if you use a Hot Spot of some type, there is no guarantee they are using temperature compensated oscillators to meet the ETSI standard. They seem to compensate for accuracy by tuning their Hot Spot to match your radio. It is possible your first radio is within the lower specification of the ETSI standard and your second radio is within the upper specifications of the ETSI standard. When you align the Hot Spot to the first radio you might go below the lower specification of the ETSI standard but because the radio is already within the lower specifications and the difference between the Hot Spot and that first radio

is within tuning range of the radio. However, when you try to test the second radio, you have a Hot Spot that is not compliant with the ETSI standard and it cannot decode reliably.

EFFECT OF THE INTERNET ON DMR RADIOS

There are two general types of transmission of packets on the internet called TCIP and UDP.

TCIP is used for transmitting data that must be right when it gets to the receiving end. An example of that is a data file or a computer program. If the far end detects a missing packet or a packet that is corrupted, the packet gets sent again. In some cases, it might take a few seconds to get a good packet through.

UDP is used for transmitting data that must be there in real time. An example would be voice or video. If you did not have the real time requirement, then you might get the voice delayed by seconds thereby preventing an intelligent conversation.

There are many reasons why the data might not get there in real time. The most common is the network is overloaded at that instant. In case of overloading, the network just throws away the excess packets. What you do in those cases is you ignore any missing packets and try to fill in the missing packets. Each packet consists of 60 milliseconds of voice data. If you missed one packet every so often no one would notice. However, if you miss a lot of packets you will either get a robotic sound if only a few packets are missing, or you would get no sound if many packets are missing.

If you are using a Hot Spot such as Open Spot or Jumbo Spot or using a networked repeater, you are communication using what is generically known as VoIP or Voice over Internet Protocol. This protocol uses UDP and is subject to loss of packets. So, if your system is not working properly, the problem might be the internet and not the radio or the Hot Spot.